static krb5_error_code
calculate_reply_hash(krb5_context context,
krb5_keyblock *key,
Kx509Response *rep)
{
krb5_error_code ret;
HMAC_CTX ctx;
HMAC_CTX_init(&ctx);
HMAC_Init_ex(&ctx, key->keyvalue.data, key->keyvalue.length,
EVP_sha1(), NULL);
ret = krb5_data_alloc(rep->hash, HMAC_size(&ctx));
if (ret) {
HMAC_CTX_cleanup(&ctx);
krb5_set_error_message(context, ENOMEM, "malloc: out of memory");
return ENOMEM;
}
HMAC_Update(&ctx, version_2_0, sizeof(version_2_0));
if (rep->error_code) {
int32_t t = *rep->error_code;
do {
unsigned char p = (t & 0xff);
HMAC_Update(&ctx, &p, 1);
t >>= 8;
} while (t);
}
static krb5_error_code
verify_req_hash(krb5_context context,
const Kx509Request *req,
krb5_keyblock *key)
{
unsigned char digest[SHA_DIGEST_LENGTH];
HMAC_CTX ctx;
if (req->pk_hash.length != sizeof(digest)) {
krb5_set_error_message(context, KRB5KDC_ERR_PREAUTH_FAILED,
"pk-hash have wrong length: %lu",
(unsigned long)req->pk_hash.length);
return KRB5KDC_ERR_PREAUTH_FAILED;
}
HMAC_CTX_init(&ctx);
HMAC_Init_ex(&ctx,
key->keyvalue.data, key->keyvalue.length,
EVP_sha1(), NULL);
if (sizeof(digest) != HMAC_size(&ctx))
krb5_abortx(context, "runtime error, hmac buffer wrong size in kx509");
HMAC_Update(&ctx, version_2_0, sizeof(version_2_0));
HMAC_Update(&ctx, req->pk_key.data, req->pk_key.length);
HMAC_Final(&ctx, digest, 0);
HMAC_CTX_cleanup(&ctx);
if (memcmp(req->pk_hash.data, digest, sizeof(digest)) != 0) {
krb5_set_error_message(context, KRB5KDC_ERR_PREAUTH_FAILED,
"pk-hash is not correct");
return KRB5KDC_ERR_PREAUTH_FAILED;
}
return 0;
}
USES_APPLE_DEPRECATED_API /* OpenSSL API has been deprecated by Apple */
#include "eap_tls.h"
#include <openssl/hmac.h>
/*
* TLS PRF from RFC 2246
*/
static void P_hash(EVP_MD const *evp_md,
unsigned char const *secret, unsigned int secret_len,
unsigned char const *seed, unsigned int seed_len,
unsigned char *out, unsigned int out_len)
{
HMAC_CTX ctx_a, ctx_out;
unsigned char a[HMAC_MAX_MD_CBLOCK];
unsigned int size;
HMAC_CTX_init(&ctx_a);
HMAC_CTX_init(&ctx_out);
HMAC_Init_ex(&ctx_a, secret, secret_len, evp_md, NULL);
HMAC_Init_ex(&ctx_out, secret, secret_len, evp_md, NULL);
size = HMAC_size(&ctx_out);
/* Calculate A(1) */
HMAC_Update(&ctx_a, seed, seed_len);
HMAC_Final(&ctx_a, a, NULL);
while (1) {
/* Calculate next part of output */
HMAC_Update(&ctx_out, a, size);
HMAC_Update(&ctx_out, seed, seed_len);
/* Check if last part */
if (out_len < size) {
HMAC_Final(&ctx_out, a, NULL);
memcpy(out, a, out_len);
break;
}
/* Place digest in output buffer */
HMAC_Final(&ctx_out, out, NULL);
HMAC_Init_ex(&ctx_out, NULL, 0, NULL, NULL);
out += size;
out_len -= size;
/* Calculate next A(i) */
HMAC_Init_ex(&ctx_a, NULL, 0, NULL, NULL);
HMAC_Update(&ctx_a, a, size);
HMAC_Final(&ctx_a, a, NULL);
}
HMAC_CTX_cleanup(&ctx_a);
HMAC_CTX_cleanup(&ctx_out);
