tasmota_fingerprint.py

#!/usr/bin/env python3

import sys
import ssl

from hashlib import sha1

# need recent pycryptodome
try:
    from Crypto.PublicKey import RSA
except ModuleNotFoundError:
    from Cryptodome.PublicKey import RSA

def to_bytes(n, length=None):
    if length is None:
        length = (n.bit_length() + 7) // 8
    return n.to_bytes(length, 'big')

def fmt_fingerprint(hexdigest):
    h = hexdigest.upper()
    return ' '.join(h[i:i+2] for i in range(0, len(h), 2))

if __name__ == '__main__':
    source = sys.argv[1]

    if ':' in source:
        parts = source.split(':')
        hostname = parts[0]
        port = int(parts[1])
        target = RSA.importKey(ssl.get_server_certificate((hostname, port)))
    else:
        with open(source, 'rb') as pem:
            target = RSA.importKey(pem.read())

    e_bytes = to_bytes(target.e)
    e_len = to_bytes(len(e_bytes), 4)
    n_bytes = to_bytes(target.n)
    n_len = to_bytes(len(n_bytes), 4)

    fp_old = sha1(b'ssh-rsa'+e_bytes+n_bytes).hexdigest()
    fp_new = sha1(b'\0\0\0\7ssh-rsa'+e_len+e_bytes+n_len+n_bytes).hexdigest()

    print('Tasmota fingerprint (old): ' + fmt_fingerprint(fp_old))
    print('Tasmota fingerprint (new): ' + fmt_fingerprint(fp_new))