rsa.py

# This file is dual licensed under the terms of the Apache License, Version
# 2.0, and the BSD License. See the LICENSE file in the root of this repository
# for complete details.

from __future__ import absolute_import, division, print_function

from cryptography import utils
from cryptography.exceptions import (
    InvalidSignature,
    UnsupportedAlgorithm,
    _Reasons,
)
from cryptography.hazmat.backends.openssl.utils import (
    _calculate_digest_and_algorithm,
    _check_not_prehashed,
    _warn_sign_verify_deprecated,
)
from cryptography.hazmat.primitives import hashes
from cryptography.hazmat.primitives.asymmetric import (
    AsymmetricSignatureContext,
    AsymmetricVerificationContext,
    rsa,
)
from cryptography.hazmat.primitives.asymmetric.padding import (
    AsymmetricPadding,
    MGF1,
    OAEP,
    PKCS1v15,
    PSS,
    calculate_max_pss_salt_length,
)
from cryptography.hazmat.primitives.asymmetric.rsa import (
    RSAPrivateKeyWithSerialization,
    RSAPublicKeyWithSerialization,
)


def _get_rsa_pss_salt_length(pss, key, hash_algorithm):
    salt = pss._salt_length

    if salt is MGF1.MAX_LENGTH or salt is PSS.MAX_LENGTH:
        return calculate_max_pss_salt_length(key, hash_algorithm)
    else:
        return salt


def _enc_dec_rsa(backend, key, data, padding):
    if not isinstance(padding, AsymmetricPadding):
        raise TypeError("Padding must be an instance of AsymmetricPadding.")

    if isinstance(padding, PKCS1v15):
        padding_enum = backend._lib.RSA_PKCS1_PADDING
    elif isinstance(padding, OAEP):
        padding_enum = backend._lib.RSA_PKCS1_OAEP_PADDING

        if not isinstance(padding._mgf, MGF1):
            raise UnsupportedAlgorithm(
                "Only MGF1 is supported by this backend.",
                _Reasons.UNSUPPORTED_MGF,
            )

        if not backend.rsa_padding_supported(padding):
            raise UnsupportedAlgorithm(
                "This combination of padding and hash algorithm is not "
                "supported by this backend.",
                _Reasons.UNSUPPORTED_PADDING,
            )

    else:
        raise UnsupportedAlgorithm(
            "{} is not supported by this backend.".format(padding.name),
            _Reasons.UNSUPPORTED_PADDING,
        )

    return _enc_dec_rsa_pkey_ctx(backend, key, data, padding_enum, padding)


def _enc_dec_rsa_pkey_ctx(backend, key, data, padding_enum, padding):
    if isinstance(key, _RSAPublicKey):
        init = backend._lib.EVP_PKEY_encrypt_init
        crypt = backend._lib.EVP_PKEY_encrypt
    else:
        init = backend._lib.EVP_PKEY_decrypt_init
        crypt = backend._lib.EVP_PKEY_decrypt

    pkey_ctx = backend._lib.EVP_PKEY_CTX_new(key._evp_pkey, backend._ffi.NULL)
    backend.openssl_assert(pkey_ctx != backend._ffi.NULL)
    pkey_ctx = backend._ffi.gc(pkey_ctx, backend._lib.EVP_PKEY_CTX_free)
    res = init(pkey_ctx)
    backend.openssl_assert(res == 1)
    res = backend._lib.EVP_PKEY_CTX_set_rsa_padding(pkey_ctx, padding_enum)
    backend.openssl_assert(res > 0)
    buf_size = backend._lib.EVP_PKEY_size(key._evp_pkey)
    backend.openssl_assert(buf_size > 0)
    if isinstance(padding, OAEP) and backend._lib.Cryptography_HAS_RSA_OAEP_MD:
        mgf1_md = backend._evp_md_non_null_from_algorithm(
            padding._mgf._algorithm
        )
        res = backend._lib.EVP_PKEY_CTX_set_rsa_mgf1_md(pkey_ctx, mgf1_md)
        backend.openssl_assert(res > 0)
        oaep_md = backend._evp_md_non_null_from_algorithm(padding._algorithm)
        res = backend._lib.EVP_PKEY_CTX_set_rsa_oaep_md(pkey_ctx, oaep_md)
        backend.openssl_assert(res > 0)

    if (
        isinstance(padding, OAEP)
        and padding._label is not None
        and len(padding._label) > 0
    ):
        # set0_rsa_oaep_label takes ownership of the char * so we need to
        # copy it into some new memory
        labelptr = backend._lib.OPENSSL_malloc(len(padding._label))
        backend.openssl_assert(labelptr != backend._ffi.NULL)
        backend._ffi.memmove(labelptr, padding._label, len(padding._label))
        res = backend._lib.EVP_PKEY_CTX_set0_rsa_oaep_label(
            pkey_ctx, labelptr, len(padding._label)
        )
        backend.openssl_assert(res == 1)

