Add config option to allow insecure decryption with RSA signing keys (#1148)

src/config/config.js

@@ -120,6 +120,14 @@ export default {
    * @property {Boolean} revocations_expire If true, expired revocation signatures are ignored
    */
   revocations_expire:       false,
+  /**
+   * Allow decryption using RSA keys without `encrypt` flag.
+   * This setting is potentially insecure, but it is needed to get around an old openpgpjs bug
+   * where key flags were ignored when selecting a key for encryption.
+   * @memberof module:config
+   * @property {Boolean} allow_insecure_decryption_with_signing_keys
+   */
+  allow_insecure_decryption_with_signing_keys: false,
 
   /**
    * @memberof module:config

src/key/helper.js

@@ -366,6 +366,12 @@ export function isValidDecryptionKeyPacket(signature) {
   if (!signature.verified) { // Sanity check
     throw new Error('Signature not verified');
   }
+
+  if (config.allow_insecure_decryption_with_signing_keys) {
+    // This is only relevant for RSA keys, all other signing ciphers cannot decrypt
+    return true;
+  }
+
   return !signature.keyFlags ||
     (signature.keyFlags[0] & enums.keyFlags.encrypt_communication) !== 0 ||
     (signature.keyFlags[0] & enums.keyFlags.encrypt_storage) !== 0;

test/general/key.js

@@ -1916,6 +1916,55 @@ vqBGKJzmO5q3cECw
 =X9kJ
 -----END PGP PRIVATE KEY BLOCK-----`;
 
+
+const rsaSignOnly = `-----BEGIN PGP PRIVATE KEY BLOCK-----
+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+=A9Ts
+-----END PGP PRIVATE KEY BLOCK-----
+`;
+
+const encryptedRsaSignOnly = `-----BEGIN PGP MESSAGE-----
+
+wcBMAwr9x5ZY6oZmAQf+Lxghg4keIFpEq8a65gFkIfW+chHTDPlfI8xnx6U9
+HdsICX3Oye5V0ToCVKkEWDxfN1yCfXiYalSNo7ScRZKR7C+j02/pC+FfR6AJ
+2cvdFoGIrLaXdjXXc/oXbsCCZA4C1DhQqpdORo2qGF0Q6Sm8659B0CfOgYSL
+fBfKQ5VJngUT5JG8Uek3YuXBufPNhzdmXLHyB2Y2CwKkldi2vo4YNAukDhrR
+2TojxdNoouhnMm+gloCE1n8huY1vw5F78/uiHen0tmHQ0dxtfk8cc1burgl/
+zUdJ3Sg6Eu+OC2ae5II63iB5fG+lCwZtfuepWnePDv8RDKNHCVP/LoBNpGOZ
+U9I6AUkZWdcsueib9ghKDDy+HbUbf2kCJWUnuyeOCKqQifDb8bsLmdQY4Wb6
+EBeLgD8oZHVsH3NLjPakPw==
+=STqy
+-----END PGP MESSAGE-----`
+
 function versionSpecificTests() {
   it('Preferences of generated key', function() {
     const testPref = function(key) {
@@ -2667,6 +2716,26 @@ describe('Key', function() {
     await expect(pubKey.getEncryptionKey()).to.be.rejectedWith('Could not find valid encryption key packet in key c076e634d32b498d');
   });
 
+  it('should not decrypt using a sign-only RSA key, unless explicitly configured', async function () {
+    const allowSigningKeyDecryption = openpgp.config.allow_insecure_decryption_with_signing_keys;
+    const { keys: [key] } = await openpgp.key.readArmored(rsaSignOnly);
+    try {
+      openpgp.config.allow_insecure_decryption_with_signing_keys = false;
+      await expect(openpgp.decrypt({
+        message: await openpgp.message.readArmored(encryptedRsaSignOnly),
+        privateKeys: key
+      })).to.be.rejectedWith(/Session key decryption failed/);
+
+      openpgp.config.allow_insecure_decryption_with_signing_keys = true;
+      await expect(openpgp.decrypt({
+        message: await openpgp.message.readArmored(encryptedRsaSignOnly),
+        privateKeys: key
+      })).to.be.fulfilled;
+    } finally {
+      openpgp.config.allow_insecure_decryption_with_signing_keys = allowSigningKeyDecryption;
+    }
+  });
+
   it('Method getExpirationTime V4 Key', async function() {
     const pubKey = (await openpgp.key.readArmored(twoKeys)).keys[1];
     expect(pubKey).to.exist;