Password-protect a file

What encrypting a file means

Encryption turns a file's content into data that means nothing without the key. Octoolo makes the key from your password with Argon2id, a method built to be slow and memory-hungry (64 MiB and 3 passes for every try, with a new random salt for every locked file), so trying one password after another takes a long time. The file is then sealed with XChaCha20-Poly1305 and a 256-bit key, in pieces of 1 MiB with a check on each: a locked file that was changed, damaged or cut short does not open, and Octoolo tells you rather than handing back a broken file. The header that holds the hint is checked too.

How safe it is still comes down to the password. A short or common one can be guessed whatever the encryption; a long passphrase of several unrelated words is far harder. The meter under the password shows how easy it is to guess, and the password generator makes good ones.

Octoolo's lock or the program's own password?

Word, Excel and PowerPoint can put a password on their own files, and PDF files can carry one too. That suits a file you send: the other person opens it in their usual program. Octoolo's lock is for keeping files private on your own PC. It works the same for every kind of file, photos, videos and plain text included, and a .olock file opens only in Octoolo, so it is not the way to send a file to someone who does not have it. For that, a ZIP with a password opens in common archivers.

Careful with the original

Locking writes the locked file first, reads it back whole and compares it with the original, and only then removes the original. If the file is open in another program, Octoolo stops before changing anything and asks you to close it there and try again. The original is deleted, not moved to the Recycle Bin, because an unlocked copy would wait there. On SSDs, deleted data is not reliably overwritten, so think of the lock as protecting the file from now on rather than wiping the old copy from the disk.