certbot-certbot/certbot/crypto_util.py

"""Certbot client crypto utility functions.

.. todo:: Make the transition to use PSS rather than PKCS1_v1_5 when the server
    is capable of handling the signatures.

"""
import hashlib
import logging
import os
import warnings

import pyrfc3339
import six
import zope.component
from cryptography.exceptions import InvalidSignature
from cryptography.hazmat.backends import default_backend
from cryptography.hazmat.primitives.asymmetric.ec import ECDSA
from cryptography.hazmat.primitives.asymmetric.ec import EllipticCurvePublicKey
from cryptography.hazmat.primitives.asymmetric.padding import PKCS1v15
from cryptography.hazmat.primitives.asymmetric.rsa import RSAPublicKey
# https://github.com/python/typeshed/tree/master/third_party/2/cryptography
from cryptography import x509 # type: ignore
from OpenSSL import crypto
from OpenSSL import SSL  # type: ignore

from acme import crypto_util as acme_crypto_util
from acme.magic_typing import IO  # pylint: disable=unused-import, no-name-in-module
from certbot import compat
from certbot import errors
from certbot import interfaces
from certbot import util


logger = logging.getLogger(__name__)


# High level functions
def init_save_key(key_size, key_dir, keyname="key-certbot.pem"):
    """Initializes and saves a privkey.

    Inits key and saves it in PEM format on the filesystem.

    .. note:: keyname is the attempted filename, it may be different if a file
        already exists at the path.

    :param int key_size: RSA key size in bits
    :param str key_dir: Key save directory.
    :param str keyname: Filename of key

    :returns: Key
    :rtype: :class:`certbot.util.Key`

    :raises ValueError: If unable to generate the key given key_size.

    """
    try:
        key_pem = make_key(key_size)
    except ValueError as err:
        logger.error("", exc_info=True)
        raise err

    config = zope.component.getUtility(interfaces.IConfig)
    # Save file
    util.make_or_verify_dir(key_dir, 0o700, compat.os_geteuid(),
                            config.strict_permissions)
    key_f, key_path = util.unique_file(
        os.path.join(key_dir, keyname), 0o600, "wb")
    with key_f:
        key_f.write(key_pem)
    logger.debug("Generating key (%d bits): %s", key_size, key_path)

    return util.Key(key_path, key_pem)


def init_save_csr(privkey, names, path):
    """Initialize a CSR with the given private key.

    :param privkey: Key to include in the CSR
    :type privkey: :class:`certbot.util.Key`

    :param set names: `str` names to include in the CSR

    :param str path: Certificate save directory.

    :returns: CSR
    :rtype: :class:`certbot.util.CSR`

    """
    config = zope.component.getUtility(interfaces.IConfig)

    csr_pem = acme_crypto_util.make_csr(
        privkey.pem, names, must_staple=config.must_staple)

    # Save CSR
    util.make_or_verify_dir(path, 0o755, compat.os_geteuid(),
                               config.strict_permissions)
    csr_f, csr_filename = util.unique_file(
        os.path.join(path, "csr-certbot.pem"), 0o644, "wb")
    with csr_f:
        csr_f.write(csr_pem)
    logger.debug("Creating CSR: %s", csr_filename)

    return util.CSR(csr_filename, csr_pem, "pem")


# WARNING: the csr and private key file are possible attack vectors for TOCTOU
# We should either...
# A. Do more checks to verify that the CSR is trusted/valid
# B. Audit the parsing code for vulnerabilities

def valid_csr(csr):
    """Validate CSR.

    Check if `csr` is a valid CSR for the given domains.

    :param str csr: CSR in PEM.

    :returns: Validity of CSR.
    :rtype: bool

    """
    try:
        req = crypto.load_certificate_request(
            crypto.FILETYPE_PEM, csr)
        return req.verify(req.get_pubkey())
    except crypto.Error:
        logger.debug("", exc_info=True)
        return False


def csr_matches_pubkey(csr, privkey):
    """Does private key correspond to the subject public key in the CSR?

