BCryptGenerateSymmetricKey

The BCryptGenerateSymmetricKey function creates a key object for use with a symmetrical key encryption algorithm from a supplied key.

Syntax

NTSTATUS BCryptGenerateSymmetricKey(
         BCRYPT_ALG_HANDLE hAlgorithm,
         BCRYPT_KEY_HANDLE *phKey,
         PUCHAR pbKeyObject,
         ULONG cbKeyObject,
         PUCHAR pbSecret,
         ULONG cbSecret,
         ULONG dwFlags
)

Parameters

hAlgorithm
Type: BCRYPT_ALG_HANDLE

[in, out] The handle of an algorithm provider created with the BCryptOpenAlgorithmProvider function. The algorithm specified when the provider was created must support symmetric key encryption.

phKey
Type: BCRYPT_KEY_HANDLE *

[out] A pointer to a BCRYPT_KEY_HANDLE that receives the handle of the key. This handle is used in subsequent functions that require a key, such as BCryