Author Archives: Chris Luke

Graphviz example: Overriding the ‘method’

Basic example demonstrating how to override the generation method; in this case to the experimental Graphlib_Dot method.

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Adding SVG support to TFO-Graphviz

A TFO-Graphviz plugin user recently posted some issues he was having with the plugin. One of his requests was to add the SVG output format which I had hitherto omitted because of the previous lack of browser support. Time has passed, it is time to fix that omission.

For maximum effect this also meant the introduction of the width and height attributes. This an example of the SVG output scaled to 100% of the width of its container on the page:

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FreeBSD ports… good but a pain.

So. I wanted to install gnupg from FreeBSD ports on an older box. Somehow it depended on something that depended on the LDAP libraries. Which broke authentication on the box. And in fixing that, lots of other dependencies needed to be updated. It turned into a horrible mess and some ports wouldn’t reinstall cleanly and no amount of portupgrade/portmaster shenanigans would fix it without removing swathes of stuff first.

In trying to find out which shared libraries were now broken, I wrote a very crude script to find out which binaries broke.
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ABC of the Sea released!

About a week ago ABC of the Sea was accepted by Apple for inclusion in the App Store! It’s a universal app that will work on all recent iOS devices but it really is visually more exciting on the iPad.

Obligatory plug: It’s only 99¢ (or other local denomination)! Go buy it!

ABC of the Sea is a children-focused animated book featuring 26 pages of hand-drawn marine life. The illustrations were originally produced by my wife many years ago but never published. Our own child can now read and a print of the book surfaced which she thoroughly enjoyed. We then had the idea to turn it into an iPad application. Each page has been carefully, but subtly animated in a fashion largely consistent with how the creature (or plant) behaves in its natural habitat, though some artistic license has been taken if the real-life movements would be virtually undetectable. Continue reading →

Using an RSA public key generated by OpenSSL in iOS

Authors note: This article was written in 2011; it is possible some of the information here is no longer accurate.

Apple have gone to pains to make cryptography in iOS (and MacOS in general) secure, building a layer between applications and the low-level stuff, like OpenSSL. The principle is to keep these functions in separate address space thus significantly reducing the surface area available for malicious code to find a weakness. In iOS this separation is enforced and, significantly, the documentation is sparse and terse. Public key use without also using certificates is mentioned but only in the context of using keys generated on the device. Posts on the Apple Developer forums indicate that using certificates is suggested because using public key pairs is “involved“. It turns out that the reason it’s involved is because of some odd implementation details and the aforementioned lack of documentation or useful examples.

I was developing a mechanism to verify some data that was generated outside the device with a public key. Using a simple key pair generated by OpenSSL at a command line it was very simple to create scripts in Perl and PHP to produce (and sign) and then decode (and validate) some data using this key pair. The functions to add a public or a private key to the keychain are there in iOS but they don’t work as expected. Continue reading →

Graphviz Plugin Demo

I came across the EHT Graphviz plugin for WordPress and, whilst useful, it has a very clumsy shortcode parser, is not well documented and only supports a subset of the Graphviz functionality. Now Graphviz is not exactly a standard for clear documentation but it is a useful tool for flow or organisational diagramming.

So I wrote my own WordPress plugin, which is demonstrated here. Continue reading →