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Stephan Mueller7d129932014-11-12 05:24:04 +01001<?xml version="1.0" encoding="UTF-8"?>
2<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook XML V4.1.2//EN"
3 "http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd" []>
4
5<book id="KernelCryptoAPI">
6 <bookinfo>
7 <title>Linux Kernel Crypto API</title>
8
9 <authorgroup>
10 <author>
11 <firstname>Stephan</firstname>
12 <surname>Mueller</surname>
13 <affiliation>
14 <address>
15 <email>smueller@chronox.de</email>
16 </address>
17 </affiliation>
18 </author>
19 <author>
20 <firstname>Marek</firstname>
21 <surname>Vasut</surname>
22 <affiliation>
23 <address>
24 <email>marek@denx.de</email>
25 </address>
26 </affiliation>
27 </author>
28 </authorgroup>
29
30 <copyright>
31 <year>2014</year>
32 <holder>Stephan Mueller</holder>
33 </copyright>
34
35
36 <legalnotice>
37 <para>
38 This documentation is free software; you can redistribute
39 it and/or modify it under the terms of the GNU General Public
40 License as published by the Free Software Foundation; either
41 version 2 of the License, or (at your option) any later
42 version.
43 </para>
44
45 <para>
46 This program is distributed in the hope that it will be
47 useful, but WITHOUT ANY WARRANTY; without even the implied
48 warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
49 See the GNU General Public License for more details.
50 </para>
51
52 <para>
53 You should have received a copy of the GNU General Public
54 License along with this program; if not, write to the Free
55 Software Foundation, Inc., 59 Temple Place, Suite 330, Boston,
56 MA 02111-1307 USA
57 </para>
58
59 <para>
60 For more details see the file COPYING in the source
61 distribution of Linux.
62 </para>
63 </legalnotice>
64 </bookinfo>
65
66 <toc></toc>
67
68 <chapter id="Intro">
69 <title>Kernel Crypto API Interface Specification</title>
70
71 <sect1><title>Introduction</title>
72
73 <para>
74 The kernel crypto API offers a rich set of cryptographic ciphers as
75 well as other data transformation mechanisms and methods to invoke
76 these. This document contains a description of the API and provides
77 example code.
78 </para>
79
80 <para>
81 To understand and properly use the kernel crypto API a brief
82 explanation of its structure is given. Based on the architecture,
83 the API can be separated into different components. Following the
84 architecture specification, hints to developers of ciphers are
85 provided. Pointers to the API function call documentation are
86 given at the end.
87 </para>
88
89 <para>
90 The kernel crypto API refers to all algorithms as "transformations".
91 Therefore, a cipher handle variable usually has the name "tfm".
92 Besides cryptographic operations, the kernel crypto API also knows
93 compression transformations and handles them the same way as ciphers.
94 </para>
95
96 <para>
97 The kernel crypto API serves the following entity types:
98
99 <itemizedlist>
100 <listitem>
101 <para>consumers requesting cryptographic services</para>
102 </listitem>
103 <listitem>
104 <para>data transformation implementations (typically ciphers)
105 that can be called by consumers using the kernel crypto
106 API</para>
107 </listitem>
108 </itemizedlist>
109 </para>
110
111 <para>
112 This specification is intended for consumers of the kernel crypto
113 API as well as for developers implementing ciphers. This API
Sharon Dvirf309f162015-02-03 01:23:41 +0200114 specification, however, does not discuss all API calls available
Stephan Mueller7d129932014-11-12 05:24:04 +0100115 to data transformation implementations (i.e. implementations of
116 ciphers and other transformations (such as CRC or even compression
117 algorithms) that can register with the kernel crypto API).
118 </para>
119
120 <para>
121 Note: The terms "transformation" and cipher algorithm are used
122 interchangably.
123 </para>
124 </sect1>
125
126 <sect1><title>Terminology</title>
127 <para>
128 The transformation implementation is an actual code or interface
129 to hardware which implements a certain transformation with precisely
130 defined behavior.
131 </para>
132
133 <para>
134 The transformation object (TFM) is an instance of a transformation
135 implementation. There can be multiple transformation objects
136 associated with a single transformation implementation. Each of
137 those transformation objects is held by a crypto API consumer or
138 another transformation. Transformation object is allocated when a
139 crypto API consumer requests a transformation implementation.
140 The consumer is then provided with a structure, which contains
141 a transformation object (TFM).
142 </para>
143
144 <para>
145 The structure that contains transformation objects may also be
146 referred to as a "cipher handle". Such a cipher handle is always
147 subject to the following phases that are reflected in the API calls
148 applicable to such a cipher handle:
149 </para>
150
151 <orderedlist>
152 <listitem>
153 <para>Initialization of a cipher handle.</para>
154 </listitem>
155 <listitem>
156 <para>Execution of all intended cipher operations applicable
157 for the handle where the cipher handle must be furnished to
158 every API call.</para>
159 </listitem>
160 <listitem>
161 <para>Destruction of a cipher handle.</para>
162 </listitem>
163 </orderedlist>
164
165 <para>
166 When using the initialization API calls, a cipher handle is
167 created and returned to the consumer. Therefore, please refer
168 to all initialization API calls that refer to the data
169 structure type a consumer is expected to receive and subsequently
170 to use. The initialization API calls have all the same naming
171 conventions of crypto_alloc_*.
172 </para>
173
174 <para>
175 The transformation context is private data associated with
176 the transformation object.
177 </para>
178 </sect1>
179 </chapter>
180
181 <chapter id="Architecture"><title>Kernel Crypto API Architecture</title>
182 <sect1><title>Cipher algorithm types</title>
183 <para>
184 The kernel crypto API provides different API calls for the
185 following cipher types:
186
187 <itemizedlist>
188 <listitem><para>Symmetric ciphers</para></listitem>
189 <listitem><para>AEAD ciphers</para></listitem>
190 <listitem><para>Message digest, including keyed message digest</para></listitem>
191 <listitem><para>Random number generation</para></listitem>
192 <listitem><para>User space interface</para></listitem>
193 </itemizedlist>
194 </para>
195 </sect1>
196
197 <sect1><title>Ciphers And Templates</title>
198 <para>
199 The kernel crypto API provides implementations of single block
200 ciphers and message digests. In addition, the kernel crypto API
201 provides numerous "templates" that can be used in conjunction
202 with the single block ciphers and message digests. Templates
203 include all types of block chaining mode, the HMAC mechanism, etc.
204 </para>
205
206 <para>
207 Single block ciphers and message digests can either be directly
208 used by a caller or invoked together with a template to form
209 multi-block ciphers or keyed message digests.
210 </para>
211
212 <para>
213 A single block cipher may even be called with multiple templates.
214 However, templates cannot be used without a single cipher.
215 </para>
216
217 <para>
218 See /proc/crypto and search for "name". For example:
219
220 <itemizedlist>
221 <listitem><para>aes</para></listitem>
222 <listitem><para>ecb(aes)</para></listitem>
223 <listitem><para>cmac(aes)</para></listitem>
224 <listitem><para>ccm(aes)</para></listitem>
225 <listitem><para>rfc4106(gcm(aes))</para></listitem>
226 <listitem><para>sha1</para></listitem>
227 <listitem><para>hmac(sha1)</para></listitem>
228 <listitem><para>authenc(hmac(sha1),cbc(aes))</para></listitem>
229 </itemizedlist>
230 </para>
231
232 <para>
233 In these examples, "aes" and "sha1" are the ciphers and all
234 others are the templates.
235 </para>
236 </sect1>
237
238 <sect1><title>Synchronous And Asynchronous Operation</title>
239 <para>
240 The kernel crypto API provides synchronous and asynchronous
241 API operations.
242 </para>
243
244 <para>
245 When using the synchronous API operation, the caller invokes
246 a cipher operation which is performed synchronously by the
247 kernel crypto API. That means, the caller waits until the
248 cipher operation completes. Therefore, the kernel crypto API
249 calls work like regular function calls. For synchronous
250 operation, the set of API calls is small and conceptually
251 similar to any other crypto library.
252 </para>
253
254 <para>
255 Asynchronous operation is provided by the kernel crypto API
256 which implies that the invocation of a cipher operation will
257 complete almost instantly. That invocation triggers the
258 cipher operation but it does not signal its completion. Before
259 invoking a cipher operation, the caller must provide a callback
260 function the kernel crypto API can invoke to signal the
261 completion of the cipher operation. Furthermore, the caller
262 must ensure it can handle such asynchronous events by applying
263 appropriate locking around its data. The kernel crypto API
264 does not perform any special serialization operation to protect
265 the caller's data integrity.
266 </para>
267 </sect1>
268
269 <sect1><title>Crypto API Cipher References And Priority</title>
270 <para>
271 A cipher is referenced by the caller with a string. That string
272 has the following semantics:
273
274 <programlisting>
275 template(single block cipher)
276 </programlisting>
277
278 where "template" and "single block cipher" is the aforementioned
279 template and single block cipher, respectively. If applicable,
280 additional templates may enclose other templates, such as
281
282 <programlisting>
283 template1(template2(single block cipher)))
284 </programlisting>
285 </para>
286
287 <para>
288 The kernel crypto API may provide multiple implementations of a
289 template or a single block cipher. For example, AES on newer
290 Intel hardware has the following implementations: AES-NI,
291 assembler implementation, or straight C. Now, when using the
292 string "aes" with the kernel crypto API, which cipher
293 implementation is used? The answer to that question is the
294 priority number assigned to each cipher implementation by the
295 kernel crypto API. When a caller uses the string to refer to a
296 cipher during initialization of a cipher handle, the kernel
297 crypto API looks up all implementations providing an
298 implementation with that name and selects the implementation
299 with the highest priority.
