Add comments and clean up encryption

1 files changed, 36 insertions, 20 deletions

diff --git a/backend/security/encrypt.go b/backend/security/encrypt.go
index fff027c..4af5e3c 100644
--- a/backend/security/encrypt.go
+++ b/backend/security/encrypt.go
@@ -4,62 +4,78 @@ import (
 	"crypto/aes"
 	"crypto/cipher"
 	"crypto/rand"
+	"errors"
 	"golang.org/x/crypto/scrypt"
 )
 
-func Encrypt(key, data []byte) ([]byte, error) {
-	blockCipher, err := aes.NewCipher(key)
+var EncryptionError = errors.New("could not encrypt the given content")
+
+func Encrypt(key, data string) (string, error) {
+	// initialize aes block cipher with given key
+	blockCipher, err := aes.NewCipher([]byte(key))
 	if err != nil {
-		return nil, err
+		return "", err
 	}
 
+	// wrap block cipher with Galois Counter Mode and standard nonce length
 	gcm, err := cipher.NewGCM(blockCipher)
 	if err != nil {
-		return nil, err
+		return "", err
 	}
 
+	// generate nonce (number once used) unique to the given key
 	nonce := make([]byte, gcm.NonceSize())
 	if _, err = rand.Read(nonce); err != nil {
-		return nil, err
+		return "", err
 	}
 
-	cipherText := gcm.Seal(nonce, nonce, data, nil)
+	// seal nonce with data to use during decryption
+	cipherText := gcm.Seal(nonce, nonce, []byte(data), nil)
 
-	return cipherText, nil
+	return string(cipherText), nil
 }
 
-func Decrypt(key, data []byte) ([]byte, error) {
-	blockCipher, err := aes.NewCipher(key)
+func Decrypt(key, data string) (string, error) {
+	// similar to encrypt, create cipher and wrap with GCM
+	blockCipher, err := aes.NewCipher([]byte(key))
 	if err != nil {
-		return nil, err
+		return "", err
 	}
 
 	gcm, err := cipher.NewGCM(blockCipher)
 	if err != nil {
-		return nil, err
+		return "", err
 	}
 
+	// extract the nonce from the data
 	nonce, cipherText := data[:gcm.NonceSize()], data[gcm.NonceSize():]
-	plaintext, err := gcm.Open(nil, nonce, cipherText, nil)
+
+	// use nonce to decrypt the data
+	plaintext, err := gcm.Open(nil, []byte(nonce), []byte(cipherText), nil)
 	if err != nil {
-		return nil, err
+		return "", err
 	}
 
-	return plaintext, nil
+	return string(plaintext), nil
 }
 
-func DeriveKey(password, salt []byte) ([]byte, []byte, error) {
+const keyBytes = 16
+const iterations = 16384
+const relativeMemoryCost = 8
+const relativeCPUCost = 1
+
+func DeriveKey(password string, salt []byte) (string, []byte, error) {
 	if salt == nil {
-		salt = make([]byte, 16)
+		salt = make([]byte, keyBytes)
 		if _, err := rand.Read(salt); err != nil {
-			return nil, nil, err
+			return "", nil, err
 		}
 	}
 
-	key, err := scrypt.Key(password, salt, 16384, 8, 1, 16)
+	key, err := scrypt.Key([]byte(password), salt, iterations, relativeMemoryCost, relativeCPUCost, keyBytes)
 	if err != nil {
-		return nil, nil, err
+		return "", nil, err
 	}
 
-	return key, salt, nil
+	return string(key), salt, nil
 }