Example C Program: Using CertOIDToAlgId and CertCompareIntegerBlob

The following example demonstrates using the CertOIDToAlgId and CertCompareIntegerBlob functions.

First, all available OIDs are enumerated using CryptEnumOIDInfo. Code used with this function also demonstrates the use of a callback function. The callback function demonstrates break logic to pause between each OID group and after presenting information on a set number of OIDs.

Second, three object identifier (OID) strings are converted into DWORD algorithm identifier integers using CertOIDToAlgId. The code also demonstrates that all OID strings do not have related algorithm identifiers.

Finally, the example demonstrates comparing integer BLOBs. This example demonstrates the truncation of leading 0x00's from positive numbers and leading 0xFF's from negative numbers.

It also shows that integers are compared as though they are stored in little-endian form with the most significant digits on the right.


#pragma comment(lib, "crypt32.lib")

#include <windows.h>
#include <stdio.h>
#include <Wincrypt.h>

//-------------------------------------------------------------------
// Copyright (C) Microsoft.  All rights reserved.
// Declare a wait function to be defined following main.

void my_wait(char *s);

//-------------------------------------------------------------------
// Callback function to print information
// saved in each CRYPT_OID_INFO structure.
// This function counts the number of lines printed
// and does a wait for each new ground and after any four
// report groups are printed.

static BOOL WINAPI EnumInfoCallback(
     PCCRYPT_OID_INFO pInfo,
     void *pvArg
    )
{
static int old_oid = 0;
static int break_counter = 0;

if( old_oid < pInfo->dwGroupId)
{
     if(old_oid > 0)
     {
          my_wait("\n Begin new group. \n Hit enter to continue.");
          break_counter=0;
     }
     old_oid = pInfo->dwGroupId;
     printf("\nNew Group ID %d \n",old_oid);
}
printf("  OID: %s\n  Name: %S\n",
       pInfo->pszOID, pInfo->pwszName);

//-------------------------------------------------------------------
// If there is an AlgId, print it.

if( pInfo->Algid > 0)
{
     printf("  Algorithm ID hexadecimal %x \n\n",pInfo->Algid);
}
else
{
     printf("\n");
}

if(++break_counter > 4)
{ 
     break_counter = 0;
     my_wait("\n   Hit enter to continue.");
}
return TRUE;
}

void main()
{
//-------------------------------------------------------------------
// Note: Integer BLOBs are treated as if they
// are stored in little-endian form with the 
// most significant digits on the right. Truncation is 
// therefore from the right.
// Integer BLOBs are also assumed to be signed numbers
// in two's compliment form.
// For negative numbers, 0xFFs on the right are 
// truncated.
// For positive numbers, 0x00s on the right are 
// truncated.

//-------------------------------------------------------------------
// Declare and initialize local variables.

DWORD Alg_Id;
CRYPT_INTEGER_BLOB  Int1, Int2;
BYTE BLOB1data[4] = {0x88, 0xFF, 0xFF, 0xFF};
BYTE BLOB2data[2] = {0x88, 0xFF};
BYTE BLOB3data[4] = {0x01, 0x00, 0x00, 0x00};
BYTE BLOB4data[2] = {0x01, 0x00};
BYTE BLOB5data[4] = {0x01, 0x00, 0x01, 0x00};

//-------------------------------------------------------------------
// Enumerate the algorithm OIDs available.
// Note that this one call to the function with
// dwGroupId set to 0 lists all OIDs in all groups. 

if(!(CryptEnumOIDInfo(
    0,                  // use 0 to enumerate the OIDs in all groups
    0,                  // dwFlags
    NULL,               // no additional parameters are to be 
                        // passed to the callback function.
    EnumInfoCallback    // name of the callback function to be 
                        // called for each OID enumerated.
    )))
{
    printf("Enumeration of algorithm OIDs did not complete.\n");
}

//-------------------------------------------------------------------
// Use CertOIDToAlgId() to 
// convert the szOID_RSA_RC4 Object Identifier string to an 
// algorithm identifier.

if( Alg_Id = CertOIDToAlgId(szOID_RSA_RC4))
{
   // Print the Alg_Id returned in hex.
   printf("szOID_RSA_RC4 / %s is %x\n\n",szOID_RSA_RC4, Alg_Id);
}
else
{
   printf("No ALG_ID for OID szOID_RSA_RC4 / %s.\n", szOID_RSA_RC4);
}

