Add google-endpoints to third_party/.

third_party/google-endpoints/jwkest/extra.py

Index: third_party/google-endpoints/jwkest/extra.py
diff --git a/third_party/google-endpoints/jwkest/extra.py b/third_party/google-endpoints/jwkest/extra.py
new file mode 100644
index 0000000000000000000000000000000000000000..284fded4d1f5184ad90afe9e3310e325b3366575
--- /dev/null
+++ b/third_party/google-endpoints/jwkest/extra.py
@@ -0,0 +1,175 @@
+from __future__ import division
+try:
+    from builtins import bytes
+except ImportError:
+    pass
+#from past.utils import old_div
+from math import ceil
+from struct import pack, unpack
+from Crypto.Cipher import AES
+from Crypto.Hash import SHA256
+from Crypto.Hash import SHA384
+from Crypto.Hash import SHA512
+from Crypto.Hash import HMAC
+
+
+LENMET = {
+    32: (16, SHA256),
+    48: (24, SHA384),
+    64: (32, SHA512)
+}
+
+
+# PKCS#5 padding, since it's not in PyCrypto
+def pkcs5pad(x):
+    """
+    Add PKCS#5 padding to an octet string
+
+    :type  x: bytes
+    :rtype: bytes
+    """
+    n = 16 - len(x) % 16
+    if n == 0:
+        n = 16
+    ns = pack('B', n)
+    return x + (ns * n)
+
+
+def pkcs5trim(x):
+    """
+    Trim PKCS#5 padding from an octet string
+
+    :type  x: bytes
+    :rtype: bytes
+    """
+    n = unpack('B', x[-1:])[0]
+    # Should never have more than 16 bytes of padding
+    # ... since we're only using this with AES
+    if n > 16:
+        raise Exception("Mal-formed PKCS#5 padding")
+    return x[:-n]
+
+
+def get_keys_seclen_dgst(key, iv):
+    # Validate input
+    if len(iv) != 16:
+        raise Exception("IV for AES-CBC must be 16 octets long")
+
+    # Select the digest to use based on key length
+    try:
+        seclen, dgst = LENMET[len(key)]
+    except KeyError:
+        raise Exception("Invalid CBC+HMAC key length: %s bytes" % len(key))
+
+    # Split the key
+    ka = key[:seclen]
+    ke = key[seclen:]
+
+    return ka, ke, seclen, dgst
+
+
+def aes_cbc_hmac_encrypt(key, iv, aad, pt):
+    """
+    Perform authenticated encryption with the combined AES-CBC
+    and HMAC algorithm.
+
+    :param key: key; length MUST be 32, 48, or 64 octets
+    :param iv: Initialization vector; length MUST be 16 octets
+    :param aad: Additional authenticated data
+    :param pt: Plaintext
+    :return: (ciphertext, tag) tuple, with each as bytes
+    """
+
+    ka, ke, seclen, dgst = get_keys_seclen_dgst(key, iv)
+
+    # Encrypt
+    cipher = AES.new(ke, AES.MODE_CBC, iv)
+    ct = cipher.encrypt(pkcs5pad(pt))
+
+    # MAC A || IV || E || AL
+    al = pack("!Q", 8*len(aad))
+    mac_input = aad + iv + ct + al
+    h = HMAC.new(ka, digestmod=dgst)
+    h.update(mac_input)
+    tag = h.digest()[:seclen]
+    return ct, tag
+
+
+def aes_cbc_hmac_decrypt(key, iv, aad, ct, tag):
+    """
+    Perform authenticated decryption with the combined AES-CBC
+    and HMAC algorithm.
+
+    :param key  : Key; length MUST be 32, 48, or 64 octets
+    :param iv : Initialization vector; length MUST be 16 octets
+    :param aad: Additional authenticated data
+    :param ct : Plaintext
+    :param tag: Authentication tag
+    :return: (plaintext, result) tuple, with plaintext as bytes
+      and result as boolean
+    """
+
+    ka, ke, seclen, dgst = get_keys_seclen_dgst(key, iv)
+
+    # Verify A || IV || E || AL
+    al = pack("!Q", 8*len(aad))
+    if isinstance(aad, str):
+        aad = aad.encode("utf-8")
+    mac_input = aad + iv + ct + al
+    h = HMAC.new(ka, digestmod=dgst)
+    h.update(mac_input)
+    candidate = h.digest()[:seclen]
+
+    # Decrypt if verified
+    if candidate == tag:
+        cipher = AES.new(ke, AES.MODE_CBC, iv)
+        pt = pkcs5trim(cipher.decrypt(ct))
+        return pt, True
+    else:
+        return None, False
+    
+
+def concat_sha256(secret, dk_len, other_info):
+    """
+    The Concat KDF, using SHA256 as the hash function.  
+
+    Note: Does not validate that otherInfo meets the requirements of 
+    SP800-56A.
+
+    :param secret: The shared secret value
+    :param dk_len: Length of key to be derived, in bits
+    :param other_info: Other info to be incorporated (see SP800-56A)
+    :return: The derived key
+    """
+    dkm = b''
+    dk_bytes = int(ceil(dk_len / 8.0))
+    counter = 0
+    while len(dkm) < dk_bytes:
+        counter += 1
+        counter_bytes = pack("!I", counter)
+        dkm += SHA256.new(counter_bytes + secret + other_info ).digest()
+    return dkm[:dk_bytes]
+
+
+def ecdh_derive_key(curve, key, epk, apu, apv, alg, dk_len):
+    """
+    ECDH key derivation, as defined by JWA
+    
+    :param curve: Curve to be used for EC computations
+    :param key  : Elliptic curve private key
+    :param epk  : Elliptic curve public key (long, long)
+    :param apu  : PartyUInfo
+    :param apv  : PartyVInfo
+    :param alg  : Algorithm identifier
+    :param dk_len: Length of key to be derived, in bits
+    :return: The derived key
+    """
+    # Compute shared secret 
+    Z = curve.dh_z(key, epk)
+    # Derive the key
+    # AlgorithmID || PartyUInfo || PartyVInfo || SuppPubInfo
+    otherInfo = bytes(alg) + \
+        pack("!I", len(apu)) + apu + \
+        pack("!I", len(apv)) + apv + \
+        pack("!I", dk_len)
+    return concat_sha256(Z, dk_len, otherInfo)