memset(a, 0, sizeof(a));
}
void
hmac_ctx_init(HMAC_CTX *ctx, const uint8_t *key, int key_len,
const EVP_MD *kt)
{
ASSERT(NULL != kt && NULL != ctx);
HMAC_CTX_reset(ctx);
HMAC_Init_ex(ctx, key, key_len, kt, NULL);
/* make sure we used a big enough key */
ASSERT(HMAC_size(ctx) <= key_len);
}
/*
* TLS PRF from RFC 2246
*/
static void P_hash(const EVP_MD *evp_md,
const unsigned char *secret, unsigned int secret_len,
const unsigned char *seed, unsigned int seed_len,
unsigned char *out, unsigned int out_len)
{
HMAC_CTX ctx_a, ctx_out;
unsigned char a[HMAC_MAX_MD_CBLOCK];
unsigned int size;
HMAC_CTX_init(&ctx_a);
HMAC_CTX_init(&ctx_out);
HMAC_Init_ex(&ctx_a, secret, secret_len, evp_md, NULL);
HMAC_Init_ex(&ctx_out, secret, secret_len, evp_md, NULL);
size = HMAC_size(&ctx_out);
/* Calculate A(1) */
HMAC_Update(&ctx_a, seed, seed_len);
HMAC_Final(&ctx_a, a, NULL);
while (1) {
/* Calculate next part of output */
HMAC_Update(&ctx_out, a, size);
HMAC_Update(&ctx_out, seed, seed_len);
/* Check if last part */
if (out_len < size) {
HMAC_Final(&ctx_out, a, NULL);
memcpy(out, a, out_len);
break;
}
/* Place digest in output buffer */
HMAC_Final(&ctx_out, out, NULL);
HMAC_Init_ex(&ctx_out, NULL, 0, NULL, NULL);
out += size;
out_len -= size;
/* Calculate next A(i) */
HMAC_Init_ex(&ctx_a, NULL, 0, NULL, NULL);
HMAC_Update(&ctx_a, a, size);
HMAC_Final(&ctx_a, a, NULL);
}
HMAC_CTX_cleanup(&ctx_a);
HMAC_CTX_cleanup(&ctx_out);
memset(a, 0, sizeof(a));
}
static size_t aead_tls_tag_len(const EVP_AEAD_CTX *ctx, const size_t in_len,
const size_t extra_in_len) {
assert(extra_in_len == 0);
AEAD_TLS_CTX *tls_ctx = (AEAD_TLS_CTX *)ctx->aead_state;
const size_t hmac_len = HMAC_size(&tls_ctx->hmac_ctx);
if (EVP_CIPHER_CTX_mode(&tls_ctx->cipher_ctx) != EVP_CIPH_CBC_MODE) {
// The NULL cipher.
return hmac_len;
}
const size_t block_size = EVP_CIPHER_CTX_block_size(&tls_ctx->cipher_ctx);
// An overflow of |in_len + hmac_len| doesn't affect the result mod
// |block_size|, provided that |block_size| is a smaller power of two.
assert(block_size != 0 && (block_size & (block_size - 1)) == 0);
const size_t pad_len = block_size - (in_len + hmac_len) % block_size;
return hmac_len + pad_len;
}
/* tls_decrypt_ticket attempts to decrypt a session ticket.
*
* etick: points to the body of the session ticket extension.
* eticklen: the length of the session tickets extenion.
* sess_id: points at the session ID.
* sesslen: the length of the session ID.
* psess: (output) on return, if a ticket was decrypted, then this is set to
* point to the resulting session.
*
* Returns:
* -1: fatal error, either from parsing or decrypting the ticket.
* 2: the ticket couldn't be decrypted.
* 3: a ticket was successfully decrypted and *psess was set.
* 4: same as 3, but the ticket needs to be renewed.
