+
+int tls_psk_do_binder(SSL *s, const EVP_MD *md, const unsigned char *msgstart,
+ size_t binderoffset, const unsigned char *binderin,
+ unsigned char *binderout,
+ SSL_SESSION *sess, int sign)
+{
+ EVP_PKEY *mackey = NULL;
+ EVP_MD_CTX *mctx = NULL;
+ unsigned char hash[EVP_MAX_MD_SIZE], binderkey[EVP_MAX_MD_SIZE];
+ unsigned char finishedkey[EVP_MAX_MD_SIZE], tmpbinder[EVP_MAX_MD_SIZE];
+ const char resumption_label[] = "resumption psk binder key";
+ size_t hashsize = EVP_MD_size(md), bindersize;
+ int ret = -1;
+
+ /* Generate the early_secret */
+ if (!tls13_generate_secret(s, md, NULL, sess->master_key,
+ sess->master_key_length,
+ (unsigned char *)&s->early_secret)) {
+ SSLerr(SSL_F_TLS_PSK_DO_BINDER, ERR_R_INTERNAL_ERROR);
+ goto err;
+ }
+
+ /*
+ * Create the handshake hash for the binder key...the messages so far are
+ * empty!
+ */
+ mctx = EVP_MD_CTX_new();
+ if (mctx == NULL
+ || EVP_DigestInit_ex(mctx, md, NULL) <= 0
+ || EVP_DigestFinal_ex(mctx, hash, NULL) <= 0) {
+ SSLerr(SSL_F_TLS_PSK_DO_BINDER, ERR_R_INTERNAL_ERROR);
+ goto err;
+ }
+
+ /* Generate the binder key */
+ if (!tls13_hkdf_expand(s, md, s->early_secret,
+ (unsigned char *)resumption_label,
+ sizeof(resumption_label) - 1, hash, binderkey,
+ hashsize)) {
+ SSLerr(SSL_F_TLS_PSK_DO_BINDER, ERR_R_INTERNAL_ERROR);
+ goto err;
+ }
+
+ /* Generate the finished key */
+ if (!tls13_derive_finishedkey(s, md, binderkey, finishedkey, hashsize)) {
+ SSLerr(SSL_F_TLS_PSK_DO_BINDER, ERR_R_INTERNAL_ERROR);
+ goto err;
+ }
+
+ /*
+ * Get a hash of the ClientHello up to the start of the binders.
+ * TODO(TLS1.3): This will need to be tweaked when we implement
+ * HelloRetryRequest to include the digest of the previous messages here.
+ */
+ if (EVP_DigestInit_ex(mctx, md, NULL) <= 0
+ || EVP_DigestUpdate(mctx, msgstart, binderoffset) <= 0
+ || EVP_DigestFinal_ex(mctx, hash, NULL) <= 0) {
+ SSLerr(SSL_F_TLS_PSK_DO_BINDER, ERR_R_INTERNAL_ERROR);
+ goto err;
+ }
+
+ mackey = EVP_PKEY_new_mac_key(EVP_PKEY_HMAC, NULL, finishedkey, hashsize);
+ if (mackey == NULL) {
+ SSLerr(SSL_F_TLS_PSK_DO_BINDER, ERR_R_INTERNAL_ERROR);
+ goto err;
+ }
+
+ if (!sign)
+ binderout = tmpbinder;
+
+ bindersize = hashsize;
+ if (EVP_DigestSignInit(mctx, NULL, md, NULL, mackey) <= 0
+ || EVP_DigestSignUpdate(mctx, hash, hashsize) <= 0
+ || EVP_DigestSignFinal(mctx, binderout, &bindersize) <= 0
+ || bindersize != hashsize) {
+ SSLerr(SSL_F_TLS_PSK_DO_BINDER, ERR_R_INTERNAL_ERROR);
+ goto err;
+ }
+
+ if (sign) {
+ ret = 1;
+ } else {
+ /* HMAC keys can't do EVP_DigestVerify* - use CRYPTO_memcmp instead */
+ ret = (CRYPTO_memcmp(binderin, binderout, hashsize) == 0);
+ }
+
+ err:
+ OPENSSL_cleanse(binderkey, sizeof(binderkey));
+ OPENSSL_cleanse(finishedkey, sizeof(finishedkey));
+ EVP_PKEY_free(mackey);
+ EVP_MD_CTX_free(mctx);
+
+ return ret;
+}