INADA Naoki
10 years ago
3 changed files with 434 additions and 443 deletions
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.. _hashlib-blake2: |
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:mod:`hashlib` --- BLAKE2 hash functions |
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======================================== |
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.. currentmodule:: hashlib |
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.. sectionauthor:: Dmitry Chestnykh |
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.. index:: |
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single: blake2b, blake2s |
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BLAKE2_ is a cryptographic hash function defined in RFC-7693_ that comes in two |
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flavors: |
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* **BLAKE2b**, optimized for 64-bit platforms and produces digests of any size |
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between 1 and 64 bytes, |
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* **BLAKE2s**, optimized for 8- to 32-bit platforms and produces digests of any |
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size between 1 and 32 bytes. |
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BLAKE2 supports **keyed mode** (a faster and simpler replacement for HMAC_), |
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**salted hashing**, **personalization**, and **tree hashing**. |
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Hash objects from this module follow the API of standard library's |
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:mod:`hashlib` objects. |
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Creating hash objects |
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--------------------- |
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New hash objects are created by calling constructor functions: |
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.. function:: blake2b(data=b'', digest_size=64, key=b'', salt=b'', \ |
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person=b'', fanout=1, depth=1, leaf_size=0, node_offset=0, \ |
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node_depth=0, inner_size=0, last_node=False) |
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.. function:: blake2s(data=b'', digest_size=32, key=b'', salt=b'', \ |
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person=b'', fanout=1, depth=1, leaf_size=0, node_offset=0, \ |
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node_depth=0, inner_size=0, last_node=False) |
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These functions return the corresponding hash objects for calculating |
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BLAKE2b or BLAKE2s. They optionally take these general parameters: |
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* *data*: initial chunk of data to hash, which must be interpretable as buffer |
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of bytes. |
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* *digest_size*: size of output digest in bytes. |
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* *key*: key for keyed hashing (up to 64 bytes for BLAKE2b, up to 32 bytes for |
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BLAKE2s). |
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* *salt*: salt for randomized hashing (up to 16 bytes for BLAKE2b, up to 8 |
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bytes for BLAKE2s). |
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* *person*: personalization string (up to 16 bytes for BLAKE2b, up to 8 bytes |
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for BLAKE2s). |
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The following table shows limits for general parameters (in bytes): |
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|
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======= =========== ======== ========= =========== |
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Hash digest_size len(key) len(salt) len(person) |
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======= =========== ======== ========= =========== |
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BLAKE2b 64 64 16 16 |
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BLAKE2s 32 32 8 8 |
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======= =========== ======== ========= =========== |
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.. note:: |
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BLAKE2 specification defines constant lengths for salt and personalization |
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parameters, however, for convenience, this implementation accepts byte |
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strings of any size up to the specified length. If the length of the |
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parameter is less than specified, it is padded with zeros, thus, for |
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example, ``b'salt'`` and ``b'salt\x00'`` is the same value. (This is not |
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the case for *key*.) |
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These sizes are available as module `constants`_ described below. |
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Constructor functions also accept the following tree hashing parameters: |
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* *fanout*: fanout (0 to 255, 0 if unlimited, 1 in sequential mode). |
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* *depth*: maximal depth of tree (1 to 255, 255 if unlimited, 1 in |
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sequential mode). |
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* *leaf_size*: maximal byte length of leaf (0 to 2**32-1, 0 if unlimited or in |
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sequential mode). |
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* *node_offset*: node offset (0 to 2**64-1 for BLAKE2b, 0 to 2**48-1 for |
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BLAKE2s, 0 for the first, leftmost, leaf, or in sequential mode). |
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* *node_depth*: node depth (0 to 255, 0 for leaves, or in sequential mode). |
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* *inner_size*: inner digest size (0 to 64 for BLAKE2b, 0 to 32 for |
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BLAKE2s, 0 in sequential mode). |
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* *last_node*: boolean indicating whether the processed node is the last |
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one (`False` for sequential mode). |
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.. figure:: hashlib-blake2-tree.png |
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:alt: Explanation of tree mode parameters. |
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See section 2.10 in `BLAKE2 specification |
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<https://blake2.net/blake2_20130129.pdf>`_ for comprehensive review of tree |
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hashing. |
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Constants |
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--------- |
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.. data:: blake2b.SALT_SIZE |
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.. data:: blake2s.SALT_SIZE |
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Salt length (maximum length accepted by constructors). |
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.. data:: blake2b.PERSON_SIZE |
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.. data:: blake2s.PERSON_SIZE |
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Personalization string length (maximum length accepted by constructors). |
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.. data:: blake2b.MAX_KEY_SIZE |
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.. data:: blake2s.MAX_KEY_SIZE |
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Maximum key size. |
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.. data:: blake2b.MAX_DIGEST_SIZE |
