static int aead_tls_open(const EVP_AEAD_CTX *ctx, uint8_t *out,
size_t *out_len, size_t max_out_len,
const uint8_t *nonce, size_t nonce_len,
const uint8_t *in, size_t in_len,
const uint8_t *ad, size_t ad_len) {
AEAD_TLS_CTX *tls_ctx = (AEAD_TLS_CTX *)ctx->aead_state;
if (tls_ctx->cipher_ctx.encrypt) {
/* Unlike a normal AEAD, a TLS AEAD may only be used in one direction. */
OPENSSL_PUT_ERROR(CIPHER, aead_tls_open, CIPHER_R_INVALID_OPERATION);
return 0;
}
if (in_len < HMAC_size(&tls_ctx->hmac_ctx)) {
OPENSSL_PUT_ERROR(CIPHER, aead_tls_open, CIPHER_R_BAD_DECRYPT);
return 0;
}
if (max_out_len < in_len) {
/* This requires that the caller provide space for the MAC, even though it
* will always be removed on return. */
OPENSSL_PUT_ERROR(CIPHER, aead_tls_open, CIPHER_R_BUFFER_TOO_SMALL);
return 0;
}
if (nonce_len != EVP_AEAD_nonce_length(ctx->aead)) {
OPENSSL_PUT_ERROR(CIPHER, aead_tls_open, CIPHER_R_INVALID_NONCE_SIZE);
return 0;
}
if (ad_len != 13 - 2 /* length bytes */) {
OPENSSL_PUT_ERROR(CIPHER, aead_tls_open, CIPHER_R_INVALID_AD_SIZE);
return 0;
}
if (in_len > INT_MAX) {
/* EVP_CIPHER takes int as input. */
OPENSSL_PUT_ERROR(CIPHER, aead_tls_open, CIPHER_R_TOO_LARGE);
return 0;
}
/* Configure the explicit IV. */
if (EVP_CIPHER_CTX_mode(&tls_ctx->cipher_ctx) == EVP_CIPH_CBC_MODE &&
!tls_ctx->implicit_iv &&
!EVP_DecryptInit_ex(&tls_ctx->cipher_ctx, NULL, NULL, NULL, nonce)) {
return 0;
}
/* Decrypt to get the plaintext + MAC + padding. */
size_t total = 0;
int len;
if (!EVP_DecryptUpdate(&tls_ctx->cipher_ctx, out, &len, in, (int)in_len)) {
return 0;
}
total += len;
if (!EVP_DecryptFinal_ex(&tls_ctx->cipher_ctx, out + total, &len)) {
return 0;
}
total += len;
assert(total == in_len);
/* Remove CBC padding. Code from here on is timing-sensitive with respect to
* |padding_ok| and |data_plus_mac_len| for CBC ciphers. */
int padding_ok;
unsigned data_plus_mac_len, data_len;
if (EVP_CIPHER_CTX_mode(&tls_ctx->cipher_ctx) == EVP_CIPH_CBC_MODE) {
padding_ok = EVP_tls_cbc_remove_padding(
&data_plus_mac_len, out, total,
EVP_CIPHER_CTX_block_size(&tls_ctx->cipher_ctx),
(unsigned)HMAC_size(&tls_ctx->hmac_ctx));
/* Publicly invalid. This can be rejected in non-constant time. */
if (padding_ok == 0) {
OPENSSL_PUT_ERROR(CIPHER, aead_tls_open, CIPHER_R_BAD_DECRYPT);
return 0;
}
} else {
padding_ok = 1;
data_plus_mac_len = total;
/* |data_plus_mac_len| = |total| = |in_len| at this point. |in_len| has
* already been checked against the MAC size at the top of the function. */
assert(data_plus_mac_len >= HMAC_size(&tls_ctx->hmac_ctx));
}
data_len = data_plus_mac_len - HMAC_size(&tls_ctx->hmac_ctx);
/* At this point, |padding_ok| is 1 or -1. If 1, the padding is valid and the
* first |data_plus_mac_size| bytes after |out| are the plaintext and
* MAC. Either way, |data_plus_mac_size| is large enough to extract a MAC. */
/* To allow for CBC mode which changes cipher length, |ad| doesn't include the
* length for legacy ciphers. */
uint8_t ad_fixed[13];
