This is a stream cipher built using the same pseudo-random number generator as RC4, the most widely used stream cipher in the world. RC4 was created by Ronald Rivest of RSA Security. NQARC4 (Not Quite Allegedly Rivest Cipher Four) is essentially a version of RC4 (or ARC4) ported to Scratch. The main change is the replacement of XOR with addition and subtraction modulo 256. I see absolutely no reason why NQARC4 should be any less secure than RC4, and since RC4 is very secure (provided the first few bytes of the keystream are discarded), then you should feel confident using NQARC4 for any encryption you might need in Scratch. But of course, I am not liable for any bad thing that happens as a direct or indirect result of this cipher in any way.
