verify_ca.c

#include <stdio.h>
#include <openssl/bn.h>

void printBN(char *msg, BIGNUM *a)
{
    char *number_str_a = BN_bn2hex(a);
    printf("%s %s\n", msg, number_str_a);
    OPENSSL_free(number_str_a);
}

int main()
{
    // init
    BN_CTX *ctx = BN_CTX_new();
    BIGNUM *n = BN_new();
    BIGNUM *e = BN_new();
    BIGNUM *M = BN_new();
    // BIGNUM *d = BN_new();
    BIGNUM *C = BN_new();
    BIGNUM *S = BN_new();

    // assign values
    BN_hex2bn(&n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
    BN_dec2bn(&e, "65537");
    BN_hex2bn(&M, "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"); //hash of the certificate body
    BN_hex2bn(&S, "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");

    // decrypt S: S^e mod n = (M^d mod)^e mod n = M
    BN_mod_exp(C, S, e, n, ctx);

    if (BN_cmp(C, M) == 0)
    {
        printf("Valid Signature! \n");
    }
    else
    {
        printf("Verification fails! \n");
    }

    // clear sensitive data
    BN_clear_free(n);
    BN_clear_free(e);
    BN_clear_free(M);
    BN_clear_free(C);
    BN_clear_free(S);

    return 0;
}