300 </para>
301
302 <para>
303 Now, a caller may have the need to refer to a specific cipher
304 implementation and thus does not want to rely on the
305 priority-based selection. To accommodate this scenario, the
306 kernel crypto API allows the cipher implementation to register
307 a unique name in addition to common names. When using that
308 unique name, a caller is therefore always sure to refer to
309 the intended cipher implementation.
310 </para>
311
312 <para>
313 The list of available ciphers is given in /proc/crypto. However,
314 that list does not specify all possible permutations of
315 templates and ciphers. Each block listed in /proc/crypto may
316 contain the following information -- if one of the components
317 listed as follows are not applicable to a cipher, it is not
318 displayed:
319 </para>
320
321 <itemizedlist>
322 <listitem>
323 <para>name: the generic name of the cipher that is subject
324 to the priority-based selection -- this name can be used by
325 the cipher allocation API calls (all names listed above are
326 examples for such generic names)</para>
327 </listitem>
328 <listitem>
329 <para>driver: the unique name of the cipher -- this name can
330 be used by the cipher allocation API calls</para>
331 </listitem>
332 <listitem>
333 <para>module: the kernel module providing the cipher
334 implementation (or "kernel" for statically linked ciphers)</para>
335 </listitem>
336 <listitem>
337 <para>priority: the priority value of the cipher implementation</para>
338 </listitem>
339 <listitem>
340 <para>refcnt: the reference count of the respective cipher
341 (i.e. the number of current consumers of this cipher)</para>
342 </listitem>
343 <listitem>
344 <para>selftest: specification whether the self test for the
345 cipher passed</para>
346 </listitem>
347 <listitem>
348 <para>type:
349 <itemizedlist>
350 <listitem>
351 <para>blkcipher for synchronous block ciphers</para>
352 </listitem>
353 <listitem>
354 <para>ablkcipher for asynchronous block ciphers</para>
355 </listitem>
356 <listitem>
357 <para>cipher for single block ciphers that may be used with
358 an additional template</para>
359 </listitem>
360 <listitem>
361 <para>shash for synchronous message digest</para>
362 </listitem>
363 <listitem>
364 <para>ahash for asynchronous message digest</para>
365 </listitem>
366 <listitem>
367 <para>aead for AEAD cipher type</para>
368 </listitem>
369 <listitem>
370 <para>compression for compression type transformations</para>
371 </listitem>
372 <listitem>
373 <para>rng for random number generator</para>
374 </listitem>
375 <listitem>
376 <para>givcipher for cipher with associated IV generator
377 (see the geniv entry below for the specification of the
378 IV generator type used by the cipher implementation)</para>
379 </listitem>
380 </itemizedlist>
381 </para>
382 </listitem>
383 <listitem>
384 <para>blocksize: blocksize of cipher in bytes</para>
385 </listitem>
386 <listitem>
387 <para>keysize: key size in bytes</para>
388 </listitem>
389 <listitem>
390 <para>ivsize: IV size in bytes</para>
391 </listitem>
392 <listitem>
393 <para>seedsize: required size of seed data for random number
394 generator</para>
395 </listitem>
396 <listitem>
397 <para>digestsize: output size of the message digest</para>
398 </listitem>
399 <listitem>
400 <para>geniv: IV generation type:
401 <itemizedlist>
402 <listitem>
403 <para>eseqiv for encrypted sequence number based IV
404 generation</para>
405 </listitem>
406 <listitem>
407 <para>seqiv for sequence number based IV generation</para>
408 </listitem>
409 <listitem>
410 <para>chainiv for chain iv generation</para>
411 </listitem>
412 <listitem>
413 <para>&lt;builtin&gt; is a marker that the cipher implements
414 IV generation and handling as it is specific to the given
415 cipher</para>
416 </listitem>
417 </itemizedlist>
418 </para>
419 </listitem>
420 </itemizedlist>
421 </sect1>
422
423 <sect1><title>Key Sizes</title>
424 <para>
425 When allocating a cipher handle, the caller only specifies the
426 cipher type. Symmetric ciphers, however, typically support
427 multiple key sizes (e.g. AES-128 vs. AES-192 vs. AES-256).
428 These key sizes are determined with the length of the provided
429 key. Thus, the kernel crypto API does not provide a separate
430 way to select the particular symmetric cipher key size.
431 </para>
432 </sect1>
433
434 <sect1><title>Cipher Allocation Type And Masks</title>
435 <para>
436 The different cipher handle allocation functions allow the
437 specification of a type and mask flag. Both parameters have
438 the following meaning (and are therefore not covered in the
439 subsequent sections).
440 </para>
441
442 <para>
443 The type flag specifies the type of the cipher algorithm.
444 The caller usually provides a 0 when the caller wants the
445 default handling. Otherwise, the caller may provide the
446 following selections which match the the aforementioned
447 cipher types:
448 </para>
449
450 <itemizedlist>
451 <listitem>
452 <para>CRYPTO_ALG_TYPE_CIPHER Single block cipher</para>
453 </listitem>
454 <listitem>
455 <para>CRYPTO_ALG_TYPE_COMPRESS Compression</para>
456 </listitem>
457 <listitem>
458 <para>CRYPTO_ALG_TYPE_AEAD Authenticated Encryption with
459 Associated Data (MAC)</para>
460 </listitem>
461 <listitem>
462 <para>CRYPTO_ALG_TYPE_BLKCIPHER Synchronous multi-block cipher</para>
463 </listitem>
464 <listitem>
465 <para>CRYPTO_ALG_TYPE_ABLKCIPHER Asynchronous multi-block cipher</para>
466 </listitem>
467 <listitem>
468 <para>CRYPTO_ALG_TYPE_GIVCIPHER Asynchronous multi-block
469 cipher packed together with an IV generator (see geniv field
470 in the /proc/crypto listing for the known IV generators)</para>
471 </listitem>
472 <listitem>
473 <para>CRYPTO_ALG_TYPE_DIGEST Raw message digest</para>
474 </listitem>
475 <listitem>
476 <para>CRYPTO_ALG_TYPE_HASH Alias for CRYPTO_ALG_TYPE_DIGEST</para>
477 </listitem>
478 <listitem>
479 <para>CRYPTO_ALG_TYPE_SHASH Synchronous multi-block hash</para>
480 </listitem>
481 <listitem>
482 <para>CRYPTO_ALG_TYPE_AHASH Asynchronous multi-block hash</para>
483 </listitem>
484 <listitem>
485 <para>CRYPTO_ALG_TYPE_RNG Random Number Generation</para>
486 </listitem>
487 <listitem>
488 <para>CRYPTO_ALG_TYPE_PCOMPRESS Enhanced version of
489 CRYPTO_ALG_TYPE_COMPRESS allowing for segmented compression /
490 decompression instead of performing the operation on one
491 segment only. CRYPTO_ALG_TYPE_PCOMPRESS is intended to replace
492 CRYPTO_ALG_TYPE_COMPRESS once existing consumers are converted.</para>
493 </listitem>
494 </itemizedlist>
495
496 <para>
497 The mask flag restricts the type of cipher. The only allowed
498 flag is CRYPTO_ALG_ASYNC to restrict the cipher lookup function
499 to asynchronous ciphers. Usually, a caller provides a 0 for the
500 mask flag.
501 </para>
502
503 <para>
504 When the caller provides a mask and type specification, the
505 caller limits the search the kernel crypto API can perform for
506 a suitable cipher implementation for the given cipher name.
507 That means, even when a caller uses a cipher name that exists
508 during its initialization call, the kernel crypto API may not
509 select it due to the used type and mask field.
510 </para>
511 </sect1>
Stephan Mueller7b24d972015-02-27 20:00:00 +0100512
513 <sect1><title>Internal Structure of Kernel Crypto API</title>
514
515 <para>
516 The kernel crypto API has an internal structure where a cipher
517 implementation may use many layers and indirections. This section
518 shall help to clarify how the kernel crypto API uses
519 various components to implement the complete cipher.
520 </para>
521
522 <para>
523 The following subsections explain the internal structure based
524 on existing cipher implementations. The first section addresses
525 the most complex scenario where all other scenarios form a logical
526 subset.
527 </para>
528
529 <sect2><title>Generic AEAD Cipher Structure</title>
530
531 <para>
532 The following ASCII art decomposes the kernel crypto API layers
533 when using the AEAD cipher with the automated IV generation. The
534 shown example is used by the IPSEC layer.
535 </para>
536
537 <para>
538 For other use cases of AEAD ciphers, the ASCII art applies as
539 well, but the caller may not use the GIVCIPHER interface. In
540 this case, the caller must generate the IV.
541 </para>
542
543 <para>
544 The depicted example decomposes the AEAD cipher of GCM(AES) based
545 on the generic C implementations (gcm.c, aes-generic.c, ctr.c,
546 ghash-generic.c, seqiv.c). The generic implementation serves as an
547 example showing the complete logic of the kernel crypto API.
548 </para>
549
550 <para>
551 It is possible that some streamlined cipher implementations (like
552 AES-NI) provide implementations merging aspects which in the view
553 of the kernel crypto API cannot be decomposed into layers any more.