    :param str csr: CSR in PEM.
    :param str privkey: Private key file contents (PEM)

    :returns: Correspondence of private key to CSR subject public key.
    :rtype: bool

    """
    req = crypto.load_certificate_request(
        crypto.FILETYPE_PEM, csr)
    pkey = crypto.load_privatekey(crypto.FILETYPE_PEM, privkey)
    try:
        return req.verify(pkey)
    except crypto.Error:
        logger.debug("", exc_info=True)
        return False


def import_csr_file(csrfile, data):
    """Import a CSR file, which can be either PEM or DER.

    :param str csrfile: CSR filename
    :param str data: contents of the CSR file

    :returns: (`crypto.FILETYPE_PEM`,
               util.CSR object representing the CSR,
               list of domains requested in the CSR)
    :rtype: tuple

    """
    PEM = crypto.FILETYPE_PEM
    load = crypto.load_certificate_request
    try:
        # Try to parse as DER first, then fall back to PEM.
        csr = load(crypto.FILETYPE_ASN1, data)
    except crypto.Error:
        try:
            csr = load(PEM, data)
        except crypto.Error:
            raise errors.Error("Failed to parse CSR file: {0}".format(csrfile))

    domains = _get_names_from_loaded_cert_or_req(csr)
    # Internally we always use PEM, so re-encode as PEM before returning.
    data_pem = crypto.dump_certificate_request(PEM, csr)
    return PEM, util.CSR(file=csrfile, data=data_pem, form="pem"), domains


def make_key(bits):
    """Generate PEM encoded RSA key.

    :param int bits: Number of bits, at least 1024.

    :returns: new RSA key in PEM form with specified number of bits
    :rtype: str

    """
    assert bits >= 1024  # XXX
    key = crypto.PKey()
    key.generate_key(crypto.TYPE_RSA, bits)
    return crypto.dump_privatekey(crypto.FILETYPE_PEM, key)


def valid_privkey(privkey):
    """Is valid RSA private key?

    :param str privkey: Private key file contents in PEM

    :returns: Validity of private key.
    :rtype: bool

    """
    try:
        return crypto.load_privatekey(
            crypto.FILETYPE_PEM, privkey).check()
    except (TypeError, crypto.Error):
        return False


def verify_renewable_cert(renewable_cert):
    """For checking that your certs were not corrupted on disk.

    Several things are checked:
        1. Signature verification for the cert.
        2. That fullchain matches cert and chain when concatenated.
        3. Check that the private key matches the certificate.

    :param `.storage.RenewableCert` renewable_cert: cert to verify

    :raises errors.Error: If verification fails.
    """
    verify_renewable_cert_sig(renewable_cert)
    verify_fullchain(renewable_cert)
    verify_cert_matches_priv_key(renewable_cert.cert, renewable_cert.privkey)


def verify_renewable_cert_sig(renewable_cert):
    """ Verifies the signature of a `.storage.RenewableCert` object.

    :param `.storage.RenewableCert` renewable_cert: cert to verify

    :raises errors.Error: If signature verification fails.
    """
    try:
        with open(renewable_cert.chain, 'rb') as chain_file:  # type: IO[bytes]
            chain = x509.load_pem_x509_certificate(chain_file.read(), default_backend())
        with open(renewable_cert.cert, 'rb') as cert_file:  # type: IO[bytes]
            cert = x509.load_pem_x509_certificate(cert_file.read(), default_backend())
        pk = chain.public_key()
        with warnings.catch_warnings():
            warnings.simplefilter("ignore")
            if isinstance(pk, RSAPublicKey):
                # https://github.com/python/typeshed/blob/master/third_party/2/cryptography/hazmat/primitives/asymmetric/rsa.pyi
                verifier = pk.verifier(  # type: ignore
                    cert.signature, PKCS1v15(), cert.signature_hash_algorithm
                )
                verifier.update(cert.tbs_certificate_bytes)
                verifier.verify()
            elif isinstance(pk, EllipticCurvePublicKey):
                verifier = pk.verifier(
                    cert.signature, ECDSA(cert.signature_hash_algorithm)
                )
                verifier.update(cert.tbs_certificate_bytes)
                verifier.verify()
            else:
                raise errors.Error("Unsupported public key type")
    except (IOError, ValueError, InvalidSignature) as e:
        error_str = "verifying the signature of the cert located at {0} has failed. \
                Details: {1}".format(renewable_cert.cert, e)
        logger.exception(error_str)
        raise errors.Error(error_str)


