1 files changed, 93 insertions, 0 deletions
diff --git a/internal/encryption/encryption.go b/internal/encryption/encryption.go
new file mode 100644
index 0000000..0f9c748
--- /dev/null
+++ b/internal/encryption/encryption.go
@@ -0,0 +1,93 @@
+package encryption
+
+import (
+	"bytes"
+	"crypto/aes"
+	"crypto/cipher"
+	"crypto/rand"
+	"encoding/base64"
+	"errors"
+	"io"
+	"strings"
+)
+
+func addBase64Padding(value string) string {
+	m := len(value) % 4
+	if m != 0 {
+		value += strings.Repeat("=", 4-m)
+	}
+
+	return value
+}
+
+func removeBase64Padding(value string) string {
+	return strings.Replace(value, "=", "", -1)
+}
+
+func pad(src []byte) []byte {
+	padding := aes.BlockSize - len(src)%aes.BlockSize
+	padtext := bytes.Repeat([]byte{byte(padding)}, padding)
+
+	return append(src, padtext...)
+}
+
+func Unpad(src []byte) ([]byte, error) {
+	length := len(src)
+	unpadding := int(src[length-1])
+
+	if unpadding > length {
+		return nil, errors.New("unpad error. This could happen when incorrect encryption key is used")
+	}
+
+	return src[:(length - unpadding)], nil
+}
+
+func Encrypt(key []byte, text string) (string, error) {
+	block, err := aes.NewCipher(key)
+	if err != nil {
+		return "", err
+	}
+
+	msg := pad([]byte(text))
+	ciphertext := make([]byte, aes.BlockSize+len(msg))
+	iv := ciphertext[:aes.BlockSize]
+
+	if _, err := io.ReadFull(rand.Reader, iv); err != nil {
+		return "", err
+	}
+
+	cfb := cipher.NewCFBEncrypter(block, iv)
+	cfb.XORKeyStream(ciphertext[aes.BlockSize:], []byte(msg))
+	finalMsg := removeBase64Padding(base64.URLEncoding.EncodeToString(ciphertext))
+
+	return finalMsg, nil
+}
+
+func Decrypt(key []byte, text string) (string, error) {
+	block, err := aes.NewCipher(key)
+	if err != nil {
+		return "", err
+	}
+
+	decodedMsg, err := base64.URLEncoding.DecodeString(addBase64Padding(text))
+	if err != nil {
+		return "", err
+	}
+
+	if (len(decodedMsg) % aes.BlockSize) != 0 {
+		return "", errors.New("blocksize must be multipe of decoded message length")
+	}
+
+	iv := decodedMsg[:aes.BlockSize]
+	msg := decodedMsg[aes.BlockSize:]
+
+	cfb := cipher.NewCFBDecrypter(block, iv)
+	cfb.XORKeyStream(msg, msg)
+
+	unpadMsg, err := Unpad(msg)
+	if err != nil {
+		return "", err
+	}
+
+	return string(unpadMsg), nil
+}