Tag Archives: Objective C

Using an RSA public key generated by OpenSSL in iOS

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

The anatomy of a page curl

As I was developing the ABC of the Sea App, which is an interactive picture-book based on a proof-of-concept Tara (my wife) made many years ago and did not publish, one of the early and obvious items on the checklist of cool things it should do is have a nice page curl transition when moving between pages. Initially I expected this to be easy – Apples Apps do this, iBooks on the iPad especially, so it’s built in, right?

Wrong. Well, mostly wrong. I quickly discovered that the only documented curling transition for a UIView goes up/down, not left/right. It’s the one that Maps uses. Some Googling then revealed that an undocumented transition did perform left/right curling. However, being undocumented means it’s not viable for an App Store submission. It may later acquire an official constant and become kosher, but not yet.

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