Add support for decrypting autoforwarded messages (#1)

src/crypto/public_key/elliptic/ecdh.js

@@ -50,9 +50,9 @@ function buildEcdhParam(public_algo, oid, kdfParams, fingerprint) {
   return util.concatUint8Array([
     oid.write(),
     new Uint8Array([public_algo]),
-    kdfParams.write(),
+    kdfParams.replacementKDFParams || kdfParams.write(),
     util.stringToUint8Array('Anonymous Sender    '),
-    fingerprint
+    kdfParams.replacementFingerprint || fingerprint
   ]);
 }
 

src/enums.js

@@ -50,6 +50,18 @@ export default {
     'brainpoolP512r1':       'brainpoolP512r1'
   },
 
+  /** KDF parameters flags
+   * Non-standard extensions (for now) to allow email forwarding
+   * @enum {Integer}
+   * @readonly
+   */
+  kdfFlags: {
+    /** Specify fingerprint to use instead of the recipient's */
+    replace_fingerprint: 0x01,
+    /** Specify custom parameters to use in the KDF digest computation */
+    replace_kdf_params: 0x02
+  },
+
   /** A string to key specifier type
    * @enum {Integer}
    * @readonly

src/type/kdf_params.js

@@ -26,22 +26,36 @@ import { UnsupportedError } from '../packet/packet';
  * Alternative 1) [NIST-SP800-56A] with the KDF hash function that is
  * SHA2-256 [FIPS-180-3] or stronger is REQUIRED.
  * @module type/kdf_params
- * @private
  */
+import util from '../util';
+import enums from '../enums';
 
 class KDFParams {
   /**
-   * @param {enums.hash} hash - Hash algorithm
-   * @param {enums.symmetric} cipher - Symmetric algorithm
+   * @param  {Integer}          version                 Version, defaults to 1
+   * @param  {enums.hash}       hash                    Hash algorithm
+   * @param  {enums.symmetric}  cipher                  Symmetric algorithm
+   * @param  {enums.kdfFlags}   flags                   (v2 only) flags
+   * @param  {Uint8Array}       replacementFingerprint  (v2 only) fingerprint to use instead of recipient one (v5 keys, the 20 leftmost bytes of the fingerprint)
+   * @param  {Uint8Array}       replacementKDFParams    (v2 only) serialized KDF params to use in KDF digest computation
    */
   constructor(data) {
     if (data) {
-      const { hash, cipher } = data;
+      const { version, hash, cipher, flags, replacementFingerprint, replacementKDFParams } = data;
+      this.version = version || 1;
       this.hash = hash;
       this.cipher = cipher;
+
+      this.flags = flags;
+      this.replacementFingerprint = replacementFingerprint;
+      this.replacementKDFParams = replacementKDFParams;
     } else {
+      this.version = null;
       this.hash = null;
       this.cipher = null;
+      this.flags = null;
+      this.replacementFingerprint = null;
+      this.replacementKDFParams = null;
     }
   }
 
@@ -51,12 +65,27 @@ class KDFParams {
    * @returns {Number} Number of read bytes.
    */
   read(input) {
-    if (input.length < 4 || input[0] !== 3 || input[1] !== 1) {
+    if (input.length < 4 || (input[1] !== 1 && input[1] !== 2)) {
       throw new UnsupportedError('Cannot read KDFParams');
     }
+    this.version = input[1];
     this.hash = input[2];
     this.cipher = input[3];
-    return 4;
+    let readBytes = 4;
+
+    if (this.version === 2) {
+      this.flags = input[readBytes++];
+      if (this.flags & enums.kdfFlags.replace_fingerprint) {
+        this.replacementFingerprint = input.slice(readBytes, readBytes + 20);
+        readBytes += 20;
+      }
+      if (this.flags & enums.kdfFlags.replace_kdf_params) {
+        const fieldLength = input[readBytes] + 1; // account for length
+        this.replacementKDFParams = input.slice(readBytes, readBytes + fieldLength);
+        readBytes += fieldLength;
+      }
+    }
+    return readBytes;
   }
 
   /**
@@ -64,8 +93,20 @@ class KDFParams {
    * @returns  {Uint8Array}  Array with the KDFParams value
    */
   write() {
+    if (!this.version || this.version === 1) {
       return new Uint8Array([3, 1, this.hash, this.cipher]);
     }
+
+    const v2Fields = util.concatUint8Array([
+      new Uint8Array([4, 2, this.hash, this.cipher, this.flags]),
+      this.replacementFingerprint || new Uint8Array(),
+      this.replacementKDFParams || new Uint8Array()
+    ]);
+
+    // update length field
+    v2Fields[0] = v2Fields.length - 1;
+    return new Uint8Array(v2Fields);
+  }
 }
 
 export default KDFParams;

