f60cf96b00
Thanks @salmonumbrella. Co-authored-by: salmonumbrella <salmonumbrella@users.noreply.github.com>
107 lines
2.5 KiB
Go
107 lines
2.5 KiB
Go
package tracking
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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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"encoding/json"
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"errors"
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"fmt"
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)
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var errCiphertextTooShort = errors.New("ciphertext too short")
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// PixelPayload is encrypted into the tracking pixel URL
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// to be decrypted by the worker.
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type PixelPayload struct {
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Recipient string `json:"r"`
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SubjectHash string `json:"s"`
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SentAt int64 `json:"t"`
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}
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// Encrypt encrypts a PixelPayload into a URL-safe base64 blob using AES-GCM
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func Encrypt(payload *PixelPayload, keyBase64 string) (string, error) {
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key, err := base64.StdEncoding.DecodeString(keyBase64)
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if err != nil {
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return "", fmt.Errorf("decode key: %w", err)
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}
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plaintext, err := json.Marshal(payload)
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if err != nil {
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return "", fmt.Errorf("marshal payload: %w", err)
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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 "", fmt.Errorf("new cipher: %w", err)
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}
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aead, err := cipher.NewGCM(block)
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if err != nil {
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return "", fmt.Errorf("new gcm: %w", err)
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}
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nonce := make([]byte, aead.NonceSize())
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if _, err := rand.Read(nonce); err != nil {
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return "", fmt.Errorf("nonce: %w", err)
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}
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ciphertext := aead.Seal(nonce, nonce, plaintext, nil)
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// URL-safe base64 encode
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return base64.RawURLEncoding.EncodeToString(ciphertext), nil
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}
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// Decrypt decrypts a URL-safe base64 blob using AES-GCM
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func Decrypt(blob string, keyBase64 string) (*PixelPayload, 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("decode key: %w", err)
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}
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ciphertext, err := base64.RawURLEncoding.DecodeString(blob)
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if err != nil {
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return nil, fmt.Errorf("decode blob: %w", err)
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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("new cipher: %w", err)
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}
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aead, err := cipher.NewGCM(block)
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if err != nil {
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return nil, fmt.Errorf("new gcm: %w", err)
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}
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if len(ciphertext) < aead.NonceSize() {
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return nil, errCiphertextTooShort
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}
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nonce := ciphertext[:aead.NonceSize()]
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ciphertext = ciphertext[aead.NonceSize():]
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plaintext, err := aead.Open(nil, nonce, ciphertext, nil)
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if err != nil {
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return nil, fmt.Errorf("decrypt: %w", err)
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}
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var payload PixelPayload
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if err := json.Unmarshal(plaintext, &payload); err != nil {
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return nil, fmt.Errorf("unmarshal payload: %w", err)
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}
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return &payload, nil
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}
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// GenerateKey generates a new 256-bit AES key as base64
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func GenerateKey() (string, error) {
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key := make([]byte, 32)
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if _, err := rand.Read(key); err != nil {
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return "", fmt.Errorf("generate key: %w", err)
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}
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return base64.StdEncoding.EncodeToString(key), nil
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}
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