From 4d6a34faa1f960bfef1f28173c8451e519e7580d Mon Sep 17 00:00:00 2001
From: Tankred Hase <tankred@whiteout.io>
Date: Tue, 21 Apr 2015 16:12:20 +0200
Subject: [PATCH] Implement Symmetric-Key Message Encryption using a passphrase
 See https://tools.ietf.org/html/rfc4880#section-3.7.2.2

---
 src/message.js        | 54 +++++++++++++++++++++++++++++++++++++++++++
 test/general/basic.js | 19 +++++++++++++++
 2 files changed, 73 insertions(+)

diff --git a/src/message.js b/src/message.js
index 0c55602c..2f73f969 100644
--- a/src/message.js
+++ b/src/message.js
@@ -177,6 +177,60 @@ Message.prototype.encrypt = function(keys) {
   return new Message(packetlist);
 };
 
+/**
+ * Encrypt the message symmetrically using a passphrase.
+ *   https://tools.ietf.org/html/rfc4880#section-3.7.2.2
+ * @param {String} passphrase
+ * @return {Array<module:message~Message>} new message with encrypted content
+ */
+Message.prototype.symEncrypt = function(passphrase) {
+  if (!passphrase) {
+    throw new Error('The passphrase cannot be empty!');
+  }
+
+  var algo = enums.read(enums.symmetric, config.encryption_cipher);
+  var packetlist = new packet.List();
+
+  // create a Symmetric-key Encrypted Session Key (ESK)
+  var symESKPacket = new packet.SymEncryptedSessionKey();
+  symESKPacket.sessionKeyAlgorithm = algo;
+  symESKPacket.decrypt(passphrase); // generate the session key
+  packetlist.push(symESKPacket);
+
+  // create integrity protected packet
+  var symEncryptedPacket = new packet.SymEncryptedIntegrityProtected();
+  symEncryptedPacket.packets = this.packets;
+  symEncryptedPacket.encrypt(algo, symESKPacket.sessionKey);
+  packetlist.push(symEncryptedPacket);
+
+  // remove packets after encryption
+  symEncryptedPacket.packets = new packet.List();
+  return new Message(packetlist);
+};
+
+/**
+ * Decrypt the message symmetrically using a passphrase.
+ *   https://tools.ietf.org/html/rfc4880#section-3.7.2.2
+ * @param {String} passphrase
+ * @return {Array<module:message~Message>} new message with decrypted content
+ */
+Message.prototype.symDecrypt = function(passphrase) {
+  var symEncryptedPacketlist = this.packets.filterByTag(enums.packet.symEncryptedSessionKey, enums.packet.symEncryptedIntegrityProtected);
+
+  // decrypt Symmetric-key Encrypted Session Key (ESK)
+  var symESKPacket = symEncryptedPacketlist[0];
+  symESKPacket.decrypt(passphrase);
+
+  // decrypt integrity protected packet
+  var symEncryptedPacket = symEncryptedPacketlist[1];
+  symEncryptedPacket.decrypt(symESKPacket.sessionKeyAlgorithm, symESKPacket.sessionKey);
+
+  var resultMsg = new Message(symEncryptedPacket.packets);
+  // remove packets after decryption
+  symEncryptedPacket.packets = new packet.List();
+  return resultMsg;
+};
+
 /**
  * Sign the message (the literal data packet of the message)
  * @param  {Array<module:key~Key>} privateKey private keys with decrypted secret key data for signing
diff --git a/test/general/basic.js b/test/general/basic.js
index a1e4c6d4..27ba1b50 100644
--- a/test/general/basic.js
+++ b/test/general/basic.js
@@ -323,6 +323,25 @@ describe('Basic', function() {
 
   });
 
+  describe('Encrypt message symmetrically using passphrase', function() {
+    it('should encrypt/decrypt successfully', function() {
+      var passphrase = 'passphrase';
+      var plaintext = 'secret stuff';
+
+      // encrypt
+      var msg = openpgp.message.fromText(plaintext);
+      msg = msg.symEncrypt(passphrase);
+      var encrypted = msg.armor();
+
+      // decrypt
+      var msg2 = openpgp.message.readArmored(encrypted);
+      msg2 = msg2.symDecrypt(passphrase);
+      var decrypted = msg2.getText();
+
+      expect(decrypted).to.equal(plaintext);
+    });
+  });
+
   describe("Message 3DES decryption", function() {
     var pgp_msg =
         ['-----BEGIN PGP MESSAGE-----',