kbe/src/lib/python/Doc/library/hashlib.rst
hashlib --- Secure hashes and message digests.. module:: hashlib :synopsis: Secure hash and message digest algorithms.
.. moduleauthor:: Gregory P. Smith [email protected] .. sectionauthor:: Gregory P. Smith [email protected]
Source code: :source:Lib/hashlib.py
.. index:: single: message digest, MD5 single: secure hash algorithm, SHA1, SHA224, SHA256, SHA384, SHA512
.. testsetup::
import hashlib
This module implements a common interface to many different secure hash and
message digest algorithms. Included are the FIPS secure hash algorithms SHA1,
SHA224, SHA256, SHA384, and SHA512 (defined in FIPS 180-2) as well as RSA's MD5
algorithm (defined in Internet :rfc:1321). The terms "secure hash" and
"message digest" are interchangeable. Older algorithms were called message
digests. The modern term is secure hash.
.. note::
If you want the adler32 or crc32 hash functions, they are available in
the :mod:zlib module.
.. warning::
Some algorithms have known hash collision weaknesses, refer to the "See also" section at the end.
.. _hash-algorithms:
There is one constructor method named for each type of :dfn:hash. All return
a hash object with the same simple interface. For example: use :func:sha256 to
create a SHA-256 hash object. You can now feed this object with :term:bytes-like objects <bytes-like object> (normally :class:bytes) using the :meth:update method.
At any point you can ask it for the :dfn:digest of the
concatenation of the data fed to it so far using the :meth:digest or
:meth:hexdigest methods.
.. note::
For better multithreading performance, the Python :term:GIL is released for
data larger than 2047 bytes at object creation or on update.
.. note::
Feeding string objects into :meth:update is not supported, as hashes work
on bytes, not on characters.
.. index:: single: OpenSSL; (use in module hashlib)
Constructors for hash algorithms that are always present in this module are
:func:sha1, :func:sha224, :func:sha256, :func:sha384,
:func:sha512, :func:blake2b, and :func:blake2s.
:func:md5 is normally available as well, though it
may be missing if you are using a rare "FIPS compliant" build of Python.
Additional algorithms may also be available depending upon the OpenSSL
library that Python uses on your platform. On most platforms the
:func:sha3_224, :func:sha3_256, :func:sha3_384, :func:sha3_512,
:func:shake_128, :func:shake_256 are also available.
.. versionadded:: 3.6
SHA3 (Keccak) and SHAKE constructors :func:sha3_224, :func:sha3_256,
:func:sha3_384, :func:sha3_512, :func:shake_128, :func:shake_256.
.. versionadded:: 3.6
:func:blake2b and :func:blake2s were added.
For example, to obtain the digest of the byte string b'Nobody inspects the spammish repetition'::
import hashlib m = hashlib.sha256() m.update(b"Nobody inspects") m.update(b" the spammish repetition") m.digest() b'\x03\x1e\xdd}Ae\x15\x93\xc5\xfe\\x00o\xa5u+7\xfd\xdf\xf7\xbcN\x84:\xa6\xaf\x0c\x95\x0fK\x94\x06' m.digest_size 32 m.block_size 64
More condensed:
hashlib.sha224(b"Nobody inspects the spammish repetition").hexdigest() 'a4337bc45a8fc544c03f52dc550cd6e1e87021bc896588bd79e901e2'
.. function:: new(name[, data])
Is a generic constructor that takes the string name of the desired
algorithm as its first parameter. It also exists to allow access to the
above listed hashes as well as any other algorithms that your OpenSSL
library may offer. The named constructors are much faster than :func:new
and should be preferred.
Using :func:new with an algorithm provided by OpenSSL:
h = hashlib.new('ripemd160') h.update(b"Nobody inspects the spammish repetition") h.hexdigest() 'cc4a5ce1b3df48aec5d22d1f16b894a0b894eccc'
Hashlib provides the following constant attributes:
.. data:: algorithms_guaranteed
A set containing the names of the hash algorithms guaranteed to be supported by this module on all platforms. Note that 'md5' is in this list despite some upstream vendors offering an odd "FIPS compliant" Python build that excludes it.
.. versionadded:: 3.2
.. data:: algorithms_available
A set containing the names of the hash algorithms that are available in the
running Python interpreter. These names will be recognized when passed to
:func:new. :attr:algorithms_guaranteed will always be a subset. The
same algorithm may appear multiple times in this set under different names
(thanks to OpenSSL).
.. versionadded:: 3.2
The following values are provided as constant attributes of the hash objects returned by the constructors:
.. data:: hash.digest_size
The size of the resulting hash in bytes.
.. data:: hash.block_size
The internal block size of the hash algorithm in bytes.
A hash object has the following attributes:
.. attribute:: hash.name
The canonical name of this hash, always lowercase and always suitable as a
parameter to :func:new to create another hash of this type.
.. versionchanged:: 3.4 The name attribute has been present in CPython since its inception, but until Python 3.4 was not formally specified, so may not exist on some platforms.
A hash object has the following methods:
.. method:: hash.update(data)
Update the hash object with the :term:bytes-like object.
