nRF9160DK Keccak256 ECDSA SAMPLE

Question

Hello! We are trying to sign our data using ECDSA ( https://developer.nordicsemi.com/nRF_Connect_SDK/doc/latest/nrf/samples/crypto/ecdsa/README.html ) , so we can send our information to an Ethereum Blockchain. The problem is that we don't have the algorithm that we need from the algorithms that Nordics provides to us. Here we are using SHA256 (PSA_ALG_SHA-256) but we need Keccak256. 
 status = psa_hash_compute(PSA_ALG_SHA_256,
 keccak,
 sizeof(keccak),
 m_hash,
 sizeof(m_hash),
 &output_len);
	if (status != PSA_SUCCESS) {
 LOG_INF("psa_hash_compute failed! (Error: %d)", status);
 return APP_ERROR;
	}

/* Sign the hash */
	status = psa_sign_hash(keypair_handle,
 PSA_ALG_DETERMINISTIC_ECDSA(PSA_ALG_SHA_256),
 m_hash,
 sizeof(m_hash),
 m_signature,
 sizeof(m_signature),
 &output_len);
	if (status != PSA_SUCCESS) {
 LOG_INF("psa_sign_hash failed! (Error: %d)", status);
 return APP_ERROR;
	}

Emil Lenngren · Accepted Answer

You can use any external library for calculating Keccak-256. A quick search gave me this: https://github.com/firefly/wallet/blob/master/source/libs/ethers/src/keccak256.c . That replaces psa_hash_compute. 
 You should be able to keep the psa_sign_hash call as it is. In contrary to RSA which includes the hash aglorithm used as part of the signature, this is not done in ECDSA. So you should be able to pass PSA_ALG_DETERMINISTIC_ECDSA(PSA_ALG_SHA_256) there without any issues.

nRF9160DK Keccak256 ECDSA SAMPLE

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