challenge9.cpp

/* 
Implement PKCS#7 padding

A block cipher transforms a fixed-sized block (usually 8 or 16 bytes) of plaintext into ciphertext. But we almost never want to transform a single block; we encrypt irregularly-sized messages.

One way we account for irregularly-sized messages is by padding, creating a plaintext that is an even multiple of the blocksize. The most popular padding scheme is called PKCS#7.

So: pad any block to a specific block length, by appending the number of bytes of padding to the end of the block. For instance,

"YELLOW SUBMARINE"

... padded to 20 bytes would be:

"YELLOW SUBMARINE\x04\x04\x04\x04"
*/

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

std::string challenge9() {
	const std::string plaintext = "YELLOW SUBMARINE";

	std::string paddedtext = padPKCS7(plaintext, 20);

	return formatAsPrintable(paddedtext);
}