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Jean-Paul Calderone897bc252008-02-18 20:50:23 -05001\documentclass{howto}
2
3\title{Python OpenSSL Manual}
4
Jean-Paul Calderone71ff3682009-04-25 08:30:11 -04005\release{0.9}
Jean-Paul Calderone897bc252008-02-18 20:50:23 -05006
Jean-Paul Calderone0ebe45a2009-04-25 10:40:31 -04007\author{Jean-Paul Calderone}
8\authoraddress{\email{exarkun@twistedmatrix.com}}
Jean-Paul Calderone897bc252008-02-18 20:50:23 -05009
10\usepackage[english]{babel}
11\usepackage[T1]{fontenc}
12
13\begin{document}
14
15\maketitle
16
17\begin{abstract}
18\noindent
19This module is a rather thin wrapper around (a subset of) the OpenSSL library.
20With thin wrapper I mean that a lot of the object methods do nothing more than
21calling a corresponding function in the OpenSSL library.
22\end{abstract}
23
24\tableofcontents
25
26
27\section{Introduction \label{intro}}
28
Jean-Paul Calderone9450d5b2008-09-01 12:04:20 -040029The reason pyOpenSSL was created is that the SSL support in the socket module
30in Python 2.1 (the contemporary version of Python when the pyOpenSSL project
31was begun) was severely limited. Other OpenSSL wrappers for Python at the time
32were also limited, though in different ways. Unfortunately, Python's standard
33library SSL support has remained weak, although other packages (such as
34M2Crypto\footnote{See \url{http://chandlerproject.org/Projects/MeTooCrypto}})
35have made great advances and now equal or exceed pyOpenSSL's functionality.
Jean-Paul Calderone897bc252008-02-18 20:50:23 -050036
Jean-Paul Calderone9450d5b2008-09-01 12:04:20 -040037The reason pyOpenSSL continues to be maintained is that there is a significant
38user community around it, as well as a large amount of software which depends
39on it. It is a great benefit to many people for pyOpenSSL to continue to exist
40and advance.
Jean-Paul Calderone897bc252008-02-18 20:50:23 -050041
42\section{Building and Installing \label{building}}
43
44These instructions can also be found in the file \verb|INSTALL|.
45
46I have tested this on Debian Linux systems (woody and sid), Solaris 2.6 and
472.7. Others have successfully compiled it on Windows and NT.
48
49\subsection{Building the Module on a Unix System \label{building-unix}}
50
51pyOpenSSL uses distutils, so there really shouldn't be any problems. To build
52the library:
53\begin{verbatim}
54python setup.py build
55\end{verbatim}
56
57If your OpenSSL header files aren't in \verb|/usr/include|, you may need to
58supply the \verb|-I| flag to let the setup script know where to look. The same
59goes for the libraries of course, use the \verb|-L| flag. Note that
60\verb|build| won't accept these flags, so you have to run first
61\verb|build_ext| and then \verb|build|! Example:
62\begin{verbatim}
63python setup.py build_ext -I/usr/local/ssl/include -L/usr/local/ssl/lib
64python setup.py build
65\end{verbatim}
66
67Now you should have a directory called \verb|OpenSSL| that contains e.g.
68\verb|SSL.so| and \verb|__init__.py| somewhere in the build dicrectory,
69so just:
70\begin{verbatim}
71python setup.py install
72\end{verbatim}
73
74If you, for some arcane reason, don't want the module to appear in the
75\verb|site-packages| directory, use the \verb|--prefix| option.
76
77You can, of course, do
78\begin{verbatim}
79python setup.py --help
80\end{verbatim}
81
82to find out more about how to use the script.
83
84\subsection{Building the Module on a Windows System \label{building-windows}}
85
86Big thanks to Itamar Shtull-Trauring and Oleg Orlov for their help with
87Windows build instructions. Same as for Unix systems, we have to separate
88the \verb|build_ext| and the \verb|build|.
89
90Building the library:
91
92\begin{verbatim}
93setup.py build_ext -I ...\openssl\inc32 -L ...\openssl\out32dll
94setup.py build
95\end{verbatim}
96
97Where \verb|...\openssl| is of course the location of your OpenSSL installation.
98
99Installation is the same as for Unix systems:
100\begin{verbatim}
101setup.py install
102\end{verbatim}
103
104And similarily, you can do
105\begin{verbatim}
106setup.py --help
107\end{verbatim}
108
109to get more information.
110
111
112\section{\module{OpenSSL} --- Python interface to OpenSSL \label{openssl}}
113
114\declaremodule{extension}{OpenSSL}
115\modulesynopsis{Python interface to OpenSSL}
116
117This package provides a high-level interface to the functions in the
118OpenSSL library. The following modules are defined:
119
120\begin{datadesc}{crypto}
121Generic cryptographic module. Note that if anything is incomplete, this module is!
122\end{datadesc}
123
124\begin{datadesc}{rand}
125An interface to the OpenSSL pseudo random number generator.
126\end{datadesc}
127
128\begin{datadesc}{SSL}
129An interface to the SSL-specific parts of OpenSSL.
130\end{datadesc}
131
132
133% % % crypto moduleOpenSSL
134
135\subsection{\module{crypto} --- Generic cryptographic module \label{openssl-crypto}}
136
137\declaremodule{extension}{crypto}
138\modulesynopsis{Generic cryptographic module}
139
140\begin{datadesc}{X509Type}
Jean-Paul Calderonefc4abd02009-07-04 16:15:36 -0400141See \class{X509}.
Jean-Paul Calderone897bc252008-02-18 20:50:23 -0500142\end{datadesc}
143
Jean-Paul Calderonefc4abd02009-07-04 16:15:36 -0400144\begin{classdesc}{X509}{}
145A class representing X.509 certificates.
146\end{classdesc}
Jean-Paul Calderone897bc252008-02-18 20:50:23 -0500147
148\begin{datadesc}{X509NameType}
Jean-Paul Calderonefc4abd02009-07-04 16:15:36 -0400149See \class{X509Name}.
Jean-Paul Calderone897bc252008-02-18 20:50:23 -0500150\end{datadesc}
151
Jean-Paul Calderonefc4abd02009-07-04 16:15:36 -0400152\begin{classdesc}{X509Name}{x509name}
153A class representing X.509 Distinguished Names.
154
155This constructor creates a copy of \var{x509name} which should be an
156instance of \class{X509Name}.
157\end{classdesc}
Jean-Paul Calderone897bc252008-02-18 20:50:23 -0500158
159\begin{datadesc}{X509ReqType}
Jean-Paul Calderonefc4abd02009-07-04 16:15:36 -0400160See \class{X509Req}.
Jean-Paul Calderone897bc252008-02-18 20:50:23 -0500161\end{datadesc}
162
Jean-Paul Calderonefc4abd02009-07-04 16:15:36 -0400163\begin{classdesc}{X509Req}{}
164A class representing X.509 certificate requests.
