“Any sufficiently complex bit of code is hard to make easily reusable without abstracting it to a level in which it is essentially useless.”

I was working on my website ValidateModel.com, and I wanted a way to protect files that are uploaded by the users. My solution is to encrypt the files with gpg when they are uploaded. Only the public key is stored on the server and the files are encrypted with this. The only way for the files to be decrypted is for them to be downloaded and then decrypted with my private key.

The steps needed in order to achieve this are:

1. Obtain gpg and generate a public/private key if you don’t already have one (gpg –gen-key)
2. Export your public key to a file (gpg -a –export > pubkey.txt)
3. Upload the pubkey.txt file to your server
4. Create a directory accessible to the webserver (apache) process
5. Create a public keyring in this directory (gpg –no-default-keyring –keyring /path/to/pubring.gpg –import pubkey.txt)
6. Make sure that this file is readable by your webserver process
7. You may now encrypt files using the command line “gpg -q –batch –no-options –no-default-keyring –keyring /path/to/pubring.gpg -r brett –always-trust –output encrypted.enc –encrypt unencrypted.txt”.

Make sure you back up your private keyring - if you lose it, your files will NEVER be decrypted!

Optimization problems are all the rage in finance, because they occur so often (or should occur often, as long as you’re on top of the basics of pricing your trades). Enter the IBM DeveloperWorks article on GNU Linear Programming Kit.

The easiest way to use CVS with ssh is to use ssh-keygen to generate a public/private key without a passphrase (so ssh won’t prompt you for a password). Upload the public key and put it in your ~/.ssh/authorized_keys directory on the ssh server. Try checking out your project now - you should be able to check it out without having to type in a password. Make sure the environment variable CVS_RSH is set to ssh so you are using ssh as the transport.

Put the following line in your .emacs file and you should be able to check stuff in and do version control using emacs and VC:

(setenv "CVS_RSH" "ssh")