    outlen = backend._ffi.new("size_t *", buf_size)
    buf = backend._ffi.new("unsigned char[]", buf_size)
    # Everything from this line onwards is written with the goal of being as
    # constant-time as is practical given the constraints of Python and our
    # API. See Bleichenbacher's '98 attack on RSA, and its many many variants.
    # As such, you should not attempt to change this (particularly to "clean it
    # up") without understanding why it was written this way (see
    # Chesterton's Fence), and without measuring to verify you have not
    # introduced observable time differences.
    res = crypt(pkey_ctx, buf, outlen, data, len(data))
    resbuf = backend._ffi.buffer(buf)[: outlen[0]]
    backend._lib.ERR_clear_error()
    if res <= 0:
        raise ValueError("Encryption/decryption failed.")
    return resbuf

def _rsa_sig_determine_padding(backend, key, padding, algorithm):
    if not isinstance(padding, AsymmetricPadding):
        raise TypeError("Expected provider of AsymmetricPadding.")

    pkey_size = backend._lib.EVP_PKEY_size(key._evp_pkey)
    backend.openssl_assert(pkey_size > 0)

    if isinstance(padding, PKCS1v15):
        padding_enum = backend._lib.RSA_PKCS1_PADDING
    elif isinstance(padding, PSS):
        if not isinstance(padding._mgf, MGF1):
            raise UnsupportedAlgorithm(
                "Only MGF1 is supported by this backend.",
                _Reasons.UNSUPPORTED_MGF,
            )

        # Size of key in bytes - 2 is the maximum
        # PSS signature length (salt length is checked later)
        if pkey_size - algorithm.digest_size - 2 < 0:
            raise ValueError(
                "Digest too large for key size. Use a larger "
                "key or different digest."
            )

        padding_enum = backend._lib.RSA_PKCS1_PSS_PADDING
    else:
        raise UnsupportedAlgorithm(
            "{} is not supported by this backend.".format(padding.name),
            _Reasons.UNSUPPORTED_PADDING,
        )

    return padding_enum


def _rsa_sig_setup(backend, padding, algorithm, key, data, init_func):
    padding_enum = _rsa_sig_determine_padding(backend, key, padding, algorithm)
    evp_md = backend._evp_md_non_null_from_algorithm(algorithm)
    pkey_ctx = backend._lib.EVP_PKEY_CTX_new(key._evp_pkey, backend._ffi.NULL)
    backend.openssl_assert(pkey_ctx != backend._ffi.NULL)
    pkey_ctx = backend._ffi.gc(pkey_ctx, backend._lib.EVP_PKEY_CTX_free)
    res = init_func(pkey_ctx)
    backend.openssl_assert(res == 1)
    res = backend._lib.EVP_PKEY_CTX_set_signature_md(pkey_ctx, evp_md)
    if res == 0:
        backend._consume_errors()
        raise UnsupportedAlgorithm(
            "{} is not supported by this backend for RSA signing.".format(
                algorithm.name
            ),
            _Reasons.UNSUPPORTED_HASH,
        )
    res = backend._lib.EVP_PKEY_CTX_set_rsa_padding(pkey_ctx, padding_enum)
    backend.openssl_assert(res > 0)
    if isinstance(padding, PSS):
        res = backend._lib.EVP_PKEY_CTX_set_rsa_pss_saltlen(
            pkey_ctx, _get_rsa_pss_salt_length(padding, key, algorithm)
        )
        backend.openssl_assert(res > 0)

        mgf1_md = backend._evp_md_non_null_from_algorithm(
            padding._mgf._algorithm
        )
        res = backend._lib.EVP_PKEY_CTX_set_rsa_mgf1_md(pkey_ctx, mgf1_md)
        backend.openssl_assert(res > 0)

    return pkey_ctx


def _rsa_sig_sign(backend, padding, algorithm, private_key, data):
    pkey_ctx = _rsa_sig_setup(
        backend,
        padding,
        algorithm,
        private_key,
        data,
        backend._lib.EVP_PKEY_sign_init,
    )
    buflen = backend._ffi.new("size_t *")
    res = backend._lib.EVP_PKEY_sign(
        pkey_ctx, backend._ffi.NULL, buflen, data, len(data)
    )
    backend.openssl_assert(res == 1)
    buf = backend._ffi.new("unsigned char[]", buflen[0])
    res = backend._lib.EVP_PKEY_sign(pkey_ctx, buf, buflen, data, len(data))
    if res != 1:
        errors = backend._consume_errors_with_text()
        raise ValueError(
            "Digest or salt length too long for key size. Use a larger key "
            "or shorter salt length if you are specifying a PSS salt",
            errors,
        )