Repeated calls are equivalent to a single call with the
concatenation of all the arguments: m.update(a); m.update(b) is
equivalent to m.update(a+b).
.. versionchanged:: 3.1 The Python GIL is released to allow other threads to run while hash updates on data larger than 2047 bytes is taking place when using hash algorithms supplied by OpenSSL.
.. method:: hash.digest()
Return the digest of the data passed to the :meth:update method so far.
This is a bytes object of size :attr:digest_size which may contain bytes in
the whole range from 0 to 255.
.. method:: hash.hexdigest()
Like :meth:digest except the digest is returned as a string object of
double length, containing only hexadecimal digits. This may be used to
exchange the value safely in email or other non-binary environments.
.. method:: hash.copy()
Return a copy ("clone") of the hash object. This can be used to efficiently compute the digests of data sharing a common initial substring.
The :func:shake_128 and :func:shake_256 algorithms provide variable
length digests with length_in_bits//2 up to 128 or 256 bits of security.
As such, their digest methods require a length. Maximum length is not limited
by the SHAKE algorithm.
.. method:: shake.digest(length)
Return the digest of the data passed to the :meth:update method so far.
This is a bytes object of size length which may contain bytes in
the whole range from 0 to 255.
.. method:: shake.hexdigest(length)
Like :meth:digest except the digest is returned as a string object of
double length, containing only hexadecimal digits. This may be used to
exchange the value safely in email or other non-binary environments.
Key derivation and key stretching algorithms are designed for secure password
hashing. Naive algorithms such as sha1(password) are not resistant against
brute-force attacks. A good password hashing function must be tunable, slow, and
include a salt <https://en.wikipedia.org/wiki/Salt_%28cryptography%29>_.
.. function:: pbkdf2_hmac(hash_name, password, salt, iterations, dklen=None)
The function provides PKCS#5 password-based key derivation function 2. It uses HMAC as pseudorandom function.
The string hash_name is the desired name of the hash digest algorithm for
HMAC, e.g. 'sha1' or 'sha256'. password and salt are interpreted as
buffers of bytes. Applications and libraries should limit password to
a sensible length (e.g. 1024). salt should be about 16 or more bytes from
a proper source, e.g. :func:os.urandom.
The number of iterations should be chosen based on the hash algorithm and computing power. As of 2013, at least 100,000 iterations of SHA-256 are suggested.
dklen is the length of the derived key. If dklen is None then the
digest size of the hash algorithm hash_name is used, e.g. 64 for SHA-512.
import hashlib, binascii dk = hashlib.pbkdf2_hmac('sha256', b'password', b'salt', 100000) binascii.hexlify(dk) b'0394a2ede332c9a13eb82e9b24631604c31df978b4e2f0fbd2c549944f9d79a5'
.. versionadded:: 3.4
.. note::
A fast implementation of *pbkdf2_hmac* is available with OpenSSL. The
Python implementation uses an inline version of :mod:`hmac`. It is about
three times slower and doesn't release the GIL.
.. function:: scrypt(password, *, salt, n, r, p, maxmem=0, dklen=64)
The function provides scrypt password-based key derivation function as
defined in :rfc:7914.
password and salt must be :term:bytes-like objects <bytes-like object>. Applications and libraries should limit password
to a sensible length (e.g. 1024). salt should be about 16 or more
bytes from a proper source, e.g. :func:os.urandom.
n is the CPU/Memory cost factor, r the block size, p parallelization factor and maxmem limits memory (OpenSSL 1.1.0 defaults to 32 MiB). dklen is the length of the derived key.
.. availability:: OpenSSL 1.1+.
.. versionadded:: 3.6
.. 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.
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
:term:bytes-like object. It can be passed only as positional argument.
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 264-1 for BLAKE2b, 0 to 248-1 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 positional 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 <https://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(digest_size=AUTH_SIZE, key=SECRET_KEY)
... h.update(cookie)
... return h.hexdigest().encode('utf-8')
>>>
>>> def verify(cookie, sig):
... good_sig = sign(cookie)
... return compare_digest(good_sig, sig)
>>>
>>> cookie = b'user-alice'
>>> sig = sign(cookie)
>>> print("{0},{1}".format(cookie.decode('utf-8'), sig))
user-alice,b'43b3c982cf697e0c5ab22172d1ca7421'
>>> verify(cookie, sig)
True
>>> verify(b'user-bob', sig)
False
>>> verify(cookie, b'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 they 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"
<https://csrc.nist.gov/publications/detail/sp/800-106/final>`_)
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 https://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:
.. _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/
.. seealso::
Module :mod:hmac
A module to generate message authentication codes using hashes.
Module :mod:base64
Another way to encode binary hashes for non-binary environments.
https://blake2.net Official BLAKE2 website.
https://csrc.nist.gov/csrc/media/publications/fips/180/2/archive/2002-08-01/documents/fips180-2.pdf The FIPS 180-2 publication on Secure Hash Algorithms.
https://en.wikipedia.org/wiki/Cryptographic_hash_function#Cryptographic_hash_algorithms Wikipedia article with information on which algorithms have known issues and what that means regarding their use.
https://www.ietf.org/rfc/rfc2898.txt PKCS #5: Password-Based Cryptography Specification Version 2.0