165\end{classdesc}
Jean-Paul Calderone897bc252008-02-18 20:50:23 -0500166
167\begin{datadesc}{X509StoreType}
168A Python type object representing the X509Store object type.
169\end{datadesc}
170
171\begin{datadesc}{PKeyType}
Jean-Paul Calderonefc4abd02009-07-04 16:15:36 -0400172See \class{PKey}.
Jean-Paul Calderone897bc252008-02-18 20:50:23 -0500173\end{datadesc}
174
Jean-Paul Calderonefc4abd02009-07-04 16:15:36 -0400175\begin{classdesc}{PKey}{}
176A class representing DSA or RSA keys.
177\end{classdesc}
Jean-Paul Calderone897bc252008-02-18 20:50:23 -0500178
179\begin{datadesc}{PKCS7Type}
180A Python type object representing the PKCS7 object type.
181\end{datadesc}
182
183\begin{datadesc}{PKCS12Type}
184A Python type object representing the PKCS12 object type.
185\end{datadesc}
186
187\begin{datadesc}{X509ExtensionType}
Jean-Paul Calderonefc4abd02009-07-04 16:15:36 -0400188See \class{X509Extension}.
Jean-Paul Calderone897bc252008-02-18 20:50:23 -0500189\end{datadesc}
190
Rick Dean47262da2009-07-08 16:17:17 -0500191\begin{classdesc}{X509Extension}{typename, critical, value\optional{, subject}\optional{, issuer}}
192A class representing an X.509 v3 certificate extensions.
193See \url{http://openssl.org/docs/apps/x509v3_config.html\#STANDARD_EXTENSIONS}
194for \var{typename} strings and their options.
195Optional parameters \var{subject} and \var{issuer} must be X509 objects.
Jean-Paul Calderonefc4abd02009-07-04 16:15:36 -0400196\end{classdesc}
Jean-Paul Calderone897bc252008-02-18 20:50:23 -0500197
198\begin{datadesc}{NetscapeSPKIType}
Jean-Paul Calderonefc4abd02009-07-04 16:15:36 -0400199See \class{NetscapeSPKI}.
Jean-Paul Calderone897bc252008-02-18 20:50:23 -0500200\end{datadesc}
201
Jean-Paul Calderonefc4abd02009-07-04 16:15:36 -0400202\begin{classdesc}{NetscapeSPKI}{\optional{enc}}
203A class representing Netscape SPKI objects.
204
205If the \var{enc} argument is present, it should be a base64-encoded string
206representing a NetscapeSPKI object, as returned by the \method{b64_encode}
207method.
208\end{classdesc}
Jean-Paul Calderone897bc252008-02-18 20:50:23 -0500209
210\begin{datadesc}{FILETYPE_PEM}
211\dataline{FILETYPE_ASN1}
212File type constants.
213\end{datadesc}
214
215\begin{datadesc}{TYPE_RSA}
216\dataline{TYPE_DSA}
217Key type constants.
218\end{datadesc}
219
220\begin{excdesc}{Error}
221Generic exception used in the \module{crypto} module.
222\end{excdesc}
223
224\begin{funcdesc}{dump_certificate}{type, cert}
225Dump the certificate \var{cert} into a buffer string encoded with the type
226\var{type}.
227\end{funcdesc}
228
229\begin{funcdesc}{dump_certificate_request}{type, req}
230Dump the certificate request \var{req} into a buffer string encoded with the
231type \var{type}.
232\end{funcdesc}
233
234\begin{funcdesc}{dump_privatekey}{type, pkey\optional{, cipher, passphrase}}
235Dump the private key \var{pkey} into a buffer string encoded with the type
236\var{type}, optionally (if \var{type} is \constant{FILETYPE_PEM}) encrypting it
237using \var{cipher} and \var{passphrase}.
238
239\var{passphrase} must be either a string or a callback for providing the
240pass phrase.
241\end{funcdesc}
242
243\begin{funcdesc}{load_certificate}{type, buffer}
244Load a certificate (X509) from the string \var{buffer} encoded with the
245type \var{type}.
246\end{funcdesc}
247
248\begin{funcdesc}{load_certificate_request}{type, buffer}
249Load a certificate request (X509Req) from the string \var{buffer} encoded with
250the type \var{type}.
251\end{funcdesc}
252
253\begin{funcdesc}{load_privatekey}{type, buffer\optional{, passphrase}}
254Load a private key (PKey) from the string \var{buffer} encoded with
255the type \var{type} (must be one of \constant{FILETYPE_PEM} and
256\constant{FILETYPE_ASN1}).
257
258\var{passphrase} must be either a string or a callback for providing the
259pass phrase.
260\end{funcdesc}
261
262\begin{funcdesc}{load_pkcs7_data}{type, buffer}
263Load pkcs7 data from the string \var{buffer} encoded with the type \var{type}.
264\end{funcdesc}
265
266\begin{funcdesc}{load_pkcs12}{buffer\optional{, passphrase}}
267Load pkcs12 data from the string \var{buffer}. If the pkcs12 structure is
268encrypted, a \var{passphrase} must be included.
269\end{funcdesc}
270
Jean-Paul Calderone897bc252008-02-18 20:50:23 -0500271\subsubsection{X509 objects \label{openssl-x509}}
272
273X509 objects have the following methods:
274
275\begin{methoddesc}[X509]{get_issuer}{}
Jean-Paul Calderone2aa2b332008-03-06 21:43:14 -0500276Return an X509Name object representing the issuer of the certificate.
Jean-Paul Calderone897bc252008-02-18 20:50:23 -0500277\end{methoddesc}
278
279\begin{methoddesc}[X509]{get_pubkey}{}
280Return a PKey object representing the public key of the certificate.
281\end{methoddesc}
282
283\begin{methoddesc}[X509]{get_serial_number}{}
284Return the certificate serial number.
285\end{methoddesc}
286
287\begin{methoddesc}[X509]{get_subject}{}
Jean-Paul Calderone2aa2b332008-03-06 21:43:14 -0500288Return an X509Name object representing the subject of the certificate.
Jean-Paul Calderone897bc252008-02-18 20:50:23 -0500289\end{methoddesc}
290
291\begin{methoddesc}[X509]{get_version}{}
292Return the certificate version.
293\end{methoddesc}
294
Jean-Paul Calderone525ef802008-03-09 20:39:42 -0400295\begin{methoddesc}[X509]{get_notBefore}{}
296Return a string giving the time before which the certificate is not valid. The
297string is formatted as an ASN1 GENERALIZEDTIME:
298\begin{verbatim}
299 YYYYMMDDhhmmssZ
300 YYYYMMDDhhmmss+hhmm
301 YYYYMMDDhhmmss-hhmm
302\end{verbatim}
Jean-Paul Calderonee0615b52008-03-09 21:44:46 -0400303If no value exists for this field, \code{None} is returned.
