Optimize padding calculation

nf404 · Jul 7, 2019 · 2905748 · 2905748
1 parent 7821ef0
commit 2905748
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Showing 3 changed files with 16 additions and 10 deletions.
diff --git a/src/hasher/hasher.mjs b/src/hasher/hasher.mjs
@@ -118,6 +118,7 @@ class Hasher {
 
   /**
    * Add PKCS7 padding to message
+   * Pad with bytes all of the same value as the number of padding bytes
    *
    * @protected
    * @param {number} length
@@ -128,6 +129,7 @@ class Hasher {
 
   /**
    * Add ISO7816-4 padding to message
+   * Pad with 0x80 followed by zero bytes
    *
    * @protected
    * @param {number} length
@@ -138,6 +140,7 @@ class Hasher {
 
   /**
    * Add zero padding to message
+   * Pad with 0x00 characters
    *
    * @protected
    * @param {number} length

diff --git a/src/hasher/hasher32be.mjs b/src/hasher/hasher32be.mjs
@@ -81,11 +81,12 @@ class Hasher32be extends Hasher {
    */
   addLengthBits() {
     // @todo fix length to 64 bit
-    this.state.message += "\x00\x00\x00\x00";
-    let lengthBits = this.state.length << 3;
-    for (let i = 3; i >= 0; i--) {
-      this.state.message += String.fromCharCode(lengthBits >> (i << 3));
-    }
+    this.state.message += "\x00\x00\x00" +
+      String.fromCharCode(this.state.length >> 29 & 0xff) +
+      String.fromCharCode(this.state.length >> 21 & 0xff) +
+      String.fromCharCode(this.state.length >> 13 & 0xff) +
+      String.fromCharCode(this.state.length >> 5 & 0xff) +
+      String.fromCharCode(this.state.length << 3 & 0xff);
   }
 }
 

diff --git a/src/hasher/hasher32le.mjs b/src/hasher/hasher32le.mjs
@@ -75,12 +75,14 @@ class Hasher32le extends Hasher {
    * @protected
    */
   addLengthBits() {
-    let lengthBits = this.state.length << 3;
-    for (let i = 0; i < 4; i++) {
-      this.state.message += String.fromCharCode(lengthBits >> (i << 3));
-    }
     // @todo fix length to 64 bit
-    this.state.message += "\x00\x00\x00\x00";
+    this.state.message +=
+      String.fromCharCode(this.state.length << 3 & 0xff) +
+      String.fromCharCode(this.state.length >> 5 & 0xff) +
+      String.fromCharCode(this.state.length >> 13 & 0xff) +
+      String.fromCharCode(this.state.length >> 21 & 0xff) +
+      String.fromCharCode(this.state.length >> 29 & 0xff) +
+      "\x00\x00\x00";
   }
 }