first commit

internal/crypto/crypto.go

@@ -0,0 +1,134 @@
+// Package crypto provides AES-256-GCM encryption for sensitive data at rest.
+package crypto
+
+import (
+	"crypto/aes"
+	"crypto/cipher"
+	"crypto/rand"
+	"encoding/base64"
+	"errors"
+	"io"
+
+	"golang.org/x/crypto/bcrypt"
+)
+
+const (
+	// BcryptCost is the bcrypt work factor for password hashing.
+	BcryptCost = 12
+)
+
+// Encryptor wraps AES-256-GCM for field-level encryption.
+type Encryptor struct {
+	key []byte // 32 bytes
+}
+
+// New creates an Encryptor from a 32-byte key.
+func New(key []byte) (*Encryptor, error) {
+	if len(key) != 32 {
+		return nil, errors.New("encryption key must be exactly 32 bytes")
+	}
+	k := make([]byte, 32)
+	copy(k, key)
+	return &Encryptor{key: k}, nil
+}
+
+// Encrypt encrypts plaintext using AES-256-GCM and returns a base64-encoded ciphertext.
+// Format: base64(nonce || ciphertext || tag)
+func (e *Encryptor) Encrypt(plaintext string) (string, error) {
+	if plaintext == "" {
+		return "", nil
+	}
+
+	block, err := aes.NewCipher(e.key)
+	if err != nil {
+		return "", err
+	}
+
+	gcm, err := cipher.NewGCM(block)
+	if err != nil {
+		return "", err
+	}
+
+	nonce := make([]byte, gcm.NonceSize())
+	if _, err = io.ReadFull(rand.Reader, nonce); err != nil {
+		return "", err
+	}
+
+	// Seal appends ciphertext+tag to nonce
+	ciphertext := gcm.Seal(nonce, nonce, []byte(plaintext), nil)
+	return base64.StdEncoding.EncodeToString(ciphertext), nil
+}
+
+// Decrypt decrypts a base64-encoded ciphertext produced by Encrypt.
+func (e *Encryptor) Decrypt(encoded string) (string, error) {
+	if encoded == "" {
+		return "", nil
+	}
+
+	data, err := base64.StdEncoding.DecodeString(encoded)
+	if err != nil {
+		return "", err
+	}
+
+	block, err := aes.NewCipher(e.key)
+	if err != nil {
+		return "", err
+	}
+
+	gcm, err := cipher.NewGCM(block)
+	if err != nil {
+		return "", err
+	}
+
+	nonceSize := gcm.NonceSize()
+	if len(data) < nonceSize {
+		return "", errors.New("ciphertext too short")
+	}
+
+	nonce, ciphertext := data[:nonceSize], data[nonceSize:]
+	plaintext, err := gcm.Open(nil, nonce, ciphertext, nil)
+	if err != nil {
+		return "", errors.New("decryption failed: data may be corrupted or key is wrong")
+	}
+
+	return string(plaintext), nil
+}
+
+// EncryptBytes encrypts raw bytes and returns base64 encoding.
+func (e *Encryptor) EncryptBytes(data []byte) (string, error) {
+	return e.Encrypt(string(data))
+}
+
+// DecryptBytes decrypts to raw bytes.
+func (e *Encryptor) DecryptBytes(encoded string) ([]byte, error) {
+	s, err := e.Decrypt(encoded)
+	if err != nil {
+		return nil, err
+	}
+	return []byte(s), nil
+}
+
+// ---- Password hashing ----
+
+// HashPassword hashes a password using bcrypt.
+func HashPassword(password string) (string, error) {
+	hash, err := bcrypt.GenerateFromPassword([]byte(password), BcryptCost)
+	if err != nil {
+		return "", err
+	}
+	return string(hash), nil
+}
+
+// CheckPassword compares a plaintext password against a bcrypt hash.
+func CheckPassword(password, hash string) error {
+	return bcrypt.CompareHashAndPassword([]byte(hash), []byte(password))
+}
+
+// GenerateToken generates a cryptographically secure random token of n bytes, base64-encoded.
+func GenerateToken(n int) (string, error) {
+	b := make([]byte, n)
+	if _, err := rand.Read(b); err != nil {
+		return "", err
+	}
+	return base64.URLEncoding.EncodeToString(b), nil
+}