ec.py

from cryptography.hazmat.primitives.asymmetric import ec

from cryptojwt.exception import KeyNotFound

from ..exception import DeSerializationNotPossible, JWKESTException, UnsupportedECurve
from ..utils import as_unicode, deser, long_to_base64
from .asym import AsymmetricKey
from .x509 import (
    import_private_key_from_pem_file,
    import_public_key_from_pem_data,
    import_public_key_from_pem_file,
)

# This is used to translate between the curve representation in
# Cryptography and the one used by NIST (and in RFC 7518)
NIST2SEC = {
    "B-571": ec.SECT571R1,
    "K-571": ec.SECT571K1,
    "K-409": ec.SECT409K1,
    "K-283": ec.SECT283K1,
    "K-233": ec.SECT233K1,
    "K-163": ec.SECT163K1,
    "P-521": ec.SECP521R1,
    "P-384": ec.SECP384R1,
    "P-256": ec.SECP256R1,
    "P-224": ec.SECP224R1,
    "P-192": ec.SECP192R1,
    "P-256K": ec.SECP256K1,
    "brainpoolp256r1": ec.BrainpoolP256R1,
    "brainpoolp384r1": ec.BrainpoolP384R1,
    "brainpoolp512r1": ec.BrainpoolP512R1,
}

# Inverted NIST2SEC dictionary
SEC2NIST = dict([(s.name, n) for n, s in NIST2SEC.items()])


def ec_construct_public(num):
    """
    Given a set of values on public attributes build a elliptic curve
    public key instance.

    :param num: A dictionary with public attributes and their values
    :return: A cryptography.hazmat.primitives.asymmetric.ec.EllipticCurvePublicKey
        instance.
    """
    try:
        _sec_crv = NIST2SEC[as_unicode(num["crv"])]
    except KeyError as exc:
        raise UnsupportedECurve("Unsupported elliptic curve: {}".format(num["crv"])) from exc

    ecpn = ec.EllipticCurvePublicNumbers(num["x"], num["y"], _sec_crv())
    return ecpn.public_key()


def ec_construct_private(num):
    """
    Given a set of values on public and private attributes build an elliptic
    curve private key instance.

    :param num: A dictionary with public and private attributes and their values
    :return: A cryptography.hazmat.primitives.asymmetric.ec.EllipticCurvePrivateKey
        instance.
    """
    pub_ecpn = ec.EllipticCurvePublicNumbers(num["x"], num["y"], NIST2SEC[as_unicode(num["crv"])]())
    priv_ecpn = ec.EllipticCurvePrivateNumbers(num["d"], pub_ecpn)
    return priv_ecpn.private_key()


class ECKey(AsymmetricKey):
    """
    JSON Web key representation of a Elliptic curve key.
    According to RFC 7517 a JWK representation of a EC key can look like
    this::

        {
          "kty":"EC",
          "crv":"P-256",
          "x":"MKBCTNIcKUSDii11ySs3526iDZ8AiTo7Tu6KPAqv7D4",
          "y":"4Etl6SRW2YiLUrN5vfvVHuhp7x8PxltmWWlbbM4IFyM",
          "d":"870MB6gfuTJ4HtUnUvYMyJpr5eUZNP4Bk43bVdj3eAE"
        }

    Parameters according to https://tools.ietf.org/html/rfc7518#section-6.2
    """

    members = AsymmetricKey.members[:]
    # The elliptic curve specific attributes
    members.extend(["crv", "x", "y", "d"])
    longs = ["x", "y", "d"]
    public_members = AsymmetricKey.public_members[:]
    public_members.extend(["kty", "alg", "use", "kid", "crv", "x", "y"])
    # required attributes
    required = ["kty", "crv", "x", "y"]

    def __init__(self, kty="EC", alg="", use="", kid="", crv="", x="", y="", d="", **kwargs):
        AsymmetricKey.__init__(self, kty, alg, use, kid, **kwargs)
        self.crv = crv
        self.x = x
        self.y = y
        self.d = d

        if not self.pub_key and not self.priv_key:
            if self.x and self.y and self.crv:
                self.verify()
                self.deserialize()
            elif any([self.x, self.y, self.crv]):
                raise JWKESTException("Missing required parameter")
        elif self.priv_key and not self.pub_key:
            self.pub_key = self.priv_key.public_key()
            self._serialize(self.priv_key)

    def deserialize(self):
        """
        Starting with information gathered from the on-the-wire representation
        of an elliptic curve key (a JWK) initiate a
        cryptography.hazmat.primitives.asymmetric.ec.EllipticCurvePublicKey
        or EllipticCurvePrivateKey instance. So we have to get from having::

            {
              "kty":"EC",
              "crv":"P-256",
              "x":"MKBCTNIcKUSDii11ySs3526iDZ8AiTo7Tu6KPAqv7D4",
              "y":"4Etl6SRW2YiLUrN5vfvVHuhp7x8PxltmWWlbbM4IFyM",
              "d":"870MB6gfuTJ4HtUnUvYMyJpr5eUZNP4Bk43bVdj3eAE"
            }

        to having a key that can be used for signing/verifying and/or
        encrypting/decrypting.
        If 'd' has value then we're dealing with a private key otherwise
        a public key. 'x' and 'y' MUST have values.
        If self.pub_key or self.priv_key has a value beforehand this will
        be overwrite.

