mbedtls: implement CTR-DRBG and HAVEGE random generators

closes #1227

lib/vtls/mbedtls.c

@@ -6,7 +6,7 @@
  *                             \___|\___/|_| \_\_____|
  *
  * Copyright (C) 2010 - 2011, Hoi-Ho Chan, <hoiho.chan@gmail.com>
- * Copyright (C) 2012 - 2016, Daniel Stenberg, <daniel@haxx.se>, et al.
+ * Copyright (C) 2012 - 2017, Daniel Stenberg, <daniel@haxx.se>, et al.
  *
  * This software is licensed as described in the file COPYING, which
  * you should have received as part of this distribution. The terms
@@ -734,6 +734,55 @@ size_t Curl_mbedtls_version(char *buffer, size_t size)
                   (version>>16)&0xff, (version>>8)&0xff);
 }
 
+CURLcode Curl_mbedtls_random(struct Curl_easy *data, unsigned char *entropy,
+                             size_t length)
+{
+#if defined(MBEDTLS_CTR_DRBG_C)
+  int ret = -1;
+  char errorbuf[128];
+  mbedtls_entropy_context ctr_entropy;
+  mbedtls_ctr_drbg_context ctr_drbg;
+  mbedtls_entropy_init(&ctr_entropy);
+  mbedtls_ctr_drbg_init(&ctr_drbg);
+  errorbuf[0]=0;
+
+  ret = mbedtls_ctr_drbg_seed(&ctr_drbg, mbedtls_entropy_func,
+                              &ctr_entropy, NULL, 0);
+
+  if(ret) {
+#ifdef MBEDTLS_ERROR_C
+    mbedtls_strerror(ret, errorbuf, sizeof(errorbuf));
+#endif /* MBEDTLS_ERROR_C */
+    failf(data, "Failed - mbedTLS: ctr_drbg_seed returned (-0x%04X) %s\n",
+          -ret, errorbuf);
+  }
+  else {
+    ret = mbedtls_ctr_drbg_random(&ctr_drbg, entropy, length);
+
+    if(ret) {
+#ifdef MBEDTLS_ERROR_C
+      mbedtls_strerror(ret, errorbuf, sizeof(errorbuf));
+#endif /* MBEDTLS_ERROR_C */
+      failf(data, "mbedTLS: ctr_drbg_init returned (-0x%04X) %s\n",
+            -ret, errorbuf);
+    }
+  }
+
+  mbedtls_ctr_drbg_free(&ctr_drbg);
+  mbedtls_entropy_free(&ctr_entropy);
+
+  return ret == 0 ? CURLE_OK : CURLE_FAILED_INIT;
+#elif defined(MBEDTLS_HAVEGE_C)
+  mbedtls_havege_state hs;
+  mbedtls_havege_init(&hs);
+  mbedtls_havege_random(&hs, entropy, length);
+  mbedtls_havege_free(&hs);
+  return CURLE_OK;
+#else
+  return CURLE_NOT_BUILT_IN;
+#endif
+}
+
 static CURLcode
 mbed_connect_common(struct connectdata *conn,
                     int sockindex,

lib/vtls/mbedtls.h

@@ -50,6 +50,9 @@ void Curl_mbedtls_session_free(void *ptr);
 size_t Curl_mbedtls_version(char *buffer, size_t size);
 int Curl_mbedtls_shutdown(struct connectdata *conn, int sockindex);
 
+CURLcode Curl_mbedtls_random(struct Curl_easy *data, unsigned char *entropy,
+                     size_t length);
+
 /* this backends supports CURLOPT_PINNEDPUBLICKEY */
 #define have_curlssl_pinnedpubkey 1
 
@@ -70,11 +73,7 @@ int Curl_mbedtls_shutdown(struct connectdata *conn, int sockindex);
 #define curlssl_data_pending(x,y) Curl_mbedtls_data_pending(x, y)
 #define CURL_SSL_BACKEND CURLSSLBACKEND_MBEDTLS
 #define curlssl_sha256sum(a,b,c,d) mbedtls_sha256(a,b,c,0)
-
-/* This might cause libcurl to use a weeker random!
-   TODO: implement proper use of Polarssl's CTR-DRBG or HMAC-DRBG and use that
-*/
-#define curlssl_random(x,y,z) (x=x, y=y, z=z, CURLE_NOT_BUILT_IN)
+#define curlssl_random(x,y,z) Curl_mbedtls_random(x, y, z)
 
 #endif /* USE_MBEDTLS */
 #endif /* HEADER_CURL_MBEDTLS_H */