Function octetstring2key

scapy/libs/rfc3961.py:1454–1479

RFC4556 octetstring2key:: octetstring2key(x) == random-to-key(K-truncate( SHA1(0x00 | x) | SHA1(0x01 | x) | SHA1(0x02 | x) | ... ))

(etype: EncryptionType, x: bytes)

############

def octetstring2key(etype: EncryptionType, x: bytes) -> Key:
    """
    RFC4556 octetstring2key::

        octetstring2key(x) == random-to-key(K-truncate(
                            SHA1(0x00 | x) |
                            SHA1(0x01 | x) |
                            SHA1(0x02 | x) |
                            ...
                            ))
    """
    try:
        ep = _enctypes[etype]
    except ValueError:
        raise ValueError("Unknown etype '%s'" % etype)

    out = b""
    count = 0
    while len(out) < ep.keysize:
        out += Hash_SHA().digest(struct.pack("!B", count) + x)
        count += 1

    return Key.random_to_key(
        etype=etype,
        seed=out[:ep.keysize],
    )