[wasm][crypto] RandomNumberGenerator mapped to Web Crypto getRandomValues

src/libraries/Native/Unix/System.Native/pal_random.c

@@ -55,6 +55,10 @@ void SystemNative_GetNonCryptographicallySecureRandomBytes(uint8_t* buffer, int3
 #endif // HAVE_ARC4RANDOM_BUF
 }
 
+#ifdef __EMSCRIPTEN__
+int32_t mono_wasm_browser_crypto_getRandomValues(uint8_t* buffer, int32_t bufferLength);
+#endif
+
 /*
 
 Generate cryptographically strong random bytes.
@@ -68,6 +72,18 @@ int32_t SystemNative_GetCryptographicallySecureRandomBytes(uint8_t* buffer, int3
 
     assert(buffer != NULL);
 
+#ifdef __EMSCRIPTEN__
+    static bool sMissingBrowserCrypto;
+    if (!sMissingBrowserCrypto)
+    {
+        int32_t bff = mono_wasm_browser_crypto_getRandomValues(buffer, bufferLength);
+        if (bff == -1)
+            sMissingBrowserCrypto = true;
+        else
+            return 0;
+    }
+#endif
+
     if (!sMissingDevURandom)
     {
         if (rand_des == -1)

src/mono/wasm/runtime/driver.c

@@ -940,3 +940,15 @@ mono_timezone_get_local_name (MonoString **result)
 	*result = mono_string_from_utf16 (tzd_local_name);
 	free (tzd_local_name);
 }
+
+EM_JS(int32_t, mono_wasm_browser_crypto_getRandomValues, (uint8_t* buffer, int32_t bufferLength),
+{
+	// check that we have crypto available
+	if (!(typeof crypto !== 'undefined' && crypto.subtle && typeof crypto.getRandomValues === 'function')) {
+		return -1;
+	}
+	// map the work array to the memory buffer passed with the length
+	var wrkArray = new Uint8Array(Module.HEAPU8.buffer, buffer, bufferLength);
+	crypto.getRandomValues(wrkArray);
+	return 0;
+});