310 lines
10 KiB
Python
310 lines
10 KiB
Python
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"""
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demo_dynamic.py v2b
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This program demonstrates Python's use of the dynamic
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language support additions to LTC, namely access to LTC
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constants, struct and union sizes, and the binding of a
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math package to LTC. Also provided are simple code
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fragments to illustrate how one might write a Python
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wrapper for LTC and how an app might call the wrapper.
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This or a similar model should work for Ruby and other
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dynamic languages.
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This instance uses Python's ctypes and requires a single
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.dylib linking together LTC and a math library. Building
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a single .dylib is needed because LTC wants a fairly tight
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relationship between itself and the mathlib. (ctypes can
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load multiple .dylibs, but it does not support this level
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of tight coupling between otherwise independent libraries.)
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My .dylib was created on OSX/macOS with the following:
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sudo make -j5 -f makefile.shared \
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CFLAGS="-DUSE_TFM -DTFM_DESC -I/usr/local/include" \
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EXTRALIBS=/usr/local/lib/libtfm.a install
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For python 2.7.12 on Ubuntu Xenial the following worked for
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me (without MPI support):
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sudo make -f makefile.shared install PREFIX="/usr"
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Reminder: you don't need to bind in a math library unless
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you are going to use LTC functions that need a
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mathlib. For example, public key crypto requires
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a mathlib; hashing and symmetric encryption do not.
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------
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This code was originally written for Python 2.7 with the
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ctypes standard library. This version is modified to run
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under both Python 2.7 and 3.6.
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Arguably the biggest change for Python3 has to do with
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strings. Under Python2, native strings are ASCII bytes and
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passing them to LTC is natural and requires no conversion.
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Under Python3 all native strings are Unicode which requires
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they be converted to bytes before use by LTC.
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Note the following for Python3.
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- ASCII keys, IVs and other string arguments must be
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'bytes'. Define them with a 'b' prefix or convert
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via the 'bytes()' function.
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- "strings" returned from LTC are bytes and conversion
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to Unicode might be necessary for proper printing.
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If so, use <string>.decode('utf-8').
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- The Python2 'print' statement becomes a function in
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Python3 which requires parenthesis, eg. 'print()'.
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NB: Unicode is achieved under Python2 by either defining
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a Unicode string with a 'u' prefix or passing ASCII
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strings thru the 'unicode()' function.
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Larry Bugbee
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March 2014 v1
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August 2017 v2b
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"""
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import sys
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from ctypes import *
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from ctypes.util import find_library
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# switches to enable/disable selected output
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SHOW_ALL_CONSTANTS = True
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SHOW_ALL_SIZES = True
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SHOW_SELECTED_CONSTANTS = True
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SHOW_SELECTED_SIZES = True
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SHOW_BUILD_OPTIONS_ALGS = True
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SHOW_SHA256_EXAMPLE = True
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SHOW_CHACHA_EXAMPLE = True
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print(' ')
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print(' demo_dynamic.py')
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def inprint(s, indent=0):
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"prints strings indented, including multline strings"
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for line in s.split('\n'):
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print(' '*indent + line)
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#-------------------------------------------------------------------------------
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# load the .dylib
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libname = 'tomcrypt'
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libpath = find_library(libname)
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print(' ')
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print(' path to library %s: %s' % (libname, libpath))
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LTC = cdll.LoadLibrary(libpath)
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print(' loaded: %s' % LTC)
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print(' ')
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#-------------------------------------------------------------------------------
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# get list of all supported constants followed by a list of all
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# supported sizes. One alternative: these lists may be parsed
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# and used as needed.
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if SHOW_ALL_CONSTANTS:
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print('-'*60)
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print(' all supported constants and their values:')
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# get size to allocate for constants output list
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str_len = c_int(0)
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ret = LTC.crypt_list_all_constants(None, byref(str_len))
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print(' need to allocate %d bytes to build list \n' % str_len.value)
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# allocate that size and get (name, size) pairs, each pair
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# separated by a newline char.
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names_sizes = c_buffer(str_len.value)
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ret = LTC.crypt_list_all_constants(names_sizes, byref(str_len))
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print(names_sizes.value.decode("utf-8"))
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print(' ')
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if SHOW_ALL_SIZES:
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print('-'*60)
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print(' all supported sizes:')
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# get size to allocate for sizes output list
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str_len = c_int(0)
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ret = LTC.crypt_list_all_sizes(None, byref(str_len))
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print(' need to allocate %d bytes to build list \n' % str_len.value)
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# allocate that size and get (name, size) pairs, each pair
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# separated by a newline char.
