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// Copyright © 2021 rsiddharth <s@ricketyspace.net>
// SPDX-License-Identifier: ISC
package challenge
import (
"fmt"
"ricketyspace.net/cryptopals/lib"
)
func C19() {
texts := []string{
"SSBoYXZlIG1ldCB0aGVtIGF0IGNsb3NlIG9mIGRheQ==",
"Q29taW5nIHdpdGggdml2aWQgZmFjZXM=",
"RnJvbSBjb3VudGVyIG9yIGRlc2sgYW1vbmcgZ3JleQ==",
"RWlnaHRlZW50aC1jZW50dXJ5IGhvdXNlcy4=",
"SSBoYXZlIHBhc3NlZCB3aXRoIGEgbm9kIG9mIHRoZSBoZWFk",
"T3IgcG9saXRlIG1lYW5pbmdsZXNzIHdvcmRzLA==",
"T3IgaGF2ZSBsaW5nZXJlZCBhd2hpbGUgYW5kIHNhaWQ=",
"UG9saXRlIG1lYW5pbmdsZXNzIHdvcmRzLA==",
"QW5kIHRob3VnaHQgYmVmb3JlIEkgaGFkIGRvbmU=",
"T2YgYSBtb2NraW5nIHRhbGUgb3IgYSBnaWJl",
"VG8gcGxlYXNlIGEgY29tcGFuaW9u",
"QXJvdW5kIHRoZSBmaXJlIGF0IHRoZSBjbHViLA==",
"QmVpbmcgY2VydGFpbiB0aGF0IHRoZXkgYW5kIEk=",
"QnV0IGxpdmVkIHdoZXJlIG1vdGxleSBpcyB3b3JuOg==",
"QWxsIGNoYW5nZWQsIGNoYW5nZWQgdXR0ZXJseTo=",
"QSB0ZXJyaWJsZSBiZWF1dHkgaXMgYm9ybi4=",
"VGhhdCB3b21hbidzIGRheXMgd2VyZSBzcGVudA==",
"SW4gaWdub3JhbnQgZ29vZCB3aWxsLA==",
"SGVyIG5pZ2h0cyBpbiBhcmd1bWVudA==",
"VW50aWwgaGVyIHZvaWNlIGdyZXcgc2hyaWxsLg==",
"V2hhdCB2b2ljZSBtb3JlIHN3ZWV0IHRoYW4gaGVycw==",
"V2hlbiB5b3VuZyBhbmQgYmVhdXRpZnVsLA==",
"U2hlIHJvZGUgdG8gaGFycmllcnM/",
"VGhpcyBtYW4gaGFkIGtlcHQgYSBzY2hvb2w=",
"QW5kIHJvZGUgb3VyIHdpbmdlZCBob3JzZS4=",
"VGhpcyBvdGhlciBoaXMgaGVscGVyIGFuZCBmcmllbmQ=",
"V2FzIGNvbWluZyBpbnRvIGhpcyBmb3JjZTs=",
"SGUgbWlnaHQgaGF2ZSB3b24gZmFtZSBpbiB0aGUgZW5kLA==",
"U28gc2Vuc2l0aXZlIGhpcyBuYXR1cmUgc2VlbWVkLA==",
"U28gZGFyaW5nIGFuZCBzd2VldCBoaXMgdGhvdWdodC4=",
"VGhpcyBvdGhlciBtYW4gSSBoYWQgZHJlYW1lZA==",
"QSBkcnVua2VuLCB2YWluLWdsb3Jpb3VzIGxvdXQu",
"SGUgaGFkIGRvbmUgbW9zdCBiaXR0ZXIgd3Jvbmc=",
"VG8gc29tZSB3aG8gYXJlIG5lYXIgbXkgaGVhcnQs",
"WWV0IEkgbnVtYmVyIGhpbSBpbiB0aGUgc29uZzs=",
"SGUsIHRvbywgaGFzIHJlc2lnbmVkIGhpcyBwYXJ0",
"SW4gdGhlIGNhc3VhbCBjb21lZHk7",
"SGUsIHRvbywgaGFzIGJlZW4gY2hhbmdlZCBpbiBoaXMgdHVybiw=",
"VHJhbnNmb3JtZWQgdXR0ZXJseTo=",
"QSB0ZXJyaWJsZSBiZWF1dHkgaXMgYm9ybi4=",
}
// English alphabets ordered by frequency
// (https://mdickens.me/typing/letter_frequency.html)
ascii := []byte{
' ', 'e', 't', 'a', 'o', 'i', 'n', 's', 'r', 'h', 'l', 'd',
'c', 'u', 'm', 'f', 'g', 'p', 'y', 'w', 'b', ',', '.',
'v', 'k', '-', '"', '_', '\'', 'x', ')', '(', ';', '0', 'j',
'1', 'q', '=', '2', ':', 'z', '/', '*', '!', '?', '$', '3',
'5', '>', '{', '}', '4', '9', '[', ']', '8', '6', '7', '\\',
'+', '|', '&', '<', '%', '@', '#', '^', '`', '~',
}
// Key: ASCII character; Value: score
asciiScores := make(map[byte]int, 0)
for pos, a := range ascii {
asciiScores[a] = 255 - pos
// Also add the uppercase version of ascii
// character if it exists.
