nRF9160-DK ECDSA Informations

[Gioele]

Hello!
We are trying to sign our data using ECDSA (developer.nordicsemi.com/.../README.html) so we are able to send to our blockchain all the information required. The problems that we are facing are:
1)How can we set the right private and public keys derived from our Ethereum account?
2)How can we understand the values of r,s and v?
Please help us! Thank's!

[Gioele]

1)I should set the private key with my private key of the Ethereum Account.
2)r,s, and v are the sign values that I should have like the output from ECDSA.

[Amanda Hsieh]

Hi, 

1) Normally, keys are generated on the device, and not downloaded to the device. I do not know enough about Ethereum key usage, but we do support psa_import_key for ECDSA indeed. Since we support PSA APIs for ECDSA, you should read the documentation from these APIs. In the documentation of the PSA APIs, you can also find references to the internals of the ECDSA algorithm like the RFCs etc.

https://armmbed.github.io/mbed-crypto/html/

2) For the r,s, and v values, you can check these APIs. They do document this in 10.7. Asymmetric signature. I also see there are tutorials, even some specifically for blockchains with google. 

-Amanda

[Gioele]

The basic problem is that we have a big gap in our project.

We have an Ethereum Account and each Ethereum account owns a personal private key. We probably need to sign our message with this key. We read the documentation but we are not able to set our key.

[Amanda Hsieh]

Hi, 

We don't have enough knowledge of the Ethereum key usage. 

As I explained in the first reply. The ECDSA sample has a "int import_ecdsa_pub_key(void)" function. Guess this will be good to import the public key. The ECDSA sample use psa_generate_key() to generate a key pair. You could import an external key by using the psa_import_key() instead.

-Amanda