OPENSSL X509證書驗證

openssl實作了标準的x509v3數字證書，其源碼在crypto/x509和crypto/x509v3中。其中x509目錄實作了數字證書以及證書申請相關的各種函數，包括了X509和X509_REQ結構的設定、讀取、列印和比較；數字證書的驗證、摘要；各種公鑰的導入導出等功能。x509v3目錄主要實作了數字證書擴充項相關的函數。

在進行身份認證時，首先要對發送給伺服器進行認證的x509證書有效性進行驗證，在Openssl中，可以用一個API接口可以實作：int X509_verify_cert(X509_STORE_CTX *ctx);

接口中形參是X509_STORE_CTX（X509證書庫上下文）類型，在X509證書庫上下文中，存在一個X509證書庫和一個待驗證的X509證書，可以加入信任的證書鍊，也可以加入CRL證書鍊（證書撤銷清單）~

對X509證書有效性進行驗證可以由以下幾個函數來完成~

X509_STORE_CTX *ctx; //證書上下文  
X509_STORE *cert_store; //證書庫，存在證書鍊  
X509* x509; //待驗證X509證書  
ctx = X509_STORE_CTX_new();  

X509_STORE_CTX_init(ctx,cert_store,x509,NULL);  

X509_verify_cert(ctx);//根據傳回值可以确認X509證書是否有效，也可以根據X509_STORE_CTX_get_error和X509_verify_cert_error_string函數來确認無效原因   
           

示例程式如下：

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

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

#define CERT_PATH       "/home/dengaj/Desktop/openssl"
#define ROOT_CERT       "RootCert.crt"
#define CARD_CERT       "CardCert.crt"
#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);
    /* 從檔案中讀取 */
    my_load_cert(ca_der, &ca_der_len, cert, MAX_LEGTH);
    /* DER編碼轉X509結構 */
    ca = der_to_x509(ca_der, ca_der_len);
    /* 加入證書存儲區 */
    ret = X509_STORE_add_cert(ca_store, ca);
    if ( ret != 1 )
    {
        fprintf(stderr, "X509_STORE_add_cert fail, ret = %d\n", ret);
        goto EXIT;
    }

    /* 需要校驗的證書 */
    GET_CUSTOM_CERT(cert, CERT_PATH, CARD_CERT);
    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;
    }
    fprintf(stdout, "X509_verify_cert successful\n");
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;
}
           

第二種方法使用

int X509_verify(X509 * x509, EVP_PKEY * pkey);
           

X509 * root;
   X509 * mycert;

//Get root certificate into root
//Get mycert into mycert.

//Get the public key.
EVP_PKEY * pubkey = X509_get_pubkey(root);

//verify. result less than or 0 means not verified or some error.
int result = X509_verify(mycert, pubkey);

//free the public key.
EVP_PKEY_free(pubkey);