challenge: do challenge 20

2 files changed, 209 insertions, 0 deletions

diff --git a/challenge/c20.go b/challenge/c20.go
new file mode 100644
index 0000000..337e958
--- /dev/null
+++ b/challenge/c20.go
@@ -0,0 +1,207 @@
+// Copyright © 2021 rsiddharth <s@ricketyspace.net>
+// SPDX-License-Identifier: ISC
+
+package challenge
+
+import (
+	"fmt"
+
+	"ricketyspace.net/cryptopals/lib"
+)
+
+func C20() {
+	texts := []string{
+		"SSdtIHJhdGVkICJSIi4uLnRoaXMgaXMgYSB3YXJuaW5nLCB5YSBiZXR0ZXIgdm9pZCAvIFBvZXRzIGFyZSBwYXJhbm9pZCwgREoncyBELXN0cm95ZWQ=",
+		"Q3V6IEkgY2FtZSBiYWNrIHRvIGF0dGFjayBvdGhlcnMgaW4gc3BpdGUtIC8gU3RyaWtlIGxpa2UgbGlnaHRuaW4nLCBJdCdzIHF1aXRlIGZyaWdodGVuaW4nIQ==",
+		"QnV0IGRvbid0IGJlIGFmcmFpZCBpbiB0aGUgZGFyaywgaW4gYSBwYXJrIC8gTm90IGEgc2NyZWFtIG9yIGEgY3J5LCBvciBhIGJhcmssIG1vcmUgbGlrZSBhIHNwYXJrOw==",
+		"WWEgdHJlbWJsZSBsaWtlIGEgYWxjb2hvbGljLCBtdXNjbGVzIHRpZ2h0ZW4gdXAgLyBXaGF0J3MgdGhhdCwgbGlnaHRlbiB1cCEgWW91IHNlZSBhIHNpZ2h0IGJ1dA==",
+		"U3VkZGVubHkgeW91IGZlZWwgbGlrZSB5b3VyIGluIGEgaG9ycm9yIGZsaWNrIC8gWW91IGdyYWIgeW91ciBoZWFydCB0aGVuIHdpc2ggZm9yIHRvbW9ycm93IHF1aWNrIQ==",
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+		"VGhpcyBpcyBvZmYgbGltaXRzLCBzbyB5b3VyIHZpc2lvbnMgYXJlIGJsdXJyeSAvIEFsbCB5YSBzZWUgaXMgdGhlIG1ldGVycyBhdCBhIHZvbHVtZQ==",
+		"VGVycm9yIGluIHRoZSBzdHlsZXMsIG5ldmVyIGVycm9yLWZpbGVzIC8gSW5kZWVkIEknbSBrbm93bi15b3VyIGV4aWxlZCE=",
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+		"U29vbiB0aGUgbHlyaWNhbCBmb3JtYXQgaXMgc3VwZXJpb3IgLyBGYWNlcyBvZiBkZWF0aCByZW1haW4=",
+		"TUMncyBkZWNheWluZywgY3V6IHRoZXkgbmV2ZXIgc3RheWVkIC8gVGhlIHNjZW5lIG9mIGEgY3JpbWUgZXZlcnkgbmlnaHQgYXQgdGhlIHNob3c=",
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+		"Q3V6IHlvdXIgYWJvdXQgdG8gc2VlIGEgZGlzYXN0cm91cyBzaWdodCAvIEEgcGVyZm9ybWFuY2UgbmV2ZXIgYWdhaW4gcGVyZm9ybWVkIG9uIGEgbWljOg==",
+		"THlyaWNzIG9mIGZ1cnkhIEEgZmVhcmlmaWVkIGZyZWVzdHlsZSEgLyBUaGUgIlIiIGlzIGluIHRoZSBob3VzZS10b28gbXVjaCB0ZW5zaW9uIQ==",
