| .. _hashlib-blake2: |
| |
| :mod:`hashlib` --- BLAKE2 hash functions |
| ======================================== |
| |
| .. module:: hashlib |
| :synopsis: BLAKE2 hash function for Python |
| .. sectionauthor:: Dmitry Chestnykh |
| |
| .. index:: |
| single: blake2b, blake2s |
| |
| BLAKE2_ is a cryptographic hash function defined in RFC-7693_ that comes in two |
| flavors: |
| |
| * **BLAKE2b**, optimized for 64-bit platforms and produces digests of any size |
| between 1 and 64 bytes, |
| |
| * **BLAKE2s**, optimized for 8- to 32-bit platforms and produces digests of any |
| size between 1 and 32 bytes. |
| |
| BLAKE2 supports **keyed mode** (a faster and simpler replacement for HMAC_), |
| **salted hashing**, **personalization**, and **tree hashing**. |
| |
| Hash objects from this module follow the API of standard library's |
| :mod:`hashlib` objects. |
| |
| |
| Module |
| ====== |
| |
| Creating hash objects |
| --------------------- |
| |
| New hash objects are created by calling constructor functions: |
| |
| |
| .. function:: blake2b(data=b'', digest_size=64, key=b'', salt=b'', \ |
| person=b'', fanout=1, depth=1, leaf_size=0, node_offset=0, \ |
| node_depth=0, inner_size=0, last_node=False) |
| |
| .. function:: blake2s(data=b'', digest_size=32, key=b'', salt=b'', \ |
| person=b'', fanout=1, depth=1, leaf_size=0, node_offset=0, \ |
| node_depth=0, inner_size=0, last_node=False) |
| |
| |
| These functions return the corresponding hash objects for calculating |
| BLAKE2b or BLAKE2s. They optionally take these general parameters: |
| |
| * *data*: initial chunk of data to hash, which must be interpretable as buffer |
| of bytes. |
| |
| * *digest_size*: size of output digest in bytes. |
| |
| * *key*: key for keyed hashing (up to 64 bytes for BLAKE2b, up to 32 bytes for |
| BLAKE2s). |
| |
| * *salt*: salt for randomized hashing (up to 16 bytes for BLAKE2b, up to 8 |
| bytes for BLAKE2s). |
| |
| * *person*: personalization string (up to 16 bytes for BLAKE2b, up to 8 bytes |
| for BLAKE2s). |
| |
| The following table shows limits for general parameters (in bytes): |
| |
| ======= =========== ======== ========= =========== |
| Hash digest_size len(key) len(salt) len(person) |
| ======= =========== ======== ========= =========== |
| BLAKE2b 64 64 16 16 |
| BLAKE2s 32 32 8 8 |
| ======= =========== ======== ========= =========== |
| |
| .. note:: |
| |
| BLAKE2 specification defines constant lengths for salt and personalization |
| parameters, however, for convenience, this implementation accepts byte |
| strings of any size up to the specified length. If the length of the |
| parameter is less than specified, it is padded with zeros, thus, for |
| example, ``b'salt'`` and ``b'salt\x00'`` is the same value. (This is not |
| the case for *key*.) |
| |
| These sizes are available as module `constants`_ described below. |
| |
| Constructor functions also accept the following tree hashing parameters: |
| |
| * *fanout*: fanout (0 to 255, 0 if unlimited, 1 in sequential mode). |
| |
| * *depth*: maximal depth of tree (1 to 255, 255 if unlimited, 1 in |
| sequential mode). |
| |
| * *leaf_size*: maximal byte length of leaf (0 to 2**32-1, 0 if unlimited or in |
| sequential mode). |
| |
| * *node_offset*: node offset (0 to 2**64-1 for BLAKE2b, 0 to 2**48-1 for |
| BLAKE2s, 0 for the first, leftmost, leaf, or in sequential mode). |
