144 lines
3.7 KiB
Go
144 lines
3.7 KiB
Go
// Package crypto handles payload encryption and decryption.
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// Uses AES-256-GCM for authenticated encryption.
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package crypto
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import (
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"crypto/aes"
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"crypto/cipher"
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"crypto/rand"
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"crypto/sha256"
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"encoding/hex"
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"errors"
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"fmt"
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"io"
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)
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const (
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// KeySize is the AES-256 key size in bytes.
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KeySize = 32
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// NonceSize is the GCM nonce size.
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NonceSize = 12
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)
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// DeriveKey derives a 32-byte AES-256 key from an arbitrary passphrase.
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// Uses SHA-256 as the KDF (simple; for production use Argon2).
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func DeriveKey(passphrase string) []byte {
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h := sha256.Sum256([]byte(passphrase))
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return h[:]
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}
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// Encrypt encrypts plaintext using AES-256-GCM with the given key.
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// The key should be 32 bytes (use DeriveKey for passphrases).
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// Returns: nonce || ciphertext || tag
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func Encrypt(plaintext, key []byte) ([]byte, error) {
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if len(key) != KeySize {
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return nil, fmt.Errorf("key must be %d bytes (got %d)", KeySize, len(key))
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}
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block, err := aes.NewCipher(key)
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if err != nil {
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return nil, fmt.Errorf("failed to create cipher: %w", err)
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}
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aesGCM, err := cipher.NewGCM(block)
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if err != nil {
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return nil, fmt.Errorf("failed to create GCM: %w", err)
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}
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nonce := make([]byte, NonceSize)
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if _, err := io.ReadFull(rand.Reader, nonce); err != nil {
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return nil, fmt.Errorf("failed to generate nonce: %w", err)
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}
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// Seal appends the encrypted data (ciphertext + tag) to nonce
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ciphertext := aesGCM.Seal(nonce, nonce, plaintext, nil)
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return ciphertext, nil
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}
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// Decrypt decrypts data using AES-256-GCM.
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// Expects: nonce || ciphertext || tag
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func Decrypt(data, key []byte) ([]byte, error) {
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if len(key) != KeySize {
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return nil, fmt.Errorf("key must be %d bytes (got %d)", KeySize, len(key))
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}
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if len(data) < NonceSize+1 {
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return nil, errors.New("ciphertext too short")
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}
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block, err := aes.NewCipher(key)
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if err != nil {
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return nil, fmt.Errorf("failed to create cipher: %w", err)
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}
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aesGCM, err := cipher.NewGCM(block)
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if err != nil {
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return nil, fmt.Errorf("failed to create GCM: %w", err)
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}
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nonce := data[:NonceSize]
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ciphertext := data[NonceSize:]
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plaintext, err := aesGCM.Open(nil, nonce, ciphertext, nil)
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if err != nil {
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return nil, fmt.Errorf("decryption failed: %w", err)
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}
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return plaintext, nil
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}
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// EncryptHex encrypts plaintext and returns hex-encoded output.
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func EncryptHex(plaintext []byte, keyHex string) (string, error) {
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key, err := hex.DecodeString(keyHex)
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if err != nil {
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return "", fmt.Errorf("invalid key hex: %w", err)
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}
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ct, err := Encrypt(plaintext, key)
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if err != nil {
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return "", err
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}
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return hex.EncodeToString(ct), nil
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}
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// DecryptHex decrypts hex-encoded data and returns plaintext.
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func DecryptHex(dataHex string, key []byte) ([]byte, error) {
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data, err := hex.DecodeString(dataHex)
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if err != nil {
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return nil, fmt.Errorf("invalid hex data: %w", err)
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}
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return Decrypt(data, key)
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}
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// HexToKey decodes a hex string into a 32-byte key.
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func HexToKey(hexStr string) ([]byte, error) {
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key, err := hex.DecodeString(hexStr)
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if err != nil {
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return nil, fmt.Errorf("invalid hex: %w", err)
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}
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if len(key) != KeySize {
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return nil, fmt.Errorf("key must be %d bytes (got %d)", KeySize, len(key))
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}
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return key, nil
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}
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// HexToKeyWithFallback accepts either a 64-char hex key (32 bytes) or any
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// passphrase and derives a key using SHA-256.
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func HexToKeyWithFallback(input string) []byte {
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if len(input) == 64 {
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if key, err := hex.DecodeString(input); err == nil && len(key) == KeySize {
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return key
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}
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}
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return DeriveKey(input)
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}
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// GenerateKey generates a random 32-byte AES-256 key and returns it as hex.
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func GenerateKey() (string, error) {
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key := make([]byte, KeySize)
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if _, err := io.ReadFull(rand.Reader, key); err != nil {
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return "", fmt.Errorf("failed to generate key: %w", err)
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}
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return hex.EncodeToString(key), nil
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}
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