# Copyright (c) 2012 The Chromium Authors. All rights reserved.
# Use of this source code is governed by a BSD-style license that can be
# found in the LICENSE file.

import asn1
import hashlib
import os


# This file implements very minimal certificate and OCSP generation. It's
# designed to test revocation checking.

def RandomNumber(length_in_bytes):
  '''RandomNumber returns a random number of length 8*|length_in_bytes| bits'''
  rand = os.urandom(length_in_bytes)
  n = 0
  for x in rand:
    n <<= 8
    n |= ord(x)
  return n


def ModExp(n, e, p):
  '''ModExp returns n^e mod p'''
  r = 1
  while e != 0:
    if e & 1:
      r = (r*n) % p
    e >>= 1
    n = (n*n) % p
  return r

# PKCS1v15_SHA256_PREFIX is the ASN.1 prefix for a SHA256 signature.
PKCS1v15_SHA256_PREFIX = '3031300d060960864801650304020105000420'.decode('hex')

class RSA(object):
  def __init__(self, modulus, e, d):
    self.m = modulus
    self.e = e
    self.d = d

    self.modlen = 0
    m = modulus
    while m != 0:
      self.modlen += 1
      m >>= 8

  def Sign(self, message):
    digest = hashlib.sha256(message).digest()
    prefix = PKCS1v15_SHA256_PREFIX

    em = ['\xff'] * (self.modlen - 1 - len(prefix) - len(digest))
    em[0] = '\x00'
    em[1] = '\x01'
    em += "\x00" + prefix + digest

    n = 0
    for x in em:
      n <<= 8
      n |= ord(x)

    s = ModExp(n, self.d, self.m)
    out = []
    while s != 0:
      out.append(s & 0xff)
      s >>= 8
    out.reverse()
    return '\x00' * (self.modlen - len(out)) + asn1.ToBytes(out)

  def ToDER(self):
    return asn1.ToDER(asn1.SEQUENCE([self.m, self.e]))


def Name(cn = None, c = None, o = None):
  names = asn1.SEQUENCE([])

  if cn is not None:
    names.children.append(
      asn1.SET([
        asn1.SEQUENCE([
          COMMON_NAME, cn,
        ])
      ])
    )

  if c is not None:
    names.children.append(
      asn1.SET([
        asn1.SEQUENCE([
          COUNTRY, c,
        ])
      ])
    )

  if o is not None:
    names.children.append(
      asn1.SET([
        asn1.SEQUENCE([
          ORGANIZATION, o,
        ])
      ])
    )

  return names


# The private key and root certificate name are hard coded here:

# This is the private key
KEY = RSA(0x00a71998f2930bfe73d031a87f133d2f378eeeeed52a77e44d0fc9ff6f07ff32cbf3da999de4ed65832afcb0807f98787506539d258a0ce3c2c77967653099a9034a9b115a876c39a8c4e4ed4acd0c64095946fb39eeeb47a0704dbb018acf48c3a1c4b895fc409fb4a340a986b1afc45519ab9eca47c30185c771c64aa5ecf07d,
          3,
          0x6f6665f70cb2a9a28acbc5aa0cd374cfb49f49e371a542de0a86aa4a0554cc87f7e71113edf399021ca875aaffbafaf8aee268c3b15ded2c84fb9a4375bbc6011d841e57833bc6f998d25daf6fa7f166b233e3e54a4bae7a5aaaba21431324967d5ff3e1d4f413827994262115ca54396e7068d0afa7af787a5782bc7040e6d3)

# And the same thing in PEM format
KEY_PEM = '''-----BEGIN RSA PRIVATE KEY-----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-----END RSA PRIVATE KEY-----
'''

# Root certificate CN
ISSUER_CN = "Testing CA"

# All certificates are issued under this policy OID, in the Google arc:
CERT_POLICY_OID = asn1.OID([1, 3, 6, 1, 4, 1, 11129, 2, 4, 1])

