If I transform natural plaintext by:
- making each letter two decimal digits, considering the whole as a decimal number;
- multiplying by the key (some integer constant), giving the ciphertext;
would frequency analysis still work?
Plaintext: G o l d U n d e r S e a Number: 071512042114040518190501 x 911 Ciphertext: 65147470365890912071546411
To get the text again simply divide by 911. Conversion of the ciphertext to letters could be added somehow.
Assuming frequency analysis is not an option, how would one break this?
Note: The question has been improved by the OP, then re-tagged and further edited for clarity. I now wish I could rescind my own vote to close it.