Jean-Paul Calderone525ef802008-03-09 20:39:42 -0400304\end{methoddesc}
305
306\begin{methoddesc}[X509]{get_notAfter}{}
307Return a string giving the time after which the certificate is not valid. The
308string is formatted as an ASN1 GENERALIZEDTIME:
309\begin{verbatim}
310 YYYYMMDDhhmmssZ
311 YYYYMMDDhhmmss+hhmm
312 YYYYMMDDhhmmss-hhmm
313\end{verbatim}
Jean-Paul Calderonee0615b52008-03-09 21:44:46 -0400314If no value exists for this field, \code{None} is returned.
Jean-Paul Calderone525ef802008-03-09 20:39:42 -0400315\end{methoddesc}
316
317\begin{methoddesc}[X509]{set_notBefore}{when}
318Change the time before which the certificate is not valid. \var{when} is a
319string formatted as an ASN1 GENERALIZEDTIME:
320\begin{verbatim}
321 YYYYMMDDhhmmssZ
322 YYYYMMDDhhmmss+hhmm
323 YYYYMMDDhhmmss-hhmm
324\end{verbatim}
325\end{methoddesc}
326
327\begin{methoddesc}[X509]{set_notAfter}{when}
328Change the time after which the certificate is not valid. \var{when} is a
329string formatted as an ASN1 GENERALIZEDTIME:
330\begin{verbatim}
331 YYYYMMDDhhmmssZ
332 YYYYMMDDhhmmss+hhmm
333 YYYYMMDDhhmmss-hhmm
334\end{verbatim}
335\end{methoddesc}
336
Jean-Paul Calderone897bc252008-02-18 20:50:23 -0500337\begin{methoddesc}[X509]{gmtime_adj_notBefore}{time}
338Adjust the timestamp (in GMT) when the certificate starts being valid.
339\end{methoddesc}
340
341\begin{methoddesc}[X509]{gmtime_adj_notAfter}{time}
342Adjust the timestamp (in GMT) when the certificate stops being valid.
343\end{methoddesc}
344
345\begin{methoddesc}[X509]{has_expired}{}
346Checks the certificate's time stamp against current time. Returns true if the
347certificate has expired and false otherwise.
348\end{methoddesc}
349
350\begin{methoddesc}[X509]{set_issuer}{issuer}
351Set the issuer of the certificate to \var{issuer}.
352\end{methoddesc}
353
354\begin{methoddesc}[X509]{set_pubkey}{pkey}
355Set the public key of the certificate to \var{pkey}.
356\end{methoddesc}
357
358\begin{methoddesc}[X509]{set_serial_number}{serialno}
359Set the serial number of the certificate to \var{serialno}.
360\end{methoddesc}
361
362\begin{methoddesc}[X509]{set_subject}{subject}
363Set the subject of the certificate to \var{subject}.
364\end{methoddesc}
365
366\begin{methoddesc}[X509]{set_version}{version}
367Set the certificate version to \var{version}.
368\end{methoddesc}
369
370\begin{methoddesc}[X509]{sign}{pkey, digest}
371Sign the certificate, using the key \var{pkey} and the message digest algorithm
372identified by the string \var{digest}.
373\end{methoddesc}
374
375\begin{methoddesc}[X509]{subject_name_hash}{}
376Return the hash of the certificate subject.
377\end{methoddesc}
378
379\begin{methoddesc}[X509]{digest}{digest_name}
380Return a digest of the certificate, using the \var{digest_name} method.
Jean-Paul Calderoneb6f0d602008-12-28 21:20:01 -0500381\var{digest_name} must be a string describing a digest algorithm supported
382by OpenSSL (by EVP_get_digestbyname, specifically). For example,
383\constant{"md5"} or \constant{"sha1"}.
Jean-Paul Calderone897bc252008-02-18 20:50:23 -0500384\end{methoddesc}
385
386\begin{methoddesc}[X509]{add_extensions}{extensions}
387Add the extensions in the sequence \var{extensions} to the certificate.
388\end{methoddesc}
389
390\subsubsection{X509Name objects \label{openssl-x509name}}
391
Jean-Paul Calderone2dd8ff52008-03-24 17:43:58 -0400392X509Name objects have the following methods:
393
394\begin{methoddesc}[X509Name]{hash}{}
395Return an integer giving the first four bytes of the MD5 digest of the DER
396representation of the name.
397\end{methoddesc}
398
Jean-Paul Calderonea6edbf82008-03-25 15:19:11 -0400399\begin{methoddesc}[X509Name]{der}{}
400Return a string giving the DER representation of the name.
401\end{methoddesc}
402
Jean-Paul Calderonec54cc182008-03-26 21:11:07 -0400403\begin{methoddesc}[X509Name]{get_components}{}
404Return a list of two-tuples of strings giving the components of the name.
405\end{methoddesc}
406
Jean-Paul Calderone897bc252008-02-18 20:50:23 -0500407X509Name objects have the following members:
408
409\begin{memberdesc}[X509Name]{countryName}
410The country of the entity. \code{C} may be used as an alias for
411\code{countryName}.
412\end{memberdesc}
413
414\begin{memberdesc}[X509Name]{stateOrProvinceName}
415The state or province of the entity. \code{ST} may be used as an alias for
416\code{stateOrProvinceName}·
417\end{memberdesc}
418
419\begin{memberdesc}[X509Name]{localityName}
420The locality of the entity. \code{L} may be used as an alias for
421\code{localityName}.
422\end{memberdesc}
423
424\begin{memberdesc}[X509Name]{organizationName}
425The organization name of the entity. \code{O} may be used as an alias for
426\code{organizationName}.
427\end{memberdesc}
428
429\begin{memberdesc}[X509Name]{organizationalUnitName}
430The organizational unit of the entity. \code{OU} may be used as an alias for
431\code{organizationalUnitName}.
432\end{memberdesc}
433
434\begin{memberdesc}[X509Name]{commonName}
435The common name of the entity. \code{CN} may be used as an alias for
436\code{commonName}.
437\end{memberdesc}
438
439\begin{memberdesc}[X509Name]{emailAddress}
440The e-mail address of the entity.
441\end{memberdesc}
442
443\subsubsection{X509Req objects \label{openssl-x509req}}
444
445X509Req objects have the following methods:
446
447\begin{methoddesc}[X509Req]{get_pubkey}{}
448Return a PKey object representing the public key of the certificate request.
449\end{methoddesc}
450
451\begin{methoddesc}[X509Req]{get_subject}{}
Jean-Paul Calderone2aa2b332008-03-06 21:43:14 -0500452Return an X509Name object representing the subject of the certificate.
Jean-Paul Calderone897bc252008-02-18 20:50:23 -0500453\end{methoddesc}
454
455\begin{methoddesc}[X509Req]{set_pubkey}{pkey}
456Set the public key of the certificate request to \var{pkey}.
457\end{methoddesc}
458
459\begin{methoddesc}[X509Req]{sign}{pkey, digest}
460Sign the certificate request, using the key \var{pkey} and the message digest
461algorithm identified by the string \var{digest}.
462\end{methoddesc}
463
464\begin{methoddesc}[X509Req]{verify}{pkey}
465Verify a certificate request using the public key \var{pkey}.
