pkg/micro-ecc/psa_uecc: convert between SEC 1 and micro-ecc public key formats

[LP-HAW]

Contribution description

micro-ecc uses the SEC 1 public key format without the 0x04 prefix [1]. This PR adds conversions between SEC 1 and micro-ecc public key formats in the micro-ecc PSA backend driver.

[1]: https://github.com/kmackay/micro-ecc/blob/master/README.md#point-representation

Testing procedure

make -C tests/sys/psa_crypto_ecdsa all test

Issues/PRs references

None

[mguetschow]

Thanks, very good catch! How did you find out about that one? If you have some testing data (aka signatures and a matching public key for verify), it would be nice to augment our tests (probably tests/sys/psa_crypto_ecdsa) to make the bug apparent.

[riot-ci]

Murdock results

✔️ PASSED

2ed082a tests/sys/psa_crypto_ecdsa: add test vector

Success	Failures	Total	Runtime
10098	0	10102	15m:06s

Artifacts

• Documentation preview

[LP-HAW]

it would be nice to augment our tests (probably tests/sys/psa_crypto_ecdsa) to make the bug apparent.

I do not have an ATECC608A but I think the psa_crypto_se_ecdsa test should already fail.

[mguetschow]

it would be nice to augment our tests (probably tests/sys/psa_crypto_ecdsa) to make the bug apparent.

I do not have an ATECC608A but I think the psa_crypto_se_ecdsa test should already fail.

Ah really? I think the tests are currently generating a new keypair and using its public part to verify a selfmade signature - which should currently succeed on both hardware and software backends. Only the interaction between different implementations would be a problem.

So a test which imports a public key and verifies a pre-signed message should have passed on the hardware but not with micro-ecc, which you are fixing here.

[LP-HAW]

Only the interaction between different implementations would be a problem.

You're right. I just misunderstood the test.

So a test which imports a public key and verifies a pre-signed message

Seems like a good idea. I gave it a try.

[mguetschow]

Thanks for adding the test vector! I can confirm that the test fails on BOARD=native before the bugfix and passes after applying it.

Just a minor note below.

[mguetschow]

Thanks a lot! :)