My friend made a bet with me that I couldn't break his custom encryption or something. I really have no idea what Im doing with this. Any help?

Answer 1

Whether one particular encryption algorithm can be broken with ease or only with a huge effort depends on the strength of the cipher.

A simple encryption algorithm such as ROT-x or XOR-n are not very hard to break, however, present-day industry-standard encryption algorithms such as many forms of AES are very hard to break. Those simple algorithms are broken by application of logic and observation; one example are common picture puzzles where shapes are used to represent different digits, and combinations of shapes represent different mathematical equations.

No encryption algorithm has been proven to be unbreakable, but some have been proven to be virtually impossible to break by brute force. Brute force attacks are done by trying out huge numbers of keys, for example. The impossibility to break a cipher in this manner is deducted from statistic probabilities about the number of attempts one would need to make in order to find the correct key.

However, some particular algorithms have known weaknesses which can be exploited. For example, a weak algorithm might produce the same output from the same input every time, or produce different output with predictable differences.

Many encryption schemes are also exploited by taking advantage of human weakness, such as trying out a list of well-known passwords, etc.

Other methods of breaking an encryption scheme involve a known plaintext content: knowing the data, or part of the data, which ought to be within the encrypted data, can allow for conclusions about the encryption algorithm. In WWII, the German Enigma encryption engine was famously broken based on such knowledge.

Therefore, an important step about an encryption code is to collect as much information about the code, its application, and its inventor, as possible. These will often give clues about the nature of the algorithm, or about particular limitations, which would then lead to planning the next steps.