554 In case of the AES-NI implementation, the CTR mode, the GHASH
555 implementation and the AES cipher are all merged into one cipher
556 implementation registered with the kernel crypto API. In this case,
557 the concept described by the following ASCII art applies too. However,
558 the decomposition of GCM into the individual sub-components
559 by the kernel crypto API is not done any more.
560 </para>
561
562 <para>
563 Each block in the following ASCII art is an independent cipher
564 instance obtained from the kernel crypto API. Each block
565 is accessed by the caller or by other blocks using the API functions
566 defined by the kernel crypto API for the cipher implementation type.
567 </para>
568
569 <para>
570 The blocks below indicate the cipher type as well as the specific
571 logic implemented in the cipher.
572 </para>
573
574 <para>
575 The ASCII art picture also indicates the call structure, i.e. who
576 calls which component. The arrows point to the invoked block
577 where the caller uses the API applicable to the cipher type
578 specified for the block.
579 </para>
580
581 <programlisting>
582<![CDATA[
583kernel crypto API | IPSEC Layer
584 |
585+-----------+ |
586| | (1)
587| givcipher | <----------------------------------- esp_output
588| (seqiv) | ---+
589+-----------+ |
590 | (2)
591+-----------+ |
592| | <--+ (2)
593| aead | <----------------------------------- esp_input
594| (gcm) | ------------+
595+-----------+ |
596 | (3) | (5)
597 v v
598+-----------+ +-----------+
599| | | |
600| ablkcipher| | ahash |
601| (ctr) | ---+ | (ghash) |
602+-----------+ | +-----------+
603 |
604+-----------+ | (4)
605| | <--+
606| cipher |
607| (aes) |
608+-----------+
609]]>
610 </programlisting>
611
612 <para>
613 The following call sequence is applicable when the IPSEC layer
614 triggers an encryption operation with the esp_output function. During
615 configuration, the administrator set up the use of rfc4106(gcm(aes)) as
616 the cipher for ESP. The following call sequence is now depicted in the
617 ASCII art above:
618 </para>
619
620 <orderedlist>
621 <listitem>
622 <para>
623 esp_output() invokes crypto_aead_givencrypt() to trigger an encryption
624 operation of the GIVCIPHER implementation.
625 </para>
626
627 <para>
628 In case of GCM, the SEQIV implementation is registered as GIVCIPHER
629 in crypto_rfc4106_alloc().
630 </para>
631
632 <para>
633 The SEQIV performs its operation to generate an IV where the core
634 function is seqiv_geniv().
635 </para>
636 </listitem>
637
638 <listitem>
639 <para>
640 Now, SEQIV uses the AEAD API function calls to invoke the associated
641 AEAD cipher. In our case, during the instantiation of SEQIV, the
642 cipher handle for GCM is provided to SEQIV. This means that SEQIV
643 invokes AEAD cipher operations with the GCM cipher handle.
644 </para>
645
646 <para>
647 During instantiation of the GCM handle, the CTR(AES) and GHASH
648 ciphers are instantiated. The cipher handles for CTR(AES) and GHASH
649 are retained for later use.
650 </para>
651
652 <para>
653 The GCM implementation is responsible to invoke the CTR mode AES and
654 the GHASH cipher in the right manner to implement the GCM
655 specification.
656 </para>
657 </listitem>
658
659 <listitem>
660 <para>
661 The GCM AEAD cipher type implementation now invokes the ABLKCIPHER API
662 with the instantiated CTR(AES) cipher handle.
663 </para>
664
665 <para>
666 During instantiation of the CTR(AES) cipher, the CIPHER type
667 implementation of AES is instantiated. The cipher handle for AES is
668 retained.
669 </para>
670
671 <para>
672 That means that the ABLKCIPHER implementation of CTR(AES) only
673 implements the CTR block chaining mode. After performing the block
674 chaining operation, the CIPHER implementation of AES is invoked.
675 </para>
676 </listitem>
677
678 <listitem>
679 <para>
680 The ABLKCIPHER of CTR(AES) now invokes the CIPHER API with the AES
681 cipher handle to encrypt one block.
682 </para>
683 </listitem>
684
685 <listitem>
686 <para>
687 The GCM AEAD implementation also invokes the GHASH cipher
688 implementation via the AHASH API.
689 </para>
690 </listitem>
691 </orderedlist>
692
693 <para>
694 When the IPSEC layer triggers the esp_input() function, the same call
695 sequence is followed with the only difference that the operation starts
696 with step (2).
697 </para>
698 </sect2>
699
700 <sect2><title>Generic Block Cipher Structure</title>
701 <para>
702 Generic block ciphers follow the same concept as depicted with the ASCII
703 art picture above.
704 </para>
705
706 <para>
707 For example, CBC(AES) is implemented with cbc.c, and aes-generic.c. The
708 ASCII art picture above applies as well with the difference that only
709 step (4) is used and the ABLKCIPHER block chaining mode is CBC.
710 </para>
711 </sect2>
712
713 <sect2><title>Generic Keyed Message Digest Structure</title>
714 <para>
715 Keyed message digest implementations again follow the same concept as
716 depicted in the ASCII art picture above.
717 </para>
718
719 <para>
720 For example, HMAC(SHA256) is implemented with hmac.c and
721 sha256_generic.c. The following ASCII art illustrates the
722 implementation:
723 </para>
724
725 <programlisting>
726<![CDATA[
727kernel crypto API | Caller
728 |
729+-----------+ (1) |
730| | <------------------ some_function
731| ahash |
732| (hmac) | ---+
733+-----------+ |
734 | (2)
735+-----------+ |
736| | <--+
737| shash |
738| (sha256) |
739+-----------+
740]]>
741 </programlisting>
742
743 <para>
744 The following call sequence is applicable when a caller triggers
745 an HMAC operation:
746 </para>
747
748 <orderedlist>
749 <listitem>
750 <para>
751 The AHASH API functions are invoked by the caller. The HMAC
752 implementation performs its operation as needed.
753 </para>
754
755 <para>
756 During initialization of the HMAC cipher, the SHASH cipher type of
757 SHA256 is instantiated. The cipher handle for the SHA256 instance is
758 retained.
759 </para>
760
761 <para>
762 At one time, the HMAC implementation requires a SHA256 operation
763 where the SHA256 cipher handle is used.
764 </para>
765 </listitem>
766
767 <listitem>
768 <para>
769 The HMAC instance now invokes the SHASH API with the SHA256
770 cipher handle to calculate the message digest.
771 </para>
772 </listitem>
773 </orderedlist>
774 </sect2>
775 </sect1>
Stephan Mueller7d129932014-11-12 05:24:04 +0100776 </chapter>
777
778 <chapter id="Development"><title>Developing Cipher Algorithms</title>
779 <sect1><title>Registering And Unregistering Transformation</title>
780 <para>
781 There are three distinct types of registration functions in
782 the Crypto API. One is used to register a generic cryptographic
783 transformation, while the other two are specific to HASH
784 transformations and COMPRESSion. We will discuss the latter
785 two in a separate chapter, here we will only look at the
786 generic ones.
787 </para>
788
789 <para>
790 Before discussing the register functions, the data structure
791 to be filled with each, struct crypto_alg, must be considered
792 -- see below for a description of this data structure.
793 </para>
794
795 <para>
796 The generic registration functions can be found in
797 include/linux/crypto.h and their definition can be seen below.
798 The former function registers a single transformation, while
799 the latter works on an array of transformation descriptions.
800 The latter is useful when registering transformations in bulk.
801 </para>
802
803 <programlisting>
804 int crypto_register_alg(struct crypto_alg *alg);
805 int crypto_register_algs(struct crypto_alg *algs, int count);
806 </programlisting>
807
808 <para>
809 The counterparts to those functions are listed below.
810 </para>
811
812 <programlisting>
813 int crypto_unregister_alg(struct crypto_alg *alg);
814 int crypto_unregister_algs(struct crypto_alg *algs, int count);
815 </programlisting>
816
817 <para>
818 Notice that both registration and unregistration functions
819 do return a value, so make sure to handle errors. A return
820 code of zero implies success. Any return code &lt; 0 implies
821 an error.
822 </para>
823
824 <para>
825 The bulk registration / unregistration functions require
826 that struct crypto_alg is an array of count size. These
827 functions simply loop over that array and register /
828 unregister each individual algorithm. If an error occurs,
829 the loop is terminated at the offending algorithm definition.
830 That means, the algorithms prior to the offending algorithm
831 are successfully registered. Note, the caller has no way of
832 knowing which cipher implementations have successfully
833 registered. If this is important to know, the caller should
834 loop through the different implementations using the single
835 instance *_alg functions for each individual implementation.
836 </para>
837 </sect1>
838
839 <sect1><title>Single-Block Symmetric Ciphers [CIPHER]</title>
840 <para>
841 Example of transformations: aes, arc4, ...
842 </para>
843
844 <para>
845 This section describes the simplest of all transformation
846 implementations, that being the CIPHER type used for symmetric
847 ciphers. The CIPHER type is used for transformations which
848 operate on exactly one block at a time and there are no
849 dependencies between blocks at all.
850 </para>
851
852 <sect2><title>Registration specifics</title>
853 <para>
854 The registration of [CIPHER] algorithm is specific in that
855 struct crypto_alg field .cra_type is empty. The .cra_u.cipher
856 has to be filled in with proper callbacks to implement this
857 transformation.
