From 294139b57a13663d0073d031d2ee2bf8b14cbac0 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Manuel=20P=C3=A9gouri=C3=A9-Gonnard?= <mpg2@elzevir.fr>
Date: Tue, 15 Sep 2015 16:55:05 +0200
Subject: [PATCH] Add client extension writing

---
 include/mbedtls/ssl.h |  2 ++
 library/ssl_cli.c     | 47 +++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 49 insertions(+)

diff --git a/include/mbedtls/ssl.h b/include/mbedtls/ssl.h
index 51a3a0638..eed441319 100644
--- a/include/mbedtls/ssl.h
+++ b/include/mbedtls/ssl.h
@@ -349,6 +349,8 @@
 
 #define MBEDTLS_TLS_EXT_SESSION_TICKET              35
 
+#define MBEDTLS_TLS_EXT_ECJPAKE_KKPP               256 /* experimental */
+
 #define MBEDTLS_TLS_EXT_RENEGOTIATION_INFO      0xFF01
 
 /*
diff --git a/library/ssl_cli.c b/library/ssl_cli.c
index ba6a6166d..bab63a711 100644
--- a/library/ssl_cli.c
+++ b/library/ssl_cli.c
@@ -280,6 +280,48 @@ static void ssl_write_supported_point_formats_ext( mbedtls_ssl_context *ssl,
 }
 #endif /* MBEDTLS_ECDH_C || MBEDTLS_ECDSA_C || MBEDTLS_ECJPAKE_C */
 
+#if defined(MBEDTLS_ECJPAKE_C)
+static void ssl_write_ecjpake_kkpp_ext( mbedtls_ssl_context *ssl,
+                                        unsigned char *buf,
+                                        size_t *olen )
+{
+    int ret;
+    unsigned char *p = buf;
+    const unsigned char *end = ssl->out_buf + MBEDTLS_SSL_MAX_CONTENT_LEN;
+    size_t kkpp_len;
+
+    *olen = 0;
+
+    /* Skip costly extension if we can't use EC J-PAKE anyway */
+    if( mbedtls_ecjpake_check( &ssl->handshake->ecjpake_ctx ) != 0 )
+        return;
+
+    MBEDTLS_SSL_DEBUG_MSG( 3, ( "client hello, adding ecjpake_kkpp extension" ) );
+
+    if( end - p < 4 )
+    {
+        MBEDTLS_SSL_DEBUG_MSG( 1, ( "buffer too small" ) );
+        return;
+    }
+
+    *p++ = (unsigned char)( ( MBEDTLS_TLS_EXT_ECJPAKE_KKPP >> 8 ) & 0xFF );
+    *p++ = (unsigned char)( ( MBEDTLS_TLS_EXT_ECJPAKE_KKPP      ) & 0xFF );
+
+    if( ( ret = mbedtls_ecjpake_write_round_one( &ssl->handshake->ecjpake_ctx,
+                    p + 2, end - p - 2, &kkpp_len,
+                    ssl->conf->f_rng, ssl->conf->p_rng ) ) != 0 )
+    {
+        MBEDTLS_SSL_DEBUG_RET( 1 , "mbedtls_ecjpake_write_round_one", ret );
+        return;
+    }
+
+    *p++ = (unsigned char)( ( kkpp_len >> 8 ) & 0xFF );
+    *p++ = (unsigned char)( ( kkpp_len      ) & 0xFF );
+
+    *olen = kkpp_len + 4;
+}
+#endif /* MBEDTLS_ECJPAKE_C */
+
 #if defined(MBEDTLS_SSL_MAX_FRAGMENT_LENGTH)
 static void ssl_write_max_fragment_length_ext( mbedtls_ssl_context *ssl,
                                                unsigned char *buf,
@@ -781,6 +823,11 @@ static int ssl_write_client_hello( mbedtls_ssl_context *ssl )
     ext_len += olen;
 #endif
 
+#if defined(MBEDTLS_ECJPAKE_C)
+    ssl_write_ecjpake_kkpp_ext( ssl, p + 2 + ext_len, &olen );
+    ext_len += olen;
+#endif
+
 #if defined(MBEDTLS_SSL_MAX_FRAGMENT_LENGTH)
     ssl_write_max_fragment_length_ext( ssl, p + 2 + ext_len, &olen );
     ext_len += olen;