Hello! The following questions appeared:

  1. Why is a true random sequence necessary to use a cipher? Why not use pseudo-random sequences?
  2. Is the sequence of characters invented by a person ( for example, the sequence anaskbbhbfyj , invented by me just now ) truly random?
  • one
    During the Second World War for the generation of ciproblocks there were special people who sat for days at a time and pulled balls with numbers. At the same time, Langley's cryptanalysts were not happy with the randomness of this data, because people sometimes were lazy and tried not to draw balls out to fill in notebooks ... - Mike

3 answers 3

  1. The pseudo-random sequence has regularities.
    Proof of the impossibility to decrypt the Verman cipher: if we iterate through all possible keys, we will receive all possible messages. We have nothing to choose from.
    But if there is a pattern, then we can choose.

  2. No sequence invented by man is random.
    There is a frequency algorithm of the game based on the last few values ​​- it always wins against a person during a long game.

    A pseudo-random sequence is the value of some recurrent function with some initial value. Accordingly, knowing this value (usually 32 or 64 bits), you can re-generate the entire key sequence and read the message.

    • It should be noted that the number of internal states of the generator can be much greater than the number of seeders. For example for the Mersenne Twister it is. - Vladimir Martyanov

    The number of internal PRNG states is much lower than the number of possible keys generated by it. Therefore, it is easier to search for the desired state of the PRNG than the key.

    "Anaskbbhbfyj" is difficult to assess, you need to know the alphabet. But it seems to me that the alphabet is "az" and then it is impossible to speak about chance: there will be about 6 letters "b" for 24 characters.

    • With the first question figured out, thanks. But I didn’t quite understand what you meant by the second question. - eanmos
    • @Eanmos Write a generator of "random" lines and see how often you will have 3 identical letters per line of 12 characters. - Vladimir Martyanov
    • @ Vladimir Martiyan, maybe this will happen not often, but this is not a criterion of chance (correct me if I'm wrong). In a random sequence can be anything, although 50 letters a in a row. - eanmos
    • @Eanmos The point is probability. Such an imbalance almost certainly indicates that either there was no generator at all, or it had features. - Vladimir Martyanov
    • And yet, is it possible to consider a sequence of numbers or characters generated by a person truly random? - eanmos