*/
static int
tls_decrypt_ticket(SSL *s, const unsigned char *etick, int eticklen,
const unsigned char *sess_id, int sesslen, SSL_SESSION **psess)
{
SSL_SESSION *sess;
unsigned char *sdec;
const unsigned char *p;
int slen, mlen, renew_ticket = 0;
unsigned char tick_hmac[EVP_MAX_MD_SIZE];
HMAC_CTX hctx;
EVP_CIPHER_CTX ctx;
SSL_CTX *tctx = s->initial_ctx;
/*
* The API guarantees EVP_MAX_IV_LENGTH bytes of space for
* the iv to tlsext_ticket_key_cb(). Since the total space
* required for a session cookie is never less than this,
* this check isn't too strict. The exact check comes later.
*/
if (eticklen < 16 + EVP_MAX_IV_LENGTH)
return 2;
/* Initialize session ticket encryption and HMAC contexts */
HMAC_CTX_init(&hctx);
EVP_CIPHER_CTX_init(&ctx);
if (tctx->internal->tlsext_ticket_key_cb) {
unsigned char *nctick = (unsigned char *)etick;
int rv = tctx->internal->tlsext_ticket_key_cb(s,
nctick, nctick + 16, &ctx, &hctx, 0);
if (rv < 0) {
HMAC_CTX_cleanup(&hctx);
EVP_CIPHER_CTX_cleanup(&ctx);
return -1;
}
if (rv == 0) {
HMAC_CTX_cleanup(&hctx);
EVP_CIPHER_CTX_cleanup(&ctx);
return 2;
}
if (rv == 2)
renew_ticket = 1;
} else {
/* Check key name matches */
if (timingsafe_memcmp(etick,
tctx->internal->tlsext_tick_key_name, 16))
return 2;
HMAC_Init_ex(&hctx, tctx->internal->tlsext_tick_hmac_key,
16, tlsext_tick_md(), NULL);
EVP_DecryptInit_ex(&ctx, EVP_aes_128_cbc(), NULL,
tctx->internal->tlsext_tick_aes_key, etick + 16);
}
/*
* Attempt to process session ticket, first conduct sanity and
* integrity checks on ticket.
*/
mlen = HMAC_size(&hctx);
if (mlen < 0) {
HMAC_CTX_cleanup(&hctx);
EVP_CIPHER_CTX_cleanup(&ctx);
return -1;
}
/* Sanity check ticket length: must exceed keyname + IV + HMAC */
if (eticklen <= 16 + EVP_CIPHER_CTX_iv_length(&ctx) + mlen) {
HMAC_CTX_cleanup(&hctx);
EVP_CIPHER_CTX_cleanup(&ctx);
return 2;
}
eticklen -= mlen;
/* Check HMAC of encrypted ticket */
if (HMAC_Update(&hctx, etick, eticklen) <= 0 ||
HMAC_Final(&hctx, tick_hmac, NULL) <= 0) {
HMAC_CTX_cleanup(&hctx);
EVP_CIPHER_CTX_cleanup(&ctx);
return -1;
}
HMAC_CTX_cleanup(&hctx);
if (timingsafe_memcmp(tick_hmac, etick + eticklen, mlen)) {
EVP_CIPHER_CTX_cleanup(&ctx);
return 2;
}
/* Attempt to decrypt session data */
/* Move p after IV to start of encrypted ticket, update length */
p = etick + 16 + EVP_CIPHER_CTX_iv_length(&ctx);
eticklen -= 16 + EVP_CIPHER_CTX_iv_length(&ctx);
sdec = malloc(eticklen);
if (sdec == NULL ||
EVP_DecryptUpdate(&ctx, sdec, &slen, p, eticklen) <= 0) {
free(sdec);
EVP_CIPHER_CTX_cleanup(&ctx);
return -1;
}
if (EVP_DecryptFinal_ex(&ctx, sdec + slen, &mlen) <= 0) {
free(sdec);
EVP_CIPHER_CTX_cleanup(&ctx);
return 2;
}
slen += mlen;
EVP_CIPHER_CTX_cleanup(&ctx);
p = sdec;
sess = d2i_SSL_SESSION(NULL, &p, slen);
free(sdec);
if (sess) {
/* The session ID, if non-empty, is used by some clients to
* detect that the ticket has been accepted. So we copy it to
* the session structure. If it is empty set length to zero
* as required by standard.
*/
if (sesslen)
memcpy(sess->session_id, sess_id, sesslen);
sess->session_id_length = sesslen;
*psess = sess;
if (renew_ticket)
return 4;
else
return 3;
}
ERR_clear_error();
/* For session parse failure, indicate that we need to send a new
* ticket. */
return 2;
}
int
hmac_ctx_size (const HMAC_CTX *ctx)
{
return HMAC_size (ctx);
}
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 tls_decrypt_ticket(SSL *s, const unsigned char *etick, int eticklen,
const unsigned char *sess_id, int sesslen,
SSL_SESSION **psess)
{
SSL_SESSION *sess;
unsigned char *sdec;
const unsigned char *p;
int slen, mlen, renew_ticket = 0;
unsigned char tick_hmac[EVP_MAX_MD_SIZE];
HMAC_CTX hctx;
EVP_CIPHER_CTX ctx;
SSL_CTX *tctx = s->initial_ctx;
/* Need at least keyname + iv + some encrypted data */
if (eticklen < 48)
goto tickerr;
/* Initialize session ticket encryption and HMAC contexts */
HMAC_CTX_init(&hctx);
EVP_CIPHER_CTX_init(&ctx);
if (tctx->tlsext_ticket_key_cb)
{
unsigned char *nctick = (unsigned char *)etick;
int rv = tctx->tlsext_ticket_key_cb(s, nctick, nctick + 16,
&ctx, &hctx, 0);
if (rv < 0)
return -1;
if (rv == 0)
goto tickerr;
if (rv == 2)
renew_ticket = 1;
}
else
{
/* Check key name matches */
if (memcmp(etick, tctx->tlsext_tick_key_name, 16))
goto tickerr;
HMAC_Init_ex(&hctx, tctx->tlsext_tick_hmac_key, 16,
tlsext_tick_md(), NULL);
EVP_DecryptInit_ex(&ctx, EVP_aes_128_cbc(), NULL,
tctx->tlsext_tick_aes_key, etick + 16);
}
/* Attempt to process session ticket, first conduct sanity and
* integrity checks on ticket.
*/
mlen = HMAC_size(&hctx);
eticklen -= mlen;
/* Check HMAC of encrypted ticket */
HMAC_Update(&hctx, etick, eticklen);
HMAC_Final(&hctx, tick_hmac, NULL);
HMAC_CTX_cleanup(&hctx);
if (memcmp(tick_hmac, etick + eticklen, mlen))
goto tickerr;
/* Attempt to decrypt session data */
/* Move p after IV to start of encrypted ticket, update length */
p = etick + 16 + EVP_CIPHER_CTX_iv_length(&ctx);
eticklen -= 16 + EVP_CIPHER_CTX_iv_length(&ctx);
sdec = OPENSSL_malloc(eticklen);
if (!sdec)
{
EVP_CIPHER_CTX_cleanup(&ctx);
return -1;
}
EVP_DecryptUpdate(&ctx, sdec, &slen, p, eticklen);
if (EVP_DecryptFinal(&ctx, sdec + slen, &mlen) <= 0)
goto tickerr;
slen += mlen;
EVP_CIPHER_CTX_cleanup(&ctx);
p = sdec;
sess = d2i_SSL_SESSION(NULL, &p, slen);
OPENSSL_free(sdec);
if (sess)
{
/* The session ID if non-empty is used by some clients to
* detect that the ticket has been accepted. So we copy it to
* the session structure. If it is empty set length to zero
* as required by standard.
*/
if (sesslen)
memcpy(sess->session_id, sess_id, sesslen);
sess->session_id_length = sesslen;
*psess = sess;
s->tlsext_ticket_expected = renew_ticket;
return 1;
}
/* If session decrypt failure indicate a cache miss and set state to
* send a new ticket
*/
tickerr:
s->tlsext_ticket_expected = 1;
return 0;
}
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;
}
