How to use the oscrypto._ffi.buffer_from_bytes function in oscrypto

signature_length = libcrypto.i2d_DSA_SIG(dsa_sig, signature_pointer)
                handle_openssl_error(signature_length)

            elif private_key.algorithm == 'ec':
                digest = getattr(hashlib, hash_algorithm)(data).digest()

                ec_key = libcrypto.EVP_PKEY_get1_EC_KEY(private_key.evp_pkey)
                if is_null(ec_key):
                    handle_openssl_error(0)

                ecdsa_sig = libcrypto.ECDSA_do_sign(digest, len(digest), ec_key)
                if is_null(ecdsa_sig):
                    handle_openssl_error(0)

                buffer_size = libcrypto.i2d_ECDSA_SIG(ecdsa_sig, null())
                signature_buffer = buffer_from_bytes(buffer_size)
                signature_pointer = buffer_pointer(signature_buffer)
                signature_length = libcrypto.i2d_ECDSA_SIG(ecdsa_sig, signature_pointer)
                handle_openssl_error(signature_length)

        else:
            buffer_size = libcrypto.EVP_PKEY_size(private_key.evp_pkey)
            signature_buffer = buffer_from_bytes(buffer_size)
            signature_length = new(libcrypto, 'size_t *', buffer_size)

            evp_pkey_ctx_pointer_pointer = new(libcrypto, 'EVP_PKEY_CTX **')
            res = libcrypto.EVP_DigestSignInit(
                evp_md_ctx,
                evp_pkey_ctx_pointer_pointer,
                evp_md,
                null(),
                private_key.evp_pkey

)
                handle_openssl_error(res)

                signature_buffer = buffer_from_bytes(buffer_size)
                signature_length = libcrypto.RSA_private_encrypt(
                    buffer_size,
                    em_buffer,
                    signature_buffer,
                    rsa,
                    LibcryptoConst.RSA_NO_PADDING
                )
                handle_openssl_error(signature_length)

            elif private_key.algorithm == 'rsa':
                buffer_size = libcrypto.EVP_PKEY_size(private_key.evp_pkey)
                signature_buffer = buffer_from_bytes(buffer_size)
                signature_length = new(libcrypto, 'unsigned int *')

                res = libcrypto.EVP_DigestInit_ex(evp_md_ctx, evp_md, null())
                handle_openssl_error(res)

                res = libcrypto.EVP_DigestUpdate(evp_md_ctx, data, len(data))
                handle_openssl_error(res)

                res = libcrypto.EVP_SignFinal(
                    evp_md_ctx,
                    signature_buffer,
                    signature_length,
                    private_key.evp_pkey
                )
                handle_openssl_error(res)

key_type = 'public' if isinstance(key_info, PublicKeyInfo) else 'private'
    algo = key_info.algorithm

    if algo == 'rsa':
        provider = Advapi32Const.MS_ENH_RSA_AES_PROV
    else:
        provider = Advapi32Const.MS_ENH_DSS_DH_PROV

    context_handle = None
    key_handle = None

    try:
        context_handle = open_context_handle(provider, verify_only=key_type == 'public')

        blob = _advapi32_create_blob(key_info, key_type, algo)
        buffer_ = buffer_from_bytes(blob)

        key_handle_pointer = new(advapi32, 'HCRYPTKEY *')
        res = advapi32.CryptImportKey(
            context_handle,
            buffer_,
            len(blob),
            null(),
            0,
            key_handle_pointer
        )
        handle_error(res)

        key_handle = unwrap(key_handle_pointer)
        output = container(key_handle, key_object)
        output.context_handle = context_handle

key_handle,
            data,
            len(data),
            null(),
            null(),
            0,
            null(),
            0,
            out_len,
            flags
        )
        handle_error(res)

        buffer_len = deref(out_len)
        buffer = buffer_from_bytes(buffer_len)
        iv_buffer = buffer_from_bytes(iv) if iv else null()

        res = bcrypt.BCryptDecrypt(
            key_handle,
            data,
            len(data),
            null(),
            iv_buffer,
            iv_len,
            buffer,
            buffer_len,
            out_len,
            flags
        )
        handle_error(res)

        return bytes_from_buffer(buffer, deref(out_len))

res = bcrypt.BCryptEncrypt(
            key_handle,
            data,
            len(data),
            null(),
            null(),
            0,
            null(),
            0,
            out_len,
            flags
        )
        handle_error(res)

