FDN-01: repository & projektgerüst

Git-Repository für bestehenden archivdms-Code initialisiert, Branch-/Commit-Konvention (feature/<ticket>-<slug>-Branches, Ticket-Prefix in Commit-Nachricht) etabliert.

internal/cryptutil/secretbox.go

@@ -0,0 +1,73 @@
+// Package cryptutil provides authenticated symmetric encryption (AES-256-GCM)
+// for secrets that must be stored at rest but read back in plaintext at
+// runtime — currently the LDAP service-bind password (internal/ldapstore).
+//
+// The 256-bit key is derived via HKDF-SHA256 from the application's existing
+// master/JWT secret (config.API.Secret), so no additional secret needs to be
+// provisioned. A distinct HKDF info label keeps this key independent from the
+// JWT signing key even though both originate from the same input secret.
+package cryptutil
+
+import (
+	"crypto/aes"
+	"crypto/cipher"
+	"crypto/rand"
+	"crypto/sha256"
+	"fmt"
+	"io"
+
+	"golang.org/x/crypto/hkdf"
+)
+
+// hkdfInfo domain-separates the secretbox key from every other key derived
+// from the same master secret (e.g. the JWT signing key uses "archivdms-jwt-v1").
+const hkdfInfo = "archivdms-ldap-secretbox-v1"
+
+// Box performs AES-256-GCM encrypt/decrypt with a key derived from a secret.
+type Box struct {
+	gcm cipher.AEAD
+}
+
+// NewBox derives a 256-bit AES key from secret via HKDF-SHA256 and returns a
+// ready-to-use Box. secret must be non-empty.
+func NewBox(secret string) (*Box, error) {
+	if secret == "" {
+		return nil, fmt.Errorf("cryptutil: empty secret")
+	}
+	key := make([]byte, 32)
+	if _, err := io.ReadFull(hkdf.New(sha256.New, []byte(secret), nil, []byte(hkdfInfo)), key); err != nil {
+		return nil, fmt.Errorf("cryptutil: derive key: %w", err)
+	}
+	block, err := aes.NewCipher(key)
+	if err != nil {
+		return nil, fmt.Errorf("cryptutil: new cipher: %w", err)
+	}
+	gcm, err := cipher.NewGCM(block)
+	if err != nil {
+		return nil, fmt.Errorf("cryptutil: new gcm: %w", err)
+	}
+	return &Box{gcm: gcm}, nil
+}
+
+// Encrypt seals plaintext, returning the ciphertext and the freshly generated
+// nonce (stored separately in the DB). Callers persist both.
+func (b *Box) Encrypt(plaintext []byte) (ciphertext, nonce []byte, err error) {
+	nonce = make([]byte, b.gcm.NonceSize())
+	if _, err := io.ReadFull(rand.Reader, nonce); err != nil {
+		return nil, nil, fmt.Errorf("cryptutil: nonce: %w", err)
+	}
+	ciphertext = b.gcm.Seal(nil, nonce, plaintext, nil)
+	return ciphertext, nonce, nil
+}
+
+// Decrypt opens ciphertext using nonce, returning the original plaintext.
+func (b *Box) Decrypt(ciphertext, nonce []byte) ([]byte, error) {
+	if len(nonce) != b.gcm.NonceSize() {
+		return nil, fmt.Errorf("cryptutil: bad nonce length %d", len(nonce))
+	}
+	plaintext, err := b.gcm.Open(nil, nonce, ciphertext, nil)
+	if err != nil {
+		return nil, fmt.Errorf("cryptutil: decrypt: %w", err)
+	}
+	return plaintext, nil
+}