How to crack unknown 8-bit encryption algorithm? Can anyone tell me how to crack the encryption of 8 bit algorithm, when you have some clue that CBC mode is used, but the algorithm is secret. You also have some encrypted data (chosen plain text), which belong from 0 to 256.

How can you crack the encryption in that case?
Assuming that there are no collisions and there exists a 1 to 1 bijection between input and output, you could construct and store a table of assignments on a single round of encryption for all 256 possible bytes regardless of the key size. From there you can extend this to subsequent rounds by simply XORing the result of the previous round to the next 8 bit block, and plugging this result into your table.