lib/jose/jwe/enc/aeskw.c

/*
 * libwebsockets - small server side websockets and web server implementation
 *
 * Copyright (C) 2010 - 2020 Andy Green <andy@warmcat.com>
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to
 * deal in the Software without restriction, including without limitation the
 * rights to use, copy, modify, merge, publish, distribute, sublicense, and/or
 * sell copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
 * IN THE SOFTWARE.
 */

#include "private-lib-core.h"
#include "private-lib-jose-jwe.h"

/*
 * RFC3394 Key Wrap uses a 128-bit key, and bloats what it is wrapping by
 * one 8-byte block.  So, if you had a 32 byte plaintext CEK to wrap, after
 * wrapping it becomes a 40 byte wrapped, enciphered, key.
 *
 * The CEK comes in from and goes out in LJWE_EKEY.  So LJWE_EKEY length
 * increases by 8 from calling this.
 */

int
lws_jwe_encrypt_aeskw_cbc_hs(struct lws_jwe *jwe, char *temp, int *temp_len)
{
	struct lws_genaes_ctx aesctx;
	/* we are wrapping a key, so size for the worst case after wrap */
	uint8_t enc_cek[LWS_JWE_LIMIT_KEY_ELEMENT_BYTES +
	                LWS_JWE_RFC3394_OVERHEAD_BYTES];
	int n, m, hlen = (int)lws_genhmac_size(jwe->jose.enc_alg->hmac_type),
			 ot = *temp_len;

	if (jwe->jws.jwk->kty != LWS_GENCRYPTO_KTY_OCT) {
		lwsl_err("%s: unexpected kty %d\n", __func__, jwe->jws.jwk->kty);

		return -1;
	}

	/* create a b64 version of the JOSE header, needed for hashing */

	if (lws_jws_encode_b64_element(&jwe->jws.map_b64, LJWE_JOSE,
				       temp, temp_len,
				       jwe->jws.map.buf[LJWE_JOSE],
				       jwe->jws.map.len[LJWE_JOSE]))
		return -1;

	/* Allocate temp space for ATAG and IV */

	if (lws_jws_alloc_element(&jwe->jws.map, LJWE_ATAG, temp + (ot - *temp_len),
				  temp_len, (unsigned int)hlen / 2, 0))
		return -1;

	if (lws_jws_alloc_element(&jwe->jws.map, LJWE_IV, temp + (ot - *temp_len),
				  temp_len, LWS_JWE_AES_IV_BYTES, 0))
		return -1;

	/* 1) Encrypt the payload...  */

	/* the CEK is 256-bit in the example encrypted with a 128-bit key */

	n = lws_jwe_encrypt_cbc_hs(jwe, (uint8_t *)jwe->jws.map.buf[LJWE_EKEY],
				   (uint8_t *)jwe->jws.map_b64.buf[LJWE_JOSE],
				   (int)jwe->jws.map_b64.len[LJWE_JOSE]);
	if (n < 0) {
		lwsl_err("%s: lws_jwe_encrypt_cbc_hs failed\n", __func__);
		return -1;
	}

	/* 2) Encrypt the JWE Encrypted Key: RFC3394 Key Wrap uses 64 bit blocks
	 *    and 128-bit input key*/

	if (lws_genaes_create(&aesctx, LWS_GAESO_ENC, LWS_GAESM_KW,
			      jwe->jws.jwk->e, 1, NULL)) {

		lwsl_notice("%s: lws_genaes_create\n", __func__);
		return -1;
	}

	/* tag size is determined by enc cipher key length */

	n = lws_genaes_crypt(&aesctx, (uint8_t *)jwe->jws.map.buf[LJWE_EKEY],
			     jwe->jws.map.len[LJWE_EKEY], enc_cek, NULL, NULL, NULL,
			     lws_gencrypto_bits_to_bytes(
					     jwe->jose.enc_alg->keybits_fixed));
	m = lws_genaes_destroy(&aesctx, NULL, 0);
	if (n < 0) {
		lwsl_err("%s: encrypt cek fail\n", __func__);
		return -1;
	}
	if (m < 0) {
		lwsl_err("%s: lws_genaes_destroy fail\n", __func__);
		return -1;
	}

	jwe->jws.map.len[LJWE_EKEY] += LWS_JWE_RFC3394_OVERHEAD_BYTES;
	memcpy((uint8_t *)jwe->jws.map.buf[LJWE_EKEY], enc_cek,
	       jwe->jws.map.len[LJWE_EKEY]);

	return (int)jwe->jws.map.len[LJWE_CTXT];
}


int
lws_jwe_auth_and_decrypt_aeskw_cbc_hs(struct lws_jwe *jwe)
{
	struct lws_genaes_ctx aesctx;
	uint8_t enc_cek[LWS_JWE_LIMIT_KEY_ELEMENT_BYTES +
	                LWS_JWE_RFC3394_OVERHEAD_BYTES];
	int n, m;

	if (jwe->jws.jwk->kty != LWS_GENCRYPTO_KTY_OCT) {
		lwsl_err("%s: unexpected kty %d\n", __func__, jwe->jws.jwk->kty);

		return -1;
	}

	/* the CEK is 256-bit in the example encrypted with a 128-bit key */

	if (jwe->jws.map.len[LJWE_EKEY] > sizeof(enc_cek))
		return -1;

	/* 1) Decrypt the JWE Encrypted Key to get the raw MAC / CEK */

	if (lws_genaes_create(&aesctx, LWS_GAESO_DEC, LWS_GAESM_KW,
			      jwe->jws.jwk->e, 1, NULL)) {

		lwsl_notice("%s: lws_genaes_create\n", __func__);
		return -1;
	}

	/*
	 * Decrypt the CEK into enc_cek
	 * tag size is determined by enc cipher key length */

	n = lws_genaes_crypt(&aesctx, (uint8_t *)jwe->jws.map.buf[LJWE_EKEY],
			     jwe->jws.map.len[LJWE_EKEY], enc_cek, NULL, NULL, NULL,
			     lws_gencrypto_bits_to_bytes(
					     jwe->jose.enc_alg->keybits_fixed));
	m = lws_genaes_destroy(&aesctx, NULL, 0);
	if (n < 0) {
		lwsl_err("%s: decrypt CEK fail\n", __func__);
		return -1;
	}
	if (m < 0) {
		lwsl_err("%s: lws_genaes_destroy fail\n", __func__);
		return -1;
	}

	/* 2) Decrypt the payload */

	n = lws_jwe_auth_and_decrypt_cbc_hs(jwe, enc_cek,
			     (uint8_t *)jwe->jws.map_b64.buf[LJWE_JOSE],
			     (int)jwe->jws.map_b64.len[LJWE_JOSE]);
	if (n < 0) {
		lwsl_err("%s: lws_jwe_auth_and_decrypt_cbc_hs failed\n",
				__func__);
		return -1;
	}

	return (int)jwe->jws.map.len[LJWE_CTXT];
}