electrum/lib/x509.py

#!/usr/bin/env python
#
# Electrum - lightweight Bitcoin client
# Copyright (C) 2014 Thomas Voegtlin
#
# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program. If not, see <http://www.gnu.org/licenses/>.


from datetime import datetime
import sys

import util
from util import profiler, print_error

from asn1tinydecoder import *
import ecdsa
import hashlib


# algo OIDs
ALGO_RSA_SHA1   = '1.2.840.113549.1.1.5'
ALGO_RSA_SHA256 = '1.2.840.113549.1.1.11'
ALGO_RSA_SHA384 = '1.2.840.113549.1.1.12'
ALGO_RSA_SHA512 = '1.2.840.113549.1.1.13'
ALGO_ECDSA_SHA256 = '1.2.840.10045.4.3.2'

# prefixes, see http://stackoverflow.com/questions/3713774/c-sharp-how-to-calculate-asn-1-der-encoding-of-a-particular-hash-algorithm
PREFIX_RSA_SHA256 = bytearray([0x30,0x31,0x30,0x0d,0x06,0x09,0x60,0x86,0x48,0x01,0x65,0x03,0x04,0x02,0x01,0x05,0x00,0x04,0x20])
PREFIX_RSA_SHA384 = bytearray([0x30,0x41,0x30,0x0d,0x06,0x09,0x60,0x86,0x48,0x01,0x65,0x03,0x04,0x02,0x02,0x05,0x00,0x04,0x30])
PREFIX_RSA_SHA512 = bytearray([0x30,0x51,0x30,0x0d,0x06,0x09,0x60,0x86,0x48,0x01,0x65,0x03,0x04,0x02,0x03,0x05,0x00,0x04,0x40])


class CertificateError(Exception):
    pass




class X509(object):

    def __init__(self, b):

        self.bytes = bytearray(b)

        der = str(b)
        root = asn1_node_root(der)
        cert = asn1_node_first_child(der, root)
        # data for signature
        self.data = asn1_get_all(der, cert)

        # optional version field
        if asn1_get_value(der, cert)[0] == chr(0xa0):
            version = asn1_node_first_child(der, cert)
            serial_number = asn1_node_next(der, version)
        else:
            serial_number = asn1_node_first_child(der, cert)
        self.serial_number = bytestr_to_int(asn1_get_value_of_type(der, serial_number, 'INTEGER'))

        # signature algorithm
        sig_algo = asn1_node_next(der, serial_number)
        ii = asn1_node_first_child(der, sig_algo)
        self.sig_algo = decode_OID(asn1_get_value_of_type(der, ii, 'OBJECT IDENTIFIER'))

        # issuer
        issuer = asn1_node_next(der, sig_algo)
        self.issuer = asn1_get_dict(der, issuer)

        # validity
        validity = asn1_node_next(der, issuer)
        ii = asn1_node_first_child(der, validity)
        self.notBefore = asn1_get_value_of_type(der, ii, 'UTCTime')
        ii = asn1_node_next(der,ii)
        self.notAfter = asn1_get_value_of_type(der, ii, 'UTCTime')

        # subject
        subject = asn1_node_next(der, validity)
        self.subject = asn1_get_dict(der, subject)

        subject_pki = asn1_node_next(der, subject)

        public_key_algo = asn1_node_first_child(der, subject_pki)
        ii = asn1_node_first_child(der, public_key_algo)
        self.public_key_algo = decode_OID(asn1_get_value_of_type(der, ii, 'OBJECT IDENTIFIER'))

        # pubkey modulus and exponent
        subject_public_key = asn1_node_next(der, public_key_algo)
        spk = asn1_get_value_of_type(der, subject_public_key, 'BIT STRING')
        spk = bitstr_to_bytestr(spk)
        r = asn1_node_root(spk)
        modulus = asn1_node_first_child(spk, r)
        exponent = asn1_node_next(spk, modulus)
        rsa_n = asn1_get_value_of_type(spk, modulus, 'INTEGER')
        rsa_e = asn1_get_value_of_type(spk, exponent, 'INTEGER')
        self.modulus = ecdsa.util.string_to_number(rsa_n)
        self.exponent = ecdsa.util.string_to_number(rsa_e)

        # extensions
        self.CA = False
        self.AKI = None
        self.SKI = None
        i = subject_pki
        while i[2] < cert[2]:
            i = asn1_node_next(der, i)
            d = asn1_get_dict(der, i)
            for oid, value in d.items():
                if oid == '2.5.29.19':
                    # Basic Constraints
                    self.CA = bool(value)
                elif oid == '2.5.29.14':
                    # Subject Key Identifier
                    r = asn1_node_root(value)
                    value = asn1_get_value_of_type(value, r, 'OCTET STRING')
                    self.SKI = value.encode('hex')
                elif oid == '2.5.29.35':
                    # Authority Key Identifier
                    self.AKI = asn1_get_sequence(value)[0].encode('hex')
                else:
                    pass

        # cert signature
        cert_sig_algo = asn1_node_next(der, cert)
        ii = asn1_node_first_child(der, cert_sig_algo)
        self.cert_sig_algo = decode_OID(asn1_get_value_of_type(der, ii, 'OBJECT IDENTIFIER'))
        cert_sig = asn1_node_next(der, cert_sig_algo)
        self.signature = asn1_get_value(der, cert_sig)[1:]
        
    def get_keyID(self):
        # http://security.stackexchange.com/questions/72077/validating-an-ssl-certificate-chain-according-to-rfc-5280-am-i-understanding-th
        return self.SKI if self.SKI else repr(self.subject)

    def get_issuer_keyID(self):
        return self.AKI if self.AKI else repr(self.issuer)

    def get_common_name(self):
        return self.subject.get('2.5.4.3', 'unknown')

    def get_signature(self):
        return self.cert_sig_algo, self.signature, self.data

    def check_ca(self):
        return self.CA

    def check_date(self):
        import time
        now = time.time()
        TIMESTAMP_FMT = '%y%m%d%H%M%SZ'
        not_before = time.mktime(time.strptime(self.notBefore, TIMESTAMP_FMT))
        not_after = time.mktime(time.strptime(self.notAfter, TIMESTAMP_FMT))
        if not_before > now:
            raise CertificateError('Certificate has not entered its valid date range.')
        if not_after <= now:
            raise CertificateError('Certificate has expired.')

    def getFingerprint(self):
        return hashlib.sha1(self.bytes).digest()





@profiler
def load_certificates(ca_path):
    import pem
    ca_list = {}
    ca_keyID = {}
    with open(ca_path, 'r') as f:
        s = f.read()
    bList = pem.dePemList(s, "CERTIFICATE")
    for b in bList:
        try:
            x = X509(b)
            x.check_date()
        except BaseException as e:
            util.print_error("cert error:", e)
            continue

        fp = x.getFingerprint()
        ca_list[fp] = x
        ca_keyID[x.get_keyID()] = fp

    return ca_list, ca_keyID