AES-CBC exploit

main.go

package main

import (
        "encoding/hex"
        "fmt"
        "os"

        "github.com/gdamore/encoding"
)

func main() {
        if os.Args[1] == "get-diff" {
                xor(toASCII(os.Args[2]), toASCII(os.Args[3]))
        } else if os.Args[1] == "apply-diff" {
                iv, _ := hex.DecodeString(os.Args[2])
                diff, _ := hex.DecodeString(os.Args[3])
                xor(iv, diff)
        }
}

func toASCII(plaintext string) []byte {
        encoder := encoding.ASCII.NewEncoder()
        result, _ := encoder.Bytes([]byte(plaintext))
        return result
}

func xor(plaintext, malicious []byte) {
        output := make([]byte, len(plaintext))
        for i := 0; i < len(plaintext); i++ {
                output[i] = plaintext[i] ^ malicious[i]
        }

        fmt.Printf("%x\n", output)
}