X-Git-Url: https://git.immae.eu/?a=blobdiff_plain;f=src%2Fjs%2Fentropy.js;h=a709c782a171855e3f3ba875af1c39ef73890ab4;hb=acf4c9b588c6abcc275b4e46df54248a2c913366;hp=d04d861dfa16b44f23b41398ebaa2418b3b129e1;hpb=87ad2c6e4c7987320d8ce147fe9310b702c5deea;p=perso%2FImmae%2FProjets%2FCryptomonnaies%2FBIP39.git

diff --git a/src/js/entropy.js b/src/js/entropy.js
index d04d861..a709c78 100644
--- a/src/js/entropy.js
+++ b/src/js/entropy.js
@@ -120,9 +120,13 @@ window.Entropy = new (function() {
         while (entropyBin.length < expectedBits) {
             entropyBin = "0" + entropyBin;
         }
+        // Calculate the number of bits per event
+        var bitsPerEvent = Math.log2(base.asInt);
         // Cards binary must be handled differently, since they're not replaced
         if (base.asInt == 52) {
-            entropyBin = getCardBinary(base.parts);
+            var cardEntropy = processCardEntropy(base.parts);
+            entropyBin = cardEntropy.binaryStr;
+            bitsPerEvent = cardEntropy.bitsPerEvent;
         }
         // Supply a 'filtered' entropy string for display purposes
         var entropyClean = base.parts.join("");
@@ -144,6 +148,7 @@ window.Entropy = new (function() {
             binaryStr: entropyBin,
             cleanStr: entropyClean,
             cleanHtml: entropyHtml,
+            bitsPerEvent: bitsPerEvent,
             base: base,
         }
         return e;
@@ -236,7 +241,7 @@ window.Entropy = new (function() {
     // total possible entropy is measured using n!, not base^n.
     // eg the second last card can be only one of two, not one of fifty two
     // so the added entropy for that card is only one bit at most
-    function getCardBinary(cards) {
+    function processCardEntropy(cards) {
         // Track how many instances of each card have been used, and thus
         // how many decks are in use.
         var cardCounts = {};
@@ -258,7 +263,12 @@ window.Entropy = new (function() {
         }
         // Work out the total number of bits for this many decks
         // See http://crypto.stackexchange.com/q/41886
-        var gainedBits = Math.log2(factorial(52 * numberOfDecks));
+        var gainedBits = 0;
+        // Equivalent of Math.log2(factorial(52*numberOfDecks))
+        // which becomes infinity for numberOfDecks > 4
+        for (var i=1; i<=52*numberOfDecks; i++) {
+            gainedBits = gainedBits + Math.log2(i);
+        }
         var lostBits = 52 * Math.log2(factorial(numberOfDecks));
         var maxBits = gainedBits - lostBits;
         // Convert the drawn cards to a binary representation.
@@ -283,15 +293,12 @@ window.Entropy = new (function() {
         // Create a normalized string of the selected cards
         var normalizedCards = cards.join("").toUpperCase();
         // Convert to binary using the SHA256 hash of the normalized cards.
-        // If the number of bits is more than 256, multiple rounds of hashing
+        // If the number of bits is more than 256, multiple hashes
         // are used until the required number of bits is reached.
         var entropyBin = "";
         var iterations = 0;
         while (entropyBin.length < numberOfBits) {
-            var hashedCards = sjcl.hash.sha256.hash(normalizedCards);
-            for (var j=0; j<iterations; j++) {
-                hashedCards = sjcl.hash.sha256.hash(hashedCards);
-            }
+            var hashedCards = sjcl.hash.sha256.hash(normalizedCards + ":" + iterations);
             var hashHex = sjcl.codec.hex.fromBits(hashedCards);
             for (var i=0; i<hashHex.length; i++) {
                 var decimal = parseInt(hashHex[i], 16);
@@ -305,7 +312,12 @@ window.Entropy = new (function() {
         }
         // Truncate to the appropriate number of bits.
         entropyBin = entropyBin.substring(0, numberOfBits);
-        return entropyBin;
+        // Get the number of bits per event
+        bitsPerEvent = maxBits / totalCards;
+        return {
+            binaryStr: entropyBin,
+            bitsPerEvent: bitsPerEvent,
+        }
     }
 
     // Polyfill for Math.log2