Initial commit

Signed-off-by: Julien Riou <julien@riou.xyz>

src/internal/encryption.go

@@ -0,0 +1,77 @@
+package internal
+
+import (
+	"crypto/cipher"
+	"crypto/rand"
+	"fmt"
+
+	"golang.org/x/crypto/argon2"
+	"golang.org/x/crypto/chacha20poly1305"
+)
+
+const (
+	SaltSize   = 32
+	KeySize    = uint32(32) // KeySize is 32 bytes (256 bits).
+	KeyTime    = uint32(5)
+	KeyMemory  = uint32(1024 * 64) // KeyMemory in KiB. here, 64 MiB.
+	KeyThreads = uint8(4)
+)
+
+// NewCipher creates a cipher using XChaCha20-Poly1305
+// https://pkg.go.dev/golang.org/x/crypto/chacha20poly1305
+// A salt is required to derive the key from a password using argon
+func NewCipher(password string, salt []byte) (cipher.AEAD, error) {
+	key := argon2.IDKey([]byte(password), salt, KeyTime, KeyMemory, KeyThreads, KeySize)
+	return chacha20poly1305.NewX(key)
+}
+
+// Encrypt to encrypt a plaintext with a password
+// Returns a byte slice with the generated salt, nonce and the ciphertext
+func Encrypt(plaintext []byte, password string) (result []byte, err error) {
+	salt := make([]byte, SaltSize)
+	if n, err := rand.Read(salt); err != nil || n != SaltSize {
+		return nil, err
+	}
+
+	aead, err := NewCipher(password, salt)
+	if err != nil {
+		return nil, err
+	}
+
+	result = append(result, salt...)
+
+	nonce := make([]byte, aead.NonceSize())
+	if m, err := rand.Read(nonce); err != nil || m != aead.NonceSize() {
+		return nil, err
+	}
+
+	result = append(result, nonce...)
+
+	ciphertext := aead.Seal(nil, nonce, plaintext, nil)
+	result = append(result, ciphertext...)
+
+	return result, nil
+}
+
+// Decrypt to decrypt a ciphertext with a password
+// Returns the plaintext
+func Decrypt(ciphertext []byte, password string) ([]byte, error) {
+	if len(ciphertext) < SaltSize {
+		return nil, fmt.Errorf("ciphertext is too short: cannot read salt")
+	}
+	salt := ciphertext[:SaltSize]
+
+	aead, err := NewCipher(password, salt)
+	if err != nil {
+		return nil, err
+	}
+
+	if len(ciphertext) < SaltSize+aead.NonceSize() {
+		return nil, fmt.Errorf("ciphertext is too short: cannot read nonce")
+	}
+
+	nonce := ciphertext[SaltSize : SaltSize+aead.NonceSize()]
+	ciphertext = ciphertext[SaltSize+aead.NonceSize():]
+
+	return aead.Open(nil, nonce, ciphertext, nil)
+}