c0d3 :: j0rg3

A collection of tips, tricks and snips. A proud Blosxom weblog. All code. No cruft.

Tue, 20 Dec 2016

Kicking the Crypto-tires

Some time ago I had begun work on my own Pastebin-type project with a few goals. Basically, I wanted to eat all the cakes — and have them too.

  • Both an online user interface and efficient CLI usage
  • Messages encrypted immediately such that database access does not provide one with the contents of the messages
  • Messages capable of self-destructing
  • Database schema that would allow rebuilding the user/message relationship, provided the same password but would not store those relationships
  • Also, JavaScript encryption to appeal to users who don’t know much about cryptography but would like to try
  • The project, honestly, was going swimmingly when derailed by the goings-on of life.

    One of the interesting components of the project was, of course, choosing crypto implementations. There are know shortcomings to handling it in JS but that’s still the most convenient for some users. Outside of the browser, server-side, you had all the same questions about which solution was best. Which protocol(s) should be available?

    Well, I’ve just learned about a project which I would have loved to have available back then. Project Wycheproof can help you test your crypto solutions against known problems and attacks. Featuring 80 tests probing at 40 known bugs, here’s a snip from the introduction:

    Project Wycheproof has tests for the most popular crypto algorithms, including

  • AES-EAXAES-GCM
  • AES-GCM
  • DH
  • DHIES
  • DSA
  • ECDH
  • ECDSA
  • ECIES
  • RSA
  • The tests detect whether a library is vulnerable to many attacks, including

  • Invalid curve attacks
  • Biased nonces in digital signature schemes
  • Of course, all Bleichenbacher’s attacks
  • And many more — we have over 80 test cases
  • Interesting stuff with exciting potential!


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    Permalink: 20161220.kicking.the.crypto.tires

    Wed, 15 May 2013

    Git: an untracked mess?

    There may be times when you find your Git repository burdened with scads of untracked files left aside while twiddling, testing bug patches, or what-have-youse.

    For the especially scatter-brained among us, these things can go unchecked until a day when the useful bits of a git status scroll off the screen due to utterly unimportant stuff. Well, hopefully unimportant.

    But we’d better not just cleave away everything that we haven’t checked in. You wonder:
    What if there’s something important in one of those files?

    You are so right!

    Let’s fix this!

    Firstly, we want a solution that’s reproducible. Only want to invent this wheel once, right?

    Let’s begin with the play-by-play:

    Git, we want a list of what isn’t tracked: git ls-files -o --exclude-standard -z

    We’ll back these files up in our home directory (~), using CPIO but we don’t want a poorly-named directory or finding anything will become its own obstacle. So we’ll take use the current date (date +%Y-%m-%d), directory (pwd) and branch we’re using (git branch) and we’ll twist all of it into a meaningful, but appropriate, directory name using sed. git ls-files -o --exclude-standard -z | cpio -pmdu ~/untracked-git-backup-`date +%Y-%m-%d`.`pwd | sed 's,^\(.*/\)\?\([^/]*\),\2,'`.`git branch | grep "*" | sed "s/* //"`/

    Then Tell Git to remove the untracked files and directories: git clean -d -f

    Ahhhh… Much better. Is there anything left out? Perhaps. What if we decide that moving these files away was a mistake? The kind of mistake that breaks something. If we realize right away, it’s easily-enough undone. But what if we break something and don’t notice for a week or two? It’d probably be best if we had an automated script to put things back the way they were. Let’s do that.

    Simple enough. We’ll just take the opposite commands and echo them into a script to be used in case of emergency.

