1 files changed, 159 insertions, 0 deletions
diff --git a/src/m_im/ImCodec.cpp b/src/m_im/ImCodec.cpp
new file mode 100644
index 0000000..54efc60
--- /dev/null
+++ b/src/m_im/ImCodec.cpp
@@ -0,0 +1,159 @@
+/**
+ * Copyright (C) 2021-2024 Saturneric <[email protected]>
+ *
+ * This file is part of GpgFrontend.
+ *
+ * GpgFrontend is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * GpgFrontend is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with GpgFrontend. If not, see <https://www.gnu.org/licenses/>.
+ *
+ * The initial version of the source code is inherited from
+ * the gpg4usb project, which is under GPL-3.0-or-later.
+ *
+ * All the source code of GpgFrontend was modified and released by
+ * Saturneric <[email protected]> starting on May 12, 2021.
+ *
+ * SPDX-License-Identifier: GPL-3.0-or-later
+ *
+ */
+
+#include "ImCodec.h"
+
+#include <QCoreApplication>
+#include <QJsonArray>
+#include <QJsonDocument>
+#include <QJsonObject>
+
+#include "ImToken.h"
+
+namespace ImCodec {
+
+namespace {
+
+constexpr char kPhraseBlobVersion = '\x01';
+
+auto Tr(const char* text) -> QString {
+  return QCoreApplication::translate("GTrC", text);
+}
+
+/**
+ * @brief The "Instant Messaging" card: how the token is framed and, above
+ * all, whether a shared book phrase is in use -- the default book only hides
+ * the format from naive scanners, so it is reported as a warning.
+ */
+auto BookCard(const QString& phrase, qsizetype payload, qsizetype token_len)
+    -> QJsonObject {
+  const bool configured = !phrase.isEmpty();
+  QJsonArray fields;
+  const auto add = [&fields](const QString& k, const QString& v) {
+    fields.append(QJsonArray{k, v});
+  };
+
+  add(Tr("Encoding"), QStringLiteral("Base58 (Bitcoin/IPFS)"));
+  add(Tr("Container Format"), QString("v%1").arg(ImToken::FormatVersion()));
+  add(Tr("Message Book"), configured ? Tr("Shared phrase (Argon2id)")
+                                     : Tr("Default, no shared phrase set"));
+  // Lets both sides confirm they are on the same book. Only meaningful with a
+  // phrase: everyone shares the default book, so its digest says nothing.
+  if (configured) {
+    add(Tr("Book Fingerprint"), ImToken::BookFingerprintOf(phrase));
+  } else {
+    add(Tr("Set a Phrase"), Tr("Settings > Instant Messaging"));
+  }
+  if (payload > 0) {
+    add(Tr("OpenPGP Payload"), Tr("%1 bytes").arg(payload));
+  }
+  if (token_len > 0) {
+    add(Tr("Token Length"), Tr("%1 characters").arg(token_len));
+  }
+  if (payload > 0 && token_len > 0) {
+    // Random padding plus Base58 expansion. The padding part is deliberately
+    // random, so this ratio does not pin down the true payload length.
+    const auto ratio =
+        static_cast<double>(token_len) / static_cast<double>(payload);
+    add(Tr("Wire Overhead"),
+        QString("+%1%").arg((ratio * 100.0) - 100.0, 0, 'f', 0));
+  }
+
+  return QJsonObject{
+      {QStringLiteral("title"), Tr("Instant Messaging")},
+      {QStringLiteral("status"),
+       configured ? QStringLiteral("ok") : QStringLiteral("warn")},
+      {QStringLiteral("fields"), fields}};
+}
+
+auto CardsJson(const QJsonObject& card) -> QString {
+  const QJsonObject payload{
+      {QStringLiteral("description"),
+       Tr("An Instant Messaging section followed by the OpenPGP result.")},
+      {QStringLiteral("cards"), QJsonArray{card}}};
+  return QString::fromUtf8(
+      QJsonDocument(payload).toJson(QJsonDocument::Compact));
+}
+
+}  // namespace
+
+auto DecodeInput(const QByteArray& input, const QString& phrase) -> Answer {
+  // The token format rejects ordinary text and armored OpenPGP on its shape
+  // alone, before the memory-hard derivation.
+  const auto result = ImToken::Decode(QString::fromUtf8(input), phrase);
+  if (!result.ok) return {};
+
+  Answer a;
+  a.outcome = Outcome::kHandled;
+  a.output = result.pgp_message;
+  a.cards = CardsJson(BookCard(phrase, 0, 0));
+  return a;
+}
+
+auto EncodeOutput(const QByteArray& pgp, const QString& phrase) -> Answer {
+  Answer a;
+  a.outcome = Outcome::kFailed;
+
+  // The payload limit exists so a token we emit is one we can read back.
+  // Checked here so the user is told what went wrong and what to do about it.
+  const auto limit = ImToken::MaxPayloadBytes();
+  if (pgp.size() > limit) {
+    a.error = Tr("This message is too long to send as an instant message.\n\n"
+                 "The encrypted message is %1 bytes, and the "
+                 "instant-messaging format carries at most %2. Shorten the "
+                 "text, or send it as a normal OpenPGP message instead.")
+                  .arg(pgp.size())
+                  .arg(limit);
+    return a;
+  }
+
+  const auto token = ImToken::Encode(pgp, phrase);
+  if (token.isEmpty()) {
+    a.error = Tr("Failed to prepare the instant message: the encrypted "
+                 "message could not be converted into a token.");
+    return a;
+  }
+
+  a.outcome = Outcome::kHandled;
+  a.output = token.toUtf8();
+  a.cards = CardsJson(BookCard(phrase, pgp.size(), token.size()));
+  return a;
+}
+
+auto EncodePhraseBlob(const QString& phrase) -> QByteArray {
+  QByteArray blob(1, kPhraseBlobVersion);
+  blob.append(phrase.trimmed().toUtf8());
+  return blob;
+}
+
+auto DecodePhraseBlob(const QByteArray& blob) -> QString {
+  if (blob.isEmpty() || blob.at(0) != kPhraseBlobVersion) return {};
+  return QString::fromUtf8(blob.mid(1)).trimmed();
+}
+
+}  // namespace ImCodec