The desktop version of Telegram stores copies of plain text text messages that anyone can see when they access the computer. The Telegram is known for its great security, enabling end to end encryption. When there is this kind of encryption, it is not possible to read the messages from an intermediary who can ".
An additional feature provided by the Telegram is the Secret chats. With this feature, messages that are exchanged by two users are not synchronized in the cloud of the service, so they are accessible only to the two devices involved in the conversation. So, as long as the device (mobile, tablet, laptop) is secure, messages are also secure.
However, when these messages are stored on the device, they are not encrypted. Instead, they remain in their normal form where everyone can "read" or see if they are pictures or audio-visual clips.
Ο Nathaniel Suchy, managed to open and view the contents of the database that automatically creates the Telegram desktop app. He stated that although on the basis he found it difficult to understand the structure, the messages are stored in unencrypted form.
Analyzing the database to a greater extent, he was able to find elements of his contacts (not just what he could find through the Telegram desktop application itself), but at some points their reading was difficult to impossible. The SQLite database used by the application keeps the data in plain text, just as Signal was discovered to do last week. The discovery was made by Nathaniel Suchy himself.
The only way to encrypt your messages is through your own operating system. In Windows, it should be used BitLocker, FileVault MAC and several distributions Linux there is the ability to encrypt when installing the operating system.