frncscrlnd's writeups

Writeups from challenges and CTFs i take part in.

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“the cryptopals crypto challenges” are 8 sets of 10 cryptography-based challenges. I’ll try to cover them all in the following writeups.

Convert hex to base64

In this challenge we need to turn an hex string into a base64 encoded string:

The string:

49276d206b696c6c696e6720796f757220627261696e206c696b65206120706f69736f6e6f7573206d757368726f6f6d

Should produce:

SSdtIGtpbGxpbmcgeW91ciBicmFpbiBsaWtlIGEgcG9pc29ub3VzIG11c2hyb29t

In order to do so, we first need to decode the hex string into ASCII characters. We’ll do this with xxd, a tool that allows both creating a hexadecimal dump and converting an hexdump back into binary form.

The correct syntax will be:

xxd -r -p [hex_file] > [plaintext_file]

This will return:

I'm killing your brain like a poisonous mushroom.

We’ll then use base64 to encode the string.

base64 [plaintext_file] > [base64_file]

This will finally return

SSdtIGtpbGxpbmcgeW91ciBicmFpbiBsaWtlIGEgcG9pc29ub3VzIG11c2hyb29t