Add Fyne GUI and portable --data-dir mode to nymdrop-reader

Extract reader logic (key management, embedded nym-client lifecycle,
receive loop, decrypt, save) into internal/reader as a Hooks-driven
package, shared by both the existing headless CLI and a new --gui mode
built with Fyne. Add --data-dir to make a reader instance fully
self-contained: privkey, inbox, and the embedded nym-client's own state
(normally fixed to $HOME/.nym) all live under the given directory via a
HOME override on the subprocess, enabling zero-trace USB operation.

CLI default behavior is unchanged (same paths, same protocol) so the
pietro deployment is unaffected.

1 files changed, 64 insertions, 0 deletions

diff --git a/internal/reader/reader_test.go b/internal/reader/reader_test.go
new file mode 100644
index 0000000..896f8c0
--- /dev/null
+++ b/internal/reader/reader_test.go
@@ -0,0 +1,64 @@
+package reader
+
+import (
+	"crypto/aes"
+	"crypto/cipher"
+	"crypto/ecdh"
+	"crypto/rand"
+	"crypto/sha256"
+	"encoding/hex"
+	"io"
+	"testing"
+
+	"golang.org/x/crypto/hkdf"
+)
+
+// Verifies the decryptMessage path still produces the correct plaintext after
+// wrapping the ECDH/HKDF secrets in memguard.LockedBuffer, using the exact
+// wire format the browser client (static/crypto.js) and relay produce.
+func TestDecryptMessageAfterMemguard(t *testing.T) {
+	readerPriv, err := ecdh.X25519().GenerateKey(rand.Reader)
+	if err != nil {
+		t.Fatal(err)
+	}
+	ephPriv, err := ecdh.X25519().GenerateKey(rand.Reader)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	shared, err := ephPriv.ECDH(readerPriv.PublicKey())
+	if err != nil {
+		t.Fatal(err)
+	}
+	aesKey := make([]byte, 32)
+	hkdfR := hkdf.New(sha256.New, shared, make([]byte, 32), []byte("nymdrop-v1"))
+	if _, err := io.ReadFull(hkdfR, aesKey); err != nil {
+		t.Fatal(err)
+	}
+	block, err := aes.NewCipher(aesKey)
+	if err != nil {
+		t.Fatal(err)
+	}
+	gcm, err := cipher.NewGCM(block)
+	if err != nil {
+		t.Fatal(err)
+	}
+	iv := make([]byte, 12)
+	if _, err := rand.Read(iv); err != nil {
+		t.Fatal(err)
+	}
+	want := "E2E memguard verification message"
+	ciphertext := gcm.Seal(nil, iv, []byte(want), nil)
+
+	packet := append(append(append([]byte{}, ephPriv.PublicKey().Bytes()...), iv...), ciphertext...)
+	noncePrefix := hex.EncodeToString(make([]byte, 16)) + ":"
+	raw := append([]byte(noncePrefix), packet...)
+
+	got, err := decryptMessage(raw, readerPriv)
+	if err != nil {
+		t.Fatalf("decryptMessage: %v", err)
+	}
+	if got != want {
+		t.Fatalf("plaintext mismatch: got %q want %q", got, want)
+	}
+}