466\end{methoddesc}
467
Jean-Paul Calderone8dd19b82008-12-28 20:41:16 -0500468\begin{methoddesc}[X509Req]{set_version}{version}
469Set the version (RFC 2459, 4.1.2.1) of the certificate request to
470\var{version}.
471\end{methoddesc}
472
473\begin{methoddesc}[X509Req]{get_version}{}
474Get the version (RFC 2459, 4.1.2.1) of the certificate request.
475\end{methoddesc}
476
Jean-Paul Calderone897bc252008-02-18 20:50:23 -0500477\subsubsection{X509Store objects \label{openssl-x509store}}
478
479The X509Store object has currently just one method:
480
481\begin{methoddesc}[X509Store]{add_cert}{cert}
482Add the certificate \var{cert} to the certificate store.
483\end{methoddesc}
484
485\subsubsection{PKey objects \label{openssl-pkey}}
486
487The PKey object has the following methods:
488
489\begin{methoddesc}[PKey]{bits}{}
490Return the number of bits of the key.
491\end{methoddesc}
492
493\begin{methoddesc}[PKey]{generate_key}{type, bits}
494Generate a public/private key pair of the type \var{type} (one of
495\constant{TYPE_RSA} and \constant{TYPE_DSA}) with the size \var{bits}.
496\end{methoddesc}
497
498\begin{methoddesc}[PKey]{type}{}
499Return the type of the key.
500\end{methoddesc}
501
502\subsubsection{PKCS7 objects \label{openssl-pkcs7}}
503
504PKCS7 objects have the following methods:
505
506\begin{methoddesc}[PKCS7]{type_is_signed}{}
507FIXME
508\end{methoddesc}
509
510\begin{methoddesc}[PKCS7]{type_is_enveloped}{}
511FIXME
512\end{methoddesc}
513
514\begin{methoddesc}[PKCS7]{type_is_signedAndEnveloped}{}
515FIXME
516\end{methoddesc}
517
518\begin{methoddesc}[PKCS7]{type_is_data}{}
519FIXME
520\end{methoddesc}
521
522\begin{methoddesc}[PKCS7]{get_type_name}{}
523Get the type name of the PKCS7.
524\end{methoddesc}
525
526\subsubsection{PKCS12 objects \label{openssl-pkcs12}}
527
528PKCS12 objects have the following methods:
529
530\begin{methoddesc}[PKCS12]{get_certificate}{}
531Return certificate portion of the PKCS12 structure.
532\end{methoddesc}
533
534\begin{methoddesc}[PKCS12]{get_privatekey}{}
535Return private key portion of the PKCS12 structure
536\end{methoddesc}
537
538\begin{methoddesc}[PKCS12]{get_ca_certificates}{}
539Return CA certificates within the PKCS12 object as a tuple. Returns
540None if no CA certificates are present.
541\end{methoddesc}
542
543\subsubsection{X509Extension objects \label{openssl-509ext}}
544
Jean-Paul Calderonef8c5fab2008-12-31 15:53:48 -0500545X509Extension objects have several methods:
Jean-Paul Calderone897bc252008-02-18 20:50:23 -0500546
547\begin{methoddesc}[X509Extension]{get_critical}{}
548Return the critical field of the extension object.
549\end{methoddesc}
550
Jean-Paul Calderonef8c5fab2008-12-31 15:53:48 -0500551\begin{methoddesc}[X509Extension]{get_short_name}{}
552Return the short type name of the extension object.
553\end{methoddesc}
554
Jean-Paul Calderone897bc252008-02-18 20:50:23 -0500555\subsubsection{NetscapeSPKI objects \label{openssl-netscape-spki}}
556
557NetscapeSPKI objects have the following methods:
558
559\begin{methoddesc}[NetscapeSPKI]{b64_encode}{}
560Return a base64-encoded string representation of the object.
561\end{methoddesc}
562
563\begin{methoddesc}[NetscapeSPKI]{get_pubkey}{}
564Return the public key of object.
565\end{methoddesc}
566
567\begin{methoddesc}[NetscapeSPKI]{set_pubkey}{key}
568Set the public key of the object to \var{key}.
569\end{methoddesc}
570
571\begin{methoddesc}[NetscapeSPKI]{sign}{key, digest_name}
Jean-Paul Calderoneb6f0d602008-12-28 21:20:01 -0500572Sign the NetscapeSPKI object using the given \var{key} and
573\var{digest_name}. \var{digest_name} must be a string describing a digest
574algorithm supported by OpenSSL (by EVP_get_digestbyname, specifically). For
575example, \constant{"md5"} or \constant{"sha1"}.
Jean-Paul Calderone897bc252008-02-18 20:50:23 -0500576\end{methoddesc}
577
578\begin{methoddesc}[NetscapeSPKI]{verify}{key}
579Verify the NetscapeSPKI object using the given \var{key}.
580\end{methoddesc}
581
582
583% % % rand module
584
585\subsection{\module{rand} --- An interface to the OpenSSL pseudo random number generator \label{openssl-rand}}
586
587\declaremodule{extension}{rand}
588\modulesynopsis{An interface to the OpenSSL pseudo random number generator}
589
590This module handles the OpenSSL pseudo random number generator (PRNG) and
591declares the following:
592
593\begin{funcdesc}{add}{string, entropy}
594Mix bytes from \var{string} into the PRNG state. The \var{entropy} argument is
595(the lower bound of) an estimate of how much randomness is contained in
596\var{string}, measured in bytes. For more information, see e.g. \rfc{1750}.
597\end{funcdesc}
598
599\begin{funcdesc}{egd}{path\optional{, bytes}}
600Query the Entropy Gathering Daemon\footnote{See
601\url{http://www.lothar.com/tech/crypto/}} on socket \var{path} for \var{bytes}
602bytes of random data and and uses \function{add} to seed the PRNG. The default
603value of \var{bytes} is 255.
604\end{funcdesc}
605
606\begin{funcdesc}{load_file}{path\optional{, bytes}}
607Read \var{bytes} bytes (or all of it, if \var{bytes} is negative) of data from
608the file \var{path} to seed the PRNG. The default value of \var{bytes} is -1.
609\end{funcdesc}
610
611\begin{funcdesc}{screen}{}
612Add the current contents of the screen to the PRNG state.
613Availability: Windows.
614\end{funcdesc}
615
616\begin{funcdesc}{seed}{string}
617This is equivalent to calling \function{add} with \var{entropy} as the length
618of the string.
619\end{funcdesc}
620
621\begin{funcdesc}{status}{}
622Returns true if the PRNG has been seeded with enough data, and false otherwise.
623\end{funcdesc}
624
625\begin{funcdesc}{write_file}{path}
626Write a number of random bytes (currently 1024) to the file \var{path}. This
627file can then be used with \function{load_file} to seed the PRNG again.
