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-
-
- """
- demo_dynamic.py v1
-
- This program demonstrates Python's use of the dynamic
- language support additions to LTC, namely access to LTC
- constants, struct and union sizes, and the binding of a
- math package to LTC. Also provided are simple code
- fragments to illustrate how one might write a Python
- wrapper for LTC and how an app might call the wrapper.
- This or a similar model should work for Ruby and other
- dynamic languages.
-
- This instance uses Python's ctypes and requires a single
- .dylib linking together LTC and a math library. Building
- a single .dylib is needed because LTC wants a fairly tight
- relationship between itself and the mathlib. (ctypes can
- load multiple .dylibs, but it does not support this level
- of tight coupling between otherwise independent libraries.)
-
- My .dylib was created on OSX with the following steps:
-
- 1- compile LTC to a .a static lib:
- CFLAGS="-DLTM_DESC -DUSE_LTM" make
-
- 2- link LTC and LTM into a single .dylib:
- ar2dylib_with tomcrypt tommath
- where ar2dylib_with is a shell script that combines
- the LTC .a with the LTM .dylib
-
- Reminder: you don't need to bind in a math library unless
- you are going to use LTC functions that depend
- on a mathlib. For example, public key crypto
- needs a mathlib; hashing and symmetric encryption
- do not.
-
- This code was written for Python 2.7.
-
- Larry Bugbee
- March 2014
-
- """
-
-
- from ctypes import *
- from ctypes.util import find_library
-
-
- #---------------------------------------------------------------
- # load the .dylib
-
- libname = 'tomcrypt'
- libpath = find_library(libname)
-
- print
- print(' demo_dynamic.py')
- print
- print(' path to library %s: %s' % (libname, libpath))
-
- LTC = cdll.LoadLibrary(libpath)
- print(' loaded: %s' % LTC)
- print
-
-
-
- #---------------------------------------------------------------
- # get list of all supported constants followed by a list of all
- # supported sizes. One alternative: these lists may be parsed
- # and used as needed.
-
- if 1:
- print ' all supported constants and their values:'
-
- # get size to allocate for constants output list
- str_len = c_int(0)
- ret = LTC.crypt_list_all_constants(None, byref(str_len))
- print ' need to allocate %d bytes \n' % str_len.value
-
- # allocate that size and get (name, size) pairs, each pair
- # separated by a newline char.
- names_sizes = c_buffer(str_len.value)
- ret = LTC.crypt_list_all_constants(names_sizes, byref(str_len))
- print names_sizes.value
- print
-
-
- if 1:
- print ' all supported sizes:'
-
- # get size to allocate for sizes output list
- str_len = c_int(0)
- ret = LTC.crypt_list_all_sizes(None, byref(str_len))
- print ' need to allocate %d bytes \n' % str_len.value
-
- # allocate that size and get (name, size) pairs, each pair
- # separated by a newline char.
- names_sizes = c_buffer(str_len.value)
- ret = LTC.crypt_list_all_sizes(names_sizes, byref(str_len))
- print names_sizes.value
- print
-
-
- #---------------------------------------------------------------
- # get individually named constants and sizes
-
- # print selected constants
- if 1:
- print '\n selected constants:'
-
- names = [
- 'ENDIAN_LITTLE',
- 'ENDIAN_64BITWORD',
- 'PK_PUBLIC',
- 'MAX_RSA_SIZE',
- 'CTR_COUNTER_BIG_ENDIAN',
- ]
- for name in names:
- const_value = c_int(0)
- rc = LTC.crypt_get_constant(name, byref(const_value))
- value = const_value.value
- print ' %-25s %d' % (name, value)
-
- # print selected sizes
- if 1:
- print '\n selected sizes:'
-
- names = [
- 'rijndael_key',
- 'rsa_key',
- 'symmetric_CTR',
- 'twofish_key',
- 'ecc_point',
- 'gcm_state',
- 'sha512_state',
- ]
- for name in names:
- size_value = c_int(0)
- rc = LTC.crypt_get_size(name, byref(size_value))
- value = size_value.value
- print ' %-25s %d' % (name, value)
-
-
- #---------------------------------------------------------------
- #---------------------------------------------------------------
- # ctypes getting a list of this build's supported algorithms
- # and compiler switches
-
- def get_named_string(lib, name):
- return c_char_p.in_dll(lib, name).value
-
- if 0:
- print '\n%s' % ('-'*60)
- print 'This is a string compiled into LTC showing compile '
- print 'options and algorithms supported by this build \n'
- print get_named_string(LTC, 'crypt_build_settings')
- print
-
-
-
- #---------------------------------------------------------------
- #---------------------------------------------------------------
- # here is an example of how a wrapper can make Python access
- # more Pythonic
-
- # - - - - - - - - - - - - -
- # a wrapper fragment...
-
- def _get_size(name):
- size = c_int(0)
- rc = LTC.crypt_get_size(name, byref(size))
- return size.value
-
- sha256_state_struct_size = _get_size('sha256_state')
- sha512_state_struct_size = _get_size('sha512_state')
-
- class SHA256(object):
- def __init__(self):
- self.state = c_buffer(sha256_state_struct_size)
- LTC.sha256_init(byref(self.state))
- def update(self, data):
- LTC.sha256_process(byref(self.state), data, len(data))
- def digest(self):
- md = c_buffer(32)
- LTC.sha256_done(byref(self.state), byref(md))
- return md.raw
-
- # - - - - - - - - - - - - -
- # an app fragment...
-
- # from wrapper import * # uncomment in real life
-
- data = 'hello world'
-
- sha256 = SHA256()
- sha256.update(data)
- md = sha256.digest()
-
- template = '\n\n the SHA256 digest for "%s" is %s \n'
- print template % (data, md.encode('hex'))
-
-
-
- #---------------------------------------------------------------
- #---------------------------------------------------------------
- #---------------------------------------------------------------
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