This information doesn't vary much in messages. Armed with this information a smart cryptanalyst works backwards and deduces from the header information the key used to encrypt the file and then decrypts the remaining data. Asier's Response Asier's Technology defeats this method by encrypting the header of the file differently from the body. Given that language is predictable, with enough message traffic the frequency of certain letters and words becomes apparent. The letter frequency forms the mathematical basis for all statistical attacks.
Every cryptanalyst has access to character frequency tables for statistical analysis.
These tables differ by languages and can differ slightly by subject matter within a given language. Asier's Response Asier's unique methods do not represent the same character in the same manner twice within a message. In any repeated message, the content is encrypted differently each time. The chances of a character being represented the same way twice within a message are over 3.3 billion to one. In other words each character is represented more uniquely than a finger print.