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+		"WW91IHdhbnQgdG8gaGVhciBzb21lIHNvdW5kcyB0aGF0IG5vdCBvbmx5IHBvdW5kcyBidXQgcGxlYXNlIHlvdXIgZWFyZHJ1bXM7IC8gSSBzaXQgYmFjayBhbmQgb2JzZXJ2ZSB0aGUgd2hvbGUgc2NlbmVyeQ==",
+		"VGhlbiBub25jaGFsYW50bHkgdGVsbCB5b3Ugd2hhdCBpdCBtZWFuIHRvIG1lIC8gU3RyaWN0bHkgYnVzaW5lc3MgSSdtIHF1aWNrbHkgaW4gdGhpcyBtb29k",
+		"QW5kIEkgZG9uJ3QgY2FyZSBpZiB0aGUgd2hvbGUgY3Jvd2QncyBhIHdpdG5lc3MhIC8gSSdtIGEgdGVhciB5b3UgYXBhcnQgYnV0IEknbSBhIHNwYXJlIHlvdSBhIGhlYXJ0",
+		"UHJvZ3JhbSBpbnRvIHRoZSBzcGVlZCBvZiB0aGUgcmh5bWUsIHByZXBhcmUgdG8gc3RhcnQgLyBSaHl0aG0ncyBvdXQgb2YgdGhlIHJhZGl1cywgaW5zYW5lIGFzIHRoZSBjcmF6aWVzdA==",
+		"TXVzaWNhbCBtYWRuZXNzIE1DIGV2ZXIgbWFkZSwgc2VlIGl0J3MgLyBOb3cgYW4gZW1lcmdlbmN5LCBvcGVuLWhlYXJ0IHN1cmdlcnk=",
+		"T3BlbiB5b3VyIG1pbmQsIHlvdSB3aWxsIGZpbmQgZXZlcnkgd29yZCdsbCBiZSAvIEZ1cmllciB0aGFuIGV2ZXIsIEkgcmVtYWluIHRoZSBmdXJ0dXJl",
+		"QmF0dGxlJ3MgdGVtcHRpbmcuLi53aGF0ZXZlciBzdWl0cyB5YSEgLyBGb3Igd29yZHMgdGhlIHNlbnRlbmNlLCB0aGVyZSdzIG5vIHJlc2VtYmxhbmNl",
+		"WW91IHRoaW5rIHlvdSdyZSBydWZmZXIsIHRoZW4gc3VmZmVyIHRoZSBjb25zZXF1ZW5jZXMhIC8gSSdtIG5ldmVyIGR5aW5nLXRlcnJpZnlpbmcgcmVzdWx0cw==",
+		"SSB3YWtlIHlhIHdpdGggaHVuZHJlZHMgb2YgdGhvdXNhbmRzIG9mIHZvbHRzIC8gTWljLXRvLW1vdXRoIHJlc3VzY2l0YXRpb24sIHJoeXRobSB3aXRoIHJhZGlhdGlvbg==",
+		"Tm92b2NhaW4gZWFzZSB0aGUgcGFpbiBpdCBtaWdodCBzYXZlIGhpbSAvIElmIG5vdCwgRXJpYyBCLidzIHRoZSBqdWRnZSwgdGhlIGNyb3dkJ3MgdGhlIGp1cnk=",
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+		"V2VsbCwgY2hlY2sgdGhpcyBvdXQsIHNpbmNlIE5vcmJ5IFdhbHRlcnMgaXMgb3VyIGFnZW5jeSwgcmlnaHQ/IC8gVHJ1ZQ==",
+		"S2FyYSBMZXdpcyBpcyBvdXIgYWdlbnQsIHdvcmQgdXAgLyBaYWtpYSBhbmQgNHRoIGFuZCBCcm9hZHdheSBpcyBvdXIgcmVjb3JkIGNvbXBhbnksIGluZGVlZA==",
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+		"Q2hlY2sgdGhpcyBvdXQsIHNpbmNlIHdlIHRhbGtpbmcgb3ZlciAvIFRoaXMgZGVmIGJlYXQgcmlnaHQgaGVyZSB0aGF0IEkgcHV0IHRvZ2V0aGVy",
+		"SSB3YW5uYSBoZWFyIHNvbWUgb2YgdGhlbSBkZWYgcmh5bWVzLCB5b3Uga25vdyB3aGF0IEknbSBzYXlpbic/IC8gQW5kIHRvZ2V0aGVyLCB3ZSBjYW4gZ2V0IHBhaWQgaW4gZnVsbA==",
