Heartnotes

Personal diary app (in the browser) which uses client-side encryption and zero-knowledge authentication.

Try it at https://web.heartnotes.me.

Get it from https://heartnotes.me.

Features:

• 256-bit AES encryption done client-side for maximum security
• Auto-save-as-you-type, with cloud sync running the background
• Full-text search using lunr.js
• Continue editing even if connection goes down.

## Technology

Main ingredients: React.js, Redux, Electron.js.

Encryption details

This uses the SJCL library for AES-256 encryption as well as for the PRNG algorithm to generate random seed data and salts.

We first derive a "master" key from the user's password as follows:

• Use Fortuna PRNG with multiple event inputs (mouse, keyboard, accelerometer etc) to generate a salt.
• Use salt and password as inputs to PBKDF2-SHA512 to generate a 512-bit key. (The number of iterations of PBKDF2 is set such that generation takes 1 second on the user's machine- on a Macbook Air 2012 this easily results in >10000 iterations.
• Store the input salt and PBKDF2 iteration count in the user's account online.
• Set the first 256 bits of the key as the MASTER key.
• Set the second 256 bits of the key as the authentication key (i.e. to login to server).

Now let's generate the encryption key:

• Generate a SHA-256 hash of: user's password + random number (generated using a non-CSRNG)
• Use Fortuna PRNG with multiple event inputs (mouse, keyboard, accelerometer etc) to generate a salt.
• Use salt and hash as inputs to PBKDF2-SHA512 to generate a 512-bit key. (The number of iterations of PBKDF2 is set such that generation takes 1 second on the user's machine- on a Macbook Air 2012 this easily results in >10000 iterations.
• Set the first 256 bits of the key as the ENCRYPTION key.

The next time the user enters the right password, we:

• Use the stored salt and iteration count to regenerate the right MASTER key.
• We use this to decrypt the bundle containing the ENCRYPTION key.

Notes:

• We use the ENCRYPTION key to encrypt the actual entry data (AES-256-GCM, random IV).
• We encrypt the ENCRYPTION key using the MASTER key (AES-256-GCM, random IV) and save it as a bundle in the user's diary file.
• The ENCRYPTION key is currently never changed. Changing the user password simply changes the master key. This allows password change without having to re-encrypt everything.

Development

Node.js 4.4.5+ required.

Setup:

$ npm install

Run web version (http://localhost:3000):

$ gulp

NOTE: Add --minified on the command-line to enable JS and CSS minification during build.

Production build

$ npm run release_web

You will find build assets in the build/ folder.

Release checklist

1. Make final commits
2. Update version in package.json
3. Commit version update and push
4. Tag commit as
5. Push tag
6. Do a production build (see above)
7. Test production build
8. Create release entry on Github and attach built executable
9. Announce to world!

License

Copyright (C) 2015-2016 Ramesh Nair

This program is free software: you can redistribute it and/or modify it under the terms of the GNU Affero General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version.

This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Affero General Public License for more details.

You should have received a copy of the GNU Affero General Public License along with this program. If not, see http://www.gnu.org/licenses/.