test/crypto/ecdh.js

@@ -362,3 +362,77 @@ export default () => describe('ECDH key exchange @lightweight', function () {
     });
   });
 });
+
+describe('KDF parameters', function () {
+  const fingerprint = new Uint8Array([
+    177, 183, 116, 123, 76, 133, 245, 212, 151, 243,
+    236, 71, 245, 86, 3, 168, 101, 74, 209, 105
+  ]);
+
+  it('Valid serialization', async function () {
+    const cipher = openpgp.enums.symmetric.aes256;
+    const hash = openpgp.enums.hash.sha256;
+
+    const v1 = new KDFParams({ cipher, hash });
+    const v1Copy = new KDFParams({});
+    v1Copy.read(v1.write());
+    expect(v1Copy).to.deep.equal(v1);
+
+    const v1Flags0x0 = new KDFParams({
+      cipher,
+      hash,
+      flags: 0x0 // discarded
+    });
+    const v1Flags0x0Copy = new KDFParams({});
+    v1Flags0x0Copy.read(v1Flags0x0.write());
+    v1Flags0x0.flags = undefined;
+    expect(v1Flags0x0Copy).to.deep.equal(v1Flags0x0);
+
+    const v2Flags0x3 = new KDFParams({
+      cipher,
+      hash,
+      version: 2,
+      flags: 0x3,
+      replacementFingerprint: fingerprint,
+      replacementKDFParams: new Uint8Array([3, 1, cipher, hash])
+    });
+    const v2Flags0x3Copy = new KDFParams();
+    v2Flags0x3Copy.read(v2Flags0x3.write());
+    expect(v2Flags0x3Copy).to.deep.equal(v2Flags0x3);
+
+    const v2Flags0x0 = new KDFParams({
+      cipher,
+      hash,
+      version: 2,
+      flags: 0x0
+    });
+    const v2Flags0x0Copy = new KDFParams({});
+    v2Flags0x0Copy.read(v2Flags0x0.write());
+
+    expect(v2Flags0x0Copy).to.deep.equal(v2Flags0x0);
+
+    const v2Flags0x1 = new KDFParams({
+      cipher,
+      hash,
+      version: 2,
+      flags: 0x1,
+      replacementFingerprint: fingerprint
+    });
+    const v2Flags0x1Copy = new KDFParams();
+    v2Flags0x1Copy.read(v2Flags0x1.write());
+    v2Flags0x1.replacementKDFParams = null;
+    expect(v2Flags0x1Copy).to.deep.equal(v2Flags0x1);
+
+    const v2Flags0x2 = new KDFParams({
+      cipher,
+      hash,
+      version: 2,
+      flags: 0x2,
+      replacementKDFParams: new Uint8Array([3, 1, cipher, hash])
+    });
+    const v2Flags0x2Copy = new KDFParams();
+    v2Flags0x2Copy.read(v2Flags0x2.write());
+    v2Flags0x2.replacementFingerprint = null;
+    expect(v2Flags0x2Copy).to.deep.equal(v2Flags0x2);
+  });
+});

test/general/forwarding.js

@@ -0,0 +1,43 @@
+import { expect } from 'chai';
+
+import openpgp from '../initOpenpgp.js';
+
+const charlieKeyArmored = `-----BEGIN PGP PRIVATE KEY BLOCK-----
+Version: OpenPGP.js v4.10.4
+Comment: https://openpgpjs.org
+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+=FVvG
+-----END PGP PRIVATE KEY BLOCK-----`;
+
+const fwdCiphertextArmored = `-----BEGIN PGP MESSAGE-----
+Version: OpenPGP.js v4.10.4
+Comment: https://openpgpjs.org
+
+wV4Dog8LAQLriGUSAQdA/I6k0IvGxyNG2SdSDHrv3bZQDWH18OhTWkcmSF0M
+Bxcw3w8KMjr2v69ro5cyZztymEXi5RemRx+oPZGKIZ9N5T+26TaOltH7h8eR
+Mu4H03Lp0k4BRsjpFNUBL3HsAuMIemNf4369g+szlpuzjNE1KQhQzZbh87AU
+T7KAKygwz0EpOWpx2RHtshDy/bZ1EC8Ia4qDAebameIqCU929OmY1uI=
+=3iIr
+-----END PGP MESSAGE-----`;
+
+export default () => describe('Forwarding', function() {
+  it('can decrypt forwarded ciphertext', async function() {
+    const charlieKey = await openpgp.readKey({ armoredKey: charlieKeyArmored });
+    const msg = await openpgp.readMessage({ armoredMessage: fwdCiphertextArmored });
+    const result = await openpgp.decrypt({ decryptionKeys: charlieKey, message: msg });
+
+    expect(result).to.exist;
+    expect(result.data).to.equal('Hello Bob, hello world');
+  });
+});

test/general/index.js

@@ -4,6 +4,7 @@ import testArmor from './armor.js';
 import testPacket from './packet.js';
 import testSignature from './signature.js';
 import testKey from './key.js';
+import testForwarding from './forwarding.js';
 import testOpenPGP from './openpgp.js';
 import testConfig from './config.js';
 import testOID from './oid.js';
@@ -20,6 +21,7 @@ export default () => describe('General', function () {
   testPacket();
   testSignature();
   testKey();
+  testForwarding();
   testOpenPGP();
   testConfig();
   testOID();