path: root/challenge/c15.go

// Copyright © 2021 siddharth ravikumar <s@ricketyspace.net>
// SPDX-License-Identifier: ISC

package challenge

import (
	"fmt"

	"ricketyspace.net/cryptopals/lib"
)

func C15() {
	ice := lib.StrToBytes("ICE ICE BABY")
	fmt.Printf("ice: %v\n", ice)

	padded_ice := lib.Pkcs7Padding(ice, 16)
	fmt.Printf("ice padded: %v\n", padded_ice)

	unpadded_ice, _ := lib.Pkcs7PaddingUndo(padded_ice)
	for i := 0; i < len(ice); i++ {
		if ice[i] != unpadded_ice[i] {
			panic("padding undo failed!")
		}
	}
	fmt.Printf("unpadded ice: %v\n", unpadded_ice)

	// Will fail.
	bad_ice := append(ice, []byte{5, 5, 5, 5}...)
	fmt.Printf("bad ice: %v\n", bad_ice)
	_, err := lib.Pkcs7PaddingUndo(bad_ice)
	if err != nil {
		fmt.Printf("bad ice upadding failed: %s\n", err.Error())
	}
	// Will fail.
	evil_ice := append(ice, []byte{1, 2, 3, 4}...)
	fmt.Printf("evil ice: %v\n", evil_ice)
	_, err = lib.Pkcs7PaddingUndo(evil_ice)
	if err != nil {
		fmt.Printf("evil ice upadding failed: %s\n", err.Error())
	}
}

// Output:
// ice: [73 67 69 32 73 67 69 32 66 65 66 89]
// ice padded: [73 67 69 32 73 67 69 32 66 65 66 89 4 4 4 4]
// unpadded ice: [73 67 69 32 73 67 69 32 66 65 66 89]
// bad ice: [73 67 69 32 73 67 69 32 66 65 66 89 5 5 5 5]
// bad ice upadding failed: input is not pkcs#7 padded
// evil ice: [73 67 69 32 73 67 69 32 66 65 66 89 1 2 3 4]
// evil ice upadding failed: input is not pkcs#7 padded