207 lines
5.8 KiB
Python
Executable File
207 lines
5.8 KiB
Python
Executable File
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"""
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demo_dynamic.py v1
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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 with the following steps:
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1- compile LTC to a .a static lib:
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CFLAGS="-DLTM_DESC -DUSE_LTM" make
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2- link LTC and LTM into a single .dylib:
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ar2dylib_with tomcrypt tommath
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where ar2dylib_with is a shell script that combines
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the LTC .a with the LTM .dylib
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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 depend
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on a mathlib. For example, public key crypto
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needs a mathlib; hashing and symmetric encryption
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do not.
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This code was written for Python 2.7.
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Larry Bugbee
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March 2014
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"""
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from ctypes import *
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from ctypes.util import find_library
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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(' demo_dynamic.py')
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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 1:
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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 \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
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print
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if 1:
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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 \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
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print
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#---------------------------------------------------------------
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# get individually named constants and sizes
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# print selected constants
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if 1:
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print '\n selected constants:'
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names = [
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'ENDIAN_LITTLE',
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'ENDIAN_64BITWORD',
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'PK_PUBLIC',
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'MAX_RSA_SIZE',
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'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, value)
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# print selected sizes
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if 1:
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print '\n selected sizes:'
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names = [
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'rijndael_key',
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'rsa_key',
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'symmetric_CTR',
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'twofish_key',
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'ecc_point',
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'gcm_state',
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'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, value)
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#---------------------------------------------------------------
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#---------------------------------------------------------------
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# ctypes getting a list of this build's supported algorithms
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# and compiler switches
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def get_named_string(lib, name):
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return c_char_p.in_dll(lib, name).value
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if 0:
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print '\n%s' % ('-'*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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print
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#---------------------------------------------------------------
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#---------------------------------------------------------------
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# here is an example of how a wrapper can make Python access
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# more Pythonic
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# - - - - - - - - - - - - -
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# a wrapper fragment...
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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(name, byref(size))
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return size.value
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sha256_state_struct_size = _get_size('sha256_state')
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sha512_state_struct_size = _get_size('sha512_state')
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class SHA256(object):
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def __init__(self):
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self.state = c_buffer(sha256_state_struct_size)
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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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# an app fragment...
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# from wrapper import * # uncomment in real life
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data = 'hello world'
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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\n the SHA256 digest for "%s" is %s \n'
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print template % (data, md.encode('hex'))
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#---------------------------------------------------------------
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#---------------------------------------------------------------
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#---------------------------------------------------------------
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