OPENSSL X509证书验证

步骤：
1）初始化环境
a.新建证书存储区X509_STORE_new()
b.新建证书校验上下文X509_STORE_CTX_new()

2）导入根证书
a.读取CA证书，从DER编码格式化为X509结构d2i_X509()
b.将CA证书导入证书存储区X509_STORE_add_cert()

3）导入要校验的证书test
a.读取证书test，从DER编码格式化为X509结构d2i_X509()
b.在证书校验上下文初始化证书test,X509_STORE_CTX_init()
c.校验X509_verify_cert

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

#include <openssl/evp.h>
#include <openssl/x509.h>

#define CERT_PATH "/home/ckelsel/work/rc4/cert"
#define ROOT_CERT "ca.cer"
#define WIN71H "win71h.cer"
#define WIN71Y "win71y.cer"


#define GET_DEFAULT_CA_CERT(str) sprintf(str, "%s/%s", CERT_PATH, ROOT_CERT)
#define GET_CUSTOM_CERT(str, path, name) sprintf(str, "%s/%s", path, name)

#define MAX_LEGTH 4096


int my_load_cert(unsigned char *str, unsigned long *str_len,
              const char *verify_cert, const unsigned int cert_len)
{
    FILE *fp;
    fp = fopen(verify_cert, "rb");
    if ( NULL == fp)
    {
        fprintf(stderr, "fopen fail\n");
        return -1;
    }

    *str_len = fread(str, 1, cert_len, fp);
    fclose(fp);
    return 0;
}

X509 *der_to_x509(const unsigned char *der_str, unsigned int der_str_len)
{
    X509 *x509;
    x509 = d2i_X509(NULL, &der_str, der_str_len);
    if ( NULL == x509 )
    {
        fprintf(stderr, "d2i_X509 fail\n");

        return NULL;
    }
    return x509;
}
int x509_verify()
{
    int ret;
    char cert[MAX_LEGTH];

    unsigned char user_der[MAX_LEGTH];
    unsigned long user_der_len;
    X509 *user = NULL;

    unsigned char ca_der[MAX_LEGTH];
    unsigned long ca_der_len;
    X509 *ca = NULL;

    X509_STORE *ca_store = NULL;
    X509_STORE_CTX *ctx = NULL;
    STACK_OF(X509) *ca_stack = NULL;

    /* x509初始化 */
    ca_store = X509_STORE_new();
    ctx = X509_STORE_CTX_new();

    /* root ca*/
    GET_DEFAULT_CA_CERT(cert);
    /* 从文件中读取 */
    my_load_cert(ca_der, &ca_der_len, cert, MAX_LEGTH);
    /* DER编码转X509结构 */
    ca = der_to_x509(ca_der, ca_der_len);
    /* 加入证书存储区 */
    ret = X509_STORE_add_cert(ca_store, ca);
    if ( ret != 1 )
    {
        fprintf(stderr, "X509_STORE_add_cert fail, ret = %d\n", ret);
        goto EXIT;
    }

    /* 需要校验的证书 */
    GET_CUSTOM_CERT(cert, CERT_PATH, WIN71H);
    my_load_cert(user_der, &user_der_len, cert, MAX_LEGTH);
    user = der_to_x509(user_der, user_der_len);

    ret = X509_STORE_CTX_init(ctx, ca_store, user, ca_stack);
    if ( ret != 1 )
    {
        fprintf(stderr, "X509_STORE_CTX_init fail, ret = %d\n", ret);
        goto EXIT;
    }

    //openssl-1.0.1c/crypto/x509/x509_vfy.h
    ret = X509_verify_cert(ctx);
    if ( ret != 1 )
    {
        fprintf(stderr, "X509_verify_cert fail, ret = %d, error id = %d, %s\n",
                ret, ctx->error, X509_verify_cert_error_string(ctx->error));
        goto EXIT;
    }
EXIT:
    X509_free(user);
    X509_free(ca);

    X509_STORE_CTX_cleanup(ctx);
    X509_STORE_CTX_free(ctx);

    X509_STORE_free(ca_store);

    return ret == 1 ? 0 : -1;
}

int main()
{
    OpenSSL_add_all_algorithms();
    x509_verify();
    return 0;
}