challenge: do challenge 4

* challenge/c04.go: Implement challenge 4.
* cryptopals.go (main): Add handling to run challenge 4.

2 files changed, 365 insertions, 0 deletions

diff --git a/challenge/c04.go b/challenge/c04.go
new file mode 100644
index 0000000..97bab0e
--- /dev/null
+++ b/challenge/c04.go
@@ -0,0 +1,363 @@
+package challenge
+
+import (
+	"fmt"
+	"ricketyspace.net/cryptopals/lib"
+)
+
+const blob = `
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+32042f46431d2c44607934ed180c1028136a5f2b26092e3b2c4e2930585a`
+
+var blobs = make([]string, 327)
+
+func init() {
+	for i, j := 1, 0; i < len(blob); i++ {
+		if blob[i] == '\n' {
+			j += 1
+			i += 1
+		}
+		blobs[j] += string(blob[i])
+	}
+}
+
+func C4() {
+	i, k, ds, scr := 0, byte(0), "", 100.0
+	for j := 0; j < len(blobs); j++ {
+		c, as, s := lib.XORCrackSingleKey(blobs[j])
+		if s < scr {
+			i = j
+			k = c
+			ds = as
+			scr = s
+		}
+	}
+	fmt.Printf("Blob encrypted with a single character: %v\n", blobs[i])
+	fmt.Printf("Key is '%c'\n", k)
+	fmt.Printf("Decrypted string: '%v' (Score: %v)\n", ds, scr)
+}
diff --git a/cryptopals.go b/cryptopals.go
index 5faa363..671564b 100644
--- a/cryptopals.go
+++ b/cryptopals.go
@@ -24,5 +24,7 @@ func main() {
 		challenge.C2()
 	case 3:
 		challenge.C3()
+	case 4:
+		challenge.C4()
 	}
 }