Data commit

Task/Vigen-re-cipher/Go/vigen-re-cipher.go

@@ -0,0 +1,69 @@
+package main
+
+import "fmt"
+
+type vkey string
+
+func newVigenère(key string) (vkey, bool) {
+    v := vkey(upperOnly(key))
+    return v, len(v) > 0 // key length 0 invalid
+}
+
+func (k vkey) encipher(pt string) string {
+    ct := upperOnly(pt)
+    for i, c := range ct {
+        ct[i] = 'A' + (c-'A'+k[i%len(k)]-'A')%26
+    }
+    return string(ct)
+}
+
+func (k vkey) decipher(ct string) (string, bool) {
+    pt := make([]byte, len(ct))
+    for i := range pt {
+        c := ct[i]
+        if c < 'A' || c > 'Z' {
+            return "", false // invalid ciphertext
+        }
+        pt[i] = 'A' + (c-k[i%len(k)]+26)%26
+    }
+    return string(pt), true
+}
+
+// upperOnly extracts letters A-Z, a-z from a string and
+// returns them all upper case in a byte slice.
+// Useful for vkey constructor and encipher function.
+func upperOnly(s string) []byte {
+    u := make([]byte, 0, len(s))
+    for i := 0; i < len(s); i++ {
+        c := s[i]
+        if c >= 'A' && c <= 'Z' {
+            u = append(u, c)
+        } else if c >= 'a' && c <= 'z' {
+            u = append(u, c-32)
+        }
+    }
+    return u
+}
+
+const testKey = "Vigenère Cipher"
+const testPT = `Beware the Jabberwock, my son!
+    The jaws that bite, the claws that catch!`
+
+func main() {
+    fmt.Println("Supplied key: ", testKey)
+    v, ok := newVigenère(testKey)
+    if !ok {
+        fmt.Println("Invalid key")
+        return
+    }
+    fmt.Println("Effective key:", v)
+    fmt.Println("Plain text:", testPT)
+    ct := v.encipher(testPT)
+    fmt.Println("Enciphered:", ct)
+    dt, ok := v.decipher(ct)
+    if !ok {
+        fmt.Println("Invalid ciphertext")
+        return
+    }
+    fmt.Println("Deciphered:", dt)
+}