CryFS asks back if a cipher without integrity is chosen

src/CryCipher.cpp

@@ -10,6 +10,8 @@ using cpputils::make_unique_ref;
 using blockstore::BlockStore;
 using std::shared_ptr;
 using std::make_shared;
+using boost::optional;
+using boost::none;
 
 using namespace cryfs;
 using namespace blockstore::encrypted;
@@ -19,13 +21,17 @@ class CryCipherInstance: public CryCipher {
 public:
     BOOST_CONCEPT_ASSERT((CipherConcept<Cipher>));
 
-    CryCipherInstance(const std::string &cipherName): _cipherName(cipherName) {
+    CryCipherInstance(const std::string &cipherName, const optional<string> warning = none): _cipherName(cipherName), _warning(warning) {
     }
 
-    string cipherName() const override {
+    const string &cipherName() const override {
         return _cipherName;
     }
 
+    const optional<string> &warning() const override {
+        return _warning;
+    }
+
     unique_ref<BlockStore> createEncryptedBlockstore(unique_ref<BlockStore> baseBlockStore, const string &encKey) const override {
         return make_unique_ref<EncryptedBlockStore<Cipher>>(std::move(baseBlockStore), Cipher::EncryptionKey::FromString(encKey));
     }
@@ -36,30 +42,33 @@ public:
 
 private:
     string _cipherName;
+    optional<string> _warning;
 };
 
+const string INTEGRITY_WARNING = "This cipher does not ensure integrity.";
+
 //We have to use shared_ptr instead of unique_ref, because c++ initializer_list needs copyable values
 const vector<shared_ptr<CryCipher>> CryCiphers::SUPPORTED_CIPHERS = {
         make_shared<CryCipherInstance<AES256_GCM>>("aes-256-gcm"),
-        make_shared<CryCipherInstance<AES256_CFB>>("aes-256-cfb"),
+        make_shared<CryCipherInstance<AES256_CFB>>("aes-256-cfb", INTEGRITY_WARNING),
         make_shared<CryCipherInstance<AES128_GCM>>("aes-128-gcm"),
-        make_shared<CryCipherInstance<AES128_CFB>>("aes-128-cfb"),
+        make_shared<CryCipherInstance<AES128_CFB>>("aes-128-cfb", INTEGRITY_WARNING),
         make_shared<CryCipherInstance<Twofish256_GCM>>("twofish-256-gcm"),
-        make_shared<CryCipherInstance<Twofish256_CFB>>("twofish-256-cfb"),
+        make_shared<CryCipherInstance<Twofish256_CFB>>("twofish-256-cfb", INTEGRITY_WARNING),
         make_shared<CryCipherInstance<Twofish128_GCM>>("twofish-128-gcm"),
-        make_shared<CryCipherInstance<Twofish128_CFB>>("twofish-128-cfb"),
+        make_shared<CryCipherInstance<Twofish128_CFB>>("twofish-128-cfb", INTEGRITY_WARNING),
         make_shared<CryCipherInstance<Serpent256_GCM>>("serpent-256-gcm"),
-        make_shared<CryCipherInstance<Serpent256_CFB>>("serpent-256-cfb"),
+        make_shared<CryCipherInstance<Serpent256_CFB>>("serpent-256-cfb", INTEGRITY_WARNING),
         make_shared<CryCipherInstance<Serpent128_GCM>>("serpent-128-gcm"),
-        make_shared<CryCipherInstance<Serpent128_CFB>>("serpent-128-cfb"),
+        make_shared<CryCipherInstance<Serpent128_CFB>>("serpent-128-cfb", INTEGRITY_WARNING),
         make_shared<CryCipherInstance<Cast256_GCM>>("cast-256-gcm"),
-        make_shared<CryCipherInstance<Cast256_CFB>>("cast-256-cfb"),
+        make_shared<CryCipherInstance<Cast256_CFB>>("cast-256-cfb", INTEGRITY_WARNING),
         make_shared<CryCipherInstance<Mars448_GCM>>("mars-448-gcm"),
-        make_shared<CryCipherInstance<Mars448_CFB>>("mars-448-cfb"),
+        make_shared<CryCipherInstance<Mars448_CFB>>("mars-448-cfb", INTEGRITY_WARNING),
         make_shared<CryCipherInstance<Mars256_GCM>>("mars-256-gcm"),
-        make_shared<CryCipherInstance<Mars256_CFB>>("mars-256-cfb"),
+        make_shared<CryCipherInstance<Mars256_CFB>>("mars-256-cfb", INTEGRITY_WARNING),
         make_shared<CryCipherInstance<Mars128_GCM>>("mars-128-gcm"),
-        make_shared<CryCipherInstance<Mars128_CFB>>("mars-128-cfb")
+        make_shared<CryCipherInstance<Mars128_CFB>>("mars-128-cfb", INTEGRITY_WARNING)
 };
 