628\end{funcdesc}
629
630
631
632% % % SSL module
633
634\subsection{\module{SSL} --- An interface to the SSL-specific parts of OpenSSL \label{openssl-ssl}}
635
636\declaremodule{extension}{SSL}
637\modulesynopsis{An interface to the SSL-specific parts of OpenSSL}
638
639This module handles things specific to SSL. There are two objects defined:
640Context, Connection.
641
642\begin{datadesc}{SSLv2_METHOD}
643\dataline{SSLv3_METHOD}
644\dataline{SSLv23_METHOD}
645\dataline{TLSv1_METHOD}
646These constants represent the different SSL methods to use when creating a
647context object.
648\end{datadesc}
649
650\begin{datadesc}{VERIFY_NONE}
651\dataline{VERIFY_PEER}
652\dataline{VERIFY_FAIL_IF_NO_PEER_CERT}
653These constants represent the verification mode used by the Context
654object's \method{set_verify} method.
655\end{datadesc}
656
657\begin{datadesc}{FILETYPE_PEM}
658\dataline{FILETYPE_ASN1}
659File type constants used with the \method{use_certificate_file} and
660\method{use_privatekey_file} methods of Context objects.
661\end{datadesc}
662
663\begin{datadesc}{OP_SINGLE_DH_USE}
664\dataline{OP_EPHEMERAL_RSA}
665\dataline{OP_NO_SSLv2}
666\dataline{OP_NO_SSLv3}
667\dataline{OP_NO_TLSv1}
668Constants used with \method{set_options} of Context objects.
669\constant{OP_SINGLE_DH_USE} means to always create a new key when using ephemeral
670Diffie-Hellman. \constant{OP_EPHEMERAL_RSA} means to always use ephemeral RSA keys
671when doing RSA operations. \constant{OP_NO_SSLv2}, \constant{OP_NO_SSLv3} and
672\constant{OP_NO_TLSv1} means to disable those specific protocols. This is
673interesting if you're using e.g. \constant{SSLv23_METHOD} to get an SSLv2-compatible
674handshake, but don't want to use SSLv2.
675\end{datadesc}
676
677\begin{datadesc}{ContextType}
Jean-Paul Calderonefc4abd02009-07-04 16:15:36 -0400678See \class{Context}.
Jean-Paul Calderone897bc252008-02-18 20:50:23 -0500679\end{datadesc}
680
Jean-Paul Calderonefc4abd02009-07-04 16:15:36 -0400681\begin{classdesc}{Context}{method}
682A class representing SSL contexts. Contexts define the parameters of one or
683more SSL connections.
684
685\var{method} should be \constant{SSLv2_METHOD}, \constant{SSLv3_METHOD},
Jean-Paul Calderone897bc252008-02-18 20:50:23 -0500686\constant{SSLv23_METHOD} or \constant{TLSv1_METHOD}.
Jean-Paul Calderonefc4abd02009-07-04 16:15:36 -0400687\end{classdesc}
Jean-Paul Calderone897bc252008-02-18 20:50:23 -0500688
689\begin{datadesc}{ConnectionType}
Jean-Paul Calderonefc4abd02009-07-04 16:15:36 -0400690See \class{Connection}.
Jean-Paul Calderone897bc252008-02-18 20:50:23 -0500691\end{datadesc}
692
Jean-Paul Calderonefc4abd02009-07-04 16:15:36 -0400693\begin{classdesc}{Connection}{context, socket}
694A class representing SSL connections.
695
696\var{context} should be an instance of \class{Context} and \var{socket}
697should be a socket \footnote{Actually, all that is required is an object
698that \emph{behaves} like a socket, you could even use files, even though
699it'd be tricky to get the handshakes right!} object. \var{socket} may be
700\var{None}; in this case, the Connection is created with a memory BIO: see
701the \method{bio_read}, \method{bio_write}, and \method{bio_shutdown}
702methods.
703\end{classdesc}
Jean-Paul Calderone897bc252008-02-18 20:50:23 -0500704
705\begin{excdesc}{Error}
706This exception is used as a base class for the other SSL-related
707exceptions, but may also be raised directly.
708
709Whenever this exception is raised directly, it has a list of error messages
710from the OpenSSL error queue, where each item is a tuple \code{(\var{lib},
711\var{function}, \var{reason})}. Here \var{lib}, \var{function} and \var{reason}
712are all strings, describing where and what the problem is. See \manpage{err}{3}
713for more information.
714\end{excdesc}
715
716\begin{excdesc}{ZeroReturnError}
717This exception matches the error return code \code{SSL_ERROR_ZERO_RETURN}, and
718is raised when the SSL Connection has been closed. In SSL 3.0 and TLS 1.0, this
719only occurs if a closure alert has occurred in the protocol, i.e. the
720connection has been closed cleanly. Note that this does not necessarily
721mean that the transport layer (e.g. a socket) has been closed.
722
723It may seem a little strange that this is an exception, but it does match an
724\code{SSL_ERROR} code, and is very convenient.
725\end{excdesc}
726
727\begin{excdesc}{WantReadError}
728The operation did not complete; the same I/O method should be called again
729later, with the same arguments. Any I/O method can lead to this since new
730handshakes can occur at any time.
731\end{excdesc}
732
733\begin{excdesc}{WantWriteError}
734See \exception{WantReadError}.
735\end{excdesc}
736
737\begin{excdesc}{WantX509LookupError}
738The operation did not complete because an application callback has asked to be
739called again. The I/O method should be called again later, with the same
740arguments. Note: This won't occur in this version, as there are no such
741callbacks in this version.
742\end{excdesc}
743
744\begin{excdesc}{SysCallError}
745The \exception{SysCallError} occurs when there's an I/O error and OpenSSL's
746error queue does not contain any information. This can mean two things: An
747error in the transport protocol, or an end of file that violates the protocol.
748The parameter to the exception is always a pair \code{(\var{errnum},
749\var{errstr})}.
750\end{excdesc}
751
752
753\subsubsection{Context objects \label{openssl-context}}
754
755Context objects have the following methods:
756
757\begin{methoddesc}[Context]{check_privatekey}{}
758Check if the private key (loaded with \method{use_privatekey\optional{_file}})
759matches the certificate (loaded with \method{use_certificate\optional{_file}}).
Jean-Paul Calderonef05fbbe2008-03-06 21:52:35 -0500760Returns \code{None} if they match, raises \exception{Error} otherwise.
Jean-Paul Calderone897bc252008-02-18 20:50:23 -0500761\end{methoddesc}
762
763\begin{methoddesc}[Context]{get_app_data}{}
764Retrieve application data as set by \method{set_app_data}.
765\end{methoddesc}
766
767\begin{methoddesc}[Context]{get_cert_store}{}
768Retrieve the certificate store (a X509Store object) that the context uses.
769This can be used to add "trusted" certificates without using the.
770\method{load_verify_locations()} method.
771\end{methoddesc}
772
773\begin{methoddesc}[Context]{get_timeout}{}
774Retrieve session timeout, as set by \method{set_timeout}. The default is 300
775seconds.
