Typo guard: kicking it old-school

If you were into microcomputers in the 1980s, you probably remember typing in BASIC programs printed in magazines. Typos were all too frequent, and they'd cause your programs to bomb. Some clever sods came up with a solution -- while you were typing in each line of the program, a checksum would be printed on screen, and before you pressed ENTER on the line, you'd ensure the checksum matched, and if it didn't, you'd fix it.

Well, that idea is now back, in the form of typo-guard. It is a simple Ruby program, with two modes:

• If you feed it a file (via a pipe or input redirection) it will print your file, with checksums prepended, like this:

    $ typo-guard </tmp/some-data
    ZVOWCGQ I love this program.
    KCW7NLQ It is so freaking cool.
  

  You can then print that (heck, run typo-guard </tmp/some-data | lpr if you like) and you've got a written copy of whatever super-important data you want to keep).

• If you just run it on the command line without any arguments, it will prompt you to start entering data. As you type, the checksum on the left will update with each character you enter. Once you get to the end of the line, you can verify the checksum matches the one on the printed copy, and if they match, you can hit ENTER to "save" it. If not, double-check your typed version against the printed copy, until you work out what is different.

The checksum only uses characters which are visually distinctive, so you don't have to worry about whether that's a 0 or a O. Your input data might not be so forgiving; however I can't control that...

Installation

You'll need Ruby installed (1.9.3 or later), and the murmurhash3 and base32 gems installed:

gem install base32 murmurhash3

Once that's in, you can copy or symlink the typo-guard program to anywhere in your PATH.

Use cases

This program was originally written to ensure archival copies of GnuPG and X.509 private keys. Checksum the encrypted, PEM-encoded keys, then print them and store a copy in a fireproof safe at your lawyer, or in a safety deposit box. If you want to be super paranoid, print out a copy of the typo-guard script, too, and keep it with the printouts themselves.

Copyright and Licence

Unless otherwise stated, all code in this repository is covered by the following:

Copyright (C) 2015 Matthew Palmer mpalmer@hezmatt.org

This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License version 3, as published by the Free Software Foundation.

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 General Public License for more details.

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

Contributions

I take bug reports and pull requests on Github, or via e-mail to theshed+typo-guard@hezmatt.org.