# These result in the following root certificate:
# -----BEGIN CERTIFICATE-----
# MIIB0TCCATqgAwIBAgIBATANBgkqhkiG9w0BAQUFADAVMRMwEQYDVQQDEwpUZXN0aW5nIENBMB4X
# DTEwMDEwMTA2MDAwMFoXDTMyMTIwMTA2MDAwMFowFTETMBEGA1UEAxMKVGVzdGluZyBDQTCBnTAN
# BgkqhkiG9w0BAQEFAAOBiwAwgYcCgYEApxmY8pML/nPQMah/Ez0vN47u7tUqd+RND8n/bwf/Msvz
# 2pmd5O1lgyr8sIB/mHh1BlOdJYoM48LHeWdlMJmpA0qbEVqHbDmoxOTtSs0MZAlZRvs57utHoHBN
# uwGKz0jDocS4lfxAn7SjQKmGsa/EVRmrnspHwwGFx3HGSqXs8H0CAQOjMzAxMBIGA1UdEwEB/wQI
# MAYBAf8CAQAwGwYDVR0gAQEABBEwDzANBgsrBgEEAdZ5AgHODzANBgkqhkiG9w0BAQUFAAOBgQA/
# STb40A6D+93jMfLGQzXc997IsaJZdoPt7tYa8PqGJBL62EiTj+erd/H5pDZx/2/bcpOG4m9J56yg
# wOohbllw2TM+oeEd8syzV6X+1SIPnGI56JRrm3UXcHYx1Rq5loM9WKAiz/WmIWmskljsEQ7+542p
# q0pkHjs8nuXovSkUYA==
# -----END CERTIFICATE-----

# If you update any of the above, you can generate a new root with the
# following line:
#   print DERToPEM(MakeCertificate(ISSUER_CN, ISSUER_CN, 1, KEY, KEY, None))


# Various OIDs

AIA_OCSP = asn1.OID([1, 3, 6, 1, 5, 5, 7, 48, 1])
AUTHORITY_INFORMATION_ACCESS = asn1.OID([1, 3, 6, 1, 5, 5, 7, 1, 1])
BASIC_CONSTRAINTS = asn1.OID([2, 5, 29, 19])
CERT_POLICIES = asn1.OID([2, 5, 29, 32])
COMMON_NAME = asn1.OID([2, 5, 4, 3])
COUNTRY = asn1.OID([2, 5, 4, 6])
HASH_SHA1 = asn1.OID([1, 3, 14, 3, 2, 26])
OCSP_TYPE_BASIC = asn1.OID([1, 3, 6, 1, 5, 5, 7, 48, 1, 1])
ORGANIZATION = asn1.OID([2, 5, 4, 10])
PUBLIC_KEY_RSA = asn1.OID([1, 2, 840, 113549, 1, 1, 1])
SHA256_WITH_RSA_ENCRYPTION = asn1.OID([1, 2, 840, 113549, 1, 1, 11])


def MakeCertificate(
    issuer_cn, subject_cn, serial, pubkey, privkey, ocsp_url = None):
  '''MakeCertificate returns a DER encoded certificate, signed by privkey.'''
  extensions = asn1.SEQUENCE([])

  # Default subject name fields
  c = "XX"
  o = "Testing Org"

  if issuer_cn == subject_cn:
    # Root certificate.
    c = None
    o = None
    extensions.children.append(
      asn1.SEQUENCE([
        basic_constraints,
        True,
        asn1.OCTETSTRING(asn1.ToDER(asn1.SEQUENCE([
          True, # IsCA
          0, # Path len
        ]))),
      ]))

  if ocsp_url is not None:
    extensions.children.append(
      asn1.SEQUENCE([
        AUTHORITY_INFORMATION_ACCESS,
        False,
        asn1.OCTETSTRING(asn1.ToDER(asn1.SEQUENCE([
          asn1.SEQUENCE([
            AIA_OCSP,
            asn1.Raw(asn1.TagAndLength(0x86, len(ocsp_url)) + ocsp_url),
          ]),
        ]))),
      ]))

  extensions.children.append(
    asn1.SEQUENCE([
      CERT_POLICIES,
      False,
      asn1.OCTETSTRING(asn1.ToDER(asn1.SEQUENCE([
        asn1.SEQUENCE([ # PolicyInformation
          CERT_POLICY_OID,
        ]),
      ]))),
    ])
  )

  tbsCert = asn1.ToDER(asn1.SEQUENCE([
      asn1.Explicit(0, 2), # Version
      serial,
      asn1.SEQUENCE([SHA256_WITH_RSA_ENCRYPTION, None]), # SignatureAlgorithm
      Name(cn = issuer_cn), # Issuer
      asn1.SEQUENCE([ # Validity
        asn1.UTCTime("100101060000Z"), # NotBefore
        asn1.UTCTime("321201060000Z"), # NotAfter
      ]),
      Name(cn = subject_cn, c = c, o = o), # Subject
      asn1.SEQUENCE([ # SubjectPublicKeyInfo
        asn1.SEQUENCE([ # Algorithm
          PUBLIC_KEY_RSA,
          None,
        ]),
        asn1.BitString(asn1.ToDER(pubkey)),
      ]),
      asn1.Explicit(3, extensions),
    ]))