 const CryCipher& CryCiphers::find(const string &cipherName) {
@@ -71,7 +80,7 @@ const CryCipher& CryCiphers::find(const string &cipherName) {
     return **found;
 }
 
-vector<string> CryCiphers::supportedCiphers() {
+vector<string> CryCiphers::supportedCipherNames() {
     vector<string> result;
     for (const auto& cipher : CryCiphers::SUPPORTED_CIPHERS) {
         result.push_back(cipher->cipherName());

src/CryCipher.h

@@ -10,14 +10,15 @@ namespace cryfs {
 
 class CryCipher {
 public:
-    virtual std::string cipherName() const = 0;
+    virtual const std::string &cipherName() const = 0;
+    virtual const boost::optional<std::string> &warning() const = 0;
     virtual cpputils::unique_ref<blockstore::BlockStore> createEncryptedBlockstore(cpputils::unique_ref<blockstore::BlockStore> baseBlockStore, const std::string &encKey) const = 0;
     virtual std::string createKey() const = 0;
 };
 
 class CryCiphers {
 public:
-    static std::vector<std::string> supportedCiphers();
+    static std::vector<std::string> supportedCipherNames();
 
     static const CryCipher& find(const std::string &cipherName);
 

src/CryConfigLoader.cpp

@@ -43,9 +43,23 @@ void CryConfigLoader::_initializeConfigWithWeakKey(CryConfig *config) {
 }
 
 void CryConfigLoader::_generateCipher(CryConfig *config) {
-  vector<string> ciphers = CryCiphers::supportedCiphers();
+  vector<string> ciphers = CryCiphers::supportedCipherNames();
-  int cipherIndex = _console->ask("Which block cipher do you want to use?", ciphers);
+  string cipherName = "";
-  config->SetCipher(ciphers[cipherIndex]);
+  bool askAgain = true;
+  while(askAgain) {
+    int cipherIndex = _console->ask("Which block cipher do you want to use?", ciphers);
+    cipherName = ciphers[cipherIndex];
+    askAgain = !_showWarningForCipherAndReturnIfOk(cipherName);
+  };
+  config->SetCipher(cipherName);
+}
+
+bool CryConfigLoader::_showWarningForCipherAndReturnIfOk(const string &cipherName) {
+  auto warning = CryCiphers::find(cipherName).warning();
+  if (warning == boost::none) {
+    return true;
+  }
+  return _console->askYesNo(string() + (*warning) + " Do you want to take this cipher nevertheless?");
 }
 
 void CryConfigLoader::_generateEncKey(CryConfig *config) {

src/CryConfigLoader.h

@@ -35,6 +35,8 @@ private:
   void _generateWeakEncKey(CryConfig *config); // TODO Rename to _generateTestEncKey
   void _generateTestCipher(CryConfig *config);
 
+  bool _showWarningForCipherAndReturnIfOk(const std::string &cipherName);
+
   cpputils::unique_ref<Console> _console;
 };