CryptGenKey

[New - Windows NT]

[New - Windows 95, OEM Service Release 2]

The CryptGenKey function generates random cryptographic keys for use with the CSP module. A handle to the key is returned in phKey. This handle can then be used as needed with any of the other CryptoAPI functions requiring key handles.

The calling application is required to specify the algorithm when calling this function. Because this algorithm type is kept bundled with the key, the application does not need to specify the algorithm later when the actual cryptographic operations are performed.

BOOL CRYPTFUNC CryptGenKey(

HCRYPTPROV hProv,
ALG_ID Algid,
DWORD dwFlags,
HCRYPTKEY *phKey
);

Parameters

hProv

[in] A handle to the application's CSP. An application obtains this handle using the CryptAcquireContext function.

Algid

[in] The identifier for the algorithm for which the key is to be generated.

The valid values for this parameter will vary, depending on the CSP that is used. See the "Remarks" section for a list of possible algorithm identifiers.

dwFlags

[in] The flags specifying the type of key generated. This parameter can be zero, or you can specify one or more of the following flags, using the binary OR operator to combine them.

CRYPT_EXPORTABLE

If this flag is set, then the key can be transferred out of the CSP into a key blob using the CryptExportKey function. Because session keys generally must be exportable, this flag should usually be set when they are created.

If this flag is not set, then the key will not be exportable. For a session key, this means that the key will only be available within the current session and only the application that created it will be able to use it. For a public/private key pair, this means that the private key cannot be transported or backed up.

This flag only applies to session key and private key blobs. It does not apply to public keys, which are always exportable.

CRYPT_CREATE_SALT

If this flag is set, then the key will be assigned a random salt value automatically. You can retrieve this salt value using the CryptGetKeyParam function with the dwParam parameter set to KP_SALT.

If this flag is not set, then the key will be given a salt value of zero.

When keys with non-zero salt values are exported (through CryptExportKey), then the salt value must also be obtained and kept with the key blob.

CRYPT_USER_PROTECTED

If this flag is set, then the user will be notified through a dialog box or another method when certain actions are attempted using this key. The precise behavior is specified by the CSP being used.

The Microsoft RSA Base Provider ignores this flag.

phKey

[out] The address that the function copies the handle of the newly generated key to.

Remarks

To generate a key to be used with a symmetric encryption algorithm (that is, a session key), use the Algid parameter to specify the algorithm. The algorithms available will most likely be different for each CSP. If you are using the Microsoft RSA Base Provider, one of the following values can be used to specify the algorithm:

• CALG_RC2 RC2 block cipher

• CALG_RC4 RC4 stream cipher

When keys are generated for symmetric block ciphers, the key by default will be set up in cipher block chaining (CBC) mode with an initialization vector of zero. This cipher mode provides a good default method for bulk encrypting data. To change these parameters, use the CryptSetKeyParam function.

In addition to generating keys for symmetric algorithms, the CryptGenKey function can also generate keys for public-key algorithms. The use of public-key algorithms is restricted to key exchange and digital signatures. Each CryptoAPI client generally possesses one key pair for each of these operations. To generate one of these key pairs, set the Algid parameter to one of the following values:

• AT_KEYEXCHANGE Key exchange

• AT_SIGNATURE Digital signature

Return Values

If the function succeeds, the return value is nonzero.

If the function fails, the return value is zero. 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.

Error	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.
NTE_BAD_ALGID	The Algid parameter specifies an algorithm that this CSP does not support.
NTE_BAD_FLAGS	The dwFlags parameter contains an invalid value.
NTE_BAD_UID	The hProv parameter does not contain a valid context handle.
NTE_FAIL	The function failed in some unexpected way.

Example

#include <wincrypt.h>

HCRYPTPROV hProv = 0;

HCRYPTKEY hKey = 0;

// Get handle to user default provider.

if(!CryptAcquireContext(&hProv, NULL, NULL, PROV_RSA_FULL, 0)) {

printf("Error %x during CryptAcquireContext!\n", GetLastError());

goto done;

}

// Create block cipher session key.

if(!CryptGenKey(hProv, CALG_RC2, CRYPT_EXPORTABLE, &hKey)) {

printf("Error %x during CryptGenKey!\n", GetLastError());

goto done;

}

// Use 'hKey' to do something.

...

done:

// Destroy session key.

if(hKey != 0) CryptDestroyKey(hKey);

// Release provider handle.

if(hProv != 0) CryptReleaseContext(hProv, 0);

See Also

CryptAcquireContext, CryptDestroyKey, CryptExportKey, CryptGetKeyParam, CryptImportKey, CryptSetKeyParam

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