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I found an algorithm described in my old math notes that I wanted to dive into further, but the name I noted is apparently completely wrong ("Bolson Adding"), so now I am trying to find the actual name of it. You have an array of digits 0-9 and add them up in pairs, starting with first+second, then third+fourth, etc., and create a new array from that. Results above 9 are subtracted 10, to keep it single digits. Next, you do the same, but with second+third, fourth+fifth, etc., finishing with last+first. You attach that array at the end of the first and get a new array the same size as the original (it must be an even amount of digits). You can then repeat the process on this new array, and so on and so on. You can always get from the original to the result, but you (supposedly!) cannot get from the result back to the original. Does anyone know the name of this?

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    $\begingroup$ Indeed one can not get back from the result to the original, because 10 originals match any given result; e.g. 0000, 1919, 2828, 3737, 4646, 5555, 6464, 7373, 8282, 9191 all yield 0000 if I get the system correctly. My reading is that this is a bad PRNG which key is the initial state. Any PRNG can be turned into a stream cipher. This one would not be secure, I'm afraid. $\endgroup$
    – fgrieu
    Sep 7, 2022 at 16:26

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Without a key or the ability to decrypt this isn't a cipher.

Possibly the second part of the string of digits could be a key, but in that case just performing modulo addition would result in the Vernam cipher and you would not need the whole construction.

If it were a hash then it is a terrible one, just start with a string of all zero digits to see why. The output would also not be compressed.

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  • $\begingroup$ Yeah, my old notes are horrible, that's why I wondered what this really is. It took me about 15 minutes to make a reverse engineering function, so what I wrote is clearly useless, but I wondered if there is more to it. Without knowing what I was writing about, however, I can't know if there is more.... $\endgroup$ Aug 8, 2022 at 14:47

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