Junos reversible passphrase generator

junos_crypt.py

def junos_crypt(plain, salt=None, stable_crypt=False):
    """
    create and return a reversible Junos crypted passphrase,
    which can be used as a passphrase in places where the plain
    text must be accessible to the RE, such as BGP peerings

    :param plain: plain text passphrase
    :param salt: salt
    :param stable_crypt: always return the same hash without rotation

    heavily inspired by http://search.cpan.org/dist/Crypt-Juniper/lib/Crypt/Juniper.pm
    """
    FAMILY = ["QzF3n6/9CAtpu0O", "B1IREhcSyrleKvMW8LXx", "7N-dVbwsY2g4oaJZGUDj", "iHkq.mPf5T"]
    EXTRA = dict()
    for x, item in enumerate(FAMILY):
        for c in item:
            EXTRA[c] = 3 - x
    NUM_ALPHA = [x for x in "".join(FAMILY)]
    ALPHA_NUM = {NUM_ALPHA[x]: x for x in range(0, len(NUM_ALPHA))}
    ENCODING = [[1, 4, 32], [1, 16, 32], [1, 8, 32], [1, 64], [1, 32], [1, 4, 16, 128], [1, 32, 64]]

    def _randc(cnt=0, stable_crypt=False):
        r = ''
        while cnt > 0:
            if stable_crypt:
                r += NUM_ALPHA[cnt]
            else:
                r += random.choice(NUM_ALPHA)
            cnt -= 1
        return r

    def _gap_encode(pc, prev, enc):
        chr_ord = ord(pc)
        crypt = ''
        gaps = []

        for mod in reversed(enc):
            gaps.insert(0, int(chr_ord / mod))
            chr_ord %= mod

        for gap in gaps:
            gap += ALPHA_NUM[prev] + 1
            prev = NUM_ALPHA[gap % len(NUM_ALPHA)]
            c = prev
            crypt += c

        return crypt

    if not salt:
        salt = _randc(1)
    rand = _randc(EXTRA[salt], stable_crypt)

    pos = 0
    prev = salt
    crypt = "$9$%s%s" % (salt, rand)

    for p in plain:
        encode = ENCODING[pos % len(ENCODING)]
        crypt += _gap_encode(p, prev, encode)
        prev = crypt[-1]
        pos += 1

    return crypt