858 </para>
859
860 <para>
861 See struct cipher_alg below.
862 </para>
863 </sect2>
864
865 <sect2><title>Cipher Definition With struct cipher_alg</title>
866 <para>
867 Struct cipher_alg defines a single block cipher.
868 </para>
869
870 <para>
871 Here are schematics of how these functions are called when
872 operated from other part of the kernel. Note that the
873 .cia_setkey() call might happen before or after any of these
874 schematics happen, but must not happen during any of these
875 are in-flight.
876 </para>
877
878 <para>
879 <programlisting>
880 KEY ---. PLAINTEXT ---.
881 v v
882 .cia_setkey() -&gt; .cia_encrypt()
883 |
884 '-----&gt; CIPHERTEXT
885 </programlisting>
886 </para>
887
888 <para>
889 Please note that a pattern where .cia_setkey() is called
890 multiple times is also valid:
891 </para>
892
893 <para>
894 <programlisting>
895
896 KEY1 --. PLAINTEXT1 --. KEY2 --. PLAINTEXT2 --.
897 v v v v
898 .cia_setkey() -&gt; .cia_encrypt() -&gt; .cia_setkey() -&gt; .cia_encrypt()
899 | |
900 '---&gt; CIPHERTEXT1 '---&gt; CIPHERTEXT2
901 </programlisting>
902 </para>
903
904 </sect2>
905 </sect1>
906
907 <sect1><title>Multi-Block Ciphers [BLKCIPHER] [ABLKCIPHER]</title>
908 <para>
909 Example of transformations: cbc(aes), ecb(arc4), ...
910 </para>
911
912 <para>
913 This section describes the multi-block cipher transformation
914 implementations for both synchronous [BLKCIPHER] and
915 asynchronous [ABLKCIPHER] case. The multi-block ciphers are
916 used for transformations which operate on scatterlists of
917 data supplied to the transformation functions. They output
918 the result into a scatterlist of data as well.
919 </para>
920
921 <sect2><title>Registration Specifics</title>
922
923 <para>
924 The registration of [BLKCIPHER] or [ABLKCIPHER] algorithms
925 is one of the most standard procedures throughout the crypto API.
926 </para>
927
928 <para>
929 Note, if a cipher implementation requires a proper alignment
930 of data, the caller should use the functions of
931 crypto_blkcipher_alignmask() or crypto_ablkcipher_alignmask()
932 respectively to identify a memory alignment mask. The kernel
933 crypto API is able to process requests that are unaligned.
934 This implies, however, additional overhead as the kernel
935 crypto API needs to perform the realignment of the data which
936 may imply moving of data.
937 </para>
938 </sect2>
939
940 <sect2><title>Cipher Definition With struct blkcipher_alg and ablkcipher_alg</title>
941 <para>
942 Struct blkcipher_alg defines a synchronous block cipher whereas
943 struct ablkcipher_alg defines an asynchronous block cipher.
944 </para>
945
946 <para>
947 Please refer to the single block cipher description for schematics
948 of the block cipher usage. The usage patterns are exactly the same
949 for [ABLKCIPHER] and [BLKCIPHER] as they are for plain [CIPHER].
950 </para>
951 </sect2>
952
953 <sect2><title>Specifics Of Asynchronous Multi-Block Cipher</title>
954 <para>
955 There are a couple of specifics to the [ABLKCIPHER] interface.
956 </para>
957
958 <para>
959 First of all, some of the drivers will want to use the
960 Generic ScatterWalk in case the hardware needs to be fed
961 separate chunks of the scatterlist which contains the
962 plaintext and will contain the ciphertext. Please refer
963 to the ScatterWalk interface offered by the Linux kernel
964 scatter / gather list implementation.
965 </para>
966 </sect2>
967 </sect1>
968
969 <sect1><title>Hashing [HASH]</title>
970
971 <para>
972 Example of transformations: crc32, md5, sha1, sha256,...
973 </para>
974
975 <sect2><title>Registering And Unregistering The Transformation</title>
976
977 <para>
978 There are multiple ways to register a HASH transformation,
979 depending on whether the transformation is synchronous [SHASH]
980 or asynchronous [AHASH] and the amount of HASH transformations
981 we are registering. You can find the prototypes defined in
982 include/crypto/internal/hash.h:
983 </para>
984
985 <programlisting>
986 int crypto_register_ahash(struct ahash_alg *alg);
987
988 int crypto_register_shash(struct shash_alg *alg);
989 int crypto_register_shashes(struct shash_alg *algs, int count);
990 </programlisting>
991
992 <para>
993 The respective counterparts for unregistering the HASH
994 transformation are as follows:
995 </para>
996
997 <programlisting>
998 int crypto_unregister_ahash(struct ahash_alg *alg);
999
1000 int crypto_unregister_shash(struct shash_alg *alg);
1001 int crypto_unregister_shashes(struct shash_alg *algs, int count);
1002 </programlisting>
1003 </sect2>
1004
1005 <sect2><title>Cipher Definition With struct shash_alg and ahash_alg</title>
1006 <para>
1007 Here are schematics of how these functions are called when
1008 operated from other part of the kernel. Note that the .setkey()
1009 call might happen before or after any of these schematics happen,
1010 but must not happen during any of these are in-flight. Please note
1011 that calling .init() followed immediately by .finish() is also a
1012 perfectly valid transformation.
1013 </para>
1014
1015 <programlisting>
1016 I) DATA -----------.
1017 v
1018 .init() -&gt; .update() -&gt; .final() ! .update() might not be called
1019 ^ | | at all in this scenario.
1020 '----' '---&gt; HASH
1021
1022 II) DATA -----------.-----------.
1023 v v
1024 .init() -&gt; .update() -&gt; .finup() ! .update() may not be called
1025 ^ | | at all in this scenario.
1026 '----' '---&gt; HASH
1027
1028 III) DATA -----------.
1029 v
1030 .digest() ! The entire process is handled
1031 | by the .digest() call.
1032 '---------------&gt; HASH
1033 </programlisting>
1034
1035 <para>
1036 Here is a schematic of how the .export()/.import() functions are
1037 called when used from another part of the kernel.
1038 </para>
1039
1040 <programlisting>
1041 KEY--. DATA--.
1042 v v ! .update() may not be called
1043 .setkey() -&gt; .init() -&gt; .update() -&gt; .export() at all in this scenario.
1044 ^ | |
1045 '-----' '--&gt; PARTIAL_HASH
1046
1047 ----------- other transformations happen here -----------
1048
1049 PARTIAL_HASH--. DATA1--.
1050 v v
1051 .import -&gt; .update() -&gt; .final() ! .update() may not be called
1052 ^ | | at all in this scenario.
1053 '----' '--&gt; HASH1
1054
1055 PARTIAL_HASH--. DATA2-.
1056 v v
1057 .import -&gt; .finup()
1058 |
1059 '---------------&gt; HASH2
1060 </programlisting>
1061 </sect2>
1062
1063 <sect2><title>Specifics Of Asynchronous HASH Transformation</title>
1064 <para>
1065 Some of the drivers will want to use the Generic ScatterWalk
1066 in case the implementation needs to be fed separate chunks of the
1067 scatterlist which contains the input data. The buffer containing
1068 the resulting hash will always be properly aligned to
1069 .cra_alignmask so there is no need to worry about this.
1070 </para>
1071 </sect2>
1072 </sect1>
1073 </chapter>
1074
Stephan Muellerdbe5fe72015-03-06 21:34:22 +01001075 <chapter id="User"><title>User Space Interface</title>
1076 <sect1><title>Introduction</title>
1077 <para>
1078 The concepts of the kernel crypto API visible to kernel space is fully
1079 applicable to the user space interface as well. Therefore, the kernel
1080 crypto API high level discussion for the in-kernel use cases applies
1081 here as well.
1082 </para>
1083
1084 <para>
1085 The major difference, however, is that user space can only act as a
1086 consumer and never as a provider of a transformation or cipher algorithm.
1087 </para>
1088
1089 <para>
1090 The following covers the user space interface exported by the kernel
1091 crypto API. A working example of this description is libkcapi that
1092 can be obtained from [1]. That library can be used by user space
1093 applications that require cryptographic services from the kernel.
1094 </para>
1095
1096 <para>
1097 Some details of the in-kernel kernel crypto API aspects do not
1098 apply to user space, however. This includes the difference between
1099 synchronous and asynchronous invocations. The user space API call
1100 is fully synchronous.
1101 </para>
1102
1103 <para>
1104 [1] http://www.chronox.de/libkcapi.html
1105 </para>
1106
1107 </sect1>
1108
1109 <sect1><title>User Space API General Remarks</title>
1110 <para>
1111 The kernel crypto API is accessible from user space. Currently,
1112 the following ciphers are accessible:
1113 </para>
1114
1115 <itemizedlist>
1116 <listitem>
1117 <para>Message digest including keyed message digest (HMAC, CMAC)</para>
1118 </listitem>
1119
1120 <listitem>
1121 <para>Symmetric ciphers</para>
1122 </listitem>
1123
1124 <listitem>
1125 <para>AEAD ciphers</para>
1126 </listitem>
1127
1128 <listitem>
1129 <para>Random Number Generators</para>
1130 </listitem>
1131 </itemizedlist>
1132
1133 <para>
1134 The interface is provided via socket type using the type AF_ALG.
1135 In addition, the setsockopt option type is SOL_ALG. In case the
1136 user space header files do not export these flags yet, use the
1137 following macros:
1138 </para>
1139
1140 <programlisting>
1141#ifndef AF_ALG
1142#define AF_ALG 38
1143#endif
1144#ifndef SOL_ALG
1145#define SOL_ALG 279
1146#endif
1147 </programlisting>
1148
1149 <para>
1150 A cipher is accessed with the same name as done for the in-kernel
1151 API calls. This includes the generic vs. unique naming schema for
1152 ciphers as well as the enforcement of priorities for generic names.
