1

internal/url_shortener/linkcrypto.go

@@ -0,0 +1,67 @@
+package urlshortener
+
+import (
+	"crypto/aes"
+	"crypto/cipher"
+	"crypto/rand"
+	"encoding/base64"
+	"fmt"
+	"io"
+)
+
+// this class works with AES. This solution without database.
+type LinkEncryption struct {
+	Key string // this is secret key, must be 32-bit, if you want to use it
+}
+
+func (l *LinkEncryption) Shorten(plainText string) (string, error) {
+	block, err := aes.NewCipher([]byte(l.Key))
+	if err != nil {
+		return "", err
+	}
+
+	gcm, err := cipher.NewGCM(block)
+	if err != nil {
+		return "", err
+	}
+
+	nonce := make([]byte, gcm.NonceSize())
+	if _, err = io.ReadFull(rand.Reader, nonce); err != nil {
+		return "", err
+	}
+
+	cipherText := gcm.Seal(nonce, nonce, []byte(plainText), nil)
+
+	return base64.URLEncoding.EncodeToString(cipherText), nil
+}
+
+func (l *LinkEncryption) Unshorten(encryptedText string) (string, error) {
+	data, err := base64.URLEncoding.DecodeString(encryptedText)
+	if err != nil {
+		return "", err
+	}
+
+	block, err := aes.NewCipher([]byte(l.Key))
+	if err != nil {
+		return "", err
+	}
+
+	gcm, err := cipher.NewGCM(block)
+	if err != nil {
+		return "", err
+	}
+
+	nonceSize := gcm.NonceSize()
+	if len(data) < nonceSize {
+		return "", fmt.Errorf("ciphertext too short")
+	}
+
+	nonce, cipherText := data[:nonceSize], data[nonceSize:]
+
+	plainText, err := gcm.Open(nil, nonce, cipherText, nil)
+	if err != nil {
+		return "", err
+	}
+
+	return string(plainText), nil
+}