776\end{methoddesc}
777
778\begin{methoddesc}[Context]{get_verify_depth}{}
779Retrieve the Context object's verify depth, as set by
780\method{set_verify_depth}.
781\end{methoddesc}
782
783\begin{methoddesc}[Context]{get_verify_mode}{}
Jean-Paul Calderoneae4238d2008-12-28 21:13:50 -0500784Retrieve the Context object's verify mode, as set by \method{set_verify}.
Jean-Paul Calderone897bc252008-02-18 20:50:23 -0500785\end{methoddesc}
786
787\begin{methoddesc}[Context]{load_client_ca}{pemfile}
788Read a file with PEM-formatted certificates that will be sent to the client
789when requesting a client certificate.
790\end{methoddesc}
791
Jean-Paul Calderone5601c242008-09-07 21:06:52 -0400792\begin{methoddesc}[Context]{load_verify_locations}{pemfile, capath}
793Specify where CA certificates for verification purposes are located. These
794are trusted certificates. Note that the certificates have to be in PEM
795format. If capath is passed, it must be a directory prepared using the
796\code{c_rehash} tool included with OpenSSL. Either, but not both, of
797\var{pemfile} or \var{capath} may be \code{None}.
798\end{methoddesc}
799
800\begin{methoddesc}[Context]{set_default_verify_paths}{}
801Specify that the platform provided CA certificates are to be used for
Jean-Paul Calderone1d287e52009-03-07 09:09:07 -0500802verification purposes. This method may not work properly on OS X.
Jean-Paul Calderone897bc252008-02-18 20:50:23 -0500803\end{methoddesc}
804
805\begin{methoddesc}[Context]{load_tmp_dh}{dhfile}
806Load parameters for Ephemeral Diffie-Hellman from \var{dhfile}.
807\end{methoddesc}
808
809\begin{methoddesc}[Context]{set_app_data}{data}
810Associate \var{data} with this Context object. \var{data} can be retrieved
811later using the \method{get_app_data} method.
812\end{methoddesc}
813
814\begin{methoddesc}[Context]{set_cipher_list}{ciphers}
815Set the list of ciphers to be used in this context. See the OpenSSL manual for
816more information (e.g. ciphers(1))
817\end{methoddesc}
818
819\begin{methoddesc}[Context]{set_info_callback}{callback}
820Set the information callback to \var{callback}. This function will be called
821from time to time during SSL handshakes.
Jean-Paul Calderone897bc252008-02-18 20:50:23 -0500822\var{callback} should take three arguments: a Connection object and two
823integers. The first integer specifies where in the SSL handshake the function
824was called, and the other the return code from a (possibly failed) internal
825function call.
826\end{methoddesc}
827
828\begin{methoddesc}[Context]{set_options}{options}
829Add SSL options. Options you have set before are not cleared!
Jean-Paul Calderone897bc252008-02-18 20:50:23 -0500830This method should be used with the \constant{OP_*} constants.
831\end{methoddesc}
832
833\begin{methoddesc}[Context]{set_passwd_cb}{callback\optional{, userdata}}
834Set the passphrase callback to \var{callback}. This function will be called
Jean-Paul Calderone1eeb29e2008-10-19 11:50:53 -0400835when a private key with a passphrase is loaded. \var{callback} must accept
836three positional arguments. First, an integer giving the maximum length of
837the passphrase it may return. If the returned passphrase is longer than
838this, it will be truncated. Second, a boolean value which will be true if
839the user should be prompted for the passphrase twice and the callback should
840verify that the two values supplied are equal. Third, the value given as the
841\var{userdata} parameter to \method{set_passwd_cb}. If an error occurs,
842\var{callback} should return a false value (e.g. an empty string).
Jean-Paul Calderone897bc252008-02-18 20:50:23 -0500843\end{methoddesc}
844
845\begin{methoddesc}[Context]{set_session_id}{name}
846Set the context \var{name} within which a session can be reused for this
847Context object. This is needed when doing session resumption, because there is
848no way for a stored session to know which Context object it is associated with.
849\var{name} may be any binary data.
850\end{methoddesc}
851
852\begin{methoddesc}[Context]{set_timeout}{timeout}
853Set the timeout for newly created sessions for this Context object to
854\var{timeout}. \var{timeout} must be given in (whole) seconds. The default
855value is 300 seconds. See the OpenSSL manual for more information (e.g.
856SSL_CTX_set_timeout(3)).
857\end{methoddesc}
858
859\begin{methoddesc}[Context]{set_verify}{mode, callback}
860Set the verification flags for this Context object to \var{mode} and specify
861that \var{callback} should be used for verification callbacks. \var{mode}
862should be one of \constant{VERIFY_NONE} and \constant{VERIFY_PEER}. If
863\constant{VERIFY_PEER} is used, \var{mode} can be OR:ed with
864\constant{VERIFY_FAIL_IF_NO_PEER_CERT} and \constant{VERIFY_CLIENT_ONCE} to
865further control the behaviour.
Jean-Paul Calderone897bc252008-02-18 20:50:23 -0500866\var{callback} should take five arguments: A Connection object, an X509 object,
867and three integer variables, which are in turn potential error number, error
868depth and return code. \var{callback} should return true if verification passes
869and false otherwise.
870\end{methoddesc}
871
872\begin{methoddesc}[Context]{set_verify_depth}{depth}
873Set the maximum depth for the certificate chain verification that shall be
874allowed for this Context object.
875\end{methoddesc}
876
877\begin{methoddesc}[Context]{use_certificate}{cert}
878Use the certificate \var{cert} which has to be a X509 object.
879\end{methoddesc}
880
Jean-Paul Calderone87b40602008-02-19 21:13:25 -0500881\begin{methoddesc}[Context]{add_extra_chain_cert}{cert}
882Adds the certificate \var{cert}, which has to be a X509 object, to the
883certificate chain presented together with the certificate.
884\end{methoddesc}
885
Jean-Paul Calderone897bc252008-02-18 20:50:23 -0500886\begin{methoddesc}[Context]{use_certificate_chain_file}{file}
887Load a certificate chain from \var{file} which must be PEM encoded.
888\end{methoddesc}
889
890\begin{methoddesc}[Context]{use_privatekey}{pkey}
891Use the private key \var{pkey} which has to be a PKey object.
892\end{methoddesc}
893
894\begin{methoddesc}[Context]{use_certificate_file}{file\optional{, format}}
895Load the first certificate found in \var{file}. The certificate must be in the
896format specified by \var{format}, which is either \constant{FILETYPE_PEM} or
897\constant{FILETYPE_ASN1}. The default is \constant{FILETYPE_PEM}.
898\end{methoddesc}
899
900\begin{methoddesc}[Context]{use_privatekey_file}{file\optional{, format}}
901Load the first private key found in \var{file}. The private key must be in the
902format specified by \var{format}, which is either \constant{FILETYPE_PEM} or
903\constant{FILETYPE_ASN1}. The default is \constant{FILETYPE_PEM}.
