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 libcrypto.EVP_PKEY_CTX_ctrl_str(pctx, 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 oid(self):
""" Returns Oid object of digest type """
return Oid(libcrypto.EVP_MD_type(self.digest))
def name(self):
""" Returns name of the digest """
if not hasattr(self, 'digest_name'):
self.digest_name = Oid(libcrypto.EVP_MD_type(
self.digest)).longname()
return self.digest_name