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.. data:: blake2s.MAX_DIGEST_SIZE |
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Maximum digest size that the hash function can output. |
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Examples |
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-------- |
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Simple hashing |
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^^^^^^^^^^^^^^ |
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To calculate hash of some data, you should first construct a hash object by |
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calling the appropriate constructor function (:func:`blake2b` or |
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:func:`blake2s`), then update it with the data by calling :meth:`update` on the |
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object, and, finally, get the digest out of the object by calling |
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:meth:`digest` (or :meth:`hexdigest` for hex-encoded string). |
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>>> from hashlib import blake2b |
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>>> h = blake2b() |
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>>> h.update(b'Hello world') |
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>>> h.hexdigest() |
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'6ff843ba685842aa82031d3f53c48b66326df7639a63d128974c5c14f31a0f33343a8c65551134ed1ae0f2b0dd2bb495dc81039e3eeb0aa1bb0388bbeac29183' |
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As a shortcut, you can pass the first chunk of data to update directly to the |
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constructor as the first argument (or as *data* keyword argument): |
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>>> from hashlib import blake2b |
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>>> blake2b(b'Hello world').hexdigest() |
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'6ff843ba685842aa82031d3f53c48b66326df7639a63d128974c5c14f31a0f33343a8c65551134ed1ae0f2b0dd2bb495dc81039e3eeb0aa1bb0388bbeac29183' |
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You can call :meth:`hash.update` as many times as you need to iteratively |
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update the hash: |
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>>> from hashlib import blake2b |
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>>> items = [b'Hello', b' ', b'world'] |
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>>> h = blake2b() |
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>>> for item in items: |
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... h.update(item) |
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>>> h.hexdigest() |
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'6ff843ba685842aa82031d3f53c48b66326df7639a63d128974c5c14f31a0f33343a8c65551134ed1ae0f2b0dd2bb495dc81039e3eeb0aa1bb0388bbeac29183' |
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Using different digest sizes |
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^^^^^^^^^^^^^^^^^^^^^^^^^^^^ |
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BLAKE2 has configurable size of digests up to 64 bytes for BLAKE2b and up to 32 |
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bytes for BLAKE2s. For example, to replace SHA-1 with BLAKE2b without changing |
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the size of output, we can tell BLAKE2b to produce 20-byte digests: |
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>>> from hashlib import blake2b |
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>>> h = blake2b(digest_size=20) |
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>>> h.update(b'Replacing SHA1 with the more secure function') |
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>>> h.hexdigest() |
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'd24f26cf8de66472d58d4e1b1774b4c9158b1f4c' |
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>>> h.digest_size |
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20 |
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>>> len(h.digest()) |
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20 |
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Hash objects with different digest sizes have completely different outputs |
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(shorter hashes are *not* prefixes of longer hashes); BLAKE2b and BLAKE2s |
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produce different outputs even if the output length is the same: |
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>>> from hashlib import blake2b, blake2s |
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>>> blake2b(digest_size=10).hexdigest() |
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'6fa1d8fcfd719046d762' |
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>>> blake2b(digest_size=11).hexdigest() |
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'eb6ec15daf9546254f0809' |
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>>> blake2s(digest_size=10).hexdigest() |
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'1bf21a98c78a1c376ae9' |
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>>> blake2s(digest_size=11).hexdigest() |
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'567004bf96e4a25773ebf4' |
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Keyed hashing |
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^^^^^^^^^^^^^ |
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Keyed hashing can be used for authentication as a faster and simpler |
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replacement for `Hash-based message authentication code |
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<http://en.wikipedia.org/wiki/Hash-based_message_authentication_code>`_ (HMAC). |
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BLAKE2 can be securely used in prefix-MAC mode thanks to the |
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indifferentiability property inherited from BLAKE. |
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This example shows how to get a (hex-encoded) 128-bit authentication code for |
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message ``b'message data'`` with key ``b'pseudorandom key'``:: |
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>>> from hashlib import blake2b |
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>>> h = blake2b(key=b'pseudorandom key', digest_size=16) |
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>>> h.update(b'message data') |
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>>> h.hexdigest() |
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'3d363ff7401e02026f4a4687d4863ced' |
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As a practical example, a web application can symmetrically sign cookies sent |
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to users and later verify them to make sure they weren't tampered with:: |
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>>> from hashlib import blake2b |
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>>> from hmac import compare_digest |
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>>> |
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>>> SECRET_KEY = b'pseudorandomly generated server secret key' |
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>>> AUTH_SIZE = 16 |
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>>> |
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>>> def sign(cookie): |
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... h = blake2b(data=cookie, digest_size=AUTH_SIZE, key=SECRET_KEY) |
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... return h.hexdigest() |
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>>> |
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>>> cookie = b'user:vatrogasac' |
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>>> sig = sign(cookie) |
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>>> print("{0},{1}".format(cookie.decode('utf-8'), sig)) |
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user:vatrogasac,349cf904533767ed2d755279a8df84d0 |
