/* Encrypt a set of strings in AES CTR mode using the same nonce
* Decrypt the resulting ciphertexts without the key or stream
*/
func c20() (actual, expected Result) {
input, _ := ioutil.ReadFile("input/20.txt")
output, _ := utils.ReadAndStripFile("output/20.txt")
expected = string(output)
strs := strings.Split(string(input), "\n")
n := len(strs)
strs = strs[:n-2]
key := crypto.NewAesKey()
nonce := uint64(0)
// Decode strings and find length of the shortest string
length := 1000
plaintexts := make([][]byte, len(strs))
for i, str := range strs {
decoded, _ := base64.StdEncoding.DecodeString(str)
if len(decoded) < length {
length = len(decoded)
}
plaintexts[i] = decoded
}
var concat []byte
for i, str := range plaintexts {
// Truncate each string to common length
plaintexts[i] = str[:length]
stream, err := crypto.Ctr(nonce, key)
if err != nil {
log.Println(err)
}
// Concatenate the ciphertexts
ciphertext := make([]byte, length)
stream.XORKeyStream(ciphertext, plaintexts[i])
concat = append(concat, ciphertext...)
}
l := []int{length}
plaintext, err := crypto.BreakXorRepeating(concat, l)
if err != nil {
log.Println(err)
}
return string(utils.Strip(plaintext)), expected
}
// Break repeating-key XOR
func c6() (actual, expected Result) {
input, _ := ioutil.ReadFile("input/6.txt")
output, _ := utils.ReadAndStripFile("output/6.txt")
expected = string(output)
inputStr := string(input)
ciphertext, err := base64.StdEncoding.DecodeString(inputStr)
if err != nil {
log.Fatal(err)
}
// Find the 3 most likely keysizes in the range 2-40
keysizes, err := crypto.FindKeysizes(ciphertext, 3, 2, 40)
if err != nil {
log.Fatal(err)
}
plaintext, err := crypto.BreakXorRepeating(ciphertext, keysizes)
if err != nil {
log.Fatal(err)
}
return string(utils.Strip(plaintext)), expected
}