From 12e4ff406090b5ffe2fb63d784a64b833984c22c Mon Sep 17 00:00:00 2001
From: mvvasilev <me@mvvasilev.dev>
Date: Tue, 29 Oct 2024 20:36:04 +0200
Subject: [PATCH] Set 1, Challenge 5

---
 set1/challenge_2.go            |  6 ++--
 set1/challenge_5.go            | 33 ++++++++++++++++++
 test/res/set-1-challenge-6.txt | 64 ++++++++++++++++++++++++++++++++++
 test/set_1_test.go             | 14 ++++++++
 4 files changed, 114 insertions(+), 3 deletions(-)
 create mode 100644 set1/challenge_5.go
 create mode 100644 test/res/set-1-challenge-6.txt

diff --git a/set1/challenge_2.go b/set1/challenge_2.go
index 3f7bb77..ec44b21 100644
--- a/set1/challenge_2.go
+++ b/set1/challenge_2.go
@@ -1,5 +1,7 @@
 package set1
 
+const HexRepresentations = "0123456789abcdef"
+
 func XORHexString(content, password string) string {
 	var hexValues = map[byte]byte{
 		'0': 0,
@@ -20,8 +22,6 @@ func XORHexString(content, password string) string {
 		'f': 15,
 	}
 
-	var hexRepresentations = []byte{'0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'a', 'b', 'c', 'd', 'e', 'f'}
-
 	contentBytes := []byte(content)
 	passwordBytes := []byte(password)
 
@@ -31,7 +31,7 @@ func XORHexString(content, password string) string {
 		contentByte := hexValues[contentBytes[i]]
 		passwordByte := hexValues[passwordBytes[i]]
 
-		buffer[i] = hexRepresentations[contentByte^passwordByte]
+		buffer[i] = HexRepresentations[contentByte^passwordByte]
 	}
 
 	return string(buffer)
diff --git a/set1/challenge_5.go b/set1/challenge_5.go
new file mode 100644
index 0000000..dfcfcf6
--- /dev/null
+++ b/set1/challenge_5.go
@@ -0,0 +1,33 @@
+package set1
+
+func XOREncryptText(plaintext string, key string) (cipher []byte) {
+
+	cursor := 0
+
+	nextKeyChar := func() (char byte) {
+		char = key[cursor]
+		cursor++
+
+		if cursor >= len(key) {
+			cursor = 0
+		}
+
+		return
+	}
+
+	cipher = make([]byte, len(plaintext), len(plaintext))
+
+	for i := 0; i < len(plaintext); i++ {
+		cipher[i] = plaintext[i] ^ nextKeyChar()
+	}
+
+	return
+}
+
+func ConvertToHex(bytes []byte) (hexBytes []byte) {
+	for i := 0; i < len(bytes); i++ {
+		hexBytes = append(hexBytes, HexRepresentations[bytes[i]>>4], HexRepresentations[0b00001111&bytes[i]])
+	}
+
+	return
+}
diff --git a/test/res/set-1-challenge-6.txt b/test/res/set-1-challenge-6.txt
new file mode 100644
index 0000000..cecdb81
--- /dev/null
+++ b/test/res/set-1-challenge-6.txt
@@ -0,0 +1,64 @@
+HUIfTQsPAh9PE048GmllH0kcDk4TAQsHThsBFkU2AB4BSWQgVB0dQzNTTmVS
+BgBHVBwNRU0HBAxTEjwMHghJGgkRTxRMIRpHKwAFHUdZEQQJAGQmB1MANxYG
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diff --git a/test/set_1_test.go b/test/set_1_test.go
index 36e98b7..88c7aaf 100644
--- a/test/set_1_test.go
+++ b/test/set_1_test.go
@@ -70,3 +70,17 @@ func Test_Challenge4(t *testing.T) {
 	t.Logf("Result: '%s' with score %d", bestResult, bestScore)
 
 }
+
+func Test_Challenge5(t *testing.T) {
+	const key = "ICE"
+
+	originalText := "Burning 'em, if you ain't quick and nimble\nI go crazy when I hear a cymbal"
+
+	expectedCypher := "0b3637272a2b2e63622c2e69692a23693a2a3c6324202d623d63343c2a26226324272765272a282b2f20430a652e2c652a3124333a653e2b2027630c692b20283165286326302e27282f"
+
+	result := string(set1.ConvertToHex(set1.XOREncryptText(originalText, key)))
+
+	if result != expectedCypher {
+		t.Fatalf("Result '%s' is not the same as expected '%s'", result, expectedCypher)
+	}
+}