electrum/lib/x509.py

#!/usr/bin/env python
#
# Electrum - lightweight Bitcoin client
# Copyright (C) 2014 Thomas Voegtlin
#
# Permission is hereby granted, free of charge, to any person
# obtaining a copy of this software and associated documentation files
# (the "Software"), to deal in the Software without restriction,
# including without limitation the rights to use, copy, modify, merge,
# publish, distribute, sublicense, and/or sell copies of the Software,
# and to permit persons to whom the Software is furnished to do so,
# subject to the following conditions:
#
# The above copyright notice and this permission notice shall be
# included in all copies or substantial portions of the Software.
#
# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
# EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
# MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
# NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
# BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
# ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
# CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
# SOFTWARE.


from datetime import datetime
import sys
import util
from util import profiler, print_error
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])

# types used in ASN1 structured data
ASN1_TYPES = {
    'BOOLEAN':           0x01,
    'INTEGER':           0x02,
    'BIT STRING':        0x03,
    'OCTET STRING':      0x04,
    'NULL':              0x05,
    'OBJECT IDENTIFIER': 0x06,
    'SEQUENCE':          0x70,
    'SET':               0x71,
    'PrintableString':   0x13,
    'IA5String':         0x16,
    'UTCTime':           0x17,
    'ENUMERATED':        0x0A,
    'UTF8String':        0x0C,
    'PrintableString':   0x13,
}

class CertificateError(Exception):
    pass

# helper functions

def bitstr_to_bytestr(s):
    if s[0] != '\x00':
        raise BaseException('no padding')
    return s[1:]

def bytestr_to_int(s):
    i = 0
    for char in s:
        i <<= 8
        i |= ord(char)
    return i

def decode_OID(s):
    s = map(ord, s)
    r = []
    r.append(s[0] / 40)
    r.append(s[0] % 40)
    k = 0
    for i in s[1:]:
        if i < 128:
            r.append(i + 128*k)
            k = 0
        else:
            k = (i - 128) + 128*k
    return '.'.join(map(str, r))


def encode_OID(oid):
    x = map(int, oid.split('.'))
    s = chr(x[0]*40 + x[1])
    for i in x[2:]:
        ss = chr(i % 128)
        while i > 128:
            i = i / 128
            ss = chr(128 + i % 128) + ss
        s += ss
    return s




class ASN1_Node(str):

    def get_node(self, ix):
        # return index of first byte, first content byte and last byte.
	first = ord(self[ix+1])
	if (ord(self[ix+1]) & 0x80) == 0:
            length = first
            ixf = ix + 2
            ixl = ixf + length - 1
	else:
            lengthbytes = first & 0x7F
            length = bytestr_to_int(self[ix+2:ix+2+lengthbytes])
            ixf = ix + 2 + lengthbytes
            ixl = ixf + length -1
	return (ix, ixf, ixl)

    def root(self):
	return self.get_node(0)

    def next_node(self, node):
        ixs, ixf, ixl = node
	return self.get_node(ixl + 1)

    def first_child(self, node):
        ixs, ixf, ixl = node
	if ord(self[ixs]) & 0x20 != 0x20:
            raise BaseException('Can only open constructed types.', hex(ord(self[ixs])))
        return self.get_node(ixf)

    def is_child_of(node1, node2):
        ixs, ixf, ixl = node1
        jxs, jxf, jxl = node2
	return ( (ixf <= jxs) and (jxl <= ixl) ) or ( (jxf <= ixs) and (ixl <= jxl) )

    def get_all(self, node):
        # return type + length + value
        ixs, ixf, ixl = node
	return self[ixs:ixl+1]

    def get_value_of_type(self, node, asn1_type):
        # verify type byte and return content
        ixs, ixf, ixl = node
	if ASN1_TYPES[asn1_type] != ord(self[ixs]):
            raise BaseException('Wrong type:', hex(ord(self[ixs])),  hex(ASN1_TYPES[asn1_type]) )
	return self[ixf:ixl+1]

