66 lines
1.4 KiB
Go
66 lines
1.4 KiB
Go
// Package crypto provides AES-256-GCM field encryption keyed from EMCLI_KEY.
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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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"io"
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"os"
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)
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var (
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ErrNoKey = errors.New("EMCLI_KEY is not set")
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ErrBadKey = errors.New("EMCLI_KEY must be base64 of exactly 32 bytes")
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)
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// KeyFromEnv reads and validates the AES-256 key from EMCLI_KEY.
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func KeyFromEnv() ([]byte, error) {
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raw := os.Getenv("EMCLI_KEY")
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if raw == "" {
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return nil, ErrNoKey
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}
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key, err := base64.StdEncoding.DecodeString(raw)
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if err != nil || len(key) != 32 {
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return nil, ErrBadKey
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}
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return key, nil
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}
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func newGCM(key []byte) (cipher.AEAD, error) {
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block, err := aes.NewCipher(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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// Seal encrypts plaintext, returning nonce||ciphertext.
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func Seal(key, plaintext []byte) ([]byte, error) {
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gcm, err := newGCM(key)
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if err != nil {
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return nil, 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 nil, err
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}
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return gcm.Seal(nonce, nonce, plaintext, nil), nil
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}
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// Open reverses Seal. A wrong key or tampered blob returns an error.
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func Open(key, blob []byte) ([]byte, error) {
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gcm, err := newGCM(key)
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if err != nil {
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return nil, err
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}
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ns := gcm.NonceSize()
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if len(blob) < ns {
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return nil, errors.New("ciphertext too short")
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}
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nonce, ct := blob[:ns], blob[ns:]
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return gcm.Open(nil, nonce, ct, nil)
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}
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