def verify_cert_matches_priv_key(cert_path, key_path):
    """ Verifies that the private key and cert match.

    :param str cert_path: path to a cert in PEM format
    :param str key_path: path to a private key file

    :raises errors.Error: If they don't match.
    """
    try:
        context = SSL.Context(SSL.SSLv23_METHOD)
        context.use_certificate_file(cert_path)
        context.use_privatekey_file(key_path)
        context.check_privatekey()
    except (IOError, SSL.Error) as e:
        error_str = "verifying the cert located at {0} matches the \
                private key located at {1} has failed. \
                Details: {2}".format(cert_path,
                        key_path, e)
        logger.exception(error_str)
        raise errors.Error(error_str)


def verify_fullchain(renewable_cert):
    """ Verifies that fullchain is indeed cert concatenated with chain.

    :param `.storage.RenewableCert` renewable_cert: cert to verify

    :raises errors.Error: If cert and chain do not combine to fullchain.
    """
    try:
        with open(renewable_cert.chain) as chain_file:  # type: IO[str]
            chain = chain_file.read()
        with open(renewable_cert.cert) as cert_file:  # type: IO[str]
            cert = cert_file.read()
        with open(renewable_cert.fullchain) as fullchain_file:  # type: IO[str]
            fullchain = fullchain_file.read()
        if (cert + chain) != fullchain:
            error_str = "fullchain does not match cert + chain for {0}!"
            error_str = error_str.format(renewable_cert.lineagename)
            raise errors.Error(error_str)
    except IOError as e:
        error_str = "reading one of cert, chain, or fullchain has failed: {0}".format(e)
        logger.exception(error_str)
        raise errors.Error(error_str)
    except errors.Error as e:
        raise e


def pyopenssl_load_certificate(data):
    """Load PEM/DER certificate.

    :raises errors.Error:

    """

    openssl_errors = []

    for file_type in (crypto.FILETYPE_PEM, crypto.FILETYPE_ASN1):
        try:
            return crypto.load_certificate(file_type, data), file_type
        except crypto.Error as error:  # TODO: other errors?
            openssl_errors.append(error)
    raise errors.Error("Unable to load: {0}".format(",".join(
        str(error) for error in openssl_errors)))


def _load_cert_or_req(cert_or_req_str, load_func,
                      typ=crypto.FILETYPE_PEM):
    try:
        return load_func(typ, cert_or_req_str)
    except crypto.Error:
        logger.error("", exc_info=True)
        raise


def _get_sans_from_cert_or_req(cert_or_req_str, load_func,
                               typ=crypto.FILETYPE_PEM):
    # pylint: disable=protected-access
    return acme_crypto_util._pyopenssl_cert_or_req_san(_load_cert_or_req(
        cert_or_req_str, load_func, typ))


def get_sans_from_cert(cert, typ=crypto.FILETYPE_PEM):
    """Get a list of Subject Alternative Names from a certificate.

    :param str cert: Certificate (encoded).
    :param typ: `crypto.FILETYPE_PEM` or `crypto.FILETYPE_ASN1`

    :returns: A list of Subject Alternative Names.
    :rtype: list

    """
    return _get_sans_from_cert_or_req(
        cert, crypto.load_certificate, typ)


def _get_names_from_cert_or_req(cert_or_req, load_func, typ):
    loaded_cert_or_req = _load_cert_or_req(cert_or_req, load_func, typ)
    return _get_names_from_loaded_cert_or_req(loaded_cert_or_req)


def _get_names_from_loaded_cert_or_req(loaded_cert_or_req):
    # pylint: disable=protected-access
    return acme_crypto_util._pyopenssl_cert_or_req_all_names(loaded_cert_or_req)


def get_names_from_cert(csr, typ=crypto.FILETYPE_PEM):
    """Get a list of domains from a cert, including the CN if it is set.