memcpy(ad_fixed, ad, 11);
ad_fixed[11] = (uint8_t)(data_len >> 8);
ad_fixed[12] = (uint8_t)(data_len & 0xff);
ad_len += 2;
/* Compute the MAC and extract the one in the record. */
uint8_t mac[EVP_MAX_MD_SIZE];
size_t mac_len;
uint8_t record_mac_tmp[EVP_MAX_MD_SIZE];
uint8_t *record_mac;
if (EVP_CIPHER_CTX_mode(&tls_ctx->cipher_ctx) == EVP_CIPH_CBC_MODE &&
EVP_tls_cbc_record_digest_supported(tls_ctx->hmac_ctx.md)) {
if (!EVP_tls_cbc_digest_record(tls_ctx->hmac_ctx.md, mac, &mac_len,
ad_fixed, out, data_plus_mac_len, total,
tls_ctx->mac_key, tls_ctx->mac_key_len)) {
OPENSSL_PUT_ERROR(CIPHER, aead_tls_open, CIPHER_R_BAD_DECRYPT);
return 0;
}
assert(mac_len == HMAC_size(&tls_ctx->hmac_ctx));
record_mac = record_mac_tmp;
EVP_tls_cbc_copy_mac(record_mac, mac_len, out, data_plus_mac_len, total);
} else {
/* We should support the constant-time path for all CBC-mode ciphers
* implemented. */
assert(EVP_CIPHER_CTX_mode(&tls_ctx->cipher_ctx) != EVP_CIPH_CBC_MODE);
HMAC_CTX hmac_ctx;
HMAC_CTX_init(&hmac_ctx);
unsigned mac_len_u;
if (!HMAC_CTX_copy_ex(&hmac_ctx, &tls_ctx->hmac_ctx) ||
!HMAC_Update(&hmac_ctx, ad_fixed, ad_len) ||
!HMAC_Update(&hmac_ctx, out, data_len) ||
!HMAC_Final(&hmac_ctx, mac, &mac_len_u)) {
HMAC_CTX_cleanup(&hmac_ctx);
return 0;
}
mac_len = mac_len_u;
HMAC_CTX_cleanup(&hmac_ctx);
assert(mac_len == HMAC_size(&tls_ctx->hmac_ctx));
record_mac = &out[data_len];
}
/* Perform the MAC check and the padding check in constant-time. It should be
* safe to simply perform the padding check first, but it would not be under a
* different choice of MAC location on padding failure. See
* EVP_tls_cbc_remove_padding. */
unsigned good = constant_time_eq_int(CRYPTO_memcmp(record_mac, mac, mac_len),
0);
good &= constant_time_eq_int(padding_ok, 1);
if (!good) {
OPENSSL_PUT_ERROR(CIPHER, aead_tls_open, CIPHER_R_BAD_DECRYPT);
return 0;
}
/* End of timing-sensitive code. */
*out_len = data_len;
return 1;
}
static int aead_tls_open(const EVP_AEAD_CTX *ctx, uint8_t *out, size_t *out_len,
size_t max_out_len, const uint8_t *nonce,
size_t nonce_len, const uint8_t *in, size_t in_len,
const uint8_t *ad, size_t ad_len) {
AEAD_TLS_CTX *tls_ctx = (AEAD_TLS_CTX *)ctx->aead_state;
if (tls_ctx->cipher_ctx.encrypt) {
// Unlike a normal AEAD, a TLS AEAD may only be used in one direction.
OPENSSL_PUT_ERROR(CIPHER, CIPHER_R_INVALID_OPERATION);
return 0;
}
if (in_len < HMAC_size(&tls_ctx->hmac_ctx)) {
OPENSSL_PUT_ERROR(CIPHER, CIPHER_R_BAD_DECRYPT);
return 0;
}
if (max_out_len < in_len) {
// This requires that the caller provide space for the MAC, even though it
// will always be removed on return.
OPENSSL_PUT_ERROR(CIPHER, CIPHER_R_BUFFER_TOO_SMALL);
return 0;
}
if (nonce_len != EVP_AEAD_nonce_length(ctx->aead)) {
OPENSSL_PUT_ERROR(CIPHER, CIPHER_R_INVALID_NONCE_SIZE);
return 0;
}
if (ad_len != 13 - 2 /* length bytes */) {
OPENSSL_PUT_ERROR(CIPHER, CIPHER_R_INVALID_AD_SIZE);
return 0;
}
if (in_len > INT_MAX) {
// EVP_CIPHER takes int as input.