    def get_value(self, node):
        ixs, ixf, ixl = node
	return self[ixf:ixl+1]

    def get_children(self, node):
        nodes = []
        ii = self.first_child(node)
        nodes.append(ii)
        while ii[2] < node[2]:
            ii = self.next_node(ii)
            nodes.append(ii)
        return nodes

    def get_sequence(self):
        return map(lambda j: self.get_value(j), self.get_children(self.root()))

    def get_dict(self, node):
        p = {}
        for ii in self.get_children(node):
            for iii in self.get_children(ii):
                iiii = self.first_child(iii)
                oid = decode_OID(self.get_value_of_type(iiii, 'OBJECT IDENTIFIER'))
                iiii = self.next_node(iiii)
                value = self.get_value(iiii)
                p[oid] = value
        return p


class X509(object):

    def __init__(self, b):

        self.bytes = bytearray(b)

        der = ASN1_Node(str(b))
        root = der.root()
        cert = der.first_child(root)
        # data for signature
        self.data = der.get_all(cert)

        # optional version field
        if der.get_value(cert)[0] == chr(0xa0):
            version = der.first_child(cert)
            serial_number = der.next_node(version)
        else:
            serial_number = der.first_child(cert)
        self.serial_number = bytestr_to_int(der.get_value_of_type(serial_number, 'INTEGER'))

        # signature algorithm
        sig_algo = der.next_node(serial_number)
        ii = der.first_child(sig_algo)
        self.sig_algo = decode_OID(der.get_value_of_type(ii, 'OBJECT IDENTIFIER'))

        # issuer
        issuer = der.next_node(sig_algo)
        self.issuer = der.get_dict(issuer)

        # validity
        validity = der.next_node(issuer)
        ii = der.first_child(validity)
        self.notBefore = der.get_value_of_type(ii, 'UTCTime')
        ii = der.next_node(ii)
        self.notAfter = der.get_value_of_type(ii, 'UTCTime')

        # subject
        subject = der.next_node(validity)
        self.subject = der.get_dict(subject)
        subject_pki = der.next_node(subject)
        public_key_algo = der.first_child(subject_pki)
        ii = der.first_child(public_key_algo)
        self.public_key_algo = decode_OID(der.get_value_of_type(ii, 'OBJECT IDENTIFIER'))

        # pubkey modulus and exponent
        subject_public_key = der.next_node(public_key_algo)
        spk = der.get_value_of_type(subject_public_key, 'BIT STRING')
        spk = ASN1_Node(bitstr_to_bytestr(spk))
        r = spk.root()
        modulus = spk.first_child(r)
        exponent = spk.next_node(modulus)
        rsa_n = spk.get_value_of_type(modulus, 'INTEGER')
        rsa_e = spk.get_value_of_type(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 = der.next_node(i)
            d = der.get_dict(i)
            for oid, value in d.items():
                value = ASN1_Node(value)
                if oid == '2.5.29.19':
                    # Basic Constraints
                    self.CA = bool(value)
                elif oid == '2.5.29.14':
                    # Subject Key Identifier
                    r = value.root()
                    value = value.get_value_of_type(r, 'OCTET STRING')
                    self.SKI = value.encode('hex')
                elif oid == '2.5.29.35':
                    # Authority Key Identifier
                    self.AKI = value.get_sequence()[0].encode('hex')
                else:
                    pass

        # cert signature
        cert_sig_algo = der.next_node(cert)
        ii = der.first_child(cert_sig_algo)
        self.cert_sig_algo = decode_OID(der.get_value_of_type(ii, 'OBJECT IDENTIFIER'))
        cert_sig = der.next_node(cert_sig_algo)
        self.signature = der.get_value(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


if __name__ == "__main__":
    import requests
    util.set_verbosity(True)
    ca_path = requests.certs.where()
    ca_list, ca_keyID = load_certificates(ca_path)