From 9db1426878ff5b81f66d6d73bf69555eb8e5b5d2 Mon Sep 17 00:00:00 2001
From: rsiddharth <s@ricketyspace.net>
Date: Sat, 29 Aug 2020 13:30:47 -0400
Subject: challenge: do challenge 2

* challenge/c02.go: Challenge 2 snafu.
* cryptopals.go: Add challenge 2.
* enc/hex.go (DecToHexChar): New function.
* enc/xor.go  (FixedXOR): New function.
---
 challenge/c02.go | 14 ++++++++++++++
 cryptopals.go    |  2 ++
 enc/hex.go       | 10 ++++++++++
 enc/xor.go       | 19 +++++++++++++++++++
 4 files changed, 45 insertions(+)
 create mode 100644 challenge/c02.go
 create mode 100644 enc/xor.go

diff --git a/challenge/c02.go b/challenge/c02.go
new file mode 100644
index 0000000..deab152
--- /dev/null
+++ b/challenge/c02.go
@@ -0,0 +1,14 @@
+package challenge
+
+import (
+	"fmt"
+	"ricketyspace.net/cryptopals/enc"
+)
+
+func C2() {
+	a := "1c0111001f010100061a024b53535009181c"
+	b := "686974207468652062756c6c277320657965"
+	c := enc.FixedXOR(a, b)
+
+	fmt.Printf("XOR(%v ^ %v) = %v\n", a, b, c)
+}
diff --git a/cryptopals.go b/cryptopals.go
index 9c1c803..37580be 100644
--- a/cryptopals.go
+++ b/cryptopals.go
@@ -20,5 +20,7 @@ func main() {
 		flag.PrintDefaults()
 	case 1:
 		challenge.C1()
+	case 2:
+		challenge.C2()
 	}
 }
diff --git a/enc/hex.go b/enc/hex.go
index 0d19538..a1b9b46 100644
--- a/enc/hex.go
+++ b/enc/hex.go
@@ -14,3 +14,13 @@ func HexCharToDec(c byte) uint16 {
 	}
 	return 0
 }
+
+func DecToHexChar(i uint16) byte {
+	switch {
+	case 0 <= i && i <= 9:
+		return byte(48 + i)
+	case 10 <= i && i <= 15:
+		return byte(97 + (i - 10))
+	}
+	return 0
+}
diff --git a/enc/xor.go b/enc/xor.go
new file mode 100644
index 0000000..423c0a2
--- /dev/null
+++ b/enc/xor.go
@@ -0,0 +1,19 @@
+package enc
+
+func FixedXOR(a, b string) string {
+	cs := ""
+	if len(a) != len(b) {
+		return cs
+	}
+
+	ab := []byte(a)
+	bb := []byte(b)
+	for i := 0; i < len(ab); i++ {
+		p := HexCharToDec(ab[i])
+		q := HexCharToDec(bb[i])
+		r := DecToHexChar(p ^ q)
+
+		cs += string(r)
+	}
+	return cs
+}
-- 
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