General

This category tests your skills in fundamental areas for understanding modern cryptography. These include data encoding, the XOR operator, and basic modular arithmetic. You may know this stuff already, but you can still gain points and have fun completing these challenges! It may be possible to solve these challenges using online converters and tools, however it will pay off later if you solve them in a programming language and learn how to do it that way instead. Of these, we suggest Python 3 (see the FAQ).

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Encoding

Challenge	Points	Solves
ASCII	5	25547
Hex	5	24481
Base64	10	21739
Bytes and Big Integers	10	17798

XOR

Challenge	Points	Solves
XOR Starter	10	14879
XOR Properties	15	12165
Favourite byte	20	12009
You either know, XOR you don't	30	10368

Mathematics

Challenge	Points	Solves
Greatest Common Divisor	15	10720