83 lines
2.4 KiB
Go
83 lines
2.4 KiB
Go
// Package crypto provides AES-256-GCM encryption utilities for storing
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// sensitive prompt data in the audit log without exposing plaintext.
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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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"encoding/base64"
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"errors"
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"fmt"
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"io"
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)
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// Encryptor encrypts and decrypts strings using AES-256-GCM.
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// A random 12-byte nonce is prepended to each ciphertext; output is base64 URL-safe.
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type Encryptor struct {
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key []byte
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}
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// NewEncryptor creates an Encryptor from a standard base64-encoded 32-byte key.
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// Returns an error if the key is not exactly 32 bytes after decoding.
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func NewEncryptor(keyBase64 string) (*Encryptor, error) {
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key, err := base64.StdEncoding.DecodeString(keyBase64)
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if err != nil {
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return nil, fmt.Errorf("crypto: invalid base64 key: %w", err)
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}
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if len(key) != 32 {
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return nil, fmt.Errorf("crypto: key must be 32 bytes, got %d", len(key))
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}
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return &Encryptor{key: key}, nil
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}
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// Encrypt encrypts plaintext and returns a base64 URL-safe string.
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// Format: base64(nonce[12] || ciphertext).
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func (e *Encryptor) Encrypt(plaintext string) (string, error) {
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block, err := aes.NewCipher(e.key)
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if err != nil {
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return "", fmt.Errorf("crypto: new cipher: %w", 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 "", fmt.Errorf("crypto: new gcm: %w", 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 "", fmt.Errorf("crypto: generate nonce: %w", err)
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}
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ciphertext := gcm.Seal(nonce, nonce, []byte(plaintext), nil)
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return base64.URLEncoding.EncodeToString(ciphertext), nil
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}
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// Decrypt decrypts a base64 URL-safe string produced by Encrypt.
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func (e *Encryptor) Decrypt(ciphertext string) (string, error) {
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data, err := base64.URLEncoding.DecodeString(ciphertext)
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if err != nil {
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return "", fmt.Errorf("crypto: invalid base64 ciphertext: %w", err)
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}
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block, err := aes.NewCipher(e.key)
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if err != nil {
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return "", fmt.Errorf("crypto: new cipher: %w", 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 "", fmt.Errorf("crypto: new gcm: %w", err)
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}
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nonceSize := gcm.NonceSize()
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if len(data) < nonceSize {
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return "", errors.New("crypto: ciphertext too short")
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}
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nonce, data := data[:nonceSize], data[nonceSize:]
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plaintext, err := gcm.Open(nil, nonce, data, nil)
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if err != nil {
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return "", fmt.Errorf("crypto: decrypt failed: %w", err)
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}
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return string(plaintext), nil
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}
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