added encryption example in go

examples/encryption.go

@@ -0,0 +1,71 @@
+package main
+
+import (
+	"crypto/aes"
+	"crypto/cipher"
+	"crypto/rand"
+)
+
+func encrypt(plaintext, key []byte) ([]byte, error) {
+	block, err := aes.NewCipher(key)
+	if err != nil {
+		return []byte{}, err
+	}
+
+	iv := make([]byte, aes.BlockSize)
+	rand.Read(iv)
+
+	plaintextPadded := pad(plaintext)
+	encrypted := make([]byte, len(plaintextPadded))
+
+	mode := cipher.NewCBCEncrypter(block, iv)
+	mode.CryptBlocks(encrypted, plaintextPadded)
+
+	return append(iv, encrypted...), nil
+}
+
+func decrypt(encryptedIVandData, key []byte) ([]byte, error) {
+	block, err := aes.NewCipher(key)
+	if err != nil {
+		return []byte{}, err
+	}
+
+	iv := encryptedIVandData[0:aes.BlockSize]
+	encrypted := encryptedIVandData[aes.BlockSize:]
+
+	mode := cipher.NewCBCDecrypter(block, iv)
+
+	plaintextPadded := make([]byte, len(encrypted))
+	mode.CryptBlocks(plaintextPadded, encrypted)
+	plaintext := unpad(plaintextPadded)
+
+	return plaintext, nil
+}
+
+func unpad(in []byte) []byte {
+	if len(in) == 0 {
+		return nil
+	}
+
+	padding := in[len(in)-1]
+	if int(padding) > len(in) || padding > aes.BlockSize {
+		return nil
+	} else if padding == 0 {
+		return nil
+	}
+
+	for i := len(in) - 1; i > len(in)-int(padding)-1; i-- {
+		if in[i] != padding {
+			return nil
+		}
+	}
+	return in[:len(in)-int(padding)]
+}
+
+func pad(in []byte) []byte {
+	padding := aes.BlockSize - (len(in) % aes.BlockSize)
+	for i := 0; i < padding; i++ {
+		in = append(in, byte(padding))
+	}
+	return in
+}