904\end{methoddesc}
905
906
907\subsubsection{Connection objects \label{openssl-connection}}
908
909Connection objects have the following methods:
910
911\begin{methoddesc}[Connection]{accept}{}
912Call the \method{accept} method of the underlying socket and set up SSL on the
913returned socket, using the Context object supplied to this Connection object at
914creation. Returns a pair \code{(\var{conn}, \var{address})}. where \var{conn}
915is the new Connection object created, and \var{address} is as returned by the
916socket's \method{accept}.
917\end{methoddesc}
918
919\begin{methoddesc}[Connection]{bind}{address}
920Call the \method{bind} method of the underlying socket.
921\end{methoddesc}
922
923\begin{methoddesc}[Connection]{close}{}
924Call the \method{close} method of the underlying socket. Note: If you want
925correct SSL closure, you need to call the \method{shutdown} method first.
926\end{methoddesc}
927
928\begin{methoddesc}[Connection]{connect}{address}
929Call the \method{connect} method of the underlying socket and set up SSL on the
930socket, using the Context object supplied to this Connection object at
931creation.
932\end{methoddesc}
933
934\begin{methoddesc}[Connection]{connect_ex}{address}
935Call the \method{connect_ex} method of the underlying socket and set up SSL on
936the socket, using the Context object supplied to this Connection object at
937creation. Note that if the \method{connect_ex} method of the socket doesn't
938return 0, SSL won't be initialized.
939\end{methoddesc}
940
941\begin{methoddesc}[Connection]{do_handshake}{}
942Perform an SSL handshake (usually called after \method{renegotiate} or one of
943\method{set_accept_state} or \method{set_accept_state}). This can raise the
944same exceptions as \method{send} and \method{recv}.
945\end{methoddesc}
946
947\begin{methoddesc}[Connection]{fileno}{}
948Retrieve the file descriptor number for the underlying socket.
949\end{methoddesc}
950
951\begin{methoddesc}[Connection]{listen}{backlog}
952Call the \method{listen} method of the underlying socket.
953\end{methoddesc}
954
955\begin{methoddesc}[Connection]{get_app_data}{}
956Retrieve application data as set by \method{set_app_data}.
957\end{methoddesc}
958
959\begin{methoddesc}[Connection]{get_cipher_list}{}
960Retrieve the list of ciphers used by the Connection object. WARNING: This API
961has changed. It used to take an optional parameter and just return a string,
962but not it returns the entire list in one go.
963\end{methoddesc}
964
965\begin{methoddesc}[Connection]{get_context}{}
966Retrieve the Context object associated with this Connection.
967\end{methoddesc}
968
969\begin{methoddesc}[Connection]{get_peer_certificate}{}
970Retrieve the other side's certificate (if any)
971\end{methoddesc}
972
973\begin{methoddesc}[Connection]{getpeername}{}
974Call the \method{getpeername} method of the underlying socket.
975\end{methoddesc}
976
977\begin{methoddesc}[Connection]{getsockname}{}
978Call the \method{getsockname} method of the underlying socket.
979\end{methoddesc}
980
981\begin{methoddesc}[Connection]{getsockopt}{level, optname\optional{, buflen}}
982Call the \method{getsockopt} method of the underlying socket.
983\end{methoddesc}
984
985\begin{methoddesc}[Connection]{pending}{}
Jean-Paul Calderoneb6f57be2008-03-06 21:22:16 -0500986Retrieve the number of bytes that can be safely read from the SSL buffer
987(\emph{not} the underlying transport buffer).
Jean-Paul Calderone897bc252008-02-18 20:50:23 -0500988\end{methoddesc}
989
990\begin{methoddesc}[Connection]{recv}{bufsize}
991Receive data from the Connection. The return value is a string representing the
992data received. The maximum amount of data to be received at once, is specified
993by \var{bufsize}.
994\end{methoddesc}
995
Jean-Paul Calderoneb6b17122009-05-01 16:36:11 -0400996\begin{methoddesc}[Connection]{bio_write}{bytes}
997If the Connection was created with a memory BIO, this method can be used to add
998bytes to the read end of that memory BIO. The Connection can then read the
999bytes (for example, in response to a call to \method{recv}).
1000\end{methoddesc}
1001
Jean-Paul Calderone897bc252008-02-18 20:50:23 -05001002\begin{methoddesc}[Connection]{renegotiate}{}
1003Renegotiate the SSL session. Call this if you wish to change cipher suites or
1004anything like that.
1005\end{methoddesc}
1006
1007\begin{methoddesc}[Connection]{send}{string}
1008Send the \var{string} data to the Connection.
1009\end{methoddesc}
1010
Jean-Paul Calderoneb6b17122009-05-01 16:36:11 -04001011\begin{methoddesc}[Connection]{bio_read}{bufsize}
1012If the Connection was created with a memory BIO, this method can be used to
1013read bytes from the write end of that memory BIO. Many Connection methods will
1014add bytes which must be read in this manner or the buffer will eventually fill
1015up and the Connection will be able to take no further actions.
1016\end{methoddesc}
1017
Jean-Paul Calderone897bc252008-02-18 20:50:23 -05001018\begin{methoddesc}[Connection]{sendall}{string}
1019Send all of the \var{string} data to the Connection. This calls \method{send}
1020repeatedly until all data is sent. If an error occurs, it's impossible to tell
1021how much data has been sent.
1022\end{methoddesc}
1023
1024\begin{methoddesc}[Connection]{set_accept_state}{}
1025Set the connection to work in server mode. The handshake will be handled
1026automatically by read/write.
1027\end{methoddesc}
1028
1029\begin{methoddesc}[Connection]{set_app_data}{data}
1030Associate \var{data} with this Connection object. \var{data} can be retrieved
1031later using the \method{get_app_data} method.
1032\end{methoddesc}
1033
1034\begin{methoddesc}[Connection]{set_connect_state}{}
1035Set the connection to work in client mode. The handshake will be handled
1036automatically by read/write.
1037\end{methoddesc}
1038
1039\begin{methoddesc}[Connection]{setblocking}{flag}
1040Call the \method{setblocking} method of the underlying socket.
1041\end{methoddesc}
1042
1043\begin{methoddesc}[Connection]{setsockopt}{level, optname, value}
1044Call the \method{setsockopt} method of the underlying socket.
1045\end{methoddesc}
1046
1047\begin{methoddesc}[Connection]{shutdown}{}
1048Send the shutdown message to the Connection. Returns true if the shutdown
1049message exchange is completed and false otherwise (in which case you call
1050\method{recv()} or \method{send()} when the connection becomes
1051readable/writeable.
1052\end{methoddesc}
1053
Jean-Paul Calderone72b8f0f2008-02-21 23:57:40 -05001054\begin{methoddesc}[Connection]{get_shutdown}{}
1055Get the shutdown state of the Connection. Returns a bitvector of either or
1056both of \var{SENT_SHUTDOWN} and \var{RECEIVED_SHUTDOWN}.
