def unbundle()

in fxa/crypto.py [0:0]

• 9 lines of code
• 3 McCabe index (conditional complexity)

def unbundle(key, namespace, payload):
    """Decrypt a response bundle using the given key."""
    # Split off the last 32 bytes, they're the HMAC.
    ciphertext = payload[:-32]
    expected_hmac = payload[-32:]
    # Derive enough key material for HMAC-check and decryption.
    size = 32 + len(ciphertext)
    key_material = derive_key(key, namespace, size)
    # Check the HMAC using the derived key.
    hmac_key = key_material[:32]
    verify_hmac(hmac_key, ciphertext, expected_hmac)
    # XOR-decrypt the ciphertext using the derived key.
    xor_key = key_material[32:]
    return xor(xor_key, ciphertext)