challenge: do challenge 3

* challenge/c03.go: Implement challenge 3
* cryptopals.go (main): Add handling to run challenge 3
* lib/brute.go (XORCrackSingleKey): New function.
* lib/hex.go (HexStrToAsciiStr, ByteToHexStr): New functions.
* lib/str.go (FillStr): New function.

1 files changed, 15 insertions, 0 deletions

diff --git a/lib/str.go b/lib/str.go
new file mode 100644
index 0000000..e0cb8ae
--- /dev/null
+++ b/lib/str.go
@@ -0,0 +1,15 @@
+// Copyright © 2020 rsiddharth <s@ricketyspace.net>
+// SPDX-License-Identifier: ISC
+
+package lib
+
+func FillStr(a string, l int) string {
+	b := ""
+	if l < 1 {
+		return b
+	}
+	for i := 0; i < l; i++ {
+		b += a
+	}
+	return b
+}