1153 </para>
1154
1155 <para>
1156 To interact with the kernel crypto API, a socket must be
1157 created by the user space application. User space invokes the cipher
1158 operation with the send()/write() system call family. The result of the
1159 cipher operation is obtained with the read()/recv() system call family.
1160 </para>
1161
1162 <para>
1163 The following API calls assume that the socket descriptor
1164 is already opened by the user space application and discusses only
1165 the kernel crypto API specific invocations.
1166 </para>
1167
1168 <para>
1169 To initialize the socket interface, the following sequence has to
1170 be performed by the consumer:
1171 </para>
1172
1173 <orderedlist>
1174 <listitem>
1175 <para>
1176 Create a socket of type AF_ALG with the struct sockaddr_alg
1177 parameter specified below for the different cipher types.
1178 </para>
1179 </listitem>
1180
1181 <listitem>
1182 <para>
1183 Invoke bind with the socket descriptor
1184 </para>
1185 </listitem>
1186
1187 <listitem>
1188 <para>
1189 Invoke accept with the socket descriptor. The accept system call
1190 returns a new file descriptor that is to be used to interact with
1191 the particular cipher instance. When invoking send/write or recv/read
1192 system calls to send data to the kernel or obtain data from the
1193 kernel, the file descriptor returned by accept must be used.
1194 </para>
1195 </listitem>
1196 </orderedlist>
1197 </sect1>
1198
1199 <sect1><title>In-place Cipher operation</title>
1200 <para>
1201 Just like the in-kernel operation of the kernel crypto API, the user
1202 space interface allows the cipher operation in-place. That means that
1203 the input buffer used for the send/write system call and the output
1204 buffer used by the read/recv system call may be one and the same.
1205 This is of particular interest for symmetric cipher operations where a
1206 copying of the output data to its final destination can be avoided.
1207 </para>
1208
1209 <para>
1210 If a consumer on the other hand wants to maintain the plaintext and
1211 the ciphertext in different memory locations, all a consumer needs
1212 to do is to provide different memory pointers for the encryption and
1213 decryption operation.
1214 </para>
1215 </sect1>
1216
1217 <sect1><title>Message Digest API</title>
1218 <para>
1219 The message digest type to be used for the cipher operation is
1220 selected when invoking the bind syscall. bind requires the caller
1221 to provide a filled struct sockaddr data structure. This data
1222 structure must be filled as follows:
1223 </para>
1224
1225 <programlisting>
1226struct sockaddr_alg sa = {
1227 .salg_family = AF_ALG,
1228 .salg_type = "hash", /* this selects the hash logic in the kernel */
1229 .salg_name = "sha1" /* this is the cipher name */
1230};
1231 </programlisting>
1232
1233 <para>
1234 The salg_type value "hash" applies to message digests and keyed
1235 message digests. Though, a keyed message digest is referenced by
1236 the appropriate salg_name. Please see below for the setsockopt
1237 interface that explains how the key can be set for a keyed message
1238 digest.
1239 </para>
1240
1241 <para>
1242 Using the send() system call, the application provides the data that
1243 should be processed with the message digest. The send system call
1244 allows the following flags to be specified:
1245 </para>
1246
1247 <itemizedlist>
1248 <listitem>
1249 <para>
1250 MSG_MORE: If this flag is set, the send system call acts like a
1251 message digest update function where the final hash is not
1252 yet calculated. If the flag is not set, the send system call
1253 calculates the final message digest immediately.
1254 </para>
1255 </listitem>
1256 </itemizedlist>
1257
1258 <para>
1259 With the recv() system call, the application can read the message
1260 digest from the kernel crypto API. If the buffer is too small for the
1261 message digest, the flag MSG_TRUNC is set by the kernel.
1262 </para>
1263
1264 <para>
1265 In order to set a message digest key, the calling application must use
1266 the setsockopt() option of ALG_SET_KEY. If the key is not set the HMAC
1267 operation is performed without the initial HMAC state change caused by
1268 the key.
1269 </para>
1270 </sect1>
1271
1272 <sect1><title>Symmetric Cipher API</title>
1273 <para>
1274 The operation is very similar to the message digest discussion.
1275 During initialization, the struct sockaddr data structure must be
1276 filled as follows:
1277 </para>
1278
1279 <programlisting>
1280struct sockaddr_alg sa = {
1281 .salg_family = AF_ALG,
1282 .salg_type = "skcipher", /* this selects the symmetric cipher */
1283 .salg_name = "cbc(aes)" /* this is the cipher name */
1284};
1285 </programlisting>
1286
1287 <para>
1288 Before data can be sent to the kernel using the write/send system
1289 call family, the consumer must set the key. The key setting is
1290 described with the setsockopt invocation below.
1291 </para>
1292
1293 <para>
1294 Using the sendmsg() system call, the application provides the data that should be processed for encryption or decryption. In addition, the IV is
1295 specified with the data structure provided by the sendmsg() system call.
1296 </para>
1297
1298 <para>
1299 The sendmsg system call parameter of struct msghdr is embedded into the
1300 struct cmsghdr data structure. See recv(2) and cmsg(3) for more
1301 information on how the cmsghdr data structure is used together with the
1302 send/recv system call family. That cmsghdr data structure holds the
1303 following information specified with a separate header instances:
1304 </para>
1305
1306 <itemizedlist>
1307 <listitem>
1308 <para>
1309 specification of the cipher operation type with one of these flags:
1310 </para>
1311 <itemizedlist>
1312 <listitem>
1313 <para>ALG_OP_ENCRYPT - encryption of data</para>
1314 </listitem>
1315 <listitem>
1316 <para>ALG_OP_DECRYPT - decryption of data</para>
1317 </listitem>
1318 </itemizedlist>
1319 </listitem>
1320
1321 <listitem>
1322 <para>
1323 specification of the IV information marked with the flag ALG_SET_IV
1324 </para>
1325 </listitem>
1326 </itemizedlist>
1327
1328 <para>
1329 The send system call family allows the following flag to be specified:
1330 </para>
1331
1332 <itemizedlist>
1333 <listitem>
1334 <para>
1335 MSG_MORE: If this flag is set, the send system call acts like a
1336 cipher update function where more input data is expected
1337 with a subsequent invocation of the send system call.
1338 </para>
1339 </listitem>
1340 </itemizedlist>
1341
1342 <para>
1343 Note: The kernel reports -EINVAL for any unexpected data. The caller
1344 must make sure that all data matches the constraints given in
1345 /proc/crypto for the selected cipher.
1346 </para>
1347
1348 <para>
1349 With the recv() system call, the application can read the result of
1350 the cipher operation from the kernel crypto API. The output buffer
1351 must be at least as large as to hold all blocks of the encrypted or
1352 decrypted data. If the output data size is smaller, only as many
1353 blocks are returned that fit into that output buffer size.
1354 </para>
1355 </sect1>
1356
1357 <sect1><title>AEAD Cipher API</title>
1358 <para>
1359 The operation is very similar to the symmetric cipher discussion.
1360 During initialization, the struct sockaddr data structure must be
1361 filled as follows:
1362 </para>
1363
1364 <programlisting>
1365struct sockaddr_alg sa = {
1366 .salg_family = AF_ALG,
1367 .salg_type = "aead", /* this selects the symmetric cipher */
1368 .salg_name = "gcm(aes)" /* this is the cipher name */
1369};
1370 </programlisting>
1371
1372 <para>
1373 Before data can be sent to the kernel using the write/send system
1374 call family, the consumer must set the key. The key setting is
1375 described with the setsockopt invocation below.
1376 </para>
1377
1378 <para>
1379 In addition, before data can be sent to the kernel using the
1380 write/send system call family, the consumer must set the authentication
1381 tag size. To set the authentication tag size, the caller must use the
1382 setsockopt invocation described below.
1383 </para>
1384
1385 <para>
1386 Using the sendmsg() system call, the application provides the data that should be processed for encryption or decryption. In addition, the IV is
1387 specified with the data structure provided by the sendmsg() system call.
1388 </para>
1389
1390 <para>
1391 The sendmsg system call parameter of struct msghdr is embedded into the
1392 struct cmsghdr data structure. See recv(2) and cmsg(3) for more
1393 information on how the cmsghdr data structure is used together with the
1394 send/recv system call family. That cmsghdr data structure holds the
1395 following information specified with a separate header instances:
1396 </para>
1397
1398 <itemizedlist>
1399 <listitem>
1400 <para>
1401 specification of the cipher operation type with one of these flags:
1402 </para>
1403 <itemizedlist>
1404 <listitem>
1405 <para>ALG_OP_ENCRYPT - encryption of data</para>
1406 </listitem>
1407 <listitem>
1408 <para>ALG_OP_DECRYPT - decryption of data</para>
1409 </listitem>
1410 </itemizedlist>
1411 </listitem>
1412
1413 <listitem>
1414 <para>
1415 specification of the IV information marked with the flag ALG_SET_IV
1416 </para>
1417 </listitem>
1418
1419 <listitem>
1420 <para>
1421 specification of the associated authentication data (AAD) with the
1422 flag ALG_SET_AEAD_ASSOCLEN. The AAD is sent to the kernel together
1423 with the plaintext / ciphertext. See below for the memory structure.
