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.

1 files changed, 10 insertions, 0 deletions

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
+}