Utilities for fingerprinting RSA keys

rsakeyfingerprint.py

import base64
from hashlib import sha1, md5
import re

from pyasn1.codec.ber import encoder
from pyasn1.type.univ import *

def rsa_key_to_der(key):
    seq = Sequence()

    for index, key in enumerate([0, key.n, key.e, key.d, key.p, key.q, key.d % (key.p - 1), key.d % (key.q - 1), paramiko.util.mod_inverse(key.q, key.p)]):
        seq.setComponentByPosition(index, Integer(key))

    return encoder.encode(seq)

def strip_pem_header_footer(data):
    return re.sub('-.*-', '', data.replace('\r', '')).replace('\n', '')

def rsa_pem_to_der(data):
    assert "RSA PRIVATE KEY" in data
    return base64.decodestring(strip_pem_header_footer(data))

def rsa_to_pkcs8_der(key=None, pem=None, der=None):
    if not der:
        if key:
            der = rsa_key_to_der(key)
        elif pem:
            der = rsa_pem_to_der(pem)

    seq = Sequence()

    seq.setComponentByPosition(0, Integer(0))
    seq.setComponentByPosition(1, Sequence().setComponentByPosition(0, ObjectIdentifier('1.2.840.113549.1.1.1')).setComponentByPosition(1, Null('')))
    seq.setComponentByPosition(2, OctetString(der))
    return encoder.encode(seq)

def format_digest(digest):
    return re.sub(r'(\w{2})(?!$)', r'\1:', digest)

def fingerprint(key=None, pem=None, der=None):
    pkcs8_der = rsa_to_pkcs8_der(key, pem, der)
    plain_sha1 = sha1(pkcs8_der).hexdigest()
    plain_md5 = md5(pkcs8_der).hexdigest()

    return {'md5' : format_digest(plain_md5), 'sha1' : format_digest(plain_sha1)}