conferences/dc31: add crypto-privacy village puzzle code

Signed-off-by: Xe Iaso <me@xeiaso.net>

1 files changed, 69 insertions, 0 deletions

diff --git a/conferences/dc31/crypto-privacy/vigenere/main.go b/conferences/dc31/crypto-privacy/vigenere/main.go
new file mode 100644
index 0000000..448303b
--- /dev/null
+++ b/conferences/dc31/crypto-privacy/vigenere/main.go
@@ -0,0 +1,69 @@
+package main
+
+import (
+	"flag"
+	"fmt"
+	"os"
+	"strings"
+
+	"within.website/x/internal"
+)
+
+func main() {
+	internal.HandleStartup()
+
+	if flag.NArg() != 3 {
+		fmt.Fprintln(os.Stderr, "usage: go run . <encrypt> <plaintext> <key>")
+		fmt.Fprintln(os.Stderr, "usage: go run . <decrypt> <ciphertext> <key>")
+		os.Exit(2)
+	}
+
+	action := flag.Arg(0)
+	plaintext := flag.Arg(1)
+	key := flag.Arg(2)
+
+	switch action {
+	case "encrypt":
+		fmt.Println(Encrypt(key, plaintext))
+	case "decrypt":
+		fmt.Println(Decrypt(key, plaintext))
+	default:
+		fmt.Fprintln(os.Stderr, "usage: go run . <encrypt> <plaintext> <key>")
+		fmt.Fprintln(os.Stderr, "usage: go run . <decrypt> <ciphertext> <key>")
+		os.Exit(2)
+	}
+}
+
+func ReplicateKey(key string, plaintextLen int) string {
+	return strings.Repeat(key, plaintextLen/len(key)+1)[:plaintextLen]
+}
+
+func Encrypt(keyRaw, plaintext string) string {
+	keyRaw = ReplicateKey(keyRaw, len(plaintext))
+	plaintextDecoded := make([]int, len(plaintext))
+	key := make([]int, len(plaintext))
+	encoded := make([]byte, len(plaintext))
+
+	for i := range plaintext {
+		plaintextDecoded[i] = int(plaintext[i] - 'A')
+		key[i] = int(keyRaw[i] - 'A')
+		encoded[i] = byte(((plaintextDecoded[i] + key[i]) % 26) + 'A')
+	}
+
+	return string(encoded)
+}
+
+func Decrypt(keyRaw, ciphertext string) string {
+	keyRaw = ReplicateKey(keyRaw, len(ciphertext))
+	ciphertextDecoded := make([]int, len(ciphertext))
+	key := make([]int, len(ciphertext))
+	encoded := make([]byte, len(ciphertext))
+
+	for i := range ciphertext {
+		ciphertextDecoded[i] = int(ciphertext[i] - 'A')
+		key[i] = int(keyRaw[i] - 'A')
+		encoded[i] = byte((((ciphertextDecoded[i] - key[i]) + 26) % 26) + 'A')
+	}
+
+	return string(encoded)
+}