Method Crypto.Substitution()->set_key()
- Method set_key
 this_programset_key(mapping(string:string|array(string))key)- Description
 Sets the encryption and decryption key. The decryption key is derived from the encryption
keyby reversing the mapping. If one index maps to an array of strings, one element from the array will be chosen at random in such substitution.- Throws
 An error is thrown if the encryption key can not be made reversible.