More portable (linux compatible) random number generation

bsspeke.c

@@ -53,6 +53,16 @@ void print_point(const char *label,
     printf("]\n");
 }
 
+void
+generate_random_bytes(uint8_t *buf, size_t len)
+{
+#ifdef linux
+    getrandom(buf, len, 0);
+#else
+    arc4random_buf(buf, len);
+#endif
+}
+
 void
 bsspeke_client_init(bsspeke_client_ctx *ctx,
                     const char* client_id, const size_t client_id_len,
@@ -116,7 +126,8 @@ bsspeke_client_generate_message1
     //    * Then use the inverse of 1/r as `r`
     //  FIXME: On second thought, monocypher seems to handle all of this complexity for us.  Let's see what happens if we just do things the straightforward way for now...
     debug(DEBUG, "Generating random blind `r`");
-    arc4random_buf(client->r, 32);
+    //arc4random_buf(client->r, 32);
+    generate_random_bytes(client->r, 32);
     print_point("r", client->r);
     debug(DEBUG, "Clamping r");
     crypto_x25519_clamp(client->r);
@@ -155,7 +166,8 @@ bsspeke_server_setup_generate_message2
     // So we have to create a new random salt for the user
     debug(DEBUG, "Generating new salt");
     user_info->salt_len = 32;
-    arc4random_buf(user_info->salt, user_info->salt_len);
+    //arc4random_buf(user_info->salt, user_info->salt_len);
+    generate_random_bytes(user_info->salt, user_info->salt_len);
     print_point("salt", user_info->salt);
 
     // Hash the salt
@@ -313,7 +325,8 @@ bsspeke_server_login_generate_message2(bsspeke_login_msg2_t *msg2,
 
     // Generate random ephemeral private key b, save it in ctx->b
     debug(DEBUG, "Generating ephemeral private key b");
-    arc4random_buf(server->b, 32);
+    //arc4random_buf(server->b, 32);
+    generate_random_bytes(server->b, 32);
     crypto_x25519_clamp(server->b);
     print_point("b", server->b);
 
@@ -406,7 +419,8 @@ bsspeke_client_login_generate_message3(bsspeke_login_msg3_t *msg3,
 
     // Generate a random ephemeral private key a, store it in ctx->a
     debug(DEBUG, "Generating ephemeral private key a");
-    arc4random_buf(client->a, 32);
+    //arc4random_buf(client->a, 32);
+    generate_random_bytes(client->a, 32);
     crypto_x25519_clamp(client->a);
     print_point("a", client->a);
     // Generate the ephemeral public key A = a * P, store it in msg3->A