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aes-gcm: only return the real mac (which is only 128b, 16B)

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code using id_hash output still expects 256b (32B), thus added a workaround for GHASH/GMAC.
This commit is contained in:
Thomas Waldmann 2015-03-23 00:36:49 +01:00
parent c759eeee1e
commit 7e1aa163a3
3 changed files with 3 additions and 4 deletions
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3
attic/crypto.pyx
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@ -179,8 +179,7 @@ cdef class AES:
# Get tag (mac) - only GCM mode. for CTR, the returned mac is undefined
if not EVP_CIPHER_CTX_ctrl(&self.ctx, EVP_CTRL_GCM_GET_TAG, MAC_SIZE, mac):
raise Exception('EVP_CIPHER_CTX_ctrl GET TAG failed')
# hack: caller wants 32B tags (256b), so we give back that amount
return (mac[:MAC_SIZE] + b'\x00'*16), out[:ctl]
return (mac[:MAC_SIZE]), out[:ctl]
finally:
free(mac)
free(out)

2
attic/key.py
View file

@ -112,7 +112,7 @@ class GHASH:
# GMAC = aes-gcm with all data as AAD, no data as to-be-encrypted data
mac_cipher.add(bytes(self.data))
hash, _ = mac_cipher.compute_mac_and_encrypt(b'')
return hash
return hash + b'\0'*16 # XXX hashindex code wants 32 bytes (256 bit)
class HMAC_SHA256(HMAC):

2
attic/testsuite/crypto.py
View file

@ -48,7 +48,7 @@ class CryptoTestCase(AtticTestCase):
# encrypt
aes = AES(mode=AES_GCM_MODE, is_encrypt=True, key=key, iv=iv)
mac, cdata = aes.compute_mac_and_encrypt(data)
self.assert_equal(hexlify(mac), b'c98aa10eb6b7031bcc2160878d9438fb00000000000000000000000000000000')
self.assert_equal(hexlify(mac), b'c98aa10eb6b7031bcc2160878d9438fb')
self.assert_equal(hexlify(cdata), b'841bcce405df769d22ee9f7f012edf5dc7fb2594d924c7400ffd050f2741')
# decrypt (correct mac/cdata)
aes = AES(mode=AES_GCM_MODE, is_encrypt=False, key=key, iv=iv)