challenge5.cpp

/*
Implement repeating-key XOR

Here is the opening stanza of an important work of the English language:

Burning 'em, if you ain't quick and nimble
I go crazy when I hear a cymbal

Encrypt it, under the key "ICE", using repeating-key XOR.

In repeating-key XOR, you'll sequentially apply each byte of the key; the first byte of plaintext will be XOR'd against I, the next C, the next E, then I again for the 4th byte, and so on.

It should come out to:

0b3637272a2b2e63622c2e69692a23693a2a3c6324202d623d63343c2a26226324272765272
a282b2f20430a652e2c652a3124333a653e2b2027630c692b20283165286326302e27282f

Encrypt a bunch of stuff using your repeating-key XOR function. Encrypt your mail. Encrypt your password file. Your .sig file. Get a feel for it. I promise, we aren't wasting your time with this.

*/

#include "challenges.h"
#include "encoding_utils.h"

std::string challenge5() {
	std::string plaintext =
		"Burning 'em, if you ain't quick and nimble\n"
		"I go crazy when I hear a cymbal";

	std::string key = "ICE";

	std::string ciphertext = repeatingXor(plaintext, key);

	return textToHex(ciphertext);
}