        x, y and d (if present) must be strings or bytes.
        """

        if isinstance(self.x, (str, bytes)):
            _x = deser(self.x)
        else:
            raise ValueError('"x" MUST be a string')

        if isinstance(self.y, (str, bytes)):
            _y = deser(self.y)
        else:
            raise ValueError('"y" MUST be a string')

        if self.d:
            try:
                if isinstance(self.d, (str, bytes)):
                    _d = deser(self.d)
                    self.priv_key = ec_construct_private(
                        {"x": _x, "y": _y, "crv": self.crv, "d": _d}
                    )
                    self.pub_key = self.priv_key.public_key()
            except ValueError as exc:
                raise DeSerializationNotPossible(str(exc)) from exc
        else:
            self.pub_key = ec_construct_public({"x": _x, "y": _y, "crv": self.crv})

    def _serialize(self, key):
        mlen = int(key.key_size / 8)
        if isinstance(key, ec.EllipticCurvePublicKey):
            pn = key.public_numbers()
            self.x = long_to_base64(pn.x, mlen)
            self.y = long_to_base64(pn.y, mlen)
            self.crv = SEC2NIST[pn.curve.name]
        elif isinstance(key, ec.EllipticCurvePrivateKey):
            pn = key.private_numbers()
            self.x = long_to_base64(pn.public_numbers.x, mlen)
            self.y = long_to_base64(pn.public_numbers.y, mlen)
            self.crv = SEC2NIST[pn.public_numbers.curve.name]
            self.d = long_to_base64(pn.private_value, mlen)

    def serialize(self, private=False):
        """
        Go from a
        cryptography.hazmat.primitives.asymmetric.ec.EllipticCurvePrivateKey
        or EllipticCurvePublicKey instance to a JWK representation.

        :param private: Whether we should include the private attributes or not.
        :return: A JWK as a dictionary
        """
        if self.priv_key:
            self._serialize(self.priv_key)
        else:
            self._serialize(self.pub_key)

        res = self.common()

        res.update({"crv": self.crv, "x": self.x, "y": self.y})

        if private and self.d:
            res["d"] = self.d

        return res

    def load_key(self, key):
        """
        Load an Elliptic curve key

        :param key: An elliptic curve key instance, private or public.
        :return: Reference to this instance
        """
        self._serialize(key)
        if isinstance(key, ec.EllipticCurvePrivateKey):
            self.priv_key = key
            self.pub_key = key.public_key()
        else:
            self.pub_key = key

        return self

    def load(self, filename):
        """
        Load an Elliptic curve key from a file.

        :param filename: File name
        """
        return self.load_key(import_private_ec_key_from_file(filename))

    def decryption_key(self):
        """
        Get a key appropriate for decrypting a message.

        :return: An ec.EllipticCurvePrivateKey instance
        """
        return self.priv_key

    def encryption_key(self):
        """
        Get a key appropriate for encrypting a message.

        :return: An ec.EllipticCurvePublicKey instance
        """
        return self.pub_key

    def __eq__(self, other):
        """
        Verify that the other key has the same properties as myself.

        :param other: The other key
        :return: True if the keys as the same otherwise False
        """

        if self.__class__ != other.__class__:
            return False

        if cmp_keys(self.pub_key, other.pub_key, ec.EllipticCurvePublicKey):
            if other.private_key():
                if cmp_keys(self.priv_key, other.priv_key, ec.EllipticCurvePrivateKey):
                    return True
            else:
                return not self.private_key()

        return False

    def key_len(self):
        if self.priv_key:
            return self.priv_key.key_size
        elif self.pub_key:
            return self.pub_key.key_size
        else:
            raise KeyNotFound


def cmp_keys(a, b, key_type):
    if isinstance(a, key_type):
        if isinstance(b, key_type):
            if a.curve.name != b.curve.name:
                return False
            if a.key_size != b.key_size:
                return False
            if isinstance(a, ec.EllipticCurvePrivateKey):
                if a.private_numbers() != b.private_numbers():
                    return False
            else:
                if a.public_numbers() != b.public_numbers():
                    return False
            return True

    return False


def new_ec_key(crv, kid="", **kwargs):
    _key = ec.generate_private_key(curve=NIST2SEC[crv]())

    _rk = ECKey(priv_key=_key, kid=kid, **kwargs)
    if not kid:
        _rk.add_kid()

    return _rk


def import_public_ec_key_from_file(filename):
    """
    Read a public Elliptic Curve key from a PEM file.

    :param filename: The name of the file
    :param passphrase: A pass phrase to use to unpack the PEM file.
    :return: A cryptography.hazmat.primitives.asymmetric.ec.EllipticCurvePublicKey instance
    """
    public_key = import_public_key_from_pem_file(filename)
    if isinstance(public_key, ec.EllipticCurvePublicKey):
        return public_key
    else:
        return ValueError("Not a Elliptic Curve key")


def import_private_ec_key_from_file(filename, passphrase=None):
    """
    Read a private Elliptic Curve key from a PEM file.

    :param filename: The name of the file
    :param passphrase: A pass phrase to use to unpack the PEM file.
    :return: A cryptography.hazmat.primitives.asymmetric.ec.EllipticCurvePrivateKey
        instance
    """
    private_key = import_private_key_from_pem_file(filename, passphrase)
    if isinstance(private_key, ec.EllipticCurvePrivateKey):
        return private_key
    else:
        return ValueError("Not a private Elliptic Curve key")


def import_ec_key(pem_data):
    """
    Extract an Elliptic Curve key from a PEM-encoded X.509 certificate

    :param pem_data: Elliptic Curve key encoded in standard form
    :return: ec.EllipticCurvePublicKey
    """
    public_key = import_public_key_from_pem_data(pem_data)
    if isinstance(public_key, ec.EllipticCurvePublicKey):
        return public_key
    else:
        return ValueError("Not a Elliptic Curve key")


def import_ec_key_from_cert_file(pem_file):
    with open(pem_file) as cert_file:
        return import_ec_key(cert_file.read())