CryptSetKeyParam

A version of this page is also available for

Windows Embedded CE 6.0 R3

4/8/2010

This function customizes various aspects of a key's operations. The values set by this function are not persisted to memory and are used only within a single session.

The Microsoft cryptographic service providers (CSPs) do not allow setting the values for key exchange or signature keys; however, custom providers may define parameters that can be set on these keys.

Syntax

BOOL WINAPI CryptSetKeyParam( 
  HCRYPTKEY hKey, 
  DWORD dwParam, 
  BYTE* pbData, 
  DWORD dwFlags
);

Parameters

• hKey
  [in] HCRYPTKEY handle to the key on which to set parameters.

• dwParam
  [in] Key parameter type.

  The following table shows the available key types.

  Key type	Description	pbData content
  KP_ALGID	Key algorithm	ALG_ID identifier for the algorithm specified when the key was created. Note that when key specifications AT_KEYEXCHANGE and AT_SIGNATURE are used, the algorithm identifiers that are used to generate the key depend on the provider. As a result, the values returned from CryptGetKeyParam for these key specifications when the KP_ALGID value is specified depend on the provider used. To determine the algorithm identifier that the different providers use for the key specifications AT_KEYEXCHANGE and AT_SIGNATURE, see ALG_ID.
  KP_BLOCKLEN	Session key or public/private key pair specified by hKey	DWORD value indicating the block length. For stream ciphers, this value is always zero. If session key is specified by hKey, the pbData parameter contains the key cipher's block length, in bits. If a public/private key pair is specified by hKey, pbData contains a BLOB with the key pair's encryption granularity, in bits.
  KP_CERTIFICATE	Certificate	A buffer containing the DER-encoded X.509 certificate. The public key in the certificate must match the corresponding signature or exchange key.
  KP_EFFECTIVE_KEYLEN	hKey specifies block cipher session key	DWORD value equal to the effective key length.
  KP_G	hKey specifies a DSS key	Prime Q from the DSS key BLOB. The length of the data is returned in the pdwDataLen parameter.
  KP_IV	Initialization vector. The hkey parameter specifies a block cipher session key	BYTE array indicating the current initialization vector. This array contains block_length/8 elements. For example, if the block length is sixty-four bits, the initialization vector consists of eight bytes.
  KP_KEYEXCHANGE_PIN	Password to unlock a smart card	A null-terminated ASCII string that sets the password used to enable the private key for the key exchange.
  KP_KEYLEN	DWORD value, in bits, used to get the actual length of the key	This value can be used to get the length of any key type. Microsoft CSPs return a key length of 64 bits for CALG_DES, 128 bits for CALG_3DES_112, and 192 bits for CALG_3DES. These lengths are different from the lengths returned when enumerating algorithms with the dwParam value of CryptGetProvParam set to PP_ENUMALGS. The length returned by this call is the actual size of the key including the parity bits included in the key. Microsoft CSPs that support the ALG_ID CALG_CYLINK_MEK return 64-four bits for that algorithm. CALG_CYLINK_MEK is a 64 key but has parity and zeroed key bits to make the key length 64 bits.
  KP_MODE	hkey specifies a block cipher session key	DWORD value indicating the mode of the cipher. For a list of valid cipher modes, see the table in the Remarks section.
  KP_MODE_BITS	Number of bits to feed back; the hkey parameter specifies a block cipher session key	DWORD value indicating the number of bits that are processed per cycle when the OFB or CFB cipher mode is used.
  KP_P	hKey specifies a DSS key	Prime modulus P from the DSS key BLOB. The length of the data is returned in the pdwDataLen parameter.
  KP_PADDING	Padding mode. The hkey parameter specifies a block cipher session key	DWORD value indicating the padding method used by the cipher. The padding method currently defined is PKCS5_PADDING — PKCS 5 (sec 6.2).
  KP_PERMISSIONS	Key permissions	DWORD value with zero or more bit permission flags set.
  KP_Q	hKey specifies a DSS key	Generator G from the key BLOB. The length of the data is returned in the pdwDataLen parameter.
  KP_SALT	Salt value	BYTE array indicating the current salt value. The size of the salt value varies depending on the CSP and algorithm being used. Salt values do not apply to public/private key pairs.
  KP_SALT_EX	Salt value	The CRYPT_DATA_BLOB that specifies the variable size salt value.
  KP_SIGNATURE_PIN	Password to unlock a smart card	A null-terminated ASCII string that sets the password used to enable the signature private key.
  KP_X	hKey specifies a DSS key	After the P, Q, and G values have been set, a call can be made to CryptSetKeyParam to specify the KP_X value for dwParam and NULL for the pbData parameter. This causes the X and Y values to be generated.

• pbData
  [in] Pointer to the data buffer. The value in this buffer must be set before calling the CryptSetKeyParam function. The form of this data varies depending on the parameter value.

• dwFlags
  [in] Reserved for future use and must be set to zero.

Return Value

TRUE indicates success. FALSE indicates failure. To get extended error information, call the GetLastError function.

The following table shows the common values for the GetLastError function. The error values prefaced by NTE are generated by the particular CSP you are using.

Example Code

#include <wincrypt.h>
HCRYPTPROV hProv = 0;
HCRYPTKEY hKey = 0;
DWORD dwMode;
BYTE pbData[16];
DWORD dwCount;
DWORD i;
// Get a handle to the user default provider using CryptAcquireContext.
// For sample code, see <A HREF="wce50lrfcryptacquirecontext.htm">CryptAcquireContext</A>.
...
...
// Create a random block cipher session key.
if(!CryptGenKey(hProv, CALG_RC2, CRYPT_EXPORTABLE, &hKey)) {
 printf("Error %x during CryptGenKey!\n", GetLastError());
 goto done;
}
// Set the cipher mode.
dwMode = CRYPT_MODE_ECB;
if(!CryptSetKeyParam(hKey, KP_MODE, &dwMode, 0)) {
 printf("Error %x during CryptSetKeyParam!\n", GetLastError());
 goto done;
}
// Generate a random initialization vector.
if(!CryptGenRandom(hProv, 8, pbData)) {
 printf("Error %x during CryptGenRandom!\n", GetLastError());
 goto done;
}
// Set the initialization vector.
if(!CryptSetKeyParam(hKey, KP_IV, pbData, 0)) {
 printf("Error %x during CryptSetKeyParam!\n", GetLastError());
 goto done;
}
// Use 'hKey' to encrypt a message.
...
done:
// Destroy the session key.
if(hKey != 0) CryptDestroyKey(hKey);
// Free the provider handle.
if(hProv != 0) CryptReleaseContext(hProv, 0);

Requirements

See Also

Reference

CryptGenKey
CryptGetKeyParam