How can we get the part of the elliptic curve from the PKEY and use it as the public key of a digital certificat

[Ericyu0412]

I am trying to get the part of the classical algorithm from the hybrid pkey, and then write it into the digital certificate, but I find that the separated form is octet_string format, which cannot be used directly. How to realize my idea?

[Ericyu0412]

@thb-sb @praveksharma I have successfully separated classical algorithm part from the hybrid pkey.When I use PEM_write_bio_PUBKEY() to process a certificate and encounter an error, what could be the reason? Could it be due to a problem with the newly created EVP_PKEY?

EVP_PKEY *extract_classical_public_key(EVP_PKEY *pkey) {
 struct KeyPair *out;
    int ret = -1;
    out = malloc(sizeof(struct KeyPair));
    if (!out) {
    fprintf(stderr, "Memory allocation for KeyPair failed.\n");
        return NULL; }
    out->pubkey = NULL;
    out->pubkey_len = 0;
    if((EVP_PKEY_get_int_param(pkey,OSSL_PKEY_PARAM_BITS,out->bits)!=1){
    fprintf(stderr, cRED "`EVP_PKEY_get_int_param` failed with param `OSSL_PKEY_PARAM_BITS`: ");
        ERR_print_errors_fp(stderr);
        fputs(cNORM "\n", stderr);
        free(out->bits);
        free(out);
        return NULL;
 }
    if (EVP_PKEY_get_octet_string_param(pkey, OSSL_PKEY_PARAM_ENCODED_PUBLIC_KEY, NULL, 0, &out->encoded_pubkey_len) != 1) {
        fprintf(stderr, cRED "`EVP_PKEY_get_octet_string_param` failed with param `OQS_HYBRID_PKEY_PARAM_CLASSICAL_PUB_KEY`: ");
        ERR_print_errors_fp(stderr);
        fputs(cNORM "\n", stderr);
        free(out);
        return NULL;
    }    
    if (!(out->encoded_pubkey = malloc(out->encoded_pubkey_len))) {
        fprintf(stderr, "Failed to allocate %#zx byte(s)\n", out->encoded_pubkey_len);
        free(out);
        return NULL;
    }  
    if (EVP_PKEY_get_octet_string_param(pkey, OSSL_PKEY_PARAM_ENCODED_PUBLIC_KEY, out->encoded_pubkey, out->encoded_pubkey_len, &out->encoded_pubkey_len) != 1) {
        fprintf(stderr, cRED "`EVP_PKEY_get_octet_string_param` failed with param `OQS_HYBRID_PKEY_PARAM_CLASSICAL_PUB_KEY`: ");
        ERR_print_errors_fp(stderr);
        fputs(cNORM "\n", stderr);
        free(out->encoded_pubkey);
        free(out);
        return NULL;
    } else {
        ret = 0;
    } 
    if (EVP_PKEY_get_octet_string_param(pkey, OQS_HYBRID_PKEY_PARAM_CLASSICAL_PUB_KEY, NULL, 0, &out->pubkey_len) != 1) {
        fprintf(stderr, cRED "`EVP_PKEY_get_octet_string_param` failed with param `OQS_HYBRID_PKEY_PARAM_CLASSICAL_PUB_KEY`: ");
        ERR_print_errors_fp(stderr);
        fputs(cNORM "\n", stderr);
        free(out);
        return NULL;
    }
    if (!(out->pubkey = malloc(out->pubkey_len))) {
        fprintf(stderr, "Failed to allocate %#zx byte(s)\n", out->pubkey_len);
        free(out);
        return NULL;
    }
    if (EVP_PKEY_get_octet_string_param(pkey, OQS_HYBRID_PKEY_PARAM_CLASSICAL_PUB_KEY, out->pubkey, out->pubkey_len, &out->pubkey_len) != 1) {
        fprintf(stderr, cRED "`EVP_PKEY_get_octet_string_param` failed with param `OQS_HYBRID_PKEY_PARAM_CLASSICAL_PUB_KEY`: ");
        ERR_print_errors_fp(stderr);
        fputs(cNORM "\n", stderr);
        free(out->pubkey);
        free(out);
        return NULL;
    } else {
        ret = 0;
    }
    EVP_PKEY *ppkey = EVP_PKEY_new();
    EVP_PKEY_copy_parameters(ppkey,pkey);
    if (ppkey == NULL) {
        fprintf(stderr, "Failed to create new EVP_PKEY.\n");
        free(out->pubkey);
        free(out);
        return NULL;
    }
    if(EVP_PKEY_set_int_param(ppkey,OSSL_PKEY_PARAM_BITS,out->bits)!=1){
    fprintf(stderr, cRED "`EVP_PKEY_set_int_param` failed with param `OSSL_PKEY_PARAM_BITS`: ");
        ERR_print_errors_fp(stderr);
        fputs(cNORM "\n", stderr);
        free(out->bits);
        free(out);
        return NULL;
    }
    if (EVP_PKEY_set_octet_string_param(ppkey, OSSL_PKEY_PARAM_PUB_KEY, out->pubkey, out->pubkey_len) != 1) {
        fprintf(stderr, cRED "`EVP_PKEY_set_octet_string_param` failed with param `OQS_HYBRID_PKEY_PARAM_CLASSICAL_PUB_KEY`: ");
        ERR_print_errors_fp(stderr);
        fputs(cNORM "\n", stderr);
        EVP_PKEY_free(ppkey);
        free(out->pubkey);
        free(out);
        return NULL;
    }    
    if (EVP_PKEY_set_octet_string_param(ppkey, OSSL_PKEY_PARAM_ENCODED_PUBLIC_KEY, out->encoded_pubkey, out->encoded_pubkey_len) != 1) {
        fprintf(stderr, cRED "`EVP_PKEY_set_octet_string_param` failed with param `OQS_HYBRID_PKEY_PARAM_CLASSICAL_PUB_KEY`: ");
        ERR_print_errors_fp(stderr);
        fputs(cNORM "\n", stderr);
        EVP_PKEY_free(ppkey);
        free(out->encoded_pubkey);
        free(out);
        return NULL;
    }
    free(out->pubkey);
    free(out);
    return ppkey;}

[Ericyu0412]

I achieved to genarate selfsigned certificate with classical and post-quantum separated .But I failed to verify it.How to solve it?