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diff --git a/Doc/library/hashlib-blake2.rst b/Doc/library/hashlib-blake2.rst new file mode 100644 index 0000000000..eb5e4414a1 --- /dev/null +++ b/Doc/library/hashlib-blake2.rst @@ -0,0 +1,444 @@ +.. _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/ + |