OPENSSL_PUT_ERROR(CIPHER, CIPHER_R_TOO_LARGE);
return 0;
}
// Configure the explicit IV.
if (EVP_CIPHER_CTX_mode(&tls_ctx->cipher_ctx) == EVP_CIPH_CBC_MODE &&
!tls_ctx->implicit_iv &&
!EVP_DecryptInit_ex(&tls_ctx->cipher_ctx, NULL, NULL, NULL, nonce)) {
return 0;
}
// Decrypt to get the plaintext + MAC + padding.
size_t total = 0;
int len;
if (!EVP_DecryptUpdate(&tls_ctx->cipher_ctx, out, &len, in, (int)in_len)) {
return 0;
}
total += len;
if (!EVP_DecryptFinal_ex(&tls_ctx->cipher_ctx, out + total, &len)) {
return 0;
}
total += len;
assert(total == in_len);
// Remove CBC padding. Code from here on is timing-sensitive with respect to
// |padding_ok| and |data_plus_mac_len| for CBC ciphers.
size_t data_plus_mac_len;
crypto_word_t padding_ok;
if (EVP_CIPHER_CTX_mode(&tls_ctx->cipher_ctx) == EVP_CIPH_CBC_MODE) {
if (!EVP_tls_cbc_remove_padding(
&padding_ok, &data_plus_mac_len, out, total,
EVP_CIPHER_CTX_block_size(&tls_ctx->cipher_ctx),
HMAC_size(&tls_ctx->hmac_ctx))) {
// Publicly invalid. This can be rejected in non-constant time.
OPENSSL_PUT_ERROR(CIPHER, CIPHER_R_BAD_DECRYPT);
return 0;
}
} else {
padding_ok = CONSTTIME_TRUE_W;
data_plus_mac_len = total;
// |data_plus_mac_len| = |total| = |in_len| at this point. |in_len| has
// already been checked against the MAC size at the top of the function.
assert(data_plus_mac_len >= HMAC_size(&tls_ctx->hmac_ctx));
}
size_t data_len = data_plus_mac_len - HMAC_size(&tls_ctx->hmac_ctx);
// At this point, if the padding is valid, the first |data_plus_mac_len| bytes
// after |out| are the plaintext and MAC. Otherwise, |data_plus_mac_len| is
// still large enough to extract a MAC, but it will be irrelevant.
// To allow for CBC mode which changes cipher length, |ad| doesn't include the
// length for legacy ciphers.
uint8_t ad_fixed[13];
OPENSSL_memcpy(ad_fixed, ad, 11);
ad_fixed[11] = (uint8_t)(data_len >> 8);
ad_fixed[12] = (uint8_t)(data_len & 0xff);
ad_len += 2;
// Compute the MAC and extract the one in the record.
uint8_t mac[EVP_MAX_MD_SIZE];
size_t mac_len;
uint8_t record_mac_tmp[EVP_MAX_MD_SIZE];
uint8_t *record_mac;
if (EVP_CIPHER_CTX_mode(&tls_ctx->cipher_ctx) == EVP_CIPH_CBC_MODE &&
EVP_tls_cbc_record_digest_supported(tls_ctx->hmac_ctx.md)) {
if (!EVP_tls_cbc_digest_record(tls_ctx->hmac_ctx.md, mac, &mac_len,
ad_fixed, out, data_plus_mac_len, total,
tls_ctx->mac_key, tls_ctx->mac_key_len)) {
OPENSSL_PUT_ERROR(CIPHER, CIPHER_R_BAD_DECRYPT);
return 0;
}
assert(mac_len == HMAC_size(&tls_ctx->hmac_ctx));
record_mac = record_mac_tmp;
EVP_tls_cbc_copy_mac(record_mac, mac_len, out, data_plus_mac_len, total);
} else {
// We should support the constant-time path for all CBC-mode ciphers
// implemented.
assert(EVP_CIPHER_CTX_mode(&tls_ctx->cipher_ctx) != EVP_CIPH_CBC_MODE);
unsigned mac_len_u;
if (!HMAC_Init_ex(&tls_ctx->hmac_ctx, NULL, 0, NULL, NULL) ||
!HMAC_Update(&tls_ctx->hmac_ctx, ad_fixed, ad_len) ||
!HMAC_Update(&tls_ctx->hmac_ctx, out, data_len) ||
!HMAC_Final(&tls_ctx->hmac_ctx, mac, &mac_len_u)) {
return 0;
}
mac_len = mac_len_u;
assert(mac_len == HMAC_size(&tls_ctx->hmac_ctx));
record_mac = &out[data_len];
}
// Perform the MAC check and the padding check in constant-time. It should be
// safe to simply perform the padding check first, but it would not be under a
// different choice of MAC location on padding failure. See
// EVP_tls_cbc_remove_padding.
crypto_word_t good =
constant_time_eq_int(CRYPTO_memcmp(record_mac, mac, mac_len), 0);
good &= padding_ok;
if (!good) {
OPENSSL_PUT_ERROR(CIPHER, CIPHER_R_BAD_DECRYPT);
return 0;
}
// End of timing-sensitive code.
*out_len = data_len;
return 1;
}
