Add warning when custom entropy is low

monero-wallet-generator.html

@@ -10741,9 +10741,10 @@ bC0zLjUsMjAuNGgtNkwyNDQuOCwzMTAuNkwyNDQuOCwzMTAuNnoiLz4KPC9nPgo8L3N2Zz4K">
     <div class="row valign-wrapper">
         <div class="col s4 right-align ">
                 <input class="btn orange" type="button" onclick="js:genwallet(null);"
-                       value="Generate wallet" action=""/>
-                <p>Custom entropy (leave empty to use PRNG)</p>
-                <input type="text" value="" id="user_entropy_widget" />
+                       value="Generate wallet" id="gen_with_custom_entropy_button" disabled="disabled" action=""/>
+                <p>Custom entropy for deterministic wallet (leave empty to use the browser's PRNG)</p>
+                <input type="text" value="" id="user_entropy_widget" oninput="js:checkEntropy();" />
+                <div style="color: red; display: none" id="user_entropy_warning_widget">WARNING: entropy is way too low for the wallet to be secure: aim for 256 bits (about a hundred dice throws)</div>
         </div>
         <div class="col s1 offset-s1"><h4>or</h4></div>
         <div class="col s5 offset-s1">
@@ -11093,6 +11094,43 @@ function genwallet_prefix()
   }
 }
 
+function checkEntropy()
+{
+  var good = true;
+  var button = document.getElementById("gen_with_custom_entropy_button")
+  var user_entropy_widget = document.getElementById("user_entropy_widget")
+  var user_entropy = user_entropy_widget.value;
+  var user_entropy_warning_widget = document.getElementById("user_entropy_warning_widget")
+  if (user_entropy.length === 0) {
+    good = false;
+    button.disabled = true
+    user_entropy_warning_widget.style.display = "none"
+    return
+  }
+
+  button.disabled = false
+  var count = new Int32Array(256);
+  for (var n = 0; n < 256; ++n)
+    count[n] = 0
+  for (var n = 0; n < user_entropy.length; ++n)
+    count[user_entropy.charCodeAt(n)]++;
+  var e = 0
+  for (var n = 0; n < 256; ++n) {
+    if (count[n] > 0) {
+      var p = count[n] / user_entropy.length
+      p *= Math.log(p) / Math.log(2)
+      e -= p
+    }
+  }
+  e *= user_entropy.length
+  if (e < 128)
+    good = false
+  if (good)
+    user_entropy_warning_widget.style.display = "none"
+  else
+    user_entropy_warning_widget.style.display = "block"
+}
+
 function toggle_qr()
 {
   address_qr_widget = document.getElementById("address_qr_widget");

monero-wallet-generator.html.asc

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