Beginner crypto challenges: length is not the algorithm

Measure before you name

Count the characters. Note the alphabet: only digits and a through f, or letters with padding, or ordinary words. Those notes describe the file. They do not say which method produced it. Two methods can emit strings of the same length.

A label in the challenge text such as “cipher” is the author’s word. It is not a proof of the method. Copy the label as a label.

What you do not conclude

Do not title the note with an algorithm because the string is 32 bytes, 64 hex characters, or a round number of letters. Do not run a decoding step you cannot explain. If you later find a reason, write the reason next to the name.

This page does not recover a key and does not turn the string into a flag. The beginner step is classification, and classification can end as “not yet classified.”

What to write down

File the filename, the length, the alphabet, and the author’s label if there is one. File the method only when you can point at a reason in the challenge text or in a check you can repeat. Otherwise write “method not classified.”

Lab: sixty-four hex characters and no name

cipher.txt from a practice bundle is 64 characters, digits and a through f only. The challenge title says “hidden.” A draft names it AES because 64 hex characters is 32 bytes, and starts a write-up titled with that algorithm.

The note says length 64, alphabet hex, author label “hidden,” method not classified. Thirty-two bytes is arithmetic, not an identification. The write-up title stays unclassified until a later check gives a reason you can cite.

file: cipher.txt
length: 64 characters
alphabet: 0-9 and a-f
author label: hidden
bytes if this is hex: 32
method: not classified
not: AES because of the length