Fix serializing GNU stripped-keys

src/packet/secret_key.js

@@ -224,7 +224,7 @@ SecretKey.prototype.write = function () {
   // - [Optional] If secret data is encrypted (string-to-key usage octet
   //   not zero), an Initial Vector (IV) of the same length as the
   //   cipher's block size.
-  if (this.s2k_usage) {
+  if (this.s2k_usage && this.s2k.type !== 'gnu-dummy') {
     optionalFieldsArr.push(...this.iv);
   }
 
@@ -385,6 +385,11 @@ SecretKey.prototype.generate = async function (bits, curve) {
  * Clear private params, return to initial state
  */
 SecretKey.prototype.clearPrivateParams = function () {
+  if (this.s2k && this.s2k.type === 'gnu-dummy') {
+    this.isEncrypted = true;
+    return;
+  }
+
   if (!this.keyMaterial) {
     throw new Error('If secret key is not encrypted, clearing private params is irreversible.');
   }

src/type/s2k.js

@@ -117,6 +117,10 @@ S2K.prototype.read = function (bytes) {
  * @returns {Uint8Array} binary representation of s2k
  */
 S2K.prototype.write = function () {
+  if (this.type === 'gnu-dummy') {
+    return new Uint8Array([101, 0, ...util.str_to_Uint8Array('GNU'), 1]);
+  }
+
   const arr = [new Uint8Array([enums.write(enums.s2k, this.type), enums.write(enums.hash, this.algorithm)])];
 
   switch (this.type) {