Verify HTTPS certificate chains using OpenSSL API

Question

I wanted verify HTTPS certificate chains using OpenSSL. After trials and errors, I managed to do this using s_client

openssl s_client -connect google.com:https -CApath root < /dev/null

where root contains two root CA certs for Google (I'm not sure if both are necessary but it this way works) that I downloaded from upstream.

$ ls -1 root
594f1775.0 // generated by c_rehash
7999be0d.0 // generated by c_rehash
Equifax_Secure_Certificate_Authority.pem
GeoTrust_Global_CA.pem

The above openssl s_client command works fine and returns 1 as expected.

depth=3 /C=US/O=Equifax/OU=Equifax Secure Certificate Authority
verify return:1
depth=2 /C=US/O=GeoTrust Inc./CN=GeoTrust Global CA
verify return:1
depth=1 /C=US/O=Google Inc/CN=Google Internet Authority G2
verify return:1
depth=0 /C=US/ST=California/L=Mountain View/O=Google Inc/CN=*.google.com
verify return:1

So far so good. However, when I tried to implement the same functionality using libssl (i.e. OpenSSL APIs) , I couldn't get it work. I've already specified root dir as CAPath (via SSL_CTX_load_verify_locations), but it kept giving error 20:

20 X509_V_ERR_UNABLE_TO_GET_ISSUER_CERT_LOCALLY: unable to get local issuer certificate the issuer certificate could not be found: this occurs if the issuer certificate of an untrusted certificate cannot be found.

I've been debugging for a while, but no clue at all. Any help is appreciated!

#include <openssl/ssl.h>
#include <openssl/bio.h>
#include <openssl/err.h>
#include <openssl/x509.h>
#include <openssl/x509v3.h>
#include <openssl/bn.h>
#include <openssl/asn1.h>
#include <openssl/x509_vfy.h>
#include <openssl/pem.h>

#include <stdio.h>
#include <string.h>

#define MAX_LENGTH 1024

int main()
{
    BIO * bio;
    SSL * ssl;
    SSL_CTX * ctx;

    int p;

    /* Set up the library */
    ERR_load_BIO_strings();
    SSL_load_error_strings();
    SSL_library_init();
    OpenSSL_add_all_algorithms();

    /* Set up the SSL context */
    const SSL_METHOD *meth = SSLv23_client_method();
    ctx = SSL_CTX_new(meth);
    if (ctx == NULL) {
        ERR_print_errors_fp(stderr);
        SSL_CTX_free(ctx);
        return -1;
    }


    char* store_path = "./root";
    if(!SSL_CTX_load_verify_locations(ctx, NULL, store_path))
    {
        fprintf(stderr, "Can't load trusted CA from %s\n", store_path);
        return -1;
    }

    /* Setup the connection */
    bio = BIO_new_ssl_connect(ctx);
    BIO_get_ssl(bio, & ssl);
    SSL_set_mode(ssl, SSL_MODE_AUTO_RETRY);

    // Set
    SSL_CTX_set_verify_depth(ctx, 50);
    SSL_CTX_set_verify(ctx, SSL_VERIFY_PEER, NULL);

    /* Create and setup the connection */

    BIO_set_conn_hostname(bio, "www.google.com:https");
    if(BIO_do_connect(bio) <= 0)
    {
        ERR_print_errors_fp(stderr);
        BIO_free_all(bio);
        SSL_CTX_free(ctx);
        return 0;
    }

    if(SSL_get_verify_result(ssl) != X509_V_OK)
    {
        fprintf(stderr, "Verification Error: %ld\n", SSL_get_verify_result(ssl));
        ERR_print_errors_fp(stderr);
        BIO_free_all(bio);
        SSL_CTX_free(ctx);
        return 0;
    }

    /* Close the connection and free the context */
    BIO_free_all(bio);
    SSL_CTX_free(ctx);
    return 0;
}

Verify HTTPS certificate chains using OpenSSL API

0 Answers0