feat(toxencrypt): add function to get min length for isEncrypted() to

succeed

Also improve documentation

src/core/toxencrypt.cpp

@@ -55,6 +55,16 @@ ToxEncrypt::ToxEncrypt(Tox_Pass_Key* key) :
 passKey{key}
 {}
 
+/**
+ * @brief  Gets the minimum number of bytes needed for isEncrypted()
+ * @return Minimum number of bytes needed to check if data was encrypted
+ *         using this module.
+ */
+int ToxEncrypt::getMinBytes()
+{
+    return TOX_PASS_ENCRYPTION_EXTRA_LENGTH;
+}
+
 /**
  * @brief Checks if the data was encrypted by this module.
  * @param ciphertext The data to check.
@@ -145,6 +155,8 @@ QByteArray ToxEncrypt::decryptPass(const QString& password, const QByteArray& ci
  * @param  password Password to use for encryption.
  * @return A std::unique_ptr containing a ToxEncrypt object on success, or an
  *         or an empty std::unique_ptr on failure.
+ *
+ *  Derives a key from the password and a new random salt.
  */
 std::unique_ptr<ToxEncrypt> ToxEncrypt::makeToxEncrypt(const QString& password)
 {
@@ -170,6 +182,8 @@ std::unique_ptr<ToxEncrypt> ToxEncrypt::makeToxEncrypt(const QString& password)
  * @param  toxSave The data to read the salt for decryption from.
  * @return A std::unique_ptr containing a ToxEncrypt object on success, or an
  *         or an empty std::unique_ptr on failure.
+ *
+ *  Derives a key from the password and the salt read from toxSave.
  */
 std::unique_ptr<ToxEncrypt> ToxEncrypt::makeToxEncrypt(const QString& password, const QByteArray& toxSave)
 {

src/core/toxencrypt.h

@@ -35,6 +35,7 @@ public:
     ToxEncrypt(const ToxEncrypt& other) = delete;
     ToxEncrypt& operator=(const ToxEncrypt& other) = delete;
 
+    static int getMinBytes();
     static bool isEncrypted(const QByteArray& ciphertext);
     static QByteArray encryptPass(const QString& password, const QByteArray& plaintext);
     static QByteArray decryptPass(const QString& password, const QByteArray& ciphertext);
@@ -44,7 +45,7 @@ public:
     QByteArray decrypt(const QByteArray& ciphertext) const;
 
 private:
-    ToxEncrypt(Tox_Pass_Key* key);
+    explicit ToxEncrypt(Tox_Pass_Key* key);
 
 private:
     Tox_Pass_Key* passKey = nullptr;