au := lib.ByteToUpper(a)
if a != au {
asciiScores[au] = 255 - pos
}
}
// Utility functions.
cipherStreamByteGroups := func(ciphers [][]byte) map[int][]byte {
kbg := make(map[int][]byte, 0)
for i := 0; i < len(ciphers); i++ {
for j := 0; j < len(ciphers[i]); j++ {
if _, ok := kbg[j]; !ok {
kbg[j] = make([]byte, 0)
}
kbg[j] = append(kbg[j], ciphers[i][j])
}
}
return kbg
}
crackOutputBlockByteForGroup := func(pos int, g []byte) byte {
po := make([][]byte, len(g)) // Potential Output block bytes
for i, c := range g {
po[i] = make([]byte, 0)
for _, a := range ascii {
o := c ^ a
po[i] = append(po[i], o)
// Also try the uppercase version of ascii
// character if it exists.
au := lib.ByteToUpper(a)
if a != au {
o := c ^ au
po[i] = append(po[i], o)
}
}
}
co := lib.BytesInCommon(po) // Common Output Block bytes.
if len(co) < 1 {
return 0 // NUL
}
if len(co) == 1 {
return co[0]
}
tob := byte(0) // The Output Block byte.
bscr := 0 // Best score.
for _, o := range co {
scr := 0
for _, c := range g {
p := c ^ o
if s, ok := asciiScores[p]; ok {
scr += s
}
if pos == 0 && lib.ByteIsUpper(p) {
scr += 1
}
}
if scr > bscr {
bscr = scr
tob = o
}
}
return tob
}
// Make ciphers from plain text data.
ciphers := make([][]byte, len(texts))
key, err := lib.RandomBytes(16)
if err != nil {
fmt.Printf("Error generating key %v", err)
return
}
nonce := uint64(lib.RandomInt(0, 10))
for i, b64 := range texts {
text := lib.Base64ToBytes(b64)
ciphers[i], err = lib.AESEncryptCTR(text, key, lib.AESGenCTRFunc(nonce))
if err != nil {
fmt.Printf("Error encrypting text:%d: %v", i, err)
return
}
}
// Group the cipher streams into groups by position of the cipher
// byte in the stream.
cbg := cipherStreamByteGroups(ciphers)
// Try get crack and get the output block stream.
obs := make(map[int]byte, 0) // Output Block Stream map.
for pos, cgrp := range cbg {
obs[pos] = crackOutputBlockByteForGroup(pos, cgrp)
}
// Decipher cipher using the output block stream.
for _, cipher := range ciphers {
for i, c := range cipher {
p := c ^ obs[i]
fmt.Printf("%c", p)
}
fmt.Printf("\n")
}
}
// Output:
// I have met them at close of day
// Coming with vivid faces
// From counter or desk among grey
// Eighteenth-century houses.
// I have passed with a nod of the heae
// Or polite meaningless words,
// Or have lingered awhile and said
// Polite meaningless words,
// And thought before I had done
// Of a mocking tale or a gibe
// To please a companion
// Around the fire at the club,
// Being certain that they and I
// But lived where motley is worn:
// All changed, changed utterly:
// A terrible beauty is born.
// That woman's days were spent
// In ignorant good will,
// Her nights in argument
// Until her voice grew shrill.
// What voice more sweet than hers
// When young and beautiful,
// She rode to harriers?
// This man had kept a school
// And rode our winged horse.
// This other his helper and friend
// Was coming into his force;
// He might have won fame in the end,
// So sensitive his nature seemed,
// So daring and sweet his thought.
// This other man I had dreamed
// A drunken, vain-glorious lout.
// He had done most bitter wrong
// To some who are near my heart,
// Yet I number him in the song;
// He, too, has resigned his part
// In the casual comedy;
// He, too, has been changed in his tus
// Transformed utterly:
// A terrible beauty is born.
// Stuff the program did not get correctly:
// 1. On the 5th line, 'heae' -> 'head'
// 2. On the 38th line, 'tus ' -> 'turn'
|
