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; }