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>>> compare_digest(cookie, sig) |
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True |
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>>> compare_digest(b'user:policajac', sig) |
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False |
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>>> compare_digesty(cookie, '0102030405060708090a0b0c0d0e0f00') |
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False |
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Even though there's a native keyed hashing mode, BLAKE2 can, of course, be used |
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in HMAC construction with :mod:`hmac` module:: |
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>>> import hmac, hashlib |
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>>> m = hmac.new(b'secret key', digestmod=hashlib.blake2s) |
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>>> m.update(b'message') |
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>>> m.hexdigest() |
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'e3c8102868d28b5ff85fc35dda07329970d1a01e273c37481326fe0c861c8142' |
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Randomized hashing |
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^^^^^^^^^^^^^^^^^^ |
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By setting *salt* parameter users can introduce randomization to the hash |
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function. Randomized hashing is useful for protecting against collision attacks |
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on the hash function used in digital signatures. |
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Randomized hashing is designed for situations where one party, the message |
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preparer, generates all or part of a message to be signed by a second |
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party, the message signer. If the message preparer is able to find |
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cryptographic hash function collisions (i.e., two messages producing the |
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same hash value), then she might prepare meaningful versions of the message |
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that would produce the same hash value and digital signature, but with |
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different results (e.g., transferring $1,000,000 to an account, rather than |
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$10). Cryptographic hash functions have been designed with collision |
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resistance as a major goal, but the current concentration on attacking |
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cryptographic hash functions may result in a given cryptographic hash |
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function providing less collision resistance than expected. Randomized |
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hashing offers the signer additional protection by reducing the likelihood |
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that a preparer can generate two or more messages that ultimately yield the |
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same hash value during the digital signature generation process --- even if |
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it is practical to find collisions for the hash function. However, the use |
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of randomized hashing may reduce the amount of security provided by a |
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digital signature when all portions of the message are prepared |
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by the signer. |
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(`NIST SP-800-106 "Randomized Hashing for Digital Signatures" |
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<http://csrc.nist.gov/publications/nistpubs/800-106/NIST-SP-800-106.pdf>`_) |
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In BLAKE2 the salt is processed as a one-time input to the hash function during |
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initialization, rather than as an input to each compression function. |
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.. warning:: |
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*Salted hashing* (or just hashing) with BLAKE2 or any other general-purpose |
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cryptographic hash function, such as SHA-256, is not suitable for hashing |
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passwords. See `BLAKE2 FAQ <https://blake2.net/#qa>`_ for more |
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information. |
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.. |
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>>> import os |
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>>> from hashlib import blake2b |
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>>> msg = b'some message' |
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>>> # Calculate the first hash with a random salt. |
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>>> salt1 = os.urandom(blake2b.SALT_SIZE) |
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>>> h1 = blake2b(salt=salt1) |
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>>> h1.update(msg) |
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>>> # Calculate the second hash with a different random salt. |
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>>> salt2 = os.urandom(blake2b.SALT_SIZE) |
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>>> h2 = blake2b(salt=salt2) |
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>>> h2.update(msg) |
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>>> # The digests are different. |
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>>> h1.digest() != h2.digest() |
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True |
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Personalization |
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^^^^^^^^^^^^^^^ |
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Sometimes it is useful to force hash function to produce different digests for |
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the same input for different purposes. Quoting the authors of the Skein hash |
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function: |
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We recommend that all application designers seriously consider doing this; |
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we have seen many protocols where a hash that is computed in one part of |
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the protocol can be used in an entirely different part because two hash |
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computations were done on similar or related data, and the attacker can |
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force the application to make the hash inputs the same. Personalizing each |
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hash function used in the protocol summarily stops this type of attack. |
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(`The Skein Hash Function Family |
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<http://www.skein-hash.info/sites/default/files/skein1.3.pdf>`_, |
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p. 21) |
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BLAKE2 can be personalized by passing bytes to the *person* argument:: |
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>>> from hashlib import blake2b |
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>>> FILES_HASH_PERSON = b'MyApp Files Hash' |
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>>> BLOCK_HASH_PERSON = b'MyApp Block Hash' |
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>>> h = blake2b(digest_size=32, person=FILES_HASH_PERSON) |
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>>> h.update(b'the same content') |
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>>> h.hexdigest() |
