According to its structure I'd say that this is SEAL (<span>Software-Optimized Encryption Algorithm). It's difficult to describe how it works, because this kind of ciphers is very tricky. This algorithm uses 160 bit key and it uses 3 tables (R, S, T) to encode and decode.
I'll attach the image where you can see a process of creating a pseudo-random function:
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I'll attach the image where you can see a process of creating a pseudo-random function:
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