def unlock(self, passphrase):
# might eventually implement the following as specced and in a separate module:
# http://www.w3.org/TR/2002/REC-xmlenc-core-20021210/Overview.html#aes256-cbc
# http://www.w3.org/2008/xmlsec/Drafts/derived-key/derived-keys.xml
# https://tools.ietf.org/html/rfc4051
# https://tools.ietf.org/html/rfc6030
# http://www.opensource.apple.com/source/libsecurity_asn1/libsecurity_asn1-29908/asn1/pkcs5.asn1
if self._privateKey:
return
encryption_elem = self._container.getElementsByTagNameNS(XMLENC_NS_URL, 'EncryptionMethod')[0]
# jumping over the structure at the moment, see above
derivation_func = PBKDF2
params_elem = encryption_elem.getElementsByTagNameNS(PKCS5_NS_URL, 'Parameters')[0]
salt_elem = params_elem.getElementsByTagNameNS(PKCS5_NS_URL, 'Salt')[0]
IV = salt = b64decode(salt_elem.firstChild.firstChild.nodeValue)
iterations_elem = params_elem.getElementsByTagNameNS(PKCS5_NS_URL, 'IterationCount')[0]
iterations = int(iterations_elem.firstChild.nodeValue)
key_length_elem = params_elem.getElementsByTagNameNS(PKCS5_NS_URL, 'KeyLength')[0]
key_length = int(key_length_elem.firstChild.nodeValue)
assert key_length % 8 == 0
prf = lambda p, s: HMAC(p, s, SHA256).digest()
key = derivation_func(passphrase, salt, count=iterations, dkLen=(key_length//8), prf=prf)
encryption_scheme = AES
encryption_mode = AES.MODE_CBC
decryptor = encryption_scheme.new(key, mode=encryption_mode, IV=IV)
# then the encrypted data
key_elem = self._container.getElementsByTagNameNS(XMLENC_NS_URL, 'CipherValue')[0]
ciphertext_elem = key_elem.firstChild
ciphertext = b64decode(ciphertext_elem.nodeValue)
padded_plaintext = decryptor.decrypt(ciphertext)
padlen = ord(padded_plaintext[-1])
if padlen not in range(encryption_scheme.block_size) or \
chr(padlen)*padlen != padded_plaintext[-padlen:]:
raise KeyLockedError("Key decryption failed")
plaintext = padded_plaintext[:-padlen]
key_elem = removeIgnorableWhitespace(parseString(plaintext))
keyparams = [RSA.bytes_to_long(b64decode(key_elem.getElementsByTagName(x)[0].firstChild.nodeValue)) for x in ['Modulus', 'Exponent', 'D', 'Q', 'P', 'InverseQ']]
self._privateKey = RSA.construct(tuple(keyparams))
self._publicKey = self._privateKey.publickey()
self.fingerprint = SHA256.new(self._publicKey.exportKey(format='DER')).hexdigest()