1424 </para>
1425 </listitem>
1426 </itemizedlist>
1427
1428 <para>
1429 The send system call family allows the following flag to be specified:
1430 </para>
1431
1432 <itemizedlist>
1433 <listitem>
1434 <para>
1435 MSG_MORE: If this flag is set, the send system call acts like a
1436 cipher update function where more input data is expected
1437 with a subsequent invocation of the send system call.
1438 </para>
1439 </listitem>
1440 </itemizedlist>
1441
1442 <para>
1443 Note: The kernel reports -EINVAL for any unexpected data. The caller
1444 must make sure that all data matches the constraints given in
1445 /proc/crypto for the selected cipher.
1446 </para>
1447
1448 <para>
1449 With the recv() system call, the application can read the result of
1450 the cipher operation from the kernel crypto API. The output buffer
1451 must be at least as large as defined with the memory structure below.
1452 If the output data size is smaller, the cipher operation is not performed.
1453 </para>
1454
1455 <para>
1456 The authenticated decryption operation may indicate an integrity error.
1457 Such breach in integrity is marked with the -EBADMSG error code.
1458 </para>
1459
1460 <sect2><title>AEAD Memory Structure</title>
1461 <para>
1462 The AEAD cipher operates with the following information that
1463 is communicated between user and kernel space as one data stream:
1464 </para>
1465
1466 <itemizedlist>
1467 <listitem>
1468 <para>plaintext or ciphertext</para>
1469 </listitem>
1470
1471 <listitem>
1472 <para>associated authentication data (AAD)</para>
1473 </listitem>
1474
1475 <listitem>
1476 <para>authentication tag</para>
1477 </listitem>
1478 </itemizedlist>
1479
1480 <para>
1481 The sizes of the AAD and the authentication tag are provided with
1482 the sendmsg and setsockopt calls (see there). As the kernel knows
1483 the size of the entire data stream, the kernel is now able to
1484 calculate the right offsets of the data components in the data
1485 stream.
1486 </para>
1487
1488 <para>
1489 The user space caller must arrange the aforementioned information
1490 in the following order:
1491 </para>
1492
1493 <itemizedlist>
1494 <listitem>
1495 <para>
1496 AEAD encryption input: AAD || plaintext
1497 </para>
1498 </listitem>
1499
1500 <listitem>
1501 <para>
1502 AEAD decryption input: AAD || ciphertext || authentication tag
1503 </para>
1504 </listitem>
1505 </itemizedlist>
1506
1507 <para>
1508 The output buffer the user space caller provides must be at least as
1509 large to hold the following data:
1510 </para>
1511
1512 <itemizedlist>
1513 <listitem>
1514 <para>
1515 AEAD encryption output: ciphertext || authentication tag
1516 </para>
1517 </listitem>
1518
1519 <listitem>
1520 <para>
1521 AEAD decryption output: plaintext
1522 </para>
1523 </listitem>
1524 </itemizedlist>
1525 </sect2>
1526 </sect1>
1527
1528 <sect1><title>Random Number Generator API</title>
1529 <para>
1530 Again, the operation is very similar to the other APIs.
1531 During initialization, the struct sockaddr data structure must be
1532 filled as follows:
1533 </para>
1534
1535 <programlisting>
1536struct sockaddr_alg sa = {
1537 .salg_family = AF_ALG,
1538 .salg_type = "rng", /* this selects the symmetric cipher */
1539 .salg_name = "drbg_nopr_sha256" /* this is the cipher name */
1540};
1541 </programlisting>
1542
1543 <para>
1544 Depending on the RNG type, the RNG must be seeded. The seed is provided
1545 using the setsockopt interface to set the key. For example, the
1546 ansi_cprng requires a seed. The DRBGs do not require a seed, but
1547 may be seeded.
1548 </para>
1549
1550 <para>
1551 Using the read()/recvmsg() system calls, random numbers can be obtained.
1552 The kernel generates at most 128 bytes in one call. If user space
1553 requires more data, multiple calls to read()/recvmsg() must be made.
1554 </para>
1555
1556 <para>
1557 WARNING: The user space caller may invoke the initially mentioned
1558 accept system call multiple times. In this case, the returned file
1559 descriptors have the same state.
1560 </para>
1561
1562 </sect1>
1563
1564 <sect1><title>Zero-Copy Interface</title>
1565 <para>
1566 In addition to the send/write/read/recv system call familty, the AF_ALG
1567 interface can be accessed with the zero-copy interface of splice/vmsplice.
1568 As the name indicates, the kernel tries to avoid a copy operation into
1569 kernel space.
1570 </para>
1571
1572 <para>
1573 The zero-copy operation requires data to be aligned at the page boundary.
1574 Non-aligned data can be used as well, but may require more operations of
1575 the kernel which would defeat the speed gains obtained from the zero-copy
1576 interface.
1577 </para>
1578
1579 <para>
1580 The system-interent limit for the size of one zero-copy operation is
1581 16 pages. If more data is to be sent to AF_ALG, user space must slice
1582 the input into segments with a maximum size of 16 pages.
1583 </para>
1584
1585 <para>
1586 Zero-copy can be used with the following code example (a complete working
1587 example is provided with libkcapi):
1588 </para>
1589
1590 <programlisting>
1591int pipes[2];
1592
1593pipe(pipes);
1594/* input data in iov */
1595vmsplice(pipes[1], iov, iovlen, SPLICE_F_GIFT);
1596/* opfd is the file descriptor returned from accept() system call */
1597splice(pipes[0], NULL, opfd, NULL, ret, 0);
1598read(opfd, out, outlen);
1599 </programlisting>
1600
1601 </sect1>
1602
1603 <sect1><title>Setsockopt Interface</title>
1604 <para>
1605 In addition to the read/recv and send/write system call handling
1606 to send and retrieve data subject to the cipher operation, a consumer
1607 also needs to set the additional information for the cipher operation.
1608 This additional information is set using the setsockopt system call
1609 that must be invoked with the file descriptor of the open cipher
1610 (i.e. the file descriptor returned by the accept system call).
1611 </para>
1612
1613 <para>
1614 Each setsockopt invocation must use the level SOL_ALG.
1615 </para>
1616
1617 <para>
1618 The setsockopt interface allows setting the following data using
1619 the mentioned optname:
1620 </para>
1621
1622 <itemizedlist>
1623 <listitem>
1624 <para>
1625 ALG_SET_KEY -- Setting the key. Key setting is applicable to:
1626 </para>
1627 <itemizedlist>
1628 <listitem>
1629 <para>the skcipher cipher type (symmetric ciphers)</para>
1630 </listitem>
1631 <listitem>
1632 <para>the hash cipher type (keyed message digests)</para>
1633 </listitem>
1634 <listitem>
1635 <para>the AEAD cipher type</para>
1636 </listitem>
1637 <listitem>
1638 <para>the RNG cipher type to provide the seed</para>
1639 </listitem>
1640 </itemizedlist>
1641 </listitem>
1642
1643 <listitem>
1644 <para>
1645 ALG_SET_AEAD_AUTHSIZE -- Setting the authentication tag size
1646 for AEAD ciphers. For a encryption operation, the authentication
1647 tag of the given size will be generated. For a decryption operation,
1648 the provided ciphertext is assumed to contain an authentication tag
1649 of the given size (see section about AEAD memory layout below).
1650 </para>
1651 </listitem>
1652 </itemizedlist>
1653
1654 </sect1>
1655
1656 <sect1><title>User space API example</title>
1657 <para>
1658 Please see [1] for libkcapi which provides an easy-to-use wrapper
1659 around the aforementioned Netlink kernel interface. [1] also contains
1660 a test application that invokes all libkcapi API calls.
