diff --git a/internal/crypto/crypto.go b/internal/crypto/crypto.go
new file mode 100644
index 0000000..5418a3e
--- /dev/null
+++ b/internal/crypto/crypto.go
@@ -0,0 +1,54 @@
+package crypto
+
+import (
+	"crypto/aes"
+	"crypto/cipher"
+	"crypto/rand"
+	"encoding/base64"
+	"fmt"
+	"io"
+)
+
+// Cipher performs AES-256-GCM encryption of provider secrets.
+type Cipher struct {
+	gcm cipher.AEAD
+}
+
+func NewCipher(key []byte) (*Cipher, error) {
+	if len(key) != 32 {
+		return nil, fmt.Errorf("crypto: key must be 32 bytes, got %d", len(key))
+	}
+	block, err := aes.NewCipher(key)
+	if err != nil {
+		return nil, err
+	}
+	gcm, err := cipher.NewGCM(block)
+	if err != nil {
+		return nil, err
+	}
+	return &Cipher{gcm: gcm}, nil
+}
+
+// Encrypt returns base64(nonce‖ciphertext).
+func (c *Cipher) Encrypt(plaintext []byte) (string, error) {
+	nonce := make([]byte, c.gcm.NonceSize())
+	if _, err := io.ReadFull(rand.Reader, nonce); err != nil {
+		return "", err
+	}
+	sealed := c.gcm.Seal(nonce, nonce, plaintext, nil)
+	return base64.StdEncoding.EncodeToString(sealed), nil
+}
+
+// Decrypt reverses Encrypt.
+func (c *Cipher) Decrypt(enc string) ([]byte, error) {
+	raw, err := base64.StdEncoding.DecodeString(enc)
+	if err != nil {
+		return nil, fmt.Errorf("crypto: invalid base64: %w", err)
+	}
+	ns := c.gcm.NonceSize()
+	if len(raw) < ns {
+		return nil, fmt.Errorf("crypto: ciphertext too short")
+	}
+	nonce, ct := raw[:ns], raw[ns:]
+	return c.gcm.Open(nil, nonce, ct, nil)
+}
diff --git a/internal/crypto/crypto_test.go b/internal/crypto/crypto_test.go
new file mode 100644
index 0000000..c93b017
--- /dev/null
+++ b/internal/crypto/crypto_test.go
@@ -0,0 +1,64 @@
+package crypto
+
+import (
+	"bytes"
+	"testing"
+)
+
+func key32() []byte {
+	k := make([]byte, 32)
+	for i := range k {
+		k[i] = byte(i + 1)
+	}
+	return k
+}
+
+func TestEncryptDecryptRoundTrip(t *testing.T) {
+	c, err := NewCipher(key32())
+	if err != nil {
+		t.Fatal(err)
+	}
+	plain := []byte("selectel-api-secret-token")
+	enc, err := c.Encrypt(plain)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if enc == string(plain) {
+		t.Fatal("ciphertext must differ from plaintext")
+	}
+	dec, err := c.Decrypt(enc)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if !bytes.Equal(dec, plain) {
+		t.Fatalf("round-trip mismatch: %q != %q", dec, plain)
+	}
+}
+
+func TestEncryptNonDeterministic(t *testing.T) {
+	c, _ := NewCipher(key32())
+	a, _ := c.Encrypt([]byte("same"))
+	b, _ := c.Encrypt([]byte("same"))
+	if a == b {
+		t.Fatal("nonce must randomize ciphertext")
+	}
+}
+
+func TestDecryptTamperFails(t *testing.T) {
+	c, _ := NewCipher(key32())
+	enc, _ := c.Encrypt([]byte("data"))
+	// испортить последний символ base64
+	tampered := enc[:len(enc)-1] + "A"
+	if tampered == enc {
+		tampered = enc[:len(enc)-1] + "B"
+	}
+	if _, err := c.Decrypt(tampered); err == nil {
+		t.Fatal("GCM must reject tampered ciphertext")
+	}
+}
+
+func TestNewCipherRejectsBadKey(t *testing.T) {
+	if _, err := NewCipher([]byte("short")); err == nil {
+		t.Fatal("expected error for non-32-byte key")
+	}
+}