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.

BOOL CRYPTFUNC CryptGetKeyParam( HCRYPTKEYhKey,DWORDdwParam,BYTE* pbData,DWORD* pdwDataLen,DWORDdwFlags);


  • 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 value indicating the algorithm specified when the key was created. Note that when key specifications AT_KEYEXCHANGE and AT_SIGNATURE are specified for the ALG_ID, the 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.
    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_SIGNATURE_PIN Password to unlock a smart card A null-terminated ASCII string that sets the password used to enable the signature private 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 for future use and must be set to zero.

Return Values

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.

Value Description
ERROR_INVALID_HANDLE One of the parameters specifies an invalid handle.
ERROR_INVALID_PARAMETER One of the parameters contains an invalid value. This is most often an illegal pointer.
ERROR_MORE_DATA If the buffer specified by the pbData parameter is not large enough to hold the returned data, the function sets the ERROR_MORE_DATA code, and stores the required buffer size, in bytes, into the variable pointed to by pdwDataLen.
NTE_BAD_FLAGS The dwFlags parameter is nonzero.
NTE_BAD_KEY or NTE_NO_KEY The key specified by the hKey parameter is invalid.
NTE_BAD_TYPE The dwParam parameter specifies an unknown parameter number.
NTE_BAD_UID The CSP context that was specified when the key was created cannot be found.


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

Cipher mode Description
CRYPT_MODE_ECB Electronic codebook
CRYPT_MODE_CBC Cipher block chaining
CRYPT_MODE_OFB Output feedback mode

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.

Permission flag Description
CRYPT_ENCRYPT Allows encryption.
CRYPT_DECRYPT Allows decryption.
CRYPT_EXPORT Allows exporting of the key.
CRYPT_READ Allows reading of the parameters.
CRYPT_WRITE Allows setting of the parameters.
CRYPT_MAC Allows using MACs with the key.
CRYPT_EXPORT_KEY Allows using the key for exporting keys.
CRYPT_IMPORT_KEY Allows using the key for importing keys.

Example Code

#include <wincrypt.h>

DWORD dwMode;
BYTE pbData[16];
DWORD dwCount;

// 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;

// 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]);


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

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


OS Versions: Windows CE 2.10 and later.
Header: Wincrypt.h.
Link Library: Coredll.lib.

See Also

CryptSetKeyParam | ALG_ID

 Last updated on Thursday, April 08, 2004

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