Incorrect `ec_params` during startup

[anssi-fr]

Incorrect `ec_params` during startup

[rben-dev]

Hi @GeorgeLyon,

Thanks for your interest in libecc. Have you found the reason behind this behaviour and consider the issue closed?

Regards,
Ryad

[GeorgeLyon]

No, but I found another thread to pull on. I will reopen with new information when I do. Sorry for being undercommunicative

[GeorgeLyon]

I found the fix, the issue was on my end but arose from a bit of confusion on the API level. Some pointer arguments to various ec_params fields (like ec_curve for prj_pt_init) are not only used for initialization, but also stored in the struct and thus must be valid for the entire duration of time that the value is in use. Normally, this isn't an issue (because when do ec_params go away?) but Swift's withUnsafePointer(to:,_:) only guarantees the validity of the pointer for the execution of the provided closure.

The local/global distinction was a red herring, since I was using the global ec_params from multiple code locations (and thus multiple invocations of withUnsafePointer(to:,_:)) but the local test happened entirely in a single invocation. The hex diff was also a red herring, since the wlen field is a single byte and any padding was free to contain junk (likely because of a Swift's interpretation of C structs) 7ffeefbfc250 and 7ffeefbf8ec8 are both actually 4 with some junk bytes on the end.

If you are interested in how I'm using this library, my code is available at https://github.com/GeorgeLyon/OPAQUE