jrnl/docs/encryption.md

Encryption

Encrypting and decrypting

If you don't choose to encrypt your file when you run jrnl for the first time, you can encrypt your existing journal file or change its password using

jrnl --encrypt

If it is already encrypted, you will first be asked for the current password. You can then enter a new password and your plain journal will replaced by the encrypted file. Conversely,

jrnl --decrypt

will replace your encrypted journal file by a Journal in plain text. You can also specify a filename, ie. jrnl --decrypt plain_text_copy.txt, to leave your original file untouched.

Storing passwords in your keychain

Whenever you encrypt your journal, you are asked whether you want to store the encryption password in your keychain. If you do this, you won't have to enter your password every time you want to write or read your journal.

If you don't initially store the password in the keychain but decide to do so at a later point -- or maybe want to store it on one computer but not on another -- you can simply run jrnl --encrypt on an encrypted journal and use the same password again.

A note on security

While jrnl follows best practises, true security is an illusion. Specifically, jrnl will leave traces in your memory and your shell history -- it's meant to keep journals secure in transit, for example when storing it on an untrusted services such as Dropbox. If you're concerned about security, disable history logging for journal in your .bashrc

HISTIGNORE="$HISTIGNORE:jrnl *"

If you are using zsh instead of bash, you can get the same behaviour adding this to your zshrc

setopt HIST_IGNORE_SPACE
alias jrnl=" jrnl"

The fish shell does not support automatically preventing logging like this. To prevent jrnl commands being logged by fish, you must make sure to type a space before every jrnl command you enter. To delete existing jrnl commands from fish’s history, run history delete --prefix 'jrnl '.

Manual decryption

Should you ever want to decrypt your journal manually, you can do so with any program that supports the AES algorithm in CBC. The key used for encryption is the SHA-256-hash of your password, the IV (initialisation vector) is stored in the first 16 bytes of the encrypted file. The plain text is encoded in UTF-8 and padded according to PKCS#7 before being encrypted. Here's a Python script that you can use to decrypt your journal

#!/usr/bin/env python3

import argparse
from Crypto.Cipher import AES
import getpass
import hashlib
import sys

parser = argparse.ArgumentParser()
parser.add_argument("filepath", help="journal file to decrypt")
args = parser.parse_args()

pwd = getpass.getpass()
key = hashlib.sha256(pwd.encode('utf-8')).digest()

with open(args.filepath, 'rb') as f:
    ciphertext = f.read()

crypto = AES.new(key, AES.MODE_CBC, ciphertext[:16])
plain = crypto.decrypt(ciphertext[16:])
plain = plain.strip(plain[-1:])
plain = plain.decode("utf-8")
print(plain)