add static decrypt and encrypt methods

Pilz.Cryptography/AESStringCrypter.cs

@@ -68,11 +68,23 @@ namespace Pilz.Cryptography
             return DecryptStringFromBytes_Aes(Convert.FromBase64String(encryptedValue), GetKey(), GetIV());
         }
 
+        public static string Decrypt(string encryptedValue, string key, string iv)
+        {
+            var crypter = new AESStringCrypter(key, iv);
+            return crypter.Decrypt(encryptedValue);
+        }
+
         public string Encrypt(string plainValue)
         {
             return Convert.ToBase64String(EncryptStringToBytes_Aes(plainValue, GetKey(), GetIV()));
         }
 
+        public static string Encrypt(string plainValue, string key, string iv)
+        {
+            var crypter = new AESStringCrypter(key, iv);
+            return crypter.Encrypt(plainValue);
+        }
+
         private byte[] GetKey(bool createIfFail = false)
         {
             byte[] keyToUse;