| |
| * *node_depth*: node depth (0 to 255, 0 for leaves, or in sequential mode). |
| |
| * *inner_size*: inner digest size (0 to 64 for BLAKE2b, 0 to 32 for |
| BLAKE2s, 0 in sequential mode). |
| |
| * *last_node*: boolean indicating whether the processed node is the last |
| one (`False` for sequential mode). |
| |
| .. figure:: hashlib-blake2-tree.png |
| :alt: Explanation of tree mode parameters. |
| |
| See section 2.10 in `BLAKE2 specification |
| <https://blake2.net/blake2_20130129.pdf>`_ for comprehensive review of tree |
| hashing. |
| |
| |
| Constants |
| --------- |
| |
| .. data:: blake2b.SALT_SIZE |
| .. data:: blake2s.SALT_SIZE |
| |
| Salt length (maximum length accepted by constructors). |
| |
| |
| .. data:: blake2b.PERSON_SIZE |
| .. data:: blake2s.PERSON_SIZE |
| |
| Personalization string length (maximum length accepted by constructors). |
| |
| |
| .. data:: blake2b.MAX_KEY_SIZE |
| .. data:: blake2s.MAX_KEY_SIZE |
| |
| Maximum key size. |
| |
| |
| .. data:: blake2b.MAX_DIGEST_SIZE |
| .. data:: blake2s.MAX_DIGEST_SIZE |
| |
| Maximum digest size that the hash function can output. |
| |
| |
| Examples |
| ======== |
| |
| Simple hashing |
| -------------- |
| |
| To calculate hash of some data, you should first construct a hash object by |
| calling the appropriate constructor function (:func:`blake2b` or |
| :func:`blake2s`), then update it with the data by calling :meth:`update` on the |
| object, and, finally, get the digest out of the object by calling |
| :meth:`digest` (or :meth:`hexdigest` for hex-encoded string). |
| |
| >>> from hashlib import blake2b |
| >>> h = blake2b() |
| >>> h.update(b'Hello world') |
| >>> h.hexdigest() |
| '6ff843ba685842aa82031d3f53c48b66326df7639a63d128974c5c14f31a0f33343a8c65551134ed1ae0f2b0dd2bb495dc81039e3eeb0aa1bb0388bbeac29183' |
| |
| |
| As a shortcut, you can pass the first chunk of data to update directly to the |
| constructor as the first argument (or as *data* keyword argument): |
| |
| >>> from hashlib import blake2b |
| >>> blake2b(b'Hello world').hexdigest() |
| '6ff843ba685842aa82031d3f53c48b66326df7639a63d128974c5c14f31a0f33343a8c65551134ed1ae0f2b0dd2bb495dc81039e3eeb0aa1bb0388bbeac29183' |
| |
| You can call :meth:`hash.update` as many times as you need to iteratively |
| update the hash: |
| |
| >>> from hashlib import blake2b |
| >>> items = [b'Hello', b' ', b'world'] |
| >>> h = blake2b() |
| >>> for item in items: |
| ... h.update(item) |
| >>> h.hexdigest() |
| '6ff843ba685842aa82031d3f53c48b66326df7639a63d128974c5c14f31a0f33343a8c65551134ed1ae0f2b0dd2bb495dc81039e3eeb0aa1bb0388bbeac29183' |
| |
| |
| Using different digest sizes |
| ---------------------------- |
| |
| BLAKE2 has configurable size of digests up to 64 bytes for BLAKE2b and up to 32 |
| bytes for BLAKE2s. For example, to replace SHA-1 with BLAKE2b without changing |
| the size of output, we can tell BLAKE2b to produce 20-byte digests: |
| |
| >>> from hashlib import blake2b |
| >>> h = blake2b(digest_size=20) |
| >>> h.update(b'Replacing SHA1 with the more secure function') |
| >>> h.hexdigest() |
| 'd24f26cf8de66472d58d4e1b1774b4c9158b1f4c' |
| >>> h.digest_size |
| 20 |
| >>> len(h.digest()) |
| 20 |
| |
| Hash objects with different digest sizes have completely different outputs |
| (shorter hashes are *not* prefixes of longer hashes); BLAKE2b and BLAKE2s |