1661 </para>
1662
1663 <para>
1664 [1] http://www.chronox.de/libkcapi.html
1665 </para>
1666
1667 </sect1>
1668
1669 </chapter>
1670
Stephan Mueller7d129932014-11-12 05:24:04 +01001671 <chapter id="API"><title>Programming Interface</title>
1672 <sect1><title>Block Cipher Context Data Structures</title>
1673!Pinclude/linux/crypto.h Block Cipher Context Data Structures
1674!Finclude/linux/crypto.h aead_request
1675 </sect1>
1676 <sect1><title>Block Cipher Algorithm Definitions</title>
1677!Pinclude/linux/crypto.h Block Cipher Algorithm Definitions
1678!Finclude/linux/crypto.h crypto_alg
1679!Finclude/linux/crypto.h ablkcipher_alg
1680!Finclude/linux/crypto.h aead_alg
1681!Finclude/linux/crypto.h blkcipher_alg
1682!Finclude/linux/crypto.h cipher_alg
1683!Finclude/linux/crypto.h rng_alg
1684 </sect1>
1685 <sect1><title>Asynchronous Block Cipher API</title>
1686!Pinclude/linux/crypto.h Asynchronous Block Cipher API
1687!Finclude/linux/crypto.h crypto_alloc_ablkcipher
1688!Finclude/linux/crypto.h crypto_free_ablkcipher
1689!Finclude/linux/crypto.h crypto_has_ablkcipher
1690!Finclude/linux/crypto.h crypto_ablkcipher_ivsize
1691!Finclude/linux/crypto.h crypto_ablkcipher_blocksize
1692!Finclude/linux/crypto.h crypto_ablkcipher_setkey
1693!Finclude/linux/crypto.h crypto_ablkcipher_reqtfm
1694!Finclude/linux/crypto.h crypto_ablkcipher_encrypt
1695!Finclude/linux/crypto.h crypto_ablkcipher_decrypt
1696 </sect1>
1697 <sect1><title>Asynchronous Cipher Request Handle</title>
1698!Pinclude/linux/crypto.h Asynchronous Cipher Request Handle
1699!Finclude/linux/crypto.h crypto_ablkcipher_reqsize
1700!Finclude/linux/crypto.h ablkcipher_request_set_tfm
1701!Finclude/linux/crypto.h ablkcipher_request_alloc
1702!Finclude/linux/crypto.h ablkcipher_request_free
1703!Finclude/linux/crypto.h ablkcipher_request_set_callback
1704!Finclude/linux/crypto.h ablkcipher_request_set_crypt
1705 </sect1>
1706 <sect1><title>Authenticated Encryption With Associated Data (AEAD) Cipher API</title>
1707!Pinclude/linux/crypto.h Authenticated Encryption With Associated Data (AEAD) Cipher API
1708!Finclude/linux/crypto.h crypto_alloc_aead
1709!Finclude/linux/crypto.h crypto_free_aead
1710!Finclude/linux/crypto.h crypto_aead_ivsize
1711!Finclude/linux/crypto.h crypto_aead_authsize
1712!Finclude/linux/crypto.h crypto_aead_blocksize
1713!Finclude/linux/crypto.h crypto_aead_setkey
1714!Finclude/linux/crypto.h crypto_aead_setauthsize
1715!Finclude/linux/crypto.h crypto_aead_encrypt
1716!Finclude/linux/crypto.h crypto_aead_decrypt
1717 </sect1>
1718 <sect1><title>Asynchronous AEAD Request Handle</title>
1719!Pinclude/linux/crypto.h Asynchronous AEAD Request Handle
1720!Finclude/linux/crypto.h crypto_aead_reqsize
1721!Finclude/linux/crypto.h aead_request_set_tfm
1722!Finclude/linux/crypto.h aead_request_alloc
1723!Finclude/linux/crypto.h aead_request_free
1724!Finclude/linux/crypto.h aead_request_set_callback
1725!Finclude/linux/crypto.h aead_request_set_crypt
1726!Finclude/linux/crypto.h aead_request_set_assoc
1727 </sect1>
1728 <sect1><title>Synchronous Block Cipher API</title>
1729!Pinclude/linux/crypto.h Synchronous Block Cipher API
1730!Finclude/linux/crypto.h crypto_alloc_blkcipher
1731!Finclude/linux/crypto.h crypto_free_blkcipher
1732!Finclude/linux/crypto.h crypto_has_blkcipher
1733!Finclude/linux/crypto.h crypto_blkcipher_name
1734!Finclude/linux/crypto.h crypto_blkcipher_ivsize
1735!Finclude/linux/crypto.h crypto_blkcipher_blocksize
1736!Finclude/linux/crypto.h crypto_blkcipher_setkey
1737!Finclude/linux/crypto.h crypto_blkcipher_encrypt
1738!Finclude/linux/crypto.h crypto_blkcipher_encrypt_iv
1739!Finclude/linux/crypto.h crypto_blkcipher_decrypt
1740!Finclude/linux/crypto.h crypto_blkcipher_decrypt_iv
1741!Finclude/linux/crypto.h crypto_blkcipher_set_iv
1742!Finclude/linux/crypto.h crypto_blkcipher_get_iv
1743 </sect1>
1744 <sect1><title>Single Block Cipher API</title>
1745!Pinclude/linux/crypto.h Single Block Cipher API
1746!Finclude/linux/crypto.h crypto_alloc_cipher
1747!Finclude/linux/crypto.h crypto_free_cipher
1748!Finclude/linux/crypto.h crypto_has_cipher
1749!Finclude/linux/crypto.h crypto_cipher_blocksize
1750!Finclude/linux/crypto.h crypto_cipher_setkey
1751!Finclude/linux/crypto.h crypto_cipher_encrypt_one
1752!Finclude/linux/crypto.h crypto_cipher_decrypt_one
1753 </sect1>
1754 <sect1><title>Synchronous Message Digest API</title>
1755!Pinclude/linux/crypto.h Synchronous Message Digest API
1756!Finclude/linux/crypto.h crypto_alloc_hash
1757!Finclude/linux/crypto.h crypto_free_hash
1758!Finclude/linux/crypto.h crypto_has_hash
1759!Finclude/linux/crypto.h crypto_hash_blocksize
1760!Finclude/linux/crypto.h crypto_hash_digestsize
1761!Finclude/linux/crypto.h crypto_hash_init
1762!Finclude/linux/crypto.h crypto_hash_update
1763!Finclude/linux/crypto.h crypto_hash_final
1764!Finclude/linux/crypto.h crypto_hash_digest
1765!Finclude/linux/crypto.h crypto_hash_setkey
1766 </sect1>
1767 <sect1><title>Message Digest Algorithm Definitions</title>
1768!Pinclude/crypto/hash.h Message Digest Algorithm Definitions
1769!Finclude/crypto/hash.h hash_alg_common
1770!Finclude/crypto/hash.h ahash_alg
1771!Finclude/crypto/hash.h shash_alg
1772 </sect1>
1773 <sect1><title>Asynchronous Message Digest API</title>
1774!Pinclude/crypto/hash.h Asynchronous Message Digest API
1775!Finclude/crypto/hash.h crypto_alloc_ahash
1776!Finclude/crypto/hash.h crypto_free_ahash
1777!Finclude/crypto/hash.h crypto_ahash_init
1778!Finclude/crypto/hash.h crypto_ahash_digestsize
1779!Finclude/crypto/hash.h crypto_ahash_reqtfm
1780!Finclude/crypto/hash.h crypto_ahash_reqsize
1781!Finclude/crypto/hash.h crypto_ahash_setkey
1782!Finclude/crypto/hash.h crypto_ahash_finup
1783!Finclude/crypto/hash.h crypto_ahash_final
1784!Finclude/crypto/hash.h crypto_ahash_digest
1785!Finclude/crypto/hash.h crypto_ahash_export
1786!Finclude/crypto/hash.h crypto_ahash_import
1787 </sect1>
1788 <sect1><title>Asynchronous Hash Request Handle</title>
1789!Pinclude/crypto/hash.h Asynchronous Hash Request Handle
1790!Finclude/crypto/hash.h ahash_request_set_tfm
1791!Finclude/crypto/hash.h ahash_request_alloc
1792!Finclude/crypto/hash.h ahash_request_free
1793!Finclude/crypto/hash.h ahash_request_set_callback
1794!Finclude/crypto/hash.h ahash_request_set_crypt
1795 </sect1>
1796 <sect1><title>Synchronous Message Digest API</title>
1797!Pinclude/crypto/hash.h Synchronous Message Digest API
1798!Finclude/crypto/hash.h crypto_alloc_shash
1799!Finclude/crypto/hash.h crypto_free_shash
1800!Finclude/crypto/hash.h crypto_shash_blocksize
1801!Finclude/crypto/hash.h crypto_shash_digestsize
1802!Finclude/crypto/hash.h crypto_shash_descsize
1803!Finclude/crypto/hash.h crypto_shash_setkey
1804!Finclude/crypto/hash.h crypto_shash_digest
1805!Finclude/crypto/hash.h crypto_shash_export
1806!Finclude/crypto/hash.h crypto_shash_import
1807!Finclude/crypto/hash.h crypto_shash_init
1808!Finclude/crypto/hash.h crypto_shash_update
1809!Finclude/crypto/hash.h crypto_shash_final
1810!Finclude/crypto/hash.h crypto_shash_finup
1811 </sect1>
1812 <sect1><title>Crypto API Random Number API</title>
1813!Pinclude/crypto/rng.h Random number generator API
1814!Finclude/crypto/rng.h crypto_alloc_rng
1815!Finclude/crypto/rng.h crypto_rng_alg
1816!Finclude/crypto/rng.h crypto_free_rng
1817!Finclude/crypto/rng.h crypto_rng_get_bytes
1818!Finclude/crypto/rng.h crypto_rng_reset
1819!Finclude/crypto/rng.h crypto_rng_seedsize
1820!Cinclude/crypto/rng.h
1821 </sect1>
1822 </chapter>
1823
1824 <chapter id="Code"><title>Code Examples</title>
1825 <sect1><title>Code Example For Asynchronous Block Cipher Operation</title>
1826 <programlisting>
1827
1828struct tcrypt_result {
1829 struct completion completion;
