I am trying to understand how an attacker knows when he has successfully decrypted a ciphertext for an assignment. As such, some pointers/hints for the following questions would be greatly appreciated.
If you double encrypt secret data with two different algorithms. How does the attacker know if he already broke the 'first layer' of encryption?
Is it possible to determine the encryption algorithm used by analyzing the cipher text?
If you find out what algorithm was used does it give you the necessary information to know when you successfully broke the 'first layer'?
Considering the above, what difference would it make if the attacker knows the open-source program or the (public available) algorithms used to protect the data?