OP-01-007 Algorithm Preferences ignored upon Encryption (Low)

src/key.js

@@ -939,6 +939,40 @@ function generate(keyType, numBits, userId, passphrase) {
   return new Key(packetlist);
 }
 
+/**
+ * Returns the preferred symmetric algorithm for a set of keys
+ * @param  {Array<module:key~Key>} keys Set of keys
+ * @return {enums.symmetric}   Preferred symmetric algorithm
+ */
+function getPreferredSymAlgo(keys) {
+  var prioMap = {};
+  for (var i = 0; i < keys.length; i++) {
+    var primaryUser = keys[i].getPrimaryUser();
+    if (!primaryUser || !primaryUser.selfCertificate.preferredSymmetricAlgorithms) {
+      return config.encryption_cipher;
+    }
+    primaryUser.selfCertificate.preferredSymmetricAlgorithms.forEach(function(algo, index) {
+      var entry = prioMap[algo] || (prioMap[algo] = {prio: 0, count: 0, algo: algo});
+      entry.prio += 64 >> index;
+      entry.count++;
+    });
+  }
+  var prefAlgo = {prio: 0, algo: config.encryption_cipher};
+  for (var algo in prioMap) {
+    try {
+      if (algo !== enums.symmetric.plaintext &&
+          algo !== enums.symmetric.idea && // not implemented
+          enums.read(enums.symmetric, algo) && // known algorithm
+          prioMap[algo].count === keys.length && // available for all keys
+          prioMap[algo].prio > prefAlgo.prio) {
+        prefAlgo = prioMap[algo];
+      }
+    } catch (e) {}
+  }
+  return prefAlgo.algo;
+}
+
 exports.Key = Key;
 exports.readArmored = readArmored;
 exports.generate = generate;
+exports.getPreferredSymAlgo = getPreferredSymAlgo;

src/message.js

@@ -28,7 +28,8 @@ var packet = require('./packet'),
   enums = require('./enums.js'),
   armor = require('./encoding/armor.js'),
   config = require('./config'),
-  crypto = require('./crypto');
+  crypto = require('./crypto'),
+  keyModule = require('./key.js');
 
 /**
  * @class
@@ -144,8 +145,8 @@ Message.prototype.getText = function() {
  */
 Message.prototype.encrypt = function(keys) {
   var packetlist = new packet.List();
-  //TODO get preferred algo from signature
-  var sessionKey = crypto.generateSessionKey(enums.read(enums.symmetric, config.encryption_cipher));
+  var symAlgo = keyModule.getPreferredSymAlgo(keys);
+  var sessionKey = crypto.generateSessionKey(enums.read(enums.symmetric, symAlgo));
   keys.forEach(function(key) {
     var encryptionKeyPacket = key.getEncryptionKeyPacket();
     if (encryptionKeyPacket) {
@@ -153,8 +154,7 @@ Message.prototype.encrypt = function(keys) {
       pkESKeyPacket.publicKeyId = encryptionKeyPacket.getKeyId();
       pkESKeyPacket.publicKeyAlgorithm = encryptionKeyPacket.algorithm;
       pkESKeyPacket.sessionKey = sessionKey;
-      //TODO get preferred algo from signature
-      pkESKeyPacket.sessionKeyAlgorithm = enums.read(enums.symmetric, config.encryption_cipher);
+      pkESKeyPacket.sessionKeyAlgorithm = enums.read(enums.symmetric, symAlgo);
       pkESKeyPacket.encrypt(encryptionKeyPacket);
       packetlist.push(pkESKeyPacket);
     } else {
@@ -168,8 +168,7 @@ Message.prototype.encrypt = function(keys) {
     symEncryptedPacket = new packet.SymmetricallyEncrypted();
   }
   symEncryptedPacket.packets = this.packets;
-  //TODO get preferred algo from signature
-  symEncryptedPacket.encrypt(enums.read(enums.symmetric, config.encryption_cipher), sessionKey);
+  symEncryptedPacket.encrypt(enums.read(enums.symmetric, symAlgo), sessionKey);
   packetlist.push(symEncryptedPacket);
   // remove packets after encryption
   symEncryptedPacket.packets = new packet.List();

test/general/key.js

@@ -454,5 +454,29 @@ describe('Key', function() {
     expect(dest.update.bind(dest, source)).to.throw('Cannot update public key with private key if subkey mismatch');
   });
 
+  it('getPreferredSymAlgo() - one key - AES256', function() {
+    var key1 = openpgp.key.readArmored(twoKeys).keys[0];
+    var prefAlgo = openpgp.key.getPreferredSymAlgo([key1]);
+    expect(prefAlgo).to.equal(openpgp.enums.symmetric.aes256);
+  });
+
+  it('getPreferredSymAlgo() - two key - AES192', function() {
+    var keys = openpgp.key.readArmored(twoKeys).keys;
+    var key1 = keys[0];
+    var key2 = keys[1];
+    key2.getPrimaryUser().selfCertificate.preferredSymmetricAlgorithms = [6,8,3];
+    var prefAlgo = openpgp.key.getPreferredSymAlgo([key1, key2]);
+    expect(prefAlgo).to.equal(openpgp.enums.symmetric.aes192);
+  });
+
+  it('getPreferredSymAlgo() - two key - one without pref', function() {
+    var keys = openpgp.key.readArmored(twoKeys).keys;
+    var key1 = keys[0];
+    var key2 = keys[1];
+    key2.getPrimaryUser().selfCertificate.preferredSymmetricAlgorithms = null;
+    var prefAlgo = openpgp.key.getPreferredSymAlgo([key1, key2]);
+    expect(prefAlgo).to.equal(openpgp.config.encryption_cipher);
+  });
+
 });