//-------------------------------------------------------------------
// Convert the szOID_RSA_RC2CBC Object Identifier string to an 
// algorithm identifier.

if( Alg_Id = CertOIDToAlgId(szOID_RSA_RC2CBC))
{
   // Print the Alg_Id returned in hex.
   printf("szOID_RSA_RC2CBC / %s is %x\n\n",szOID_RSA_RC2CBC, 
      Alg_Id);
}
else
{
   printf("No ALG_ID for szOID_RSA_RC2CBC / %s.\n",szOID_RSA_RC2CBC);
}

//-------------------------------------------------------------------
// Convert the szOID_RSA_RC5_CBCPad Object Identifier string to an 
// algorithm identifier.

if( Alg_Id = CertOIDToAlgId(szOID_RSA_RC5_CBCPad))
{
   // Print the Alg_Id returned in hex.
   printf("szOID_RSA_RC5_CBCPad / %s is %x\n",szOID_RSA_RC5_CBCPad, 
      Alg_Id);
}
else
{
    printf("No ALG_ID for szOID_RSA_RC5_CBCPad: %s.\n",
      szOID_RSA_RC5_CBCPad);
}

//-------------------------------------------------------------------
// Initialize Int1 and Int2. 

Int1.pbData = (BYTE*)&BLOB1data;
Int2.pbData = (BYTE*)&BLOB2data;

//-------------------------------------------------------------------
// Set the cbData members so that only 
// the leftmost two bytes of the 
// first are compared to the leftmost bytes 
// of the second.

Int1.cbData = 4;  // sizeof(BLOB1data);
Int2.cbData = 2;  // sizeof(BLOB2data);

if( CertCompareIntegerBlob(
     &Int1, 
     &Int2))
{
   printf("The first two bytes of the BLOBs are identical.\n");
}
else
{
   printf("The first two bytes BLOBs are not identical.\n");
}

//-------------------------------------------------------------------
// Reset the cbData members to compare only 
// 1 byte from each.

Int1.cbData=1;
Int2.cbData=1;

if( CertCompareIntegerBlob(
       &Int1, 
       &Int2))
{
    printf("The BLOBs of different length are identical.\n");
}
else
{
    printf("The BLOBs of different length are not identical.\n");
}

//-------------------------------------------------------------------
// Reset to check the positive numbers.

Int1.cbData = 4;
Int2.cbData = 2;
Int1.pbData = BLOB3data;
Int2.pbData = BLOB4data;

if( CertCompareIntegerBlob(
       &Int1, 
       &Int2))
{
   printf("The BLOBs 3 and 4 are identical.\n");
}
else
{
   printf("The BLOBs 3 and 4 are not identical.\n");
}

//-------------------------------------------------------------------
// Compare BLOB 1 and BLOB 3.

Int1.cbData = 4;
Int2.cbData = 4;
Int1.pbData = BLOB1data;
Int2.pbData = BLOB3data;

if( CertCompareIntegerBlob(
       &Int1, 
       &Int2))
{
   printf("BLOBs 1 and 3 are identical.\n");
}
else
{
   printf("BLOBs 1 and 3 are not identical.\n");
}

//-------------------------------------------------------------------
// Compare BLOB 3 and BLOB 5.

Int1.cbData = 4;
Int2.cbData = 4;
Int1.pbData = BLOB5data;
Int2.pbData = BLOB3data;

if( CertCompareIntegerBlob(
       &Int1, 
       &Int2))
{
   printf("BLOBs 5 and 3 are identical.\n");
}
else
{
   printf("BLOBs 5 and 3 are not identical.\n");
}

//-------------------------------------------------------------------
// Compare the first two bytes of BLOB 3 and BLOB 5.

Int1.cbData = 2;
Int2.cbData = 2;
Int1.pbData = BLOB5data;
Int2.pbData = BLOB3data;

if( CertCompareIntegerBlob(
       &Int1, 
       &Int2))
{
   printf("The first two bytes of BLOBs 5 and 3 are identical.\n");
}
else
{
   printf("The first two bytes of BLOBs 5 and 3 not identical.\n");
}
} // end main

//-------------------------------------------------------------------
// Define the my_wait function.
void my_wait(char* s)
{
     printf(s);
     getchar();
}


 

 

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