  return asn1.ToDER(asn1.SEQUENCE([
    asn1.Raw(tbsCert),
    asn1.SEQUENCE([
      SHA256_WITH_RSA_ENCRYPTION,
      None,
    ]),
    asn1.BitString(privkey.Sign(tbsCert)),
  ]))


def MakeOCSPResponse(issuer_cn, issuer_key, serial, ocsp_state):
  # https://tools.ietf.org/html/rfc2560
  issuer_name_hash = asn1.OCTETSTRING(
      hashlib.sha1(asn1.ToDER(Name(cn = issuer_cn))).digest())

  issuer_key_hash = asn1.OCTETSTRING(
      hashlib.sha1(asn1.ToDER(issuer_key)).digest())

  cert_status = None
  if ocsp_state == OCSP_STATE_REVOKED:
    cert_status = asn1.Explicit(1, asn1.GeneralizedTime("20100101060000Z"))
  elif ocsp_state == OCSP_STATE_UNKNOWN:
    cert_status = asn1.Raw(asn1.TagAndLength(0x80 | 2, 0))
  elif ocsp_state == OCSP_STATE_GOOD:
    cert_status = asn1.Raw(asn1.TagAndLength(0x80 | 0, 0))
  else:
    raise ValueError('Bad OCSP state: ' + str(ocsp_state))

  basic_resp_data_der = asn1.ToDER(asn1.SEQUENCE([
    asn1.Explicit(2, issuer_key_hash),
    asn1.GeneralizedTime("20100101060000Z"), # producedAt
    asn1.SEQUENCE([
      asn1.SEQUENCE([ # SingleResponse
        asn1.SEQUENCE([ # CertID
          asn1.SEQUENCE([ # hashAlgorithm
            HASH_SHA1,
            None,
          ]),
          issuer_name_hash,
          issuer_key_hash,
          serial,
        ]),
        cert_status,
        asn1.GeneralizedTime("20100101060000Z"), # thisUpdate
        asn1.Explicit(0, asn1.GeneralizedTime("20300101060000Z")), # nextUpdate
      ]),
    ]),
  ]))

  basic_resp = asn1.SEQUENCE([
    asn1.Raw(basic_resp_data_der),
    asn1.SEQUENCE([
      SHA256_WITH_RSA_ENCRYPTION,
      None,
    ]),
    asn1.BitString(issuer_key.Sign(basic_resp_data_der)),
  ])

  resp = asn1.SEQUENCE([
    asn1.ENUMERATED(0),
    asn1.Explicit(0, asn1.SEQUENCE([
      OCSP_TYPE_BASIC,
      asn1.OCTETSTRING(asn1.ToDER(basic_resp)),
    ]))
  ])

  return asn1.ToDER(resp)


def DERToPEM(der):
  pem = '-----BEGIN CERTIFICATE-----\n'
  pem += der.encode('base64')
  pem += '-----END CERTIFICATE-----\n'
  return pem

OCSP_STATE_GOOD = 1
OCSP_STATE_REVOKED = 2
OCSP_STATE_INVALID = 3
OCSP_STATE_UNAUTHORIZED = 4
OCSP_STATE_UNKNOWN = 5

# unauthorizedDER is an OCSPResponse with a status of 6:
# SEQUENCE { ENUM(6) }
unauthorizedDER = '30030a0106'.decode('hex')

def GenerateCertKeyAndOCSP(subject = "127.0.0.1",
                           ocsp_url = "http://127.0.0.1",
                           ocsp_state = OCSP_STATE_GOOD,
                           serial = 0):
  '''GenerateCertKeyAndOCSP returns a (cert_and_key_pem, ocsp_der) where:
       * cert_and_key_pem contains a certificate and private key in PEM format
         with the given subject common name and OCSP URL.
       * ocsp_der contains a DER encoded OCSP response or None if ocsp_url is
         None'''

  if serial == 0:
    serial = RandomNumber(16)
  cert_der = MakeCertificate(ISSUER_CN, bytes(subject), serial, KEY, KEY,
                             bytes(ocsp_url))
  cert_pem = DERToPEM(cert_der)

  ocsp_der = None
  if ocsp_url is not None:
    if ocsp_state == OCSP_STATE_UNAUTHORIZED:
      ocsp_der = unauthorizedDER
    elif ocsp_state == OCSP_STATE_INVALID:
      ocsp_der = '3'
    else:
      ocsp_der = MakeOCSPResponse(ISSUER_CN, KEY, serial, ocsp_state)

  return (cert_pem + KEY_PEM, ocsp_der)