    return backend._ffi.buffer(buf)[:]


def _rsa_sig_verify(backend, padding, algorithm, public_key, signature, data):
    pkey_ctx = _rsa_sig_setup(
        backend,
        padding,
        algorithm,
        public_key,
        data,
        backend._lib.EVP_PKEY_verify_init,
    )
    res = backend._lib.EVP_PKEY_verify(
        pkey_ctx, signature, len(signature), data, len(data)
    )
    # The previous call can return negative numbers in the event of an
    # error. This is not a signature failure but we need to fail if it
    # occurs.
    backend.openssl_assert(res >= 0)
    if res == 0:
        backend._consume_errors()
        raise InvalidSignature


@utils.register_interface(AsymmetricSignatureContext)
class _RSASignatureContext(object):
    def __init__(self, backend, private_key, padding, algorithm):
        self._backend = backend
        self._private_key = private_key

        # We now call _rsa_sig_determine_padding in _rsa_sig_setup. However
        # we need to make a pointless call to it here so we maintain the
        # API of erroring on init with this context if the values are invalid.
        _rsa_sig_determine_padding(backend, private_key, padding, algorithm)
        self._padding = padding
        self._algorithm = algorithm
        self._hash_ctx = hashes.Hash(self._algorithm, self._backend)

    def update(self, data):
        self._hash_ctx.update(data)

    def finalize(self):
        return _rsa_sig_sign(
            self._backend,
            self._padding,
            self._algorithm,
            self._private_key,
            self._hash_ctx.finalize(),
        )


@utils.register_interface(AsymmetricVerificationContext)
class _RSAVerificationContext(object):
    def __init__(self, backend, public_key, signature, padding, algorithm):
        self._backend = backend
        self._public_key = public_key
        self._signature = signature
        self._padding = padding
        # We now call _rsa_sig_determine_padding in _rsa_sig_setup. However
        # we need to make a pointless call to it here so we maintain the
        # API of erroring on init with this context if the values are invalid.
        _rsa_sig_determine_padding(backend, public_key, padding, algorithm)

        padding = padding
        self._algorithm = algorithm
        self._hash_ctx = hashes.Hash(self._algorithm, self._backend)

    def update(self, data):
        self._hash_ctx.update(data)

    def verify(self):
        return _rsa_sig_verify(
            self._backend,
            self._padding,
            self._algorithm,
            self._public_key,
            self._signature,
            self._hash_ctx.finalize(),
        )


@utils.register_interface(RSAPrivateKeyWithSerialization)
class _RSAPrivateKey(object):
    def __init__(self, backend, rsa_cdata, evp_pkey):
        res = backend._lib.RSA_check_key(rsa_cdata)
        if res != 1:
            errors = backend._consume_errors_with_text()
            raise ValueError("Invalid private key", errors)

        self._backend = backend
        self._rsa_cdata = rsa_cdata
        self._evp_pkey = evp_pkey

        n = self._backend._ffi.new("BIGNUM **")
        self._backend._lib.RSA_get0_key(
            self._rsa_cdata,
            n,
            self._backend._ffi.NULL,
            self._backend._ffi.NULL,
        )
        self._backend.openssl_assert(n[0] != self._backend._ffi.NULL)
        self._key_size = self._backend._lib.BN_num_bits(n[0])

    key_size = utils.read_only_property("_key_size")

    def signer(self, padding, algorithm):
        _warn_sign_verify_deprecated()
        _check_not_prehashed(algorithm)
        return _RSASignatureContext(self._backend, self, padding, algorithm)

    def decrypt(self, ciphertext, padding):
        key_size_bytes = (self.key_size + 7) // 8
        if key_size_bytes != len(ciphertext):
            raise ValueError("Ciphertext length must be equal to key size.")