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+		"U28gSSBkaWcgaW50byBteSBwb2NrZXQsIGFsbCBteSBtb25leSBpcyBzcGVudCAvIFNvIEkgZGlnIGRlZXBlciBidXQgc3RpbGwgY29taW4nIHVwIHdpdGggbGludA==",
+		"U28gSSBzdGFydCBteSBtaXNzaW9uLCBsZWF2ZSBteSByZXNpZGVuY2UgLyBUaGlua2luJyBob3cgY291bGQgSSBnZXQgc29tZSBkZWFkIHByZXNpZGVudHM=",
+		"SSBuZWVkIG1vbmV5LCBJIHVzZWQgdG8gYmUgYSBzdGljay11cCBraWQgLyBTbyBJIHRoaW5rIG9mIGFsbCB0aGUgZGV2aW91cyB0aGluZ3MgSSBkaWQ=",
+		"SSB1c2VkIHRvIHJvbGwgdXAsIHRoaXMgaXMgYSBob2xkIHVwLCBhaW4ndCBudXRoaW4nIGZ1bm55IC8gU3RvcCBzbWlsaW5nLCBiZSBzdGlsbCwgZG9uJ3QgbnV0aGluJyBtb3ZlIGJ1dCB0aGUgbW9uZXk=",
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+		"QW5kIGNvdW50IG91ciBtb25leSAvIFlvLCB3ZWxsIGNoZWNrIHRoaXMgb3V0LCB5byBFbGk=",
+		"VHVybiBkb3duIHRoZSBiYXNzIGRvd24gLyBBbmQgbGV0IHRoZSBiZWF0IGp1c3Qga2VlcCBvbiByb2NraW4n",
+		"QW5kIHdlIG91dHRhIGhlcmUgLyBZbywgd2hhdCBoYXBwZW5lZCB0byBwZWFjZT8gLyBQZWFjZQ==",
+	}
+	findKey := func(block []byte) byte {
+		var k byte
+		var s int
+
+		s = 0
+		for i := byte(0); i < 255; i++ {
+			ks := lib.FillBytes(i, len(block))
+			xs := lib.FixedXORBytes(block, ks)
+
+			score := lib.AlphaPunchScore(xs)
+			if score > s {
+				s = score
+				k = i
+			}
+		}
+		return k
+	}
+	// 'bs' is the data to decrypt.
+	// 'ks' is the key size.
+	crack := func(bs []byte, ks int) ([]byte, []byte) {
+		blocks := lib.BreakIntoBlocks(bs, ks)
+		blocks = lib.TransposeBlocks(blocks, ks)
+
+		key := make([]byte, 0)
+		for i := 0; i < len(blocks); i++ {
+			k := findKey(blocks[i])
+
+			key = append(key, k)
+		}
+		return key, lib.RepeatingXOR(bs, key)
+	}
+
+	// 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
+		}
+	}
+	// Find the shortest cipher. This cipher's length will
+	// become the keys size for the repeating XOR.
+	keySize := 2000
+	for _, cipher := range ciphers {
+		if len(cipher) < keySize {
+			keySize = len(cipher)
+		}
+	}
+	// Make a cipher stream.
+	cipherStream := make([]byte, 0)
+	for _, cipher := range ciphers {
+		cipherStream = append(cipherStream, cipher[0:keySize]...)
+	}
+	// Crack and barf text stream.
+	_, textStream := crack(cipherStream, keySize)
+	for i, b := range textStream {
+		if i > 0 && i%keySize == 0 {
+			fmt.Printf("\n")
+		}
+		fmt.Printf("%s", string(b))
+	}
+	fmt.Printf("\n")
+}
+
+// Output:
+// I'm ratbd "R"...this is a warning, ya better void / P
+// Cuz I cfme back to attack others in spite- / Strike l
+// But don t be afraid in the dark, in a park / Not a sc
+// Ya tremele like a alcoholic, muscles tighten up / Wha
+// Suddenl~ you feel like your in a horror flick / You g
+// Music's'the clue, when I come your warned / Apocalyps
+// Haven't'you ever heard of a MC-murderer? / This is th
+// Death wnsh, so come on, step to this / Hysterical ide
+// Friday she thirteenth, walking down Elm Street / You
+// This is'off limits, so your visions are blurry / All
+// Terror nn the styles, never error-files / Indeed I'm
+// For thote that oppose to be level or next to this / I
+// Worse toan a nightmare, you don't have to sleep a win
+// Flashbadks interfere, ya start to hear: / The R-A-K-I
+// Then thb beat is hysterical / That makes Eric go get
+// Soon thb lyrical format is superior / Faces of death
+// MC's dedaying, cuz they never stayed / The scene of a
+// The fieid of a rhyme on the mic that you know / It's
+// Melodiet-unmakable, pattern-unescapable / A horn if w
+// I bless'the child, the earth, the gods and bomb the r
+// Hazardors to your health so be friendly / A matter of
+// Shake 'sill your clear, make it disappear, make the n
+// If not,'my soul'll release! / The scene is recreated,
+// Cuz youu about to see a disastrous sight / A performa
+// Lyrics hf fury! A fearified freestyle! / The "R" is i
+// Make suue the system's loud when I mention / Phrases
+// You wans to hear some sounds that not only pounds but
+// Then noichalantly tell you what it mean to me / Stric
+// And I dhn't care if the whole crowd's a witness! / I'
+// Program'into the speed of the rhyme, prepare to start
+// Musical'madness MC ever made, see it's / Now an emerg
+// Open yorr mind, you will find every word'll be / Furi
+// Battle't tempting...whatever suits ya! / For words th
+// You thiik you're ruffer, then suffer the consequences
+// I wake ~a with hundreds of thousands of volts / Mic-t
+// Novocaii ease the pain it might save him / If not, Er
+// Yo Rakij, what's up? / Yo, I'm doing the knowledge, E
+// Well, coeck this out, since Norby Walters is our agen
+// Kara Lepis is our agent, word up / Zakia and 4th and
+// Okay, sh who we rollin' with then? We rollin' with Ru
+// Check tois out, since we talking over / This def beat
+// I wanna'hear some of them def rhymes, you know what I
+// Thinkin  of a master plan / 'Cuz ain't nuthin' but sw
+// So I di` into my pocket, all my money is spent / So I
+// So I stfrt my mission, leave my residence / Thinkin'
+// I need joney, I used to be a stick-up kid / So I thin
+// I used so roll up, this is a hold up, ain't nuthin' f
+// But now'I learned to earn 'cuz I'm righteous / I feel
+// Search aor a nine to five, if I strive / Then maybe I
+// So I wakk up the street whistlin' this / Feelin' out
+// A pen aid a paper, a stereo, a tape of / Me and Eric
+// Fish, woich is my favorite dish / But without no mone
+// 'Cuz I con't like to dream about gettin' paid / So I
+// So now so test to see if I got pull / Hit the studio,
+// Rakim, dheck this out, yo / You go to your girl house
+// 'Cause jy girl is definitely mad / 'Cause it took us
+// Yo, I hbar what you're saying / So let's just pump th
+// And couit our money / Yo, well check this out, yo Eli
+// Turn dopn the bass down / And let the beat just keep
+// And we hutta here / Yo, what happened to peace? / Pea
diff --git a/cryptopals.go b/cryptopals.go
index 4448d7e..103bfbb 100644
--- a/cryptopals.go
+++ b/cryptopals.go
@@ -57,5 +57,7 @@ func main() {
 		challenge.C18()
 	case 19:
 		challenge.C19()
+	case 20:
+		challenge.C20()
 	}
 }