1830 int err;
1831};
1832
1833/* tie all data structures together */
1834struct ablkcipher_def {
1835 struct scatterlist sg;
1836 struct crypto_ablkcipher *tfm;
1837 struct ablkcipher_request *req;
1838 struct tcrypt_result result;
1839};
1840
1841/* Callback function */
1842static void test_ablkcipher_cb(struct crypto_async_request *req, int error)
1843{
1844 struct tcrypt_result *result = req-&gt;data;
1845
1846 if (error == -EINPROGRESS)
1847 return;
1848 result-&gt;err = error;
1849 complete(&amp;result-&gt;completion);
1850 pr_info("Encryption finished successfully\n");
1851}
1852
1853/* Perform cipher operation */
1854static unsigned int test_ablkcipher_encdec(struct ablkcipher_def *ablk,
1855 int enc)
1856{
1857 int rc = 0;
1858
1859 if (enc)
1860 rc = crypto_ablkcipher_encrypt(ablk-&gt;req);
1861 else
1862 rc = crypto_ablkcipher_decrypt(ablk-&gt;req);
1863
1864 switch (rc) {
1865 case 0:
1866 break;
1867 case -EINPROGRESS:
1868 case -EBUSY:
1869 rc = wait_for_completion_interruptible(
1870 &amp;ablk-&gt;result.completion);
1871 if (!rc &amp;&amp; !ablk-&gt;result.err) {
1872 reinit_completion(&amp;ablk-&gt;result.completion);
1873 break;
1874 }
1875 default:
1876 pr_info("ablkcipher encrypt returned with %d result %d\n",
1877 rc, ablk-&gt;result.err);
1878 break;
1879 }
1880 init_completion(&amp;ablk-&gt;result.completion);
1881
1882 return rc;
1883}
1884
1885/* Initialize and trigger cipher operation */
1886static int test_ablkcipher(void)
1887{
1888 struct ablkcipher_def ablk;
1889 struct crypto_ablkcipher *ablkcipher = NULL;
1890 struct ablkcipher_request *req = NULL;
1891 char *scratchpad = NULL;
1892 char *ivdata = NULL;
1893 unsigned char key[32];
1894 int ret = -EFAULT;
1895
1896 ablkcipher = crypto_alloc_ablkcipher("cbc-aes-aesni", 0, 0);
1897 if (IS_ERR(ablkcipher)) {
1898 pr_info("could not allocate ablkcipher handle\n");
1899 return PTR_ERR(ablkcipher);
1900 }
1901
1902 req = ablkcipher_request_alloc(ablkcipher, GFP_KERNEL);
1903 if (IS_ERR(req)) {
1904 pr_info("could not allocate request queue\n");
1905 ret = PTR_ERR(req);
1906 goto out;
1907 }
1908
1909 ablkcipher_request_set_callback(req, CRYPTO_TFM_REQ_MAY_BACKLOG,
1910 test_ablkcipher_cb,
1911 &amp;ablk.result);
1912
1913 /* AES 256 with random key */
1914 get_random_bytes(&amp;key, 32);
1915 if (crypto_ablkcipher_setkey(ablkcipher, key, 32)) {
1916 pr_info("key could not be set\n");
1917 ret = -EAGAIN;
1918 goto out;
1919 }
1920
1921 /* IV will be random */
1922 ivdata = kmalloc(16, GFP_KERNEL);
1923 if (!ivdata) {
1924 pr_info("could not allocate ivdata\n");
1925 goto out;
1926 }
1927 get_random_bytes(ivdata, 16);
1928
1929 /* Input data will be random */
1930 scratchpad = kmalloc(16, GFP_KERNEL);
1931 if (!scratchpad) {
1932 pr_info("could not allocate scratchpad\n");
1933 goto out;
1934 }
1935 get_random_bytes(scratchpad, 16);
1936
1937 ablk.tfm = ablkcipher;
1938 ablk.req = req;
1939
1940 /* We encrypt one block */
1941 sg_init_one(&amp;ablk.sg, scratchpad, 16);
1942 ablkcipher_request_set_crypt(req, &amp;ablk.sg, &amp;ablk.sg, 16, ivdata);
1943 init_completion(&amp;ablk.result.completion);
1944
1945 /* encrypt data */
1946 ret = test_ablkcipher_encdec(&amp;ablk, 1);
1947 if (ret)
1948 goto out;
1949
1950 pr_info("Encryption triggered successfully\n");
1951
1952out:
1953 if (ablkcipher)
1954 crypto_free_ablkcipher(ablkcipher);
1955 if (req)
1956 ablkcipher_request_free(req);
1957 if (ivdata)
1958 kfree(ivdata);
1959 if (scratchpad)
1960 kfree(scratchpad);
1961 return ret;
1962}
1963 </programlisting>
1964 </sect1>
1965
1966 <sect1><title>Code Example For Synchronous Block Cipher Operation</title>
1967 <programlisting>
1968
1969static int test_blkcipher(void)
1970{
1971 struct crypto_blkcipher *blkcipher = NULL;
1972 char *cipher = "cbc(aes)";
1973 // AES 128
1974 charkey =
1975"\x12\x34\x56\x78\x90\xab\xcd\xef\x12\x34\x56\x78\x90\xab\xcd\xef";
1976 chariv =
1977"\x12\x34\x56\x78\x90\xab\xcd\xef\x12\x34\x56\x78\x90\xab\xcd\xef";
1978 unsigned int ivsize = 0;
1979 char *scratchpad = NULL; // holds plaintext and ciphertext
1980 struct scatterlist sg;
1981 struct blkcipher_desc desc;
1982 int ret = -EFAULT;
1983
1984 blkcipher = crypto_alloc_blkcipher(cipher, 0, 0);
1985 if (IS_ERR(blkcipher)) {
1986 printk("could not allocate blkcipher handle for %s\n", cipher);
1987 return -PTR_ERR(blkcipher);
1988 }
1989
1990 if (crypto_blkcipher_setkey(blkcipher, key, strlen(key))) {
1991 printk("key could not be set\n");
1992 ret = -EAGAIN;
1993 goto out;
1994 }
1995
1996 ivsize = crypto_blkcipher_ivsize(blkcipher);
1997 if (ivsize) {
1998 if (ivsize != strlen(iv))
1999 printk("IV length differs from expected length\n");
2000 crypto_blkcipher_set_iv(blkcipher, iv, ivsize);
2001 }
2002
2003 scratchpad = kmalloc(crypto_blkcipher_blocksize(blkcipher), GFP_KERNEL);
2004 if (!scratchpad) {
2005 printk("could not allocate scratchpad for %s\n", cipher);
2006 goto out;
2007 }
2008 /* get some random data that we want to encrypt */
2009 get_random_bytes(scratchpad, crypto_blkcipher_blocksize(blkcipher));
2010
2011 desc.flags = 0;
2012 desc.tfm = blkcipher;
2013 sg_init_one(&amp;sg, scratchpad, crypto_blkcipher_blocksize(blkcipher));
2014
2015 /* encrypt data in place */
2016 crypto_blkcipher_encrypt(&amp;desc, &amp;sg, &amp;sg,
2017 crypto_blkcipher_blocksize(blkcipher));
2018
2019 /* decrypt data in place
2020 * crypto_blkcipher_decrypt(&amp;desc, &amp;sg, &amp;sg,
2021 */ crypto_blkcipher_blocksize(blkcipher));
2022
2023
2024 printk("Cipher operation completed\n");
2025 return 0;
2026
2027out:
2028 if (blkcipher)
2029 crypto_free_blkcipher(blkcipher);
2030 if (scratchpad)
2031 kzfree(scratchpad);
2032 return ret;
2033}
2034 </programlisting>
2035 </sect1>
2036
2037 <sect1><title>Code Example For Use of Operational State Memory With SHASH</title>
2038 <programlisting>
2039
2040struct sdesc {
2041 struct shash_desc shash;
2042 char ctx[];
2043};
2044
2045static struct sdescinit_sdesc(struct crypto_shash *alg)
2046{
2047 struct sdescsdesc;
2048 int size;
2049
2050 size = sizeof(struct shash_desc) + crypto_shash_descsize(alg);
2051 sdesc = kmalloc(size, GFP_KERNEL);
2052 if (!sdesc)
2053 return ERR_PTR(-ENOMEM);
2054 sdesc-&gt;shash.tfm = alg;
2055 sdesc-&gt;shash.flags = 0x0;
2056 return sdesc;
2057}
2058
2059static int calc_hash(struct crypto_shashalg,
2060 const unsigned chardata, unsigned int datalen,
2061 unsigned chardigest) {
2062 struct sdescsdesc;
2063 int ret;
2064
2065 sdesc = init_sdesc(alg);
2066 if (IS_ERR(sdesc)) {
2067 pr_info("trusted_key: can't alloc %s\n", hash_alg);
2068 return PTR_ERR(sdesc);
2069 }
2070
2071 ret = crypto_shash_digest(&amp;sdesc-&gt;shash, data, datalen, digest);
2072 kfree(sdesc);
2073 return ret;
2074}
2075 </programlisting>
2076 </sect1>
2077
2078 <sect1><title>Code Example For Random Number Generator Usage</title>
2079 <programlisting>
2080
2081static int get_random_numbers(u8 *buf, unsigned int len)
2082{
2083 struct crypto_rngrng = NULL;
2084 chardrbg = "drbg_nopr_sha256"; /* Hash DRBG with SHA-256, no PR */
2085 int ret;
2086
2087 if (!buf || !len) {
2088 pr_debug("No output buffer provided\n");
2089 return -EINVAL;
2090 }
2091
2092 rng = crypto_alloc_rng(drbg, 0, 0);
2093 if (IS_ERR(rng)) {
2094 pr_debug("could not allocate RNG handle for %s\n", drbg);
2095 return -PTR_ERR(rng);
2096 }
2097
2098 ret = crypto_rng_get_bytes(rng, buf, len);
2099 if (ret &lt; 0)
2100 pr_debug("generation of random numbers failed\n");
2101 else if (ret == 0)
2102 pr_debug("RNG returned no data");
2103 else
2104 pr_debug("RNG returned %d bytes of data\n", ret);
2105
2106out:
2107 crypto_free_rng(rng);
2108 return ret;
2109}
2110 </programlisting>
2111 </sect1>
2112 </chapter>
2113 </book>