Added support for MAC

[oss/ctypescrypto.git] / ctypescrypto / mac.py

diff --git a/ctypescrypto/mac.py b/ctypescrypto/mac.py
new file mode 100644 (file)
index 0000000..e5e8f55
--- /dev/null
+++ b/ctypescrypto/mac.py
@@ -0,0 +1,95 @@
+# -*- encoding: utf-8 -*-
+"""
+This module provides interface to OpenSSL MAC functions.
+
+It has not only HMAC support, but can support other types of MAC.
+
+"""
+
+from ctypescrypto.digest import Digest,DigestType,DigestError
+from ctypescrypto.oid import Oid
+from ctypescrypto import libcrypto
+from ctypes import c_int,c_char_p, c_void_p, c_size_t,POINTER,create_string_buffer,pointer
+
+__all__ = ['MAC','DigestError']
+class MAC(Digest):
+       """
+               This object represents MAC context. It is quite simular
+               to digest algorithm. It is simular to hmac objects provided
+               by standard library
+       """
+       def __init__(self,algorithm,key,digest=None,**kwargs):
+               """
+               Constructor has to obligatory arguments:
+                       
+                       @param algorithm - which is name of MAC algorithm i.e 'hmac' or 
+                                       'gost-mac' or equivalent Oid object
+                       @param key - byte buffer with key.
+
+               Optional parameters are:
+                       digest - Oid or name of the digest algorithm to use. If none
+                               specified, OpenSSL will try to derive one from the MAC
+                               algorithm (or if algorithm is hmac, we'll substititute md5
+                               for compatibility with standard hmac module
+
+                       any other keyword argument is passed to EVP_PKEY_CTX as string
+                       option.
+
+               """
+               if isinstance(algorithm,str):
+                       self.algorithm=Oid(algorithm)
+               elif isinstance(algorithm,Oid):
+                       self.algorithm=algorithm
+               else:
+                       raise TypeError("Algorthm must be string or Oid")
+               if self.algorithm==Oid('hmac') and digest is None:
+                               digest='md5'
+               self.name=self.algorithm.shortname().lower()
+               if digest is not None:
+                       self.digest_type=DigestType(digest)
+                       self.name+='-'+self.digest_type.digest_name
+                       d=self.digest_type.digest
+               else:
+                       self.digest_type=None
+                       d=None
+               self.key=libcrypto.EVP_PKEY_new_mac_key(self.algorithm.nid,None,key,len(key))
+               if self.key is None:
+                       raise DigestError("EVP_PKEY_new_mac_key")
+               pctx=c_void_p()
+               self.ctx = libcrypto.EVP_MD_CTX_create()
+               if self.ctx == 0:
+                       raise DigestError("Unable to create digest context")
+               if libcrypto.EVP_DigestSignInit(self.ctx,pointer(pctx),d,None,self.key) <= 0:
+                       raise DigestError("Unable to intialize digest context")
+               self.digest_finalized=False
+               if self.digest_type is None:
+                       self.digest_type=DigestType(Oid(libcrypto.EVP_MD_type(libcrypto.EVP_MD_CTX_md(self.ctx))))
+               for (name,val) in kwargs.items():
+                       if EVP_PKEY_CTX_ctrl_str(ctx,name,val)<=0:
+                               raise DigestError("Unable to set mac parameter")
+               self.digest_size = self.digest_type.digest_size()
+               self.block_size = self.digest_type.block_size()
+       def digest(self,data=None):
+               """
+               Method digest is redefined to return keyed MAC value instead of
+               just digest.
+               """
+               if data is not None:
+                       self.update(data)
+               b=create_string_buffer(256)
+               size=c_size_t(256)
+               if libcrypto.EVP_DigestSignFinal(self.ctx,b,pointer(size))<=0:
+                       raise DigestError('SignFinal')
+               self.digest_finalized=True
+               return b.raw[:size.value]
+
+libcrypto.EVP_DigestSignFinal.argtypes=(c_void_p,c_char_p,POINTER(c_size_t))
+libcrypto.EVP_DigestSignFinal.restype=c_int
+libcrypto.EVP_DigestSignInit.argtypes=(c_void_p,POINTER(c_void_p),c_void_p,c_void_p,c_void_p)
+libcrypto.EVP_DigestSignInit.restype=c_int
+libcrypto.EVP_PKEY_CTX_ctrl_str.argtypes=(c_void_p,c_char_p,c_char_p)
+libcrypto.EVP_PKEY_CTX_ctrl_str.restype=c_int
+libcrypto.EVP_PKEY_new_mac_key.argtypes=(c_int,c_void_p,c_char_p,c_int)
+libcrypto.EVP_PKEY_new_mac_key.restype=c_void_p
+libcrypto.EVP_MD_CTX_md.argtypes=(c_void_p,)
+libcrypto.EVP_MD_CTX_md.restype=c_void_p