Support for Storing Larger PQC Certificates Across Multiple Flash Sectors on RP2040

[devi1207]

I’m working on integrating Post-Quantum Cryptography (PQC) into the Pico-FIDO firmware using the ML-DSA-65 algorithm . The certificate I need to store (including metadata, public key, and signature) is approximately 6000+ bytes, which exceeds the 4KB flash sector size of the RP2040.

I noticed that the current certificate storage logic seems to use a single 4KB sector (4096 bytes). Since my PQC certificate does not fit into one sector, I would like to know:

Is there any existing support in the code to span certificate storage across multiple flash sectors?

If not, would you recommend a safe way to implement multi-sector certificate storage without affecting other areas of flash?

Any memory layout constraints or reserved areas I should be aware of while modifying flash writes?

[polhenarejos]

It's hard to say. RP Pico uses flash sectors of 4 kB and the filesystem is designed to put the files within a single page. I wrote a basic cache system to avoid multiple writes. Increasing page size will increase notably the memory, not sure how it will respond. Besides this, there's nothing special. I put the material at the end of the flash to avoid overwrites on successive updates (RP2040) or in a dedicated partition (RP2350). So, no other layout constraints.

From what you mention, probably you only need to store the secret material and not the entire certificate (public key and signature can be generated on-the-fly).