    Create the restore script (restore.sh), to excuse faulty memory: echo "(cd ~/untracked-git-backup-`date +%Y-%m-%d`.`pwd | sed 's,^\(.*/\)\?\([^/]*\),\2,'`.`git branch | grep "*" | sed "s/* //"`/; find . -type f \( ! -iname 'restore.sh' \) | cpio -pdm `pwd`)" > ~/untracked-git-backup-`date +%Y-%m-%d`.`pwd | sed 's,^\(.*/\)\?\([^/]*\),\2,'`.`git branch | grep "*" | sed "s/* //"`/restore.sh

    Make the restore script executable: chmod u+x ~/untracked-git-backup-`date +%Y-%m-%d`.`pwd | sed 's,^\(.*/\)\?\([^/]*\),\2,'`.`git branch | grep "*" | sed "s/* //"`/restore.sh

    Lastly, the magic, compressed into one line that will stop if any command does not report success: a='untracked-git-backup-'`date +%Y-%m-%d`.`pwd | sed 's,^\(.*/\)\?\([^/]*\),\2,'`.`git branch | grep "*" | sed "s/* //"`; git ls-files -o --exclude-standard -z | cpio -pmdu ~/$a/ && git clean -d -f && echo "(cd ~/$a/; find . -type f \( ! -iname 'restore.sh' \) | cpio -pdm `pwd`)" > ~/$a/restore.sh && chmod +x ~/$a/restore.sh; unset a


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    Permalink: 20130515.git.untracked.mess

    Mon, 13 May 2013

    Zsh and hash

    Documentation for this one seems a bit hard to come by but it is one of the things I love about Zsh.

    I’ve seen many .bashrc files that have things like:
    alias www='cd /var/www'
    alias music='cd /home/j0rg3/music'

    And that’s a perfectly sensible way to make life a little easier, especially if the paths are very long.

    In Zsh, however, we can use the hash command and the shortcut we get from it works fully as the path. Other words, using the version above, if we want to edit ‘index.html’ in the ‘www’ directory, we would have to issue the shortcut to get there and then edit the file, in two steps:
    > www
    > vim index.html

    The improved version in .zshrc would look like:
    hash www=/var/www
    hash -d www=/var/www

    Then, at any time, you can use tilde (~) and your shortcut in place of path.
    > vim ~www/index.html

    Even better, it integrates with Zsh’s robust completions so you can, for example, type cd ~www/ and then use the tab key to cycle through subdirectories and files.

    On this system, I’m using something like this:
    (.zshrc)
    hash posts=/home/j0rg3/weblog/posts
    hash -d posts=/home/j0rg3/weblog/posts

    Then we can make a function to create a new post, to paste into .zshrc. Since we want to be able to edit and save, without partial posts becoming visible, while we are working, we’ll use an extra .tmp extension at the end:
    post() { vim ~posts/`date +%Y-%m`/`date +%Y%m%d`.$1.txt.tmp }

    [ In-line date command unfamiliar? See earlier explanation ]

    But, surely there is going to be a point when we need to save a post and finish it later. For now, let’s assume that only a single post will be in limbo at any time. We definitely don’t want to have to remember the exact name of the post — and we don’t want to have hunt it down every time.

    We can make those things easier like this:
    alias resume="vim `find ~posts/ -name '*.txt.tmp'`"

    Now, we can just enter resume and the system will go find the post we were working on and open it up for us to finish. The file will need the extension renamed from .txt.tmp to only .txt to publish the post but, for the sake of brevity, we’ll think about that (and having multiple posts in editing) on another day.


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    Permalink: 20130513.zsh.and.hash

    Wed, 08 May 2013

    Deleting backup files left behind by Vim

    It’s generally a great idea to have Vim keep backups. Once in awhile, they can really save your bacon.

    The other side of that coin, though, is that they can get left behind here and there, eventually causing aggravation.

    Here’s a snippet to find and eliminate those files from the current directory down:

    find ./ -name '*~' -exec rm '{}' \; -print -or -name ".*~" -exec rm {} \; -print
    This uses find from the current directory down (./) to execute an rm statement on all files with an extension ending in tilde (~)
    Alternatively, you could just store your backups elsewhere. In Vim, use :help backupdir for more information.


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    Permalink: 20130508.delete.vim.backups