1057\end{methoddesc}
1058
1059\begin{methoddesc}[Connection]{set_shutdown}{state}
1060Set the shutdown state of the Connection. \var{state} is a bitvector of
1061either or both of \var{SENT_SHUTDOWN} and \var{RECEIVED_SHUTDOWN}.
1062\end{methoddesc}
1063
Jean-Paul Calderone897bc252008-02-18 20:50:23 -05001064\begin{methoddesc}[Connection]{sock_shutdown}{how}
1065Call the \method{shutdown} method of the underlying socket.
1066\end{methoddesc}
1067
Jean-Paul Calderoneb6b17122009-05-01 16:36:11 -04001068\begin{methoddesc}[Connection]{bio_shutdown}{}
1069If the Connection was created with a memory BIO, this method can be used to
1070indicate that ``end of file'' has been reached on the read end of that memory
1071BIO.
1072\end{methoddesc}
1073
Jean-Paul Calderone897bc252008-02-18 20:50:23 -05001074\begin{methoddesc}[Connection]{state_string}{}
1075Retrieve a verbose string detailing the state of the Connection.
1076\end{methoddesc}
1077
Jean-Paul Calderonefd236f32009-05-03 19:45:07 -04001078\begin{methoddesc}[Connection]{client_random}{}
1079Retrieve the random value used with the client hello message.
1080\end{methoddesc}
1081
1082\begin{methoddesc}[Connection]{server_random}{}
1083Retrieve the random value used with the server hello message.
1084\end{methoddesc}
1085
1086\begin{methoddesc}[Connection]{master_key}{}
1087Retrieve the value of the master key for this session.
1088\end{methoddesc}
1089
Jean-Paul Calderone897bc252008-02-18 20:50:23 -05001090\begin{methoddesc}[Connection]{want_read}{}
1091Checks if more data has to be read from the transport layer to complete an
1092operation.
1093\end{methoddesc}
1094
1095\begin{methoddesc}[Connection]{want_write}{}
1096Checks if there is data to write to the transport layer to complete an
1097operation.
1098\end{methoddesc}
1099
1100
1101
1102\section{Internals \label{internals}}
1103
1104We ran into three main problems developing this: Exceptions, callbacks and
1105accessing socket methods. This is what this chapter is about.
1106
1107\subsection{Exceptions \label{exceptions}}
1108
1109We realized early that most of the exceptions would be raised by the I/O
1110functions of OpenSSL, so it felt natural to mimic OpenSSL's error code system,
1111translating them into Python exceptions. This naturally gives us the exceptions
1112\exception{SSL.ZeroReturnError}, \exception{SSL.WantReadError},
1113\exception{SSL.WantWriteError}, \exception{SSL.WantX509LookupError} and
1114\exception{SSL.SysCallError}.
1115
1116For more information about this, see section \ref{openssl-ssl}.
1117
1118
1119\subsection{Callbacks \label{callbacks}}
1120
1121There are a number of problems with callbacks. First of all, OpenSSL is written
1122as a C library, it's not meant to have Python callbacks, so a way around that
1123is needed. Another problem is thread support. A lot of the OpenSSL I/O
1124functions can block if the socket is in blocking mode, and then you want other
1125Python threads to be able to do other things. The real trouble is if you've
Jean-Paul Calderoneb7d6db22008-09-21 18:57:56 -04001126released the global CPython interpreter lock to do a potentially blocking
1127operation, and the operation calls a callback. Then we must take the GIL back,
1128since calling Python APIs without holding it is not allowed.
Jean-Paul Calderone897bc252008-02-18 20:50:23 -05001129
1130There are two solutions to the first problem, both of which are necessary. The
1131first solution to use is if the C callback allows ''userdata'' to be passed to
1132it (an arbitrary pointer normally). This is great! We can set our Python
1133function object as the real userdata and emulate userdata for the Python
1134function in another way. The other solution can be used if an object with an
1135''app_data'' system always is passed to the callback. For example, the SSL
1136object in OpenSSL has app_data functions and in e.g. the verification
1137callbacks, you can retrieve the related SSL object. What we do is to set our
1138wrapper \class{Connection} object as app_data for the SSL object, and we can
1139easily find the Python callback.
1140
Jean-Paul Calderoneb7d6db22008-09-21 18:57:56 -04001141The other problem is solved using thread local variables. Whenever the GIL is
1142released before calling into an OpenSSL API, the PyThreadState pointer returned
1143by \cfunction{PyEval_SaveState} is stored in a global thread local variable
1144(using Python's own TLS API, \cfunction{PyThread_set_key_value}). When it is
1145necessary to re-acquire the GIL, either after the OpenSSL API returns or in a C
1146callback invoked by that OpenSSL API, the value of the thread local variable is
1147retrieved (\cfunction{PyThread_get_key_value}) and used to re-acquire the GIL.
1148This allows Python threads to execute while OpenSSL APIs are running and allows
1149use of any particular pyOpenSSL object from any Python thread, since there is
1150no per-thread state associated with any of these objects and since OpenSSL is
1151threadsafe (as long as properly initialized, as pyOpenSSL initializes it).
Jean-Paul Calderone897bc252008-02-18 20:50:23 -05001152
1153
1154\subsection{Acessing Socket Methods \label{socket-methods}}
1155
1156We quickly saw the benefit of wrapping socket methods in the
1157\class{SSL.Connection} class, for an easy transition into using SSL. The
1158problem here is that the \module{socket} module lacks a C API, and all the
1159methods are declared static. One approach would be to have \module{OpenSSL} as
1160a submodule to the \module{socket} module, placing all the code in
1161\file{socketmodule.c}, but this is obviously not a good solution, since you
1162might not want to import tonnes of extra stuff you're not going to use when
1163importing the \module{socket} module. The other approach is to somehow get a
1164pointer to the method to be called, either the C function, or a callable Python
1165object. This is not really a good solution either, since there's a lot of
1166lookups involved.
1167
1168The way it works is that you have to supply a ``\class{socket}-like'' transport
1169object to the \class{SSL.Connection}. The only requirement of this object is
1170that it has a \method{fileno()} method that returns a file descriptor that's
1171valid at the C level (i.e. you can use the system calls read and write). If you
1172want to use the \method{connect()} or \method{accept()} methods of the
1173\class{SSL.Connection} object, the transport object has to supply such
1174methods too. Apart from them, any method lookups in the \class{SSL.Connection}
1175object that fail are passed on to the underlying transport object.
1176
1177Future changes might be to allow Python-level transport objects, that instead
1178of having \method{fileno()} methods, have \method{read()} and \method{write()}
1179methods, so more advanced features of Python can be used. This would probably
1180entail some sort of OpenSSL ``BIOs'', but converting Python strings back and
1181forth is expensive, so this shouldn't be used unless necessary. Other nice
1182things would be to be able to pass in different transport objects for reading
1183and writing, but then the \method{fileno()} method of \class{SSL.Connection}
1184becomes virtually useless. Also, should the method resolution be used on the
1185read-transport or the write-transport?
1186
1187
1188\end{document}