CryptGetKeyParam (Compact 2013)

3/28/2014

This function lets applications retrieve data that governs the operations of a key. In the Microsoft cryptographic service providers (CSPs), the base symmetric keying material is not obtainable by this or any other function.

Syntax

BOOL CRYPTFUNC CryptGetKeyParam( 
  HCRYPTKEY hKey,
  DWORD dwParam, 
  BYTE* pbData, 
  DWORD* pdwDataLen, 
  DWORD dwFlags
);

Parameters

• hKey
  [in] HCRYPTKEY handle to the key to query.

• dwParam
  [in] Specifies the key parameter type. The following table shows the available key types.

  Key type	Description	pbData content
  KP_IV	Initialization vector	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_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_PADDING	Padding mode	DWORD value indicating the padding method used by the cipher. The padding method currently defined is PKCS5_PADDING - PKCS 5 (sec 6.2).
  KP_MODE	Cipher mode	DWORD value indicating the mode of the cipher. For a list of valid cipher modes, refer to the table in the Remarks section.
  KP_MODE_BITS	Number of bits to feed back	DWORD value indicating the number of bits that are processed per cycle when the OFB or CFB cipher modes are used.
  KP_PERMISSIONS	Key permissions	DWORD value with zero or more bit permission flags set. For a description of each of these flags, refer to the permission flag table at the end of this Remarks section.
  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, algorithm identifiers that are used to generate the key depend on the provider used. 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 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_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 bits for that algorithm. CALG_CYLINK_MEK is a 40-bit key but has parity and zeroed key bits to make the key length 64 bits.
  KP_SALT_EX	Salt value	The CRYPT_DATA_BLOB that specifies the variable size salt value.
  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_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_Q	hKey specifies a DSS key	Generator G from the key BLOB. The length of the data is returned in the pdwDataLen parameter.
  KP_EFFECTIVE_KEYLEN	hKey specifies block cipher session key	DWORD value equal to the effective key length.
  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.

• pbData
  [out] Pointer to a buffer that receives the parameter data. The function returns the specified data in this buffer. The form of this data varies depending on the parameter number. This parameter can be NULL to set the size of this buffer for memory allocation purposes.

• pdwDataLen
  [in, out] On input, pointer to a DWORD value specifying the size, in bytes, of the buffer pointed to by the pbData parameter. On output, the function returns the DWORD value containing the number of bytes stored in the buffer.

  When processing the data returned in the buffer, applications must 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 ensure 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
  [in] Reserved; set to 0 (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.

Remarks

The following table shows the common values for the KP_MODE parameter. These cipher modes are discussed in the topics under Cryptography.

The following table shows the flags in the bit field when the KP_PERMISSIONS parameter is read. The Microsoft Base Cryptographic Provider ignores these permission flags. However, custom CSPs can use these flags to restrict operations on keys.

Example Code

#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 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;
}
// 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);
// Free the provider handle.
if(hProv != 0) CryptReleaseContext(hProv, 0);

Requirements

See Also

Reference

Cryptography Functions
CryptSetKeyParam
ALG_ID