        buffer_len = deref(out_len)
        buffer = buffer_from_bytes(buffer_len)
        iv_buffer = buffer_from_bytes(iv) if iv else null()

        res = bcrypt.BCryptEncrypt(
            key_handle,
            data,
            len(data),
            null(),
            iv_buffer,
            iv_len,
            buffer,
            buffer_len,
            out_len,
            flags
        )
        handle_error(res)

evp_cipher_ctx,
                    LibcryptoConst.EVP_CTRL_SET_RC2_KEY_BITS,
                    len(key) * 8,
                    null()
                )
                handle_openssl_error(res)
            evp_cipher = null()

        res = libcrypto.EVP_DecryptInit_ex(evp_cipher_ctx, evp_cipher, null(), key, iv)
        handle_openssl_error(res)

        if padding is not None:
            res = libcrypto.EVP_CIPHER_CTX_set_padding(evp_cipher_ctx, int(padding))
            handle_openssl_error(res)

        buffer = buffer_from_bytes(buffer_size)
        output_length = new(libcrypto, 'int *')

        res = libcrypto.EVP_DecryptUpdate(evp_cipher_ctx, buffer, output_length, data, len(data))
        handle_openssl_error(res)

        output = bytes_from_buffer(buffer, deref(output_length))

        res = libcrypto.EVP_DecryptFinal_ex(evp_cipher_ctx, buffer, output_length)
        handle_openssl_error(res)

        output += bytes_from_buffer(buffer, deref(output_length))

        return output

    finally:
        if evp_cipher_ctx:

oscrypto.errors.TLSError - when a TLS-related error occurs
            oscrypto.errors.TLSDisconnectError - when the connection disconnects
            oscrypto.errors.TLSGracefulDisconnectError - when the remote end gracefully closed the connection
            ValueError - when any of the parameters contain an invalid value
            TypeError - when any of the parameters are of the wrong type
            OSError - when an error is returned by the OS crypto library
        """

        if self._session_context is None:
            self._raise_closed()

        processed_pointer = new(Security, 'size_t *')

        data_len = len(data)
        while data_len:
            write_buffer = buffer_from_bytes(data)
            result = Security.SSLWrite(
                self._session_context,
                write_buffer,
                data_len,
                processed_pointer
            )
            if self._exception is not None:
                exception = self._exception
                self._exception = None
                raise exception
            handle_sec_error(result, TLSError)

            bytes_written = deref(processed_pointer)
            data = data[bytes_written:]
            data_len = len(data)
            if data_len > 0:

repr(hash_algorithm)
            ))

        alg_constant = {
            'sha1': BcryptConst.BCRYPT_SHA1_ALGORITHM,
            'sha256': BcryptConst.BCRYPT_SHA256_ALGORITHM,
            'sha384': BcryptConst.BCRYPT_SHA384_ALGORITHM,
            'sha512': BcryptConst.BCRYPT_SHA512_ALGORITHM
        }[hash_algorithm]

        alg_handle = None

        try:
            alg_handle = open_alg_handle(alg_constant, BcryptConst.BCRYPT_ALG_HANDLE_HMAC_FLAG)

            output_buffer = buffer_from_bytes(key_length)
            res = bcrypt.BCryptDeriveKeyPBKDF2(
                alg_handle,
                password,
                len(password),
                salt,
                len(salt),
                iterations,
                output_buffer,
                key_length,
                0
            )
            handle_error(res)

            return bytes_from_buffer(output_buffer)
        finally:
            if alg_handle:

public_key = PublicKeyInfo({
                'algorithm': PublicKeyAlgorithm({
                    'algorithm': 'ec',
                    'parameters': ECDomainParameters(
                        name='named',
                        value=curve
                    )
                }),
                'public_key': public_key_point_bytes
            })
            public_key_bytes = public_key.dump()

            buffer_length = libcrypto.i2d_ECPrivateKey(ec_key, null())
            if buffer_length < 0:
                handle_openssl_error(buffer_length)
            buffer = buffer_from_bytes(buffer_length)
            result = libcrypto.i2d_ECPrivateKey(ec_key, buffer_pointer(buffer))
            if result < 0:
                handle_openssl_error(result)
            private_key_bytes = bytes_from_buffer(buffer, buffer_length)

        finally:
            if ec_key:
                libcrypto.EC_KEY_free(ec_key)

    return (load_public_key(public_key_bytes), load_private_key(private_key_bytes))