From ccfaaf39f8e8fd3b14f7e89759372ec0f3b25cd1 Mon Sep 17 00:00:00 2001
From: mvvasilev <me@mvvasilev.dev>
Date: Mon, 28 Oct 2024 00:05:33 +0200
Subject: [PATCH] Finish Challenge 1

---
 README.md           |   5 ++
 go.mod              |   3 ++
 set1/challenge_1.go | 123 ++++++++++++++++++++++++++++++++++++++++++++
 test/set_1_test.go  |  19 +++++++
 4 files changed, 150 insertions(+)
 create mode 100644 README.md
 create mode 100644 go.mod
 create mode 100644 set1/challenge_1.go
 create mode 100644 test/set_1_test.go

diff --git a/README.md b/README.md
new file mode 100644
index 0000000..bc443af
--- /dev/null
+++ b/README.md
@@ -0,0 +1,5 @@
+# cryptopals
+
+Exercises in cryptography from https://cryptopals.com
+
+The goal is to do each challenge with no imports from the Go stdlib.
\ No newline at end of file
diff --git a/go.mod b/go.mod
new file mode 100644
index 0000000..94fae72
--- /dev/null
+++ b/go.mod
@@ -0,0 +1,3 @@
+module mvvasilev.dev/cryptopals
+
+go 1.23.2
diff --git a/set1/challenge_1.go b/set1/challenge_1.go
new file mode 100644
index 0000000..49ab843
--- /dev/null
+++ b/set1/challenge_1.go
@@ -0,0 +1,123 @@
+package set1
+
+const Base64Alphabet = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/"
+const Base64PaddingCharacter = "="
+
+// NOTE: Unused
+func HexDecode(hex string) (value string, success bool) {
+	size := len(hex)
+
+	var hexValues = map[byte]byte{
+		'0': 0,
+		'1': 1,
+		'2': 2,
+		'3': 3,
+		'4': 4,
+		'5': 5,
+		'6': 6,
+		'7': 7,
+		'8': 8,
+		'9': 9,
+		'a': 10,
+		'b': 11,
+		'c': 12,
+		'd': 13,
+		'e': 14,
+		'f': 15,
+	}
+
+	if size%2 != 0 {
+		return "", false
+	}
+
+	buffer := make([]byte, 0, size/2)
+
+	for i := 0; i < size; i += 2 {
+		first := hexValues[hex[i]] << 4
+		second := hexValues[hex[i+1]]
+
+		buffer = append(buffer, first^second)
+	}
+
+	return string(buffer), true
+}
+
+// NOTE: Unused
+func Base64Encode(value string) (base64 string) {
+	originalBytes := []byte(value)
+	size := len(originalBytes)
+
+	buffer := make([]byte, 0, size+size/3)
+
+	for i := 0; i < size; i += 3 {
+
+		// TODO: Handle end case to add padding
+
+		originals := originalBytes[i : i+3]
+
+		first := originals[0] >> 2
+		second := (0b00110000 & (originals[0] << 4)) ^ (originals[1] >> 4)
+		third := (0b00111100 & (originals[1] << 2)) ^ (originals[2] >> 6)
+		fourth := 0b00111111 & originals[2]
+
+		buffer = append(buffer, Base64Alphabet[first], Base64Alphabet[second], Base64Alphabet[third], Base64Alphabet[fourth])
+	}
+
+	return string(buffer)
+}
+
+func HexToBase64(hexValue string) (base64 string, success bool) {
+	hexSize := len(hexValue)
+
+	var hexValues = map[byte]byte{
+		'0': 0,
+		'1': 1,
+		'2': 2,
+		'3': 3,
+		'4': 4,
+		'5': 5,
+		'6': 6,
+		'7': 7,
+		'8': 8,
+		'9': 9,
+		'a': 10,
+		'b': 11,
+		'c': 12,
+		'd': 13,
+		'e': 14,
+		'f': 15,
+	}
+
+	if hexSize%2 != 0 {
+		return "", false
+	}
+
+	plainBuffer := make([]byte, 0, hexSize/2)
+
+	for i := 0; i < hexSize; i += 2 {
+		first := hexValues[hexValue[i]] << 4
+		second := hexValues[hexValue[i+1]]
+
+		plainBuffer = append(plainBuffer, first^second)
+	}
+
+	plainSize := len(plainBuffer)
+
+	base64Buffer := make([]byte, 0, plainSize+plainSize/3)
+
+	for i := 0; i < plainSize; i += 3 {
+
+		// TODO: Handle end case to add padding
+
+		originals := plainBuffer[i : i+3]
+
+		first := originals[0] >> 2
+		second := (0b00110000 & (originals[0] << 4)) ^ (originals[1] >> 4)
+		third := (0b00111100 & (originals[1] << 2)) ^ (originals[2] >> 6)
+		fourth := 0b00111111 & originals[2]
+
+		base64Buffer = append(base64Buffer, Base64Alphabet[first], Base64Alphabet[second], Base64Alphabet[third], Base64Alphabet[fourth])
+	}
+
+	return string(base64Buffer), true
+}
diff --git a/test/set_1_test.go b/test/set_1_test.go
new file mode 100644
index 0000000..7b5d312
--- /dev/null
+++ b/test/set_1_test.go
@@ -0,0 +1,19 @@
+package cryptopals_test
+
+import (
+	"testing"
+
+	"mvvasilev.dev/cryptopals/set1"
+)
+
+const Challenge1HexValue = "49276d206b696c6c696e6720796f757220627261696e206c696b65206120706f69736f6e6f7573206d757368726f6f6d"
+
+func Test_Challenge1(t *testing.T) {
+	const expected = "SSdtIGtpbGxpbmcgeW91ciBicmFpbiBsaWtlIGEgcG9pc29ub3VzIG11c2hyb29t"
+
+	value, success := set1.HexToBase64(Challenge1HexValue)
+
+	if !success || value != expected {
+		t.Fatal("Set 1, Challenge 1 has failed")
+	}
+}