Add getExpirationTime method to Key and SubKey

src/key.js

@@ -440,12 +440,42 @@ Key.prototype.verifyPrimaryKey = function() {
   }
   // check V4 expiration time
   if (this.primaryKey.version == 4 && primaryUser.selfCertificate.keyNeverExpires === false &&
-    Date.now() > (primaryUser.selfCertificate.created.getTime() + primaryUser.selfCertificate.keyExpirationTime*1000)) {
+    Date.now() > (this.primaryKey.created.getTime() + primaryUser.selfCertificate.keyExpirationTime*1000)) {
     return enums.keyStatus.expired;
   }
   return enums.keyStatus.valid;
 };
 
+/**
+ * Returns the expiration time of the primary key or null if key does not expire
+ * @return {Date|null}
+ */
+Key.prototype.getExpirationTime = function() {
+  if (this.primaryKey.version == 3) {
+    return getExpirationTime(this.primaryKey);
+  }
+  if (this.primaryKey.version == 4) {
+    var primaryUser = this.getPrimaryUser();
+    if (!primaryUser) {
+      return null;
+    }
+    return getExpirationTime(this.primaryKey, primaryUser.selfCertificate);
+  }
+};
+
+
+function getExpirationTime(keyPacket, selfCertificate) {
+  // check V3 expiration time
+  if (keyPacket.version == 3 && keyPacket.expirationTimeV3 !== 0) {
+    return new Date(keyPacket.created.getTime() + keyPacket.expirationTimeV3*24*3600*1000);
+  }
+  // check V4 expiration time
+  if (this.primaryKey.version == 4 && selfCertificate.keyNeverExpires === false) {
+    return new Date(keyPacket.created.getTime() + selfCertificate.keyExpirationTime*1000);
+  }
+  return null;
+};
+
 /**
  * Returns primary user and most significant (latest valid) self signature
  * - if multiple users are marked as primary users returns the one with the latest self signature
@@ -668,6 +698,14 @@ SubKey.prototype.verify = function(primaryKey) {
   return enums.keyStatus.valid;
 };
 
+/**
+ * Returns the expiration time of the subkey or null if key does not expire
+ * @return {Date|null}
+ */
+SubKey.prototype.getExpirationTime = function() {
+  return getExpirationTime(this.subKey, this.bindingSignature);
+};
+
 /**
  * Reads an OpenPGP armored text and returns one or multiple key objects
  * @param {String} armoredText text to be parsed