    :param str cert: Certificate (encoded).
    :param typ: `crypto.FILETYPE_PEM` or `crypto.FILETYPE_ASN1`

    :returns: A list of domain names.
    :rtype: list

    """
    return _get_names_from_cert_or_req(
        csr, crypto.load_certificate, typ)


def dump_pyopenssl_chain(chain, filetype=crypto.FILETYPE_PEM):
    """Dump certificate chain into a bundle.

    :param list chain: List of `crypto.X509` (or wrapped in
        :class:`josepy.util.ComparableX509`).

    """
    # XXX: returns empty string when no chain is available, which
    # shuts up RenewableCert, but might not be the best solution...
    return acme_crypto_util.dump_pyopenssl_chain(chain, filetype)


def notBefore(cert_path):
    """When does the cert at cert_path start being valid?

    :param str cert_path: path to a cert in PEM format

    :returns: the notBefore value from the cert at cert_path
    :rtype: :class:`datetime.datetime`

    """
    return _notAfterBefore(cert_path, crypto.X509.get_notBefore)


def notAfter(cert_path):
    """When does the cert at cert_path stop being valid?

    :param str cert_path: path to a cert in PEM format

    :returns: the notAfter value from the cert at cert_path
    :rtype: :class:`datetime.datetime`

    """
    return _notAfterBefore(cert_path, crypto.X509.get_notAfter)


def _notAfterBefore(cert_path, method):
    """Internal helper function for finding notbefore/notafter.

    :param str cert_path: path to a cert in PEM format
    :param function method: one of ``crypto.X509.get_notBefore``
        or ``crypto.X509.get_notAfter``

    :returns: the notBefore or notAfter value from the cert at cert_path
    :rtype: :class:`datetime.datetime`

    """
    # pylint: disable=redefined-outer-name
    with open(cert_path) as f:
        x509 = crypto.load_certificate(crypto.FILETYPE_PEM,
                                               f.read())
    # pyopenssl always returns bytes
    timestamp = method(x509)
    reformatted_timestamp = [timestamp[0:4], b"-", timestamp[4:6], b"-",
                             timestamp[6:8], b"T", timestamp[8:10], b":",
                             timestamp[10:12], b":", timestamp[12:]]
    timestamp_str = b"".join(reformatted_timestamp)
    # pyrfc3339 uses "native" strings. That is, bytes on Python 2 and unicode
    # on Python 3
    if six.PY3:
        timestamp_str = timestamp_str.decode('ascii')
    return pyrfc3339.parse(timestamp_str)


def sha256sum(filename):
    """Compute a sha256sum of a file.

    NB: In given file, platform specific newlines characters will be converted
    into their equivalent unicode counterparts before calculating the hash.

    :param str filename: path to the file whose hash will be computed

    :returns: sha256 digest of the file in hexadecimal
    :rtype: str
    """
    sha256 = hashlib.sha256()
    with open(filename, 'rU') as file_d:
        sha256.update(file_d.read().encode('UTF-8'))
    return sha256.hexdigest()

def cert_and_chain_from_fullchain(fullchain_pem):
    """Split fullchain_pem into cert_pem and chain_pem

    :param str fullchain_pem: concatenated cert + chain

    :returns: tuple of string cert_pem and chain_pem
    :rtype: tuple

    """
    cert = crypto.dump_certificate(crypto.FILETYPE_PEM,
        crypto.load_certificate(crypto.FILETYPE_PEM, fullchain_pem)).decode()
    chain = fullchain_pem[len(cert):].lstrip()
    return (cert, chain)