how to get the Keyusage value from the X509 certificate?

Question

I want to retrieve the Key usage value from the X509 structured certificate , i tried the following code

 X509* lcert=NULL;
 lCert=PEM_read(filename); // fun         


        

Answer 1

I used the below code to get the Key usage value . Method 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
    }                

method 2:

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