ECDSA with nrfutil generated key

RE: ECDSA with nrfutil generated key

Vidar Berg — Tue, 25 May 2021 09:28:03 GMT

The returned signature contains both the r and s component. First half is the r (byte 0 - 31), and the second half is the s (byte 32 - 63). Hope this helps.

RE: ECDSA with nrfutil generated key

MLai — Mon, 24 May 2021 06:53:47 GMT

Thx for your reply, I can use the key generated from openssl now. But now I am trying to change the p1363 format of my signature to ASN1 format. I would like to know is there any way to do this in sdk 15.2. The function I am using now needs to state what is r and s, can I have any information when I generated the signature from nrf_crypto_ecdsa_sign, I look into the function and found that backend_implementation return the whole signature.

RE: ECDSA with nrfutil generated key

Vidar Berg — Wed, 19 May 2021 12:41:45 GMT

Hi MLai,

I think the discrepancy may be explained by different endianesses. openssl use big-endian while nrfutil use little endian. If you look at the bootloader implementation, you can see that we use nrf_crypto_internal_double_swap_endian() to changes the endianess prior to calling the nrf_crypto_ecc_public_key_from_raw() function.

Best regards,

Vidar