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passlib.utils.scrypt -- scrypt hash frontend and help utilities
XXX: add this module to public docs?
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helper which validates a set of scrypt config parameters.
scrypt will take ``O(n * r * p)`` time and ``O(n * r)`` memory.
limitations are that ``n = 2**<positive integer>``, ``n < 2**(16*r)``, ``r * p < 2 ** 30``.
:param n: scrypt rounds
:param r: scrypt block size
:param p: scrypt parallel factor
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calculate memory required for parameter combination.
assumes parameters have already been validated.
.. warning::
this is derived from OpenSSL's scrypt maxmem formula;
and may not be correct for other implementations
(additional buffers, different parallelism tradeoffs, etc).
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r c C sZ t |||� t| dd�} t|dd�}|dk r4td��|tkrHtdt ��t| |||||�S )a4 run SCrypt key derivation function using specified parameters.
:arg secret:
passphrase string (unicode is encoded to bytes using utf-8).
:arg salt:
salt string (unicode is encoded to bytes using utf-8).
:arg n:
integer 'N' parameter
:arg r:
integer 'r' parameter
:arg p:
integer 'p' parameter
:arg keylen:
number of bytes of key to generate.
defaults to 32 (the internal block size).
:returns:
a *keylen*-sized bytes instance
SCrypt imposes a number of constraints on it's input parameters:
* ``r * p < 2**30`` -- due to a limitation of PBKDF2-HMAC-SHA256.
* ``keylen < (2**32 - 1) * 32`` -- due to a limitation of PBKDF2-HMAC-SHA256.
* ``n`` must a be a power of 2, and > 1 -- internal limitation of scrypt() implementation
:raises ValueError: if the provided parameters are invalid (see constraints above).
.. warning::
Unless the third-party ``scrypt <https://pypi.python.org/pypi/scrypt/>``_ package
is installed, passlib will use a builtin pure-python implementation of scrypt,
which is *considerably* slower (and thus requires a much lower / less secure
``n`` value in order to be usuable). Installing the :mod:`!scrypt` package
is strongly recommended.
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Load pure-python scrypt implementation built into passlib.
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Try to import the ctypes-based scrypt hash function provided by the
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Attempt to load stdlib scrypt() implement and return wrapper.
Returns None if not found.
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set backend for scrypt(). if name not specified, loads first available.
:raises ~passlib.exc.MissingBackendError: if backend can't be found
.. note:: mainly intended to be called by unittests, and scrypt hash handler
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