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names_sizes = c_buffer(str_len.value)
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ret = LTC.crypt_list_all_sizes(names_sizes, byref(str_len))
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print(names_sizes.value.decode("utf-8"))
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print(' ')
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#-------------------------------------------------------------------------------
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# get individually named constants and sizes
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if SHOW_SELECTED_CONSTANTS:
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print('-'*60)
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print('\n selected constants:')
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names = [
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b'ENDIAN_LITTLE',
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b'ENDIAN_64BITWORD',
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b'PK_PUBLIC',
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b'LTC_MILLER_RABIN_REPS',
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b'CTR_COUNTER_BIG_ENDIAN',
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]
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for name in names:
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const_value = c_int(0)
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rc = LTC.crypt_get_constant(name, byref(const_value))
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value = const_value.value
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print(' %-25s %d' % (name.decode("utf-8"), value))
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print(' ')
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if SHOW_SELECTED_SIZES:
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print('-'*60)
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print('\n selected sizes:')
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names = [
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b'rijndael_key',
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b'rsa_key',
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b'symmetric_CTR',
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b'twofish_key',
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b'ecc_point',
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b'gcm_state',
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b'sha512_state',
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]
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for name in names:
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size_value = c_int(0)
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rc = LTC.crypt_get_size(name, byref(size_value))
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value = size_value.value
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print(' %-25s %d' % (name.decode("utf-8"), value))
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print(' ')
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#-------------------------------------------------------------------------------
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#-------------------------------------------------------------------------------
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# LibTomCrypt exposes one interesting string that can be accessed
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# via Python's ctypes module, "crypt_build_settings", which
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# provides a list of this build's compiler switches and supported
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# algorithms. If someday LTC exposes other interesting strings,
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# they can be found with:
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# nm /usr/local/lib/libtomcrypt.dylib | grep " D "
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def get_named_string(lib, name):
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return c_char_p.in_dll(lib, name).value.decode("utf-8")
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if SHOW_BUILD_OPTIONS_ALGS:
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print('-'*60)
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print('This is a string compiled into LTC showing compile')
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print('options and algorithms supported by this build \n')
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# print(get_named_string(LTC, 'crypt_build_settings'))
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inprint(get_named_string(LTC, 'crypt_build_settings'), 4)
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#-------------------------------------------------------------------------------
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#-------------------------------------------------------------------------------
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# here is an example of how Python code can be written to access
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# LTC's implementation of SHA256 and ChaCha,
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# - - - - - - - - - - - - -
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# definitions
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from binascii import hexlify, unhexlify
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def _err2str(err):
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# define return type
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errstr = LTC.error_to_string
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errstr.restype = c_char_p
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# get and return err string
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return errstr(err)
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def _get_size(name):
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size = c_int(0)
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rc = LTC.crypt_get_size(bytes(name), byref(size))
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if rc != 0:
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raise Exception('LTC.crypt_get_size(%s) rc = %d' % (name, rc))
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return size.value
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def _get_constant(name):
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constant = c_int(0)
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rc = LTC.crypt_get_constant(bytes(name), byref(constant))
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if rc != 0:
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raise Exception('LTC.crypt_get_constant(%s) rc = %d' % (name, rc))
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return constant.value
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CRYPT_OK = _get_constant(b'CRYPT_OK')
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class SHA256(object):
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def __init__(self):
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self.state = c_buffer(_get_size(b'sha256_state'))
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LTC.sha256_init(byref(self.state))
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def update(self, data):
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LTC.sha256_process(byref(self.state), data, len(data))
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def digest(self):
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md = c_buffer(32)
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LTC.sha256_done(byref(self.state), byref(md))
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return md.raw
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# - - - - - - - - - - - - -
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# a SHA256 app fragment
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if SHOW_SHA256_EXAMPLE:
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print('-'*60)
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data = b'hello world' # we want bytes, not Unicode
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sha256 = SHA256()
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sha256.update(data)
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md = sha256.digest()
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template = '\n the SHA256 digest for "%s" is %s \n'
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print(template % (data, hexlify(md)))
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class ChaCha(object):
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def __init__(self, key, rounds):
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self.state = c_buffer(_get_size(b'chacha_state'))
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self.counter = c_uint(1)
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err = LTC.chacha_setup(byref(self.state), key, len(key), rounds)
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if err != CRYPT_OK:
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raise Exception('LTC.chacha_setup(), err = %d, "%s"' % (err, _err2str(err)))
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def set_iv32(self, iv):
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err = LTC.chacha_ivctr32(byref(self.state), iv, len(iv), self.counter)
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if err != CRYPT_OK:
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raise Exception('LTC.chacha_ivctr32(), err = %d, "%s"' % (err, _err2str(err)))
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def crypt(self, datain):
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dataout = c_buffer(len(datain))
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err = LTC.chacha_crypt(byref(self.state), datain, len(datain), byref(dataout))
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if err != CRYPT_OK:
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raise Exception('LTC.chacha_crypt(), err = %d, "%s"' % (err, _err2str(err)))
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return dataout.raw
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# - - - - - - - - - - - - -
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# a ChaCha app fragment
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if SHOW_CHACHA_EXAMPLE:
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print('-'*60)
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key = b'hownowbrowncow\x00\x00' # exactly 16 or 32 bytes
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rounds = 12 # common values: 8, 12, 20
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iv = b'123456789012' # exactly 12 bytes
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plain = b'Kilroy was here, there, and everywhere!'
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cha = ChaCha(key, rounds)
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cha.set_iv32(iv)
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cipher = cha.crypt(plain)
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template = '\n ChaCha%d ciphertext for "%s" is "%s"'
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print(template % (rounds, plain, hexlify(cipher)))
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cha.set_iv32(iv) # reset to decrypt
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decrypted = cha.crypt(cipher)
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template = ' ChaCha%d decoded text for "%s" is "%s" \n'
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print(template % (rounds, plain, decrypted.decode("utf-8")))
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# Footnote: Keys should be erased fm memory as soon as possible after use,
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# and that includes Python. For a tip on how to do that in Python, see
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# http://buggywhip.blogspot.com/2010/12/erase-keys-and-credit-card-numbers-in.html
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#-------------------------------------------------------------------------------
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#-------------------------------------------------------------------------------
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#-------------------------------------------------------------------------------
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