Trilium is meant to store all kinds of data - including potentially sensitive data like journals or credentials etc.

For such sensitive data Trilium can protect these notes which essentially means:

• encrypting the note with encryption key based on your password.
  • This means that without your password, protected notes are not decipherable so even if somebody managed to steal your Trilium document, your protected notes could not be read.
• time-limited access to protected notes
  • To first access protected notes you need to enter your password which will decrypt the note and allow you to read / write them. But after certain time period (by default 10 minutes) this decrypted note is unloaded from memory and to read it again you need to enter your password again.
    • This time limit counts from the last interaction with protected session - so e.g. if you continuously write into a protected note, session is getting extended automatically, and you are not kicked out. Once you change to an unprotected note, expiration starts counting and session ends in 10 minutes (unless you again interact with protected notes).
  • This protects against a possible scenario where you leave your computer unlocked for a long time and somebody can access your Trilium application.
• protected notes protect only confidentiality and partially integrity of the notes. User outside the protected sessions can still e.g. delete the protected notes or move them to a new location.

Notes are by default unprotected. If you want your note to be protected, click on shield icon next to the note title as seen here:

In principle Trilium encrypts data, but doesn't encrypt metadata. This specifically means:

Encrypted:

• note title
• note content
• images
• file attachments

Not encrypted:

• structure of the notes - i.e. you can still see that there are protected notes.
• various metadata - e.g. date of last modification
• attributes

... how we get from password to decrypted note:

1. User enters password
2. Password is put into scrypt algorithm together with "password verification" salt to verify that password is correct
3. Password is put into scrypt algorithm together with "encryption" salt which produces a hash
   • here we use scrypt for key stretching
4. Hash produced in the last step is used to decrypt actual data encryption key
   • data encryption key is encrypted with AES-128 with random IV
   • data encryption key is random key generated at the time of document initialization and is constant over the lifetime of the document. If we change password, we re-encrypt only this key.
5. We use data encryption key to decrypt actual data - note title and content.
   • encryption used is again AES-128 with CBC chaining. Unique IV is generated with every encryption operation and stored together with the cipher text.

Please note that protected notes cannot be shared like regular notes.