133 lines
3.5 KiB
Go
133 lines
3.5 KiB
Go
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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"encoding/base64"
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"errors"
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"io"
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)
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// Encryptor 字段加密器接口。Encrypt 永远用主密钥，Decrypt 先试主密钥、失败试 legacy 密钥。
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type Encryptor interface {
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Encrypt(plaintext string) (string, error)
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Decrypt(ciphertext string) (string, error)
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}
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// aesKey 持有一个 AES-GCM 密钥及其 cipher。
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type aesKey struct {
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key []byte
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}
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func newAESKey(key string) (*aesKey, error) {
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keyBytes := []byte(key)
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if len(keyBytes) != 16 && len(keyBytes) != 24 && len(keyBytes) != 32 {
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return nil, errors.New("invalid key length: must be 16, 24, or 32 bytes")
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}
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return &aesKey{key: keyBytes}, nil
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}
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// FieldEncryptor 持有主密钥 + 可选 legacy 密钥列表。
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// Encrypt 永远用 primary；Decrypt 先试 primary，gcm.Open 认证失败依次试 legacy，
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// 用于密钥轮换期间透明解出旧密文。
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type FieldEncryptor struct {
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primary *aesKey
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legacy []*aesKey
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}
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// NewFieldEncryptor 创建字段加密器。primary 为主密钥，legacy 为可选的旧密钥（用于回退解密）。
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func NewFieldEncryptor(primary string, legacy ...string) (*FieldEncryptor, error) {
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primaryKey, err := newAESKey(primary)
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if err != nil {
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return nil, err
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}
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legacyKeys := make([]*aesKey, 0, len(legacy))
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for _, l := range legacy {
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if l == "" || l == primary {
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continue
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}
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k, err := newAESKey(l)
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if err != nil {
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return nil, err
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}
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legacyKeys = append(legacyKeys, k)
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}
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return &FieldEncryptor{primary: primaryKey, legacy: legacyKeys}, nil
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}
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// Encrypt 使用 AES-GCM 加密明文，输出 base64(nonce || ciphertext || gcmTag)。
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func (e *FieldEncryptor) Encrypt(plaintext string) (string, error) {
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if plaintext == "" {
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return "", nil
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}
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gcm, err := e.gcm(e.primary)
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if err != nil {
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return "", err
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}
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nonce := make([]byte, gcm.NonceSize())
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if _, err := io.ReadFull(rand.Reader, nonce); err != nil {
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return "", err
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}
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ciphertext := gcm.Seal(nonce, nonce, []byte(plaintext), nil)
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return base64.StdEncoding.EncodeToString(ciphertext), nil
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}
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// Decrypt 解密密文。先试主密钥，gcm.Open 认证失败依次试 legacy 密钥。
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func (e *FieldEncryptor) Decrypt(ciphertext string) (string, error) {
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if ciphertext == "" {
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return "", nil
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}
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decoded, err := base64.StdEncoding.DecodeString(ciphertext)
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if err != nil {
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return "", err
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}
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for _, k := range append([]*aesKey{e.primary}, e.legacy...) {
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plaintext, err := decryptWithKey(k, decoded)
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if err == nil {
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return plaintext, nil
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}
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}
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return "", errors.New("decrypt failed: no matching key")
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}
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func (e *FieldEncryptor) gcm(k *aesKey) (cipher.AEAD, error) {
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block, err := aes.NewCipher(k.key)
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if err != nil {
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return nil, err
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}
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return cipher.NewGCM(block)
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}
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func decryptWithKey(k *aesKey, decoded []byte) (string, error) {
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block, err := aes.NewCipher(k.key)
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if err != nil {
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return "", err
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}
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gcm, err := cipher.NewGCM(block)
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if err != nil {
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return "", err
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}
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nonceSize := gcm.NonceSize()
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if len(decoded) < nonceSize {
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return "", errors.New("ciphertext too short")
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}
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nonce, body := decoded[:nonceSize], decoded[nonceSize:]
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plaintext, err := gcm.Open(nil, nonce, body, nil)
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if err != nil {
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return "", err
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}
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return string(plaintext), nil
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}
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// MockEncryptor 测试用直通加密器，明文不加密。
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type MockEncryptor struct{}
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func (e *MockEncryptor) Encrypt(plaintext string) (string, error) {
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return plaintext, nil
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}
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func (e *MockEncryptor) Decrypt(ciphertext string) (string, error) {
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return ciphertext, nil
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}
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