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'20d9cd024d4fb086aae819a1432dd2466de12947831b75c5a30cf2676095d3b4' |
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>>> h = blake2b(digest_size=32, person=BLOCK_HASH_PERSON) |
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>>> h.update(b'the same content') |
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>>> h.hexdigest() |
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'cf68fb5761b9c44e7878bfb2c4c9aea52264a80b75005e65619778de59f383a3' |
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Personalization together with the keyed mode can also be used to derive different |
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keys from a single one. |
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>>> from hashlib import blake2s |
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>>> from base64 import b64decode, b64encode |
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>>> orig_key = b64decode(b'Rm5EPJai72qcK3RGBpW3vPNfZy5OZothY+kHY6h21KM=') |
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>>> enc_key = blake2s(key=orig_key, person=b'kEncrypt').digest() |
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>>> mac_key = blake2s(key=orig_key, person=b'kMAC').digest() |
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>>> print(b64encode(enc_key).decode('utf-8')) |
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rbPb15S/Z9t+agffno5wuhB77VbRi6F9Iv2qIxU7WHw= |
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>>> print(b64encode(mac_key).decode('utf-8')) |
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G9GtHFE1YluXY1zWPlYk1e/nWfu0WSEb0KRcjhDeP/o= |
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Tree mode |
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^^^^^^^^^ |
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Here's an example of hashing a minimal tree with two leaf nodes:: |
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10 |
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/ \ |
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00 01 |
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This example uses 64-byte internal digests, and returns the 32-byte final |
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digest:: |
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>>> from hashlib import blake2b |
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>>> |
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>>> FANOUT = 2 |
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>>> DEPTH = 2 |
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>>> LEAF_SIZE = 4096 |
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>>> INNER_SIZE = 64 |
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>>> |
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>>> buf = bytearray(6000) |
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>>> |
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>>> # Left leaf |
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... h00 = blake2b(buf[0:LEAF_SIZE], fanout=FANOUT, depth=DEPTH, |
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... leaf_size=LEAF_SIZE, inner_size=INNER_SIZE, |
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... node_offset=0, node_depth=0, last_node=False) |
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>>> # Right leaf |
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... h01 = blake2b(buf[LEAF_SIZE:], fanout=FANOUT, depth=DEPTH, |
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... leaf_size=LEAF_SIZE, inner_size=INNER_SIZE, |
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... node_offset=1, node_depth=0, last_node=True) |
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>>> # Root node |
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... h10 = blake2b(digest_size=32, fanout=FANOUT, depth=DEPTH, |
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... leaf_size=LEAF_SIZE, inner_size=INNER_SIZE, |
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... node_offset=0, node_depth=1, last_node=True) |
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>>> h10.update(h00.digest()) |
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>>> h10.update(h01.digest()) |
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>>> h10.hexdigest() |
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'3ad2a9b37c6070e374c7a8c508fe20ca86b6ed54e286e93a0318e95e881db5aa' |
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Credits |
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------- |
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|
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BLAKE2_ was designed by *Jean-Philippe Aumasson*, *Samuel Neves*, *Zooko |
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Wilcox-O'Hearn*, and *Christian Winnerlein* based on SHA-3_ finalist BLAKE_ |
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created by *Jean-Philippe Aumasson*, *Luca Henzen*, *Willi Meier*, and |
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*Raphael C.-W. Phan*. |
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|
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It uses core algorithm from ChaCha_ cipher designed by *Daniel J. Bernstein*. |
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The stdlib implementation is based on pyblake2_ module. It was written by |
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*Dmitry Chestnykh* based on C implementation written by *Samuel Neves*. The |
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documentation was copied from pyblake2_ and written by *Dmitry Chestnykh*. |
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|
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The C code was partly rewritten for Python by *Christian Heimes*. |
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|
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The following public domain dedication applies for both C hash function |
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implementation, extension code, and this documentation: |
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|
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To the extent possible under law, the author(s) have dedicated all copyright |
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and related and neighboring rights to this software to the public domain |
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worldwide. This software is distributed without any warranty. |
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|
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You should have received a copy of the CC0 Public Domain Dedication along |
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with this software. If not, see |
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http://creativecommons.org/publicdomain/zero/1.0/. |
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|
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The following people have helped with development or contributed their changes |
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to the project and the public domain according to the Creative Commons Public |
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Domain Dedication 1.0 Universal: |
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|
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* *Alexandr Sokolovskiy* |
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.. seealso:: Official BLAKE2 website: https://blake2.net |
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.. _RFC-7693: https://tools.ietf.org/html/rfc7693 |
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.. _BLAKE2: https://blake2.net |
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.. _HMAC: https://en.wikipedia.org/wiki/Hash-based_message_authentication_code |
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.. _BLAKE: https://131002.net/blake/ |
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.. _SHA-3: https://en.wikipedia.org/wiki/NIST_hash_function_competition |
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.. _ChaCha: https://cr.yp.to/chacha.html |
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.. _pyblake2: https://pythonhosted.org/pyblake2/ |
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|
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