ctypescrypto/mac.py

   1 # -*- encoding: utf-8 -*-
   2 """
   3 This module provides interface to OpenSSL MAC functions.
   4
   5 It has not only HMAC support, but can support other types of MAC.
   6
   7 """
   8
   9 from ctypescrypto.digest import Digest,DigestType,DigestError
  10 from ctypescrypto.oid import Oid
  11 from ctypescrypto import libcrypto
  12 from ctypes import c_int,c_char_p, c_void_p, c_size_t,POINTER,create_string_buffer,pointer
  13
  14 __all__ = ['MAC','DigestError']
  15 class MAC(Digest):
  16     """
  17         This object represents MAC context. It is quite simular
  18         to digest algorithm. It is simular to hmac objects provided
  19         by standard library
  20     """
  21     def __init__(self,algorithm,key,digest=None,**kwargs):
  22         """
  23         Constructor has to obligatory arguments:
  24
  25             @param algorithm - which is name of MAC algorithm i.e 'hmac' or
  26                     'gost-mac' or equivalent Oid object
  27             @param key - byte buffer with key.
  28
  29         Optional parameters are:
  30             digest - Oid or name of the digest algorithm to use. If none
  31                 specified, OpenSSL will try to derive one from the MAC
  32                 algorithm (or if algorithm is hmac, we'll substititute md5
  33                 for compatibility with standard hmac module
  34
  35             any other keyword argument is passed to EVP_PKEY_CTX as string
  36             option.
  37
  38         """
  39         if isinstance(algorithm,str):
  40             self.algorithm=Oid(algorithm)
  41         elif isinstance(algorithm,Oid):
  42             self.algorithm=algorithm
  43         else:
  44             raise TypeError("Algorthm must be string or Oid")
  45         if self.algorithm==Oid('hmac') and digest is None:
  46                 digest='md5'
  47         self.name=self.algorithm.shortname().lower()
  48         if digest is not None:
  49             self.digest_type=DigestType(digest)
  50             self.name+='-'+self.digest_type.digest_name
  51             d=self.digest_type.digest
  52         else:
  53             self.digest_type=None
  54             d=None
  55         self.key=libcrypto.EVP_PKEY_new_mac_key(self.algorithm.nid,None,key,len(key))
  56         if self.key is None:
  57             raise DigestError("EVP_PKEY_new_mac_key")
  58         pctx=c_void_p()
  59         self.ctx = self.newctx()
  60         if self.ctx == 0:
  61             raise DigestError("Unable to create digest context")
  62         if libcrypto.EVP_DigestSignInit(self.ctx,pointer(pctx),d,None,self.key) <= 0:
  63             raise DigestError("Unable to intialize digest context")
  64         self.digest_finalized=False
  65         if self.digest_type is None:
  66             self.digest_type=DigestType(Oid(libcrypto.EVP_MD_type(libcrypto.EVP_MD_CTX_md(self.ctx))))
  67         for (name,val) in kwargs.items():
  68             if libcrypto.EVP_PKEY_CTX_ctrl_str(pctx,name,val)<=0:
  69                 raise DigestError("Unable to set mac parameter")
  70         self.digest_size = self.digest_type.digest_size
  71         self.block_size = self.digest_type.block_size
  72     def digest(self,data=None):
  73         """
  74         Method digest is redefined to return keyed MAC value instead of
  75         just digest.
  76         """
  77         if data is not None:
  78             self.update(data)
  79         b=create_string_buffer(256)
  80         size=c_size_t(256)
  81         if libcrypto.EVP_DigestSignFinal(self.ctx,b,pointer(size))<=0:
  82             raise DigestError('SignFinal')
  83         self.digest_finalized=True
  84         return b.raw[:size.value]
  85
  86 libcrypto.EVP_DigestSignFinal.argtypes=(c_void_p,c_char_p,POINTER(c_size_t))
  87 libcrypto.EVP_DigestSignFinal.restype=c_int
  88 libcrypto.EVP_DigestSignInit.argtypes=(c_void_p,POINTER(c_void_p),c_void_p,c_void_p,c_void_p)
  89 libcrypto.EVP_DigestSignInit.restype=c_int
  90 libcrypto.EVP_PKEY_CTX_ctrl_str.argtypes=(c_void_p,c_char_p,c_char_p)
  91 libcrypto.EVP_PKEY_CTX_ctrl_str.restype=c_int
  92 libcrypto.EVP_PKEY_new_mac_key.argtypes=(c_int,c_void_p,c_char_p,c_int)
  93 libcrypto.EVP_PKEY_new_mac_key.restype=c_void_p
  94 libcrypto.EVP_MD_CTX_md.argtypes=(c_void_p,)
  95 libcrypto.EVP_MD_CTX_md.restype=c_void_p