diff --git a/config.json b/config.json
index a9b33ed43..e7b75d83f 100644
--- a/config.json
+++ b/config.json
@@ -17,6 +17,7 @@
     "hamming",
     "sum-of-multiples",
     "pythagorean-triplet",
+    "crypto-square",
     "luhn",
     "largest-series-product",
     "sieve",
diff --git a/crypto-square/crypto_square_test.go b/crypto-square/crypto_square_test.go
new file mode 100644
index 000000000..f4d8807af
--- /dev/null
+++ b/crypto-square/crypto_square_test.go
@@ -0,0 +1,93 @@
+package cryptosquare
+
+import "testing"
+
+var tests = []struct {
+	pt string
+	ct string
+}{
+	{
+		"s#$%^&plunk",
+		"supnl k",
+	},
+	{
+		"1, 2, 3 GO!",
+		"1g2o3",
+	},
+	{
+		"1234",
+		"1324",
+	},
+	{
+		"123456789",
+		"14725 8369",
+	},
+	{
+		"123456789abc",
+		"15926 a37b4 8c",
+	},
+	{
+		"Never vex thine heart with idle woes",
+		"neewl exhie vtetw ehaho ririe vntds",
+	},
+	{
+		"ZOMG! ZOMBIES!!!",
+		"zzioo emmsg b",
+	},
+	{
+		"Time is an illusion. Lunchtime doubly so.",
+		"tasne yinic dsmio hooel ntuil libsu uml",
+	},
+	{
+		"We all know interspecies romance is weird.",
+		"wneia weore neaws scili prerl neoid ktcms",
+	},
+	{
+		"Madness, and then illumination.",
+		"msemo aanin dninn dlaet ltshu i",
+	},
+	{
+		"Vampires are people too!",
+		"vrela epems etpao oirpo",
+	},
+	{
+		"",
+		"",
+	},
+	{
+		"1",
+		"1",
+	},
+	{
+		"12",
+		"12",
+	},
+	{
+		"123",
+		"132",
+	},
+	{
+		"12345678",
+		"14725 836",
+	},
+	{
+		"123456789a",
+		"15926 a3748",
+	},
+}
+
+func TestEncode(t *testing.T) {
+	for _, test := range tests {
+		if ct := Encode(test.pt); ct != test.ct {
+			t.Fatalf("Encode(%q) = %q, want %q", test.pt, ct, test.ct)
+		}
+	}
+}
+
+func BenchmarkEncode(b *testing.B) {
+	for i := 0; i < b.N; i++ {
+		for _, test := range tests {
+			Encode(test.pt)
+		}
+	}
+}
diff --git a/crypto-square/example.go b/crypto-square/example.go
new file mode 100644
index 000000000..0adb5cde7
--- /dev/null
+++ b/crypto-square/example.go
@@ -0,0 +1,35 @@
+package cryptosquare
+
+import (
+	"math"
+	"strings"
+)
+
+func norm(r rune) rune {
+	switch {
+	case r >= 'a' && r <= 'z' || r >= '0' && r <= '9':
+		return r
+	case r >= 'A' && r <= 'Z':
+		return r + 'a' - 'A'
+	}
+	return -1
+}
+
+func Encode(pt string) string {
+	pt = strings.Map(norm, pt)
+	cols := int(math.Ceil(math.Sqrt(float64(len(pt)))))
+	b := make([]byte, len(pt)+(len(pt)-1)/5)
+	px := 0
+	for bx := range b {
+		if (bx+1)%6 == 0 {
+			b[bx] = ' '
+		} else {
+			b[bx] = pt[px]
+			px += cols
+			if px >= len(pt) {
+				px = (px + 1) % cols
+			}
+		}
+	}
+	return string(b)
+}