At the time of transmission, the file is encrypted and transmitted so that the contents of the file being transferred can not be known by others.
File transfer using the 6-digit key transfers files directly between the two devices, and does not store files on the server. So you do not have to worry about file leaks.
For link sharing and send to device, files are uploaded to the server temporarily. All files are encrypted and stored to protect against external attacks and spills. Stored files are automatically deleted from the server after expiration.