first commit

internal/crypto/crypto.go

@@ -0,0 +1,55 @@
+// Package crypto provides AES-256-GCM encrypt/decrypt for exchange
+// credentials stored in the database, keyed by the app_secret from
+// data/settings.conf (see internal/config).
+package crypto
+
+import (
+	"crypto/aes"
+	"crypto/cipher"
+	"crypto/rand"
+	"encoding/base64"
+	"fmt"
+)
+
+// Encrypt returns nonce||ciphertext, base64-encoded, for storage in a DB column.
+func Encrypt(key []byte, plaintext string) (string, error) {
+	block, err := aes.NewCipher(key)
+	if err != nil {
+		return "", err
+	}
+	gcm, err := cipher.NewGCM(block)
+	if err != nil {
+		return "", err
+	}
+	nonce := make([]byte, gcm.NonceSize())
+	if _, err := rand.Read(nonce); err != nil {
+		return "", err
+	}
+	sealed := gcm.Seal(nonce, nonce, []byte(plaintext), nil)
+	return base64.StdEncoding.EncodeToString(sealed), nil
+}
+
+// Decrypt reverses Encrypt.
+func Decrypt(key []byte, encoded string) (string, error) {
+	raw, err := base64.StdEncoding.DecodeString(encoded)
+	if err != nil {
+		return "", err
+	}
+	block, err := aes.NewCipher(key)
+	if err != nil {
+		return "", err
+	}
+	gcm, err := cipher.NewGCM(block)
+	if err != nil {
+		return "", err
+	}
+	if len(raw) < gcm.NonceSize() {
+		return "", fmt.Errorf("ciphertext too short")
+	}
+	nonce, ciphertext := raw[:gcm.NonceSize()], raw[gcm.NonceSize():]
+	plaintext, err := gcm.Open(nil, nonce, ciphertext, nil)
+	if err != nil {
+		return "", err
+	}
+	return string(plaintext), nil
+}