Question

我想从X509结构化证书中检索密钥使用价值，我尝试了以下代码

 X509* lcert=NULL;
 lCert=PEM_read(filename); // function will return the certificate in X509
unsigned long lKeyusage= lCert->ex_kusage;

当我打印lKeyusage值时...有时候我得到128 ...有时我得到0相同的证书.. 任何人都能告诉我这是错误吗？如果我做错了，请给我一些示例代码或正确的API ..

Answer 1

我认为最简单的方法是使用内存BIO：

...
X509 *lcert = NULL;
BUF_MEM *bptr = NULL;
char *buf = NULL;
int loc;

FILE *f = fopen("your cert goes here", "rb");
if( (lcert = PEM_read_X509(f, &lcert, NULL, NULL)) == NULL){
    // error handling...
}

loc = X509_get_ext_by_NID( lcert, NID_key_usage, -1);
X509_EXTENSION *ex = X509_get_ext(lcert, loc);

BIO *bio = BIO_new(BIO_s_mem());
if(!X509V3_EXT_print(bio, ex, 0, 0)){
    // error handling...
}
BIO_flush(bio);
BIO_get_mem_ptr(bio, &bptr);

// now bptr contains the strings of the key_usage, take 
// care that bptr->data is NOT NULL terminated, so
// to print it well, let's do something..
buf = (char *)malloc( (bptr->length + 1)*sizeof(char) );

memcpy(buf, bptr->data, bptr->length);
buf[bptr->length] = '\0';

// Now you can printf it or parse it, the way you want...
printf ("%s\n", buf);

...

就我而言，对于teste证书，它已经打印了＃34;数字签名，不可否认，密钥加密＆＃34;

还有其他方法，例如使用ASN1_BIT_STRING *。如果上述内容不符合您的需求，我可以告诉您。

问候。

Answer 2

我使用以下代码获取Key使用价值。方法1;

   //iCertificate is in X509 format
   ASN1_BIT_STRING* lASN1UsageStr;
   lASN1UsageStr=(ASN1_BIT_STRING *)X509_get_ext_d2i(iCertificate,NID_key_usage,NULL,NULL);
    if(lASN1UsageStr == NULL)
    {
        cout<<" get ext_d2i function returns errors";
    }
    else if(lASN1UsageStr->length > 0) 
    {
        lKeyUsage = lASN1UsageStr->data[0];
        if(lASN1UsageStr->length > 1)
        { 
               lKeyUsage |= lASN1UsageStr->data[1] << 8;
        }// else{}     
    } else 
    {
        lKeyUsage = -1;    //invalid keyusage
    }

方法2：

     X509_check_ca(lcert) ;       
     //need to call before the 
     unsigned long lKeyusage= lCert->ex_kusage;

Answer 3

来自ssl\ssl_lib.c，第2365行，OpenSSL v 1.0.2d：

/* This call populates extension flags (ex_flags) */

X509_check_purpose(x, -1, 0);

所以OpenSSL开发人员就是这样使用的。

如果深入挖掘，你可能会发现呼叫x509v3_cache_extensions，填充标志，由锁保护。

如何从X509证书中获取Keyusage值？

3 个答案: