challenge: do challenge 25

1 files changed, 234 insertions, 0 deletions

diff --git a/challenge/c25.go b/challenge/c25.go
new file mode 100644
index 0000000..6c698fc
--- /dev/null
+++ b/challenge/c25.go
@@ -0,0 +1,234 @@
+// Copyright © 2021 rsiddharth <s@ricketyspace.net>
+// SPDX-License-Identifier: ISC
+
+package challenge
+
+import (
+	"fmt"
+
+	"ricketyspace.net/cryptopals/lib"
+)
+
+func C25() {
+	//
+	plain := lib.AESDecryptECB(
+		lib.Base64ToBytes(`CRIwqt4+szDbqkNY+I0qbDe3LQz0wiw0SuxBQtAM5TDdMbjCMD/venUDW9BL
+PEXODbk6a48oMbAY6DDZsuLbc0uR9cp9hQ0QQGATyyCESq2NSsvhx5zKlLtz
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+S15AVD2QS1V6fhRimJSVyT6QuGb8tKRsl2N+a2Xze36vgMhw7XK7zh//jC2H`),
+		lib.StrToBytes("YELLOW SUBMARINE"))
+
+	// Generate Nonce for AES counter function.
+	nonce := uint64(lib.RandomInt(0, 10))
+
+	// Generate random key.
+	key, err := lib.RandomBytes(16)
+	if err != nil {
+		fmt.Printf("Error generating key %v", err)
+		return
+	}
+
+	// Function for editing AES CTR cipher.
+	editCipher := func(cipher, key []byte, offset int, newtxt []byte) []byte {
+		if len(key) != 16 {
+			return cipher // key must be 16 bytes.
+		}
+		if offset+len(newtxt) > len(cipher) {
+			return cipher // Cannot edit.
+		}
+
+		// Get counter function.
+		ctrFunc := lib.AESGenCTRFunc(nonce)
+
+		// Get output block for the cipher.
+		ob := make([]byte, 0)
+		for {
+			ob = append(ob, lib.AESCipher(ctrFunc(), key)...)
+			if len(ob) >= len(cipher) {
+				break
+			}
+		}
+
+		// Make a copy of the cipher.
+		cipherc := make([]byte, len(cipher))
+		copy(cipherc, cipher)
+
+		// Edit.
+		c := lib.FixedXORBytes(newtxt, ob[offset:offset+len(newtxt)])
+		for i, j := offset, 0; j < len(newtxt); i, j = i+1, j+1 {
+			cipherc[i] = c[j]
+		}
+		return cipherc
+	}
+
+	// API Function for editing AES CTR cipher.
+	apiEditCipher := func(cipher []byte, offset int, newtxt []byte) []byte {
+		return editCipher(cipher, key, offset, newtxt)
+	}
+
+	// Cracks cipher using API function
+	crack := func(cipher []byte) []byte {
+		as := lib.FillBytes('A', len(cipher)) // 'A's.
+		ec := apiEditCipher(cipher, 0, as)    // Edited cipher.
+
+		// Get output block.
+		ob := lib.FixedXORBytes(as, ec)
+
+		// Crack cipher.
+		p := lib.FixedXORBytes(cipher, ob)
+
+		return p
+	}
+
+	// Get AES CTR cipher from plain text.
+	cipher, err := lib.AESEncryptCTR(plain, key, lib.AESGenCTRFunc(nonce))
+	if err != nil {
+		fmt.Printf("Error encrypting plain: %v", err)
+		return
+	}
+
+	// Crack plain text using API function.
+	p := crack(cipher)
+	fmt.Printf("%v", lib.BytesToStr(p))
+}
+
+// Output:
+// I'm back and I'm ringin' the bell
+// A rockin' on the mike while the fly girls yell
+// In ecstasy in the back of me
+// Well that's my DJ Deshay cuttin' all them Z's
+// Hittin' hard and the girlies goin' crazy
+// Vanilla's on the mike, man I'm not lazy.
+//
+// I'm lettin' my drug kick in
+// It controls my mouth and I begin
+// To just let it flow, let my concepts go
+// My posse's to the side yellin', Go Vanilla Go!
+//
+// Smooth 'cause that's the way I will be
+// And if you don't give a damn, then
+// Why you starin' at me
+// So get off 'cause I control the stage
+// There's no dissin' allowed
+// I'm in my own phase
+// The girlies sa y they love me and that is ok
+// And I can dance better than any kid n' play
+//
+// Stage 2 -- Yea the one ya' wanna listen to
+// It's off my head so let the beat play through
+// So I can funk it up and make it sound good
+// 1-2-3 Yo -- Knock on some wood
+// For good luck, I like my rhymes atrocious
+// Supercalafragilisticexpialidocious
+// I'm an effect and that you can bet
+// I can take a fly girl and make her wet.
+//
+// I'm like Samson -- Samson to Delilah
+// There's no denyin', You can try to hang
+// But you'll keep tryin' to get my style
+// Over and over, practice makes perfect
+// But not if you're a loafer.
+//
+// You'll get nowhere, no place, no time, no girls
+// Soon -- Oh my God, homebody, you probably eat
+// Spaghetti with a spoon! Come on and say it!
+//
+// VIP. Vanilla Ice yep, yep, I'm comin' hard like a rhino
+// Intoxicating so you stagger like a wino
+// So punks stop trying and girl stop cryin'
+// Vanilla Ice is sellin' and you people are buyin'
+// 'Cause why the freaks are jockin' like Crazy Glue
+// Movin' and groovin' trying to sing along
+// All through the ghetto groovin' this here song
+// Now you're amazed by the VIP posse.
+//
+// Steppin' so hard like a German Nazi
+// Startled by the bases hittin' ground
+// There's no trippin' on mine, I'm just gettin' down
+// Sparkamatic, I'm hangin' tight like a fanatic
+// You trapped me once and I thought that
+// You might have it
+// So step down and lend me your ear
+// '89 in my time! You, '90 is my year.
+//
+// You're weakenin' fast, YO! and I can tell it
+// Your body's gettin' hot, so, so I can smell it
+// So don't be mad and don't be sad
+// 'Cause the lyrics belong to ICE, You can call me Dad
+// You're pitchin' a fit, so step back and endure
+// Let the witch doctor, Ice, do the dance to cure
+// So come up close and don't be square
+// You wanna battle me -- Anytime, anywhere
+//
+// You thought that I was weak, Boy, you're dead wrong
+// So come on, everybody and sing this song
+//
+// Say -- Play that funky music Say, go white boy, go white boy go
+// play that funky music Go white boy, go white boy, go
+// Lay down and boogie and play that funky music till you die.
+//
+// Play that funky music Come on, Come on, let me hear
+// Play that funky music white boy you say it, say it
+// Play that funky music A little louder now
+// Play that funky music, white boy Come on, Come on, Come on
+// Play that funky music