CryptGetKeyParam

The CryptGetKeyParam function retrieves data that govern the operations of a key. Note that in the Microsoft Cryptographic Service Providers, the base symmetric keying material is not obtainable by this function or any other function.

#include <wincrypt.h>
BOOL WINAPI CryptGetKeyParam(
  HCRYPTKEY hKey,  // in
  DWORD dwParam,   // in
  BYTE *pbData,    // out
  DWORD *pcbData,  // in/out
  DWORD dwFlags    // in
);
 

Parameters

hKey

Handle to the key on which to query parameters.

dwParam

Parameter number. See the "Remarks" section for a list of valid parameters.

pbData

Pointer to a buffer that receives the parameter data. The function will copy the specified parameter data to this buffer. The form of this data will vary, depending on the parameter number.

This parameter can be NULL to set the size of this information for memory allocation purposes. For more information, see Common In/Out Parameter Conventions.

pcbData

Pointer to a variable that specifies the size, in bytes, of the buffer pointed to by the pbData parameter. When the function returns, the variable pointed to by the pcbData parameter contains the number of bytes stored in the buffer. This parameter can be NULL, only if pbData is NULL.

Note that when processing the data returned in the buffer, applications need to use the actual size of the data returned. The actual size may be slightly smaller than the size of the buffer specified on input. (On input, buffer sizes are usually specified large enough to insure that the largest possible output data will fit in the buffer.) On output, the variable pointed to by this parameter is updated to reflect the actual size of the data copied to the buffer.

dwFlags

Flag values. This parameter is reserved for future use and should always be zero.

Return Values

If the function succeeds, the return value is TRUE. If it fails, the return value is FALSE. To retrieve extended error information, use the GetLastError function.

The following table lists the error codes most commonly returned by the GetLastError function. The error codes prefaced by "NTE" are generated by the particular CSP you are using.

Remarks

For all key types, the dwParam value can be set to one of the following key parameter types.

If a DSS key is specified by hKey, the dwParam value can also be set to one of the following parameter types.

If a block cipher session key is specified by hKey, the dwParam value can also be set to one of the following parameter types.

The following table lists the possible values for the KP_MODE parameter. These cipher modes are discussed in Encrypting and Decrypting Data.

The following table lists the flags in the bit field that are obtained when the KP_PERMISSIONS parameter is read. These permission flags are ignored by the Microsoft Base Cryptographic Provider. However, custom CSPs can use these flags to restrict operations on keys.

Example

#include <wincrypt.h>

HCRYPTPROV hProv = 0;
HCRYPTKEY hKey = 0;
DWORD dwMode;
BYTE pbData[16];
DWORD dwCount;
DWORD i;

// Get a handle to user default provider.
if(!CryptAcquireContext(&hProv, NULL, NULL, PROV_RSA_FULL, 0)) {
    printf("Error %x during CryptAcquireContext!\n", GetLastError());
    goto done;
}

// Create a random block cipher session key.
if(!CryptGenKey(hProv, CALG_RC2, CRYPT_EXPORTABLE, &hKey)) {
    printf("Error %x during CryptGenKey!\n", GetLastError());
    goto done;
}

// Read the cipher mode.
dwCount = sizeof(DWORD);
if(!CryptGetKeyParam(hKey, KP_MODE, &dwMode, &dwCount, 0)) {
    printf("Error %x during CryptGetKeyParam!\n", GetLastError());
    goto done;
}
assert(dwCount==sizeof(BYTE));

// Print out the cipher mode.
printf("Default cipher mode: %d\n", dwMode);

// Read the initialization vector.
dwCount = 16;
if(!CryptGetKeyParam(hKey, KP_IV, pbData, &dwCount, 0)) {
    printf("Error %x during CryptGetKeyParam!\n", GetLastError());
    goto done;
}
// Print out the initialization vector.
printf("Default IV:");
for(i=0;i<dwCount;i++) printf("%2.2x ",pbData[i]);
printf("\n");

done:

// Destroy the session key.
if(hKey != 0) CryptDestroyKey(hKey);

// Release the provider handle.
if(hProv != 0) CryptReleaseContext(hProv, 0);
 

QuickInfo

  Windows NT: Requires version 4.0 or later.
  Windows: Requires Windows 95 OSR2 or later (or Windows 95 with IE 3.02 or later).
  Windows CE: Unsupported.
  Header: Declared in wincrypt.h.
  Import Library: Use advapi32.lib.

See Also

CryptSetKeyParam