Add and remove PKCS5 padding

src/crypto/index.js

@@ -13,6 +13,7 @@ import publicKey from './public_key';
 import signature from './signature';
 import random from './random';
 import pkcs1 from './pkcs1';
+import pkcs5 from './pkcs5.js';
 import crypto from './crypto.js';
 import rfc3394 from './rfc3394.js';
 
@@ -33,6 +34,8 @@ const mod = {
   random: random,
   /** @see module:crypto/pkcs1 */
   pkcs1: pkcs1,
+  /** @see module:crypto/pkcs5 */
+  pkcs5: pkcs5,
   /** @see module:crypto/rfc3394 */
   rfc3394: rfc3394,
 };

src/crypto/pkcs5.js

@@ -0,0 +1,62 @@
+// OpenPGP.js - An OpenPGP implementation in javascript
+// Copyright (C) 2015-2016 Decentral
+//
+// This library is free software; you can redistribute it and/or
+// modify it under the terms of the GNU Lesser General Public
+// License as published by the Free Software Foundation; either
+// version 3.0 of the License, or (at your option) any later version.
+//
+// This library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+// Lesser General Public License for more details.
+//
+// You should have received a copy of the GNU Lesser General Public
+// License along with this library; if not, write to the Free Software
+// Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
+
+// Functions to add and remove PKCS5 padding
+
+/**
+ * PKCS5 padding
+ * @module crypto/pkcs5
+ */
+
+function getPkcs5Padding(length) {
+  const c = 8 - (length % 8);
+  var result = [];
+  for (var i = 0; i < c; ++i) {
+    result.push(String.fromCharCode(c));
+  }
+  return result.join("");
+}
+
+/**
+ * Add pkcs5 padding to a text.
+ * @param  {String}  msg  Text to add padding
+ * @return {String}       Text with padding added
+ */
+function addPadding(msg) {
+  return msg + getPkcs5Padding(msg.length);
+}
+
+/**
+ * Remove pkcs5 padding from a string.
+ * @param  {String}  msg  Text to remove padding from
+ * @return {String}       Text with padding removed
+ */
+function removePadding(msg) {
+  var len = msg.length;
+  if (len > 0) {
+    var c = msg.charCodeAt(len - 1);
+    if (c >= 1 && c <= 8) {
+      return msg.substr(0, len - c);
+    }
+  }
+  throw new Error('Invalid padding');
+}
+
+module.exports = {
+  addPadding: addPadding,
+  removePadding: removePadding
+};

test/crypto/index.js

@@ -3,5 +3,6 @@ describe('Crypto', function () {
   require('./hash');
   require('./random.js');
   require('./crypto.js');
+  require('./pkcs5.js');
   require('./rfc3394.js');
 });

test/crypto/pkcs5.js

@@ -0,0 +1,41 @@
+'use strict';
+
+var openpgp = typeof window !== 'undefined' && window.openpgp ? window.openpgp : require('../../dist/openpgp');
+
+var expect = require('chai').expect;
+
+describe('PKCS5 padding', function() {
+  function repeat(pattern, count) {
+    var result = '';
+    for (var k=0; k<count; ++k) {
+      result += pattern;
+    }
+    return result;
+  }
+  var pkcs5 = openpgp.crypto.pkcs5;
+  it('Add padding', function () {
+    var s = '';
+    while (s.length < 16) {
+      var r = pkcs5.addPadding(s);
+      // 0..7 -> 8, 8..15 -> 16
+      var l = Math.ceil((s.length+1)/8)*8;
+      var c = l - s.length;
+      expect(r.length).to.equal(l);
+      expect(c).is.at.least(1).is.at.most(8);
+      expect(r.substr(-1)).to.equal(String.fromCharCode(c));
+      s += ' ';
+    }
+  });
+  it('Remove padding', function () {
+    for (var k=1; k<=8; ++k) {
+      var s = repeat(' ', 8-k);
+      var r = s + repeat(String.fromCharCode(k), k);
+      var t = pkcs5.removePadding(r);
+      expect(t).to.equal(s);
+    }
+  });
+  it('Invalid padding', function () {
+    expect(function () {pkcs5.removePadding(' ');}).to.throw(Error, /Invalid padding/);
+    expect(function () {pkcs5.removePadding('');}).to.throw(Error, /Invalid padding/);
+  });
+});