How to verify ECC Signature from wolfSSL with OpenSSL - c

Question

I am new to Elliptic Curve Cryptography, openSSL and wolfSSL. My context is that I generate KeyPair from command line with openssl and import the private key to my code. Then I use wolfSSL to generate signature and output it.
I save the output in DER format and try to verify with openSSL, the verification fails.
If I Sign and Verify inside my code with wolfSSL, it verifies successfully and also it's successful if I sign and verify in command line with openSSL.
Is there an encoding issue, which I am not sure about?
Update Code
// ECC public key
const uint8_t pubKey[] ={Hex Format key};
// ECC Signature from wolfSSL
char* sigString = {Signature from wolfSSL returned as char};
/* TYPE CONVERTIONS*/
const uint8_t *der_bytes_copy;
const uint8_t *pub_bytes_copy;
der_bytes_copy = (const unsigned char*)sigString;
pub_bytes_copy = pubKey;
EC_KEY *ECpubkey;
size_t keySize = sizeof(pubKey);
int eccgrp;
eccgrp = OBJ_txt2nid("secp256r1");
ECpubkey = EC_KEY_new_by_curve_name(eccgrp);
o2i_ECPublicKey(&ECpubkey, &pub_bytes_copy, keySize);
ECDSA_SIG *signature;
signature = d2i_ECDSA_SIG(NULL, &der_bytes_copy, signedSize);
uint8_t digest[36];
int verified;
const char message[] = "Test for Authenticate Kernel with ECC";
SHA256_CTX ctx;
SHA256_Init(&ctx);
SHA256_Update(&ctx, (const uint8_t*)message,sizeof(message));
SHA256_Final(digest, &ctx);
verified = ECDSA_do_verify(digest, sizeof(digest), signature, ECpubkey);
The private key is used with wolfSSL to sign the message and then the public key with openssl to verify, but this stops abruptly.

Answer 1

In the past when working with openSSL and comparing sign values to wolfSSL I have found that OpenSSL does the following steps when signing:
Read in and decode the key
compute a hash
Signature Encode the hash
sign the encoded hash
Base64 Encode the signature
OpenSSL does not make this apparent or user-friendly so unfortunately it's something you have to discover as you have.
Please use the following steps in wolfSSL to achieve your desired output:
1 Create or import your ECC key
2 Compute the sha hash on the input as you did previously
3 Encode the hash with this API call: encodedSz = wc_EncodeSignature(encodedOutput, hashInput, SHA256_DIGEST_SIZE, SHA256h);
4 Sign the encoded hash
5 Now do the verify
Let us know if that works for you.