| produce different outputs even if the output length is the same: |
| |
| >>> from hashlib import blake2b, blake2s |
| >>> blake2b(digest_size=10).hexdigest() |
| '6fa1d8fcfd719046d762' |
| >>> blake2b(digest_size=11).hexdigest() |
| 'eb6ec15daf9546254f0809' |
| >>> blake2s(digest_size=10).hexdigest() |
| '1bf21a98c78a1c376ae9' |
| >>> blake2s(digest_size=11).hexdigest() |
| '567004bf96e4a25773ebf4' |
| |
| |
| Keyed hashing |
| ------------- |
| |
| Keyed hashing can be used for authentication as a faster and simpler |
| replacement for `Hash-based message authentication code |
| <http://en.wikipedia.org/wiki/Hash-based_message_authentication_code>`_ (HMAC). |
| BLAKE2 can be securely used in prefix-MAC mode thanks to the |
| indifferentiability property inherited from BLAKE. |
| |
| This example shows how to get a (hex-encoded) 128-bit authentication code for |
| message ``b'message data'`` with key ``b'pseudorandom key'``:: |
| |
| >>> from hashlib import blake2b |
| >>> h = blake2b(key=b'pseudorandom key', digest_size=16) |
| >>> h.update(b'message data') |
| >>> h.hexdigest() |
| '3d363ff7401e02026f4a4687d4863ced' |
| |
| |
| As a practical example, a web application can symmetrically sign cookies sent |
| to users and later verify them to make sure they weren't tampered with:: |
| |
| >>> from hashlib import blake2b |
| >>> from hmac import compare_digest |
| >>> |
| >>> SECRET_KEY = b'pseudorandomly generated server secret key' |
| >>> AUTH_SIZE = 16 |
| >>> |
| >>> def sign(cookie): |
| ... h = blake2b(data=cookie, digest_size=AUTH_SIZE, key=SECRET_KEY) |
| ... return h.hexdigest() |
| >>> |
| >>> cookie = b'user:vatrogasac' |
| >>> sig = sign(cookie) |
| >>> print("{0},{1}".format(cookie.decode('utf-8'), sig)) |
| user:vatrogasac,349cf904533767ed2d755279a8df84d0 |
| >>> compare_digest(cookie, sig) |
| True |
| >>> compare_digest(b'user:policajac', sig) |
| False |
| >>> compare_digesty(cookie, '0102030405060708090a0b0c0d0e0f00') |
| False |
| |
| Even though there's a native keyed hashing mode, BLAKE2 can, of course, be used |
| in HMAC construction with :mod:`hmac` module:: |
| |
| >>> import hmac, hashlib |
| >>> m = hmac.new(b'secret key', digestmod=hashlib.blake2s) |
| >>> m.update(b'message') |
| >>> m.hexdigest() |
| 'e3c8102868d28b5ff85fc35dda07329970d1a01e273c37481326fe0c861c8142' |
| |
| |
| Randomized hashing |
| ------------------ |
| |
| By setting *salt* parameter users can introduce randomization to the hash |
| function. Randomized hashing is useful for protecting against collision attacks |
| on the hash function used in digital signatures. |
| |
| Randomized hashing is designed for situations where one party, the message |
| preparer, generates all or part of a message to be signed by a second |
| party, the message signer. If the message preparer is able to find |
| cryptographic hash function collisions (i.e., two messages producing the |
| same hash value), then she might prepare meaningful versions of the message |
| that would produce the same hash value and digital signature, but with |
| different results (e.g., transferring $1,000,000 to an account, rather than |
| $10). Cryptographic hash functions have been designed with collision |
| resistance as a major goal, but the current concentration on attacking |
| cryptographic hash functions may result in a given cryptographic hash |
