From 90ed7f7f5e56427218d03d98befbb7534a9d65f6 Mon Sep 17 00:00:00 2001
From: Max Fillinger <maximilian.fillinger@foxcrypto.com>
Date: Mon, 22 Jul 2024 14:44:09 +0200
Subject: [PATCH] Add TLS-Exporter options to ssl_server2

The program prints out the derived symmetric key for testing purposes.

Signed-off-by: Max Fillinger <maximilian.fillinger@foxcrypto.com>
---
 programs/ssl/ssl_server2.c | 35 +++++++++++++++++++++++++++++++++++
 1 file changed, 35 insertions(+)

diff --git a/programs/ssl/ssl_server2.c b/programs/ssl/ssl_server2.c
index 5de734f7eb..01be48ab7f 100644
--- a/programs/ssl/ssl_server2.c
+++ b/programs/ssl/ssl_server2.c
@@ -71,6 +71,8 @@ int main(void)
 #define DFL_NBIO                0
 #define DFL_EVENT               0
 #define DFL_READ_TIMEOUT        0
+#define DFL_EXP_LABEL           NULL
+#define DFL_EXP_LEN             20
 #define DFL_CA_FILE             ""
 #define DFL_CA_PATH             ""
 #define DFL_CRT_FILE            ""
@@ -519,6 +521,10 @@ int main(void)
     "    event=%%d            default: 0 (loop)\n"                            \
     "                        options: 1 (level-triggered, implies nbio=1),\n" \
     "    read_timeout=%%d     default: 0 ms (no timeout)\n"    \
+    "    exp_label=%%s       Label to input into TLS-Exporter\n" \
+    "                         default: None (don't try to export a key)\n" \
+    "    exp_len=%%d         Length of key to extract from TLS-Exporter \n" \
+    "                         default: 20\n" \
     "\n"                                                    \
     USAGE_DTLS                                              \
     USAGE_SRTP                                              \
@@ -610,6 +616,8 @@ struct options {
     int nbio;                   /* should I/O be blocking?                  */
     int event;                  /* loop or event-driven IO? level or edge triggered? */
     uint32_t read_timeout;      /* timeout on mbedtls_ssl_read() in milliseconds    */
+    const char *exp_label;      /* label to input into mbedtls_ssl_export_keying_material() */
+    int exp_len;                /* Lenght of key to export using mbedtls_ssl_export_keying_material() */
     int response_size;          /* pad response with header to requested size */
     uint16_t buffer_size;       /* IO buffer size */
     const char *ca_file;        /* the file with the CA certificate(s)      */
@@ -1699,6 +1707,8 @@ int main(int argc, char *argv[])
     opt.cid_val             = DFL_CID_VALUE;
     opt.cid_val_renego      = DFL_CID_VALUE_RENEGO;
     opt.read_timeout        = DFL_READ_TIMEOUT;
+    opt.exp_label           = DFL_EXP_LABEL;
+    opt.exp_len             = DFL_EXP_LEN;
     opt.ca_file             = DFL_CA_FILE;
     opt.ca_path             = DFL_CA_PATH;
     opt.crt_file            = DFL_CRT_FILE;
@@ -1877,6 +1887,10 @@ usage:
             }
         } else if (strcmp(p, "read_timeout") == 0) {
             opt.read_timeout = atoi(q);
+        } else if (strcmp(p, "exp_label") == 0) {
+            opt.exp_label = q;
+        } else if (strcmp(p, "exp_len") == 0) {
+            opt.exp_len = atoi(q);
         } else if (strcmp(p, "buffer_size") == 0) {
             opt.buffer_size = atoi(q);
             if (opt.buffer_size < 1) {
@@ -3642,6 +3656,27 @@ handshake:
         mbedtls_printf("\n");
     }
 
+    if (opt.exp_label != NULL && opt.exp_len > 0) {
+        unsigned char *exported_key = calloc((size_t)opt.exp_len, sizeof(unsigned int));
+        if (exported_key == NULL) {
+            mbedtls_printf("Could not allocate %d bytes\n", opt.exp_len);
+            ret = 3;
+            goto exit;
+        }
+        ret = mbedtls_ssl_export_keying_material(&ssl, exported_key, (size_t)opt.exp_len,
+                                                 opt.exp_label, strlen(opt.exp_label),
+                                                 NULL, 0, 0);
+        if (ret != 0) {
+            goto exit;
+        }
+        mbedtls_printf("Exporting key of length %d with label \"%s\": 0x", opt.exp_len, opt.exp_label);
+        for (i = 0; i < opt.exp_len; i++) {
+            mbedtls_printf("%02X", exported_key[i]);
+        }
+        mbedtls_printf("\n\n");
+        fflush(stdout);
+    }
+
 #if defined(MBEDTLS_SSL_DTLS_SRTP)
     else if (opt.use_srtp != 0) {
         size_t j = 0;