        return _enc_dec_rsa(self._backend, self, ciphertext, padding)

    def public_key(self):
        ctx = self._backend._lib.RSAPublicKey_dup(self._rsa_cdata)
        self._backend.openssl_assert(ctx != self._backend._ffi.NULL)
        ctx = self._backend._ffi.gc(ctx, self._backend._lib.RSA_free)
        res = self._backend._lib.RSA_blinding_on(ctx, self._backend._ffi.NULL)
        self._backend.openssl_assert(res == 1)
        evp_pkey = self._backend._rsa_cdata_to_evp_pkey(ctx)
        return _RSAPublicKey(self._backend, ctx, evp_pkey)

    def private_numbers(self):
        n = self._backend._ffi.new("BIGNUM **")
        e = self._backend._ffi.new("BIGNUM **")
        d = self._backend._ffi.new("BIGNUM **")
        p = self._backend._ffi.new("BIGNUM **")
        q = self._backend._ffi.new("BIGNUM **")
        dmp1 = self._backend._ffi.new("BIGNUM **")
        dmq1 = self._backend._ffi.new("BIGNUM **")
        iqmp = self._backend._ffi.new("BIGNUM **")
        self._backend._lib.RSA_get0_key(self._rsa_cdata, n, e, d)
        self._backend.openssl_assert(n[0] != self._backend._ffi.NULL)
        self._backend.openssl_assert(e[0] != self._backend._ffi.NULL)
        self._backend.openssl_assert(d[0] != self._backend._ffi.NULL)
        self._backend._lib.RSA_get0_factors(self._rsa_cdata, p, q)
        self._backend.openssl_assert(p[0] != self._backend._ffi.NULL)
        self._backend.openssl_assert(q[0] != self._backend._ffi.NULL)
        self._backend._lib.RSA_get0_crt_params(
            self._rsa_cdata, dmp1, dmq1, iqmp
        )
        self._backend.openssl_assert(dmp1[0] != self._backend._ffi.NULL)
        self._backend.openssl_assert(dmq1[0] != self._backend._ffi.NULL)
        self._backend.openssl_assert(iqmp[0] != self._backend._ffi.NULL)
        return rsa.RSAPrivateNumbers(
            p=self._backend._bn_to_int(p[0]),
            q=self._backend._bn_to_int(q[0]),
            d=self._backend._bn_to_int(d[0]),
            dmp1=self._backend._bn_to_int(dmp1[0]),
            dmq1=self._backend._bn_to_int(dmq1[0]),
            iqmp=self._backend._bn_to_int(iqmp[0]),
            public_numbers=rsa.RSAPublicNumbers(
                e=self._backend._bn_to_int(e[0]),
                n=self._backend._bn_to_int(n[0]),
            ),
        )

    def private_bytes(self, encoding, format, encryption_algorithm):
        return self._backend._private_key_bytes(
            encoding,
            format,
            encryption_algorithm,
            self,
            self._evp_pkey,
            self._rsa_cdata,
        )

    def sign(self, data, padding, algorithm):
        data, algorithm = _calculate_digest_and_algorithm(
            self._backend, data, algorithm
        )
        return _rsa_sig_sign(self._backend, padding, algorithm, self, data)


@utils.register_interface(RSAPublicKeyWithSerialization)
class _RSAPublicKey(object):
    def __init__(self, backend, rsa_cdata, evp_pkey):
        self._backend = backend
        self._rsa_cdata = rsa_cdata
        self._evp_pkey = evp_pkey

        n = self._backend._ffi.new("BIGNUM **")
        self._backend._lib.RSA_get0_key(
            self._rsa_cdata,
            n,
            self._backend._ffi.NULL,
            self._backend._ffi.NULL,
        )
        self._backend.openssl_assert(n[0] != self._backend._ffi.NULL)
        self._key_size = self._backend._lib.BN_num_bits(n[0])

    key_size = utils.read_only_property("_key_size")

    def verifier(self, signature, padding, algorithm):
        _warn_sign_verify_deprecated()
        utils._check_bytes("signature", signature)

        _check_not_prehashed(algorithm)
        return _RSAVerificationContext(
            self._backend, self, signature, padding, algorithm
        )

    def encrypt(self, plaintext, padding):
        return _enc_dec_rsa(self._backend, self, plaintext, padding)

    def public_numbers(self):
        n = self._backend._ffi.new("BIGNUM **")
        e = self._backend._ffi.new("BIGNUM **")
        self._backend._lib.RSA_get0_key(
            self._rsa_cdata, n, e, self._backend._ffi.NULL
        )
        self._backend.openssl_assert(n[0] != self._backend._ffi.NULL)
        self._backend.openssl_assert(e[0] != self._backend._ffi.NULL)
        return rsa.RSAPublicNumbers(
            e=self._backend._bn_to_int(e[0]),
            n=self._backend._bn_to_int(n[0]),
        )

    def public_bytes(self, encoding, format):
        return self._backend._public_key_bytes(
            encoding, format, self, self._evp_pkey, self._rsa_cdata
        )

    def verify(self, signature, data, padding, algorithm):
        data, algorithm = _calculate_digest_and_algorithm(
            self._backend, data, algorithm
        )
        return _rsa_sig_verify(
            self._backend, padding, algorithm, self, signature, data
        )