| function providing less collision resistance than expected. Randomized |
| hashing offers the signer additional protection by reducing the likelihood |
| that a preparer can generate two or more messages that ultimately yield the |
| same hash value during the digital signature generation process – even if |
| it is practical to find collisions for the hash function. However, the use |
| of randomized hashing may reduce the amount of security provided by a |
| digital signature when all portions of the message are prepared |
| by the signer. |
| |
| (`NIST SP-800-106 "Randomized Hashing for Digital Signatures" |
| <http://csrc.nist.gov/publications/nistpubs/800-106/NIST-SP-800-106.pdf>`_) |
| |
| In BLAKE2 the salt is processed as a one-time input to the hash function during |
| initialization, rather than as an input to each compression function. |
| |
| .. warning:: |
| |
| *Salted hashing* (or just hashing) with BLAKE2 or any other general-purpose |
| cryptographic hash function, such as SHA-256, is not suitable for hashing |
| passwords. See `BLAKE2 FAQ <https://blake2.net/#qa>`_ for more |
| information. |
| .. |
| |
| >>> import os |
| >>> from hashlib import blake2b |
| >>> msg = b'some message' |
| >>> # Calculate the first hash with a random salt. |
| >>> salt1 = os.urandom(blake2b.SALT_SIZE) |
| >>> h1 = blake2b(salt=salt1) |
| >>> h1.update(msg) |
| >>> # Calculate the second hash with a different random salt. |
| >>> salt2 = os.urandom(blake2b.SALT_SIZE) |
| >>> h2 = blake2b(salt=salt2) |
| >>> h2.update(msg) |
| >>> # The digests are different. |
| >>> h1.digest() != h2.digest() |
| True |
| |
| |
| Personalization |
| --------------- |
| |
| Sometimes it is useful to force hash function to produce different digests for |
| the same input for different purposes. Quoting the authors of the Skein hash |
| function: |
| |
| We recommend that all application designers seriously consider doing this; |
| we have seen many protocols where a hash that is computed in one part of |
| the protocol can be used in an entirely different part because two hash |
| computations were done on similar or related data, and the attacker can |
| force the application to make the hash inputs the same. Personalizing each |
| hash function used in the protocol summarily stops this type of attack. |
| |
| (`The Skein Hash Function Family |
| <http://www.skein-hash.info/sites/default/files/skein1.3.pdf>`_, |
| p. 21) |
| |
| BLAKE2 can be personalized by passing bytes to the *person* argument:: |
| |
| >>> from hashlib import blake2b |
| >>> FILES_HASH_PERSON = b'MyApp Files Hash' |
| >>> BLOCK_HASH_PERSON = b'MyApp Block Hash' |
| >>> h = blake2b(digest_size=32, person=FILES_HASH_PERSON) |
| >>> h.update(b'the same content') |
| >>> h.hexdigest() |
| '20d9cd024d4fb086aae819a1432dd2466de12947831b75c5a30cf2676095d3b4' |
| >>> h = blake2b(digest_size=32, person=BLOCK_HASH_PERSON) |
| >>> h.update(b'the same content') |
| >>> h.hexdigest() |
| 'cf68fb5761b9c44e7878bfb2c4c9aea52264a80b75005e65619778de59f383a3' |
| |
| Personalization together with the keyed mode can also be used to derive different |
| keys from a single one. |
| |
| >>> from hashlib import blake2s |
| >>> from base64 import b64decode, b64encode |
| >>> orig_key = b64decode(b'Rm5EPJai72qcK3RGBpW3vPNfZy5OZothY+kHY6h21KM=') |
