Initial commit

internal/crypto/crypto.go

@@ -0,0 +1,94 @@
+package crypto
+
+import (
+	"crypto/aes"
+	"crypto/cipher"
+	"crypto/rand"
+	"crypto/sha256"
+	"encoding/base64"
+	"errors"
+	"fmt"
+	"io"
+	"strings"
+
+	"golang.org/x/crypto/hkdf"
+)
+
+const (
+	prefix    = "enc:"
+	infoLabel = "veola-v1"
+	keyLen    = 32
+	nonceLen  = 12
+)
+
+// DeriveKey derives a 32-byte AES key from raw key material via HKDF-SHA256.
+func DeriveKey(rawKey []byte) ([]byte, error) {
+	if len(rawKey) < 32 {
+		return nil, errors.New("raw encryption key must be at least 32 bytes")
+	}
+	r := hkdf.New(sha256.New, rawKey, nil, []byte(infoLabel))
+	out := make([]byte, keyLen)
+	if _, err := io.ReadFull(r, out); err != nil {
+		return nil, fmt.Errorf("derive key: %w", err)
+	}
+	return out, nil
+}
+
+func Encrypt(key []byte, plaintext string) (string, error) {
+	if plaintext == "" {
+		return "", nil
+	}
+	block, err := aes.NewCipher(key)
+	if err != nil {
+		return "", err
+	}
+	gcm, err := cipher.NewGCM(block)
+	if err != nil {
+		return "", err
+	}
+	nonce := make([]byte, nonceLen)
+	if _, err := io.ReadFull(rand.Reader, nonce); err != nil {
+		return "", err
+	}
+	ct := gcm.Seal(nil, nonce, []byte(plaintext), nil)
+	buf := make([]byte, 0, len(nonce)+len(ct))
+	buf = append(buf, nonce...)
+	buf = append(buf, ct...)
+	return prefix + base64.StdEncoding.EncodeToString(buf), nil
+}
+
+func Decrypt(key []byte, value string) (string, error) {
+	if value == "" {
+		return "", nil
+	}
+	if !IsEncrypted(value) {
+		// Plaintext passthrough lets us decrypt rows that pre-date encryption
+		// without a separate migration.
+		return value, nil
+	}
+	raw, err := base64.StdEncoding.DecodeString(strings.TrimPrefix(value, prefix))
+	if err != nil {
+		return "", fmt.Errorf("decode ciphertext: %w", err)
+	}
+	if len(raw) < nonceLen {
+		return "", errors.New("ciphertext too short")
+	}
+	block, err := aes.NewCipher(key)
+	if err != nil {
+		return "", err
+	}
+	gcm, err := cipher.NewGCM(block)
+	if err != nil {
+		return "", err
+	}
+	nonce, ct := raw[:nonceLen], raw[nonceLen:]
+	pt, err := gcm.Open(nil, nonce, ct, nil)
+	if err != nil {
+		return "", fmt.Errorf("decrypt: %w", err)
+	}
+	return string(pt), nil
+}
+
+func IsEncrypted(value string) bool {
+	return strings.HasPrefix(value, prefix)
+}