| >>> enc_key = blake2s(key=orig_key, person=b'kEncrypt').digest() |
| >>> mac_key = blake2s(key=orig_key, person=b'kMAC').digest() |
| >>> print(b64encode(enc_key).decode('utf-8')) |
| rbPb15S/Z9t+agffno5wuhB77VbRi6F9Iv2qIxU7WHw= |
| >>> print(b64encode(mac_key).decode('utf-8')) |
| G9GtHFE1YluXY1zWPlYk1e/nWfu0WSEb0KRcjhDeP/o= |
| |
| Tree mode |
| --------- |
| |
| Here's an example of hashing a minimal tree with two leaf nodes:: |
| |
| 10 |
| / \ |
| 00 01 |
| |
| This example uses 64-byte internal digests, and returns the 32-byte final |
| digest:: |
| |
| >>> from hashlib import blake2b |
| >>> |
| >>> FANOUT = 2 |
| >>> DEPTH = 2 |
| >>> LEAF_SIZE = 4096 |
| >>> INNER_SIZE = 64 |
| >>> |
| >>> buf = bytearray(6000) |
| >>> |
| >>> # Left leaf |
| ... h00 = blake2b(buf[0:LEAF_SIZE], fanout=FANOUT, depth=DEPTH, |
| ... leaf_size=LEAF_SIZE, inner_size=INNER_SIZE, |
| ... node_offset=0, node_depth=0, last_node=False) |
| >>> # Right leaf |
| ... h01 = blake2b(buf[LEAF_SIZE:], fanout=FANOUT, depth=DEPTH, |
| ... leaf_size=LEAF_SIZE, inner_size=INNER_SIZE, |
| ... node_offset=1, node_depth=0, last_node=True) |
| >>> # Root node |
| ... h10 = blake2b(digest_size=32, fanout=FANOUT, depth=DEPTH, |
| ... leaf_size=LEAF_SIZE, inner_size=INNER_SIZE, |
| ... node_offset=0, node_depth=1, last_node=True) |
| >>> h10.update(h00.digest()) |
| >>> h10.update(h01.digest()) |
| >>> h10.hexdigest() |
| '3ad2a9b37c6070e374c7a8c508fe20ca86b6ed54e286e93a0318e95e881db5aa' |
| |
| Credits |
| ======= |
| |
| BLAKE2_ was designed by *Jean-Philippe Aumasson*, *Samuel Neves*, *Zooko |
| Wilcox-O'Hearn*, and *Christian Winnerlein* based on SHA-3_ finalist BLAKE_ |
| created by *Jean-Philippe Aumasson*, *Luca Henzen*, *Willi Meier*, and |
| *Raphael C.-W. Phan*. |
| |
| It uses core algorithm from ChaCha_ cipher designed by *Daniel J. Bernstein*. |
| |
| The stdlib implementation is based on pyblake2_ module. It was written by |
| *Dmitry Chestnykh* based on C implementation written by *Samuel Neves*. The |
| documentation was copied from pyblake2_ and written by *Dmitry Chestnykh*. |
| |
| The C code was partly rewritten for Python by *Christian Heimes*. |
| |
| The following public domain dedication applies for both C hash function |
| implementation, extension code, and this documentation: |
| |
| To the extent possible under law, the author(s) have dedicated all copyright |
| and related and neighboring rights to this software to the public domain |
| worldwide. This software is distributed without any warranty. |
| |
| You should have received a copy of the CC0 Public Domain Dedication along |
| with this software. If not, see |
| http://creativecommons.org/publicdomain/zero/1.0/. |
| |
| The following people have helped with development or contributed their changes |
| to the project and the public domain according to the Creative Commons Public |
| Domain Dedication 1.0 Universal: |
| |
| * *Alexandr Sokolovskiy* |
| |
| .. seealso:: Official BLAKE2 website: https://blake2.net |
| |
| .. _RFC-7693: https://tools.ietf.org/html/rfc7693 |
| .. _BLAKE2: https://blake2.net |
| .. _HMAC: https://en.wikipedia.org/wiki/Hash-based_message_authentication_code |
| .. _BLAKE: https://131002.net/blake/ |
| .. _SHA-3: https://en.wikipedia.org/wiki/NIST_hash_function_competition |
| .. _ChaCha: https://cr.yp.to/chacha.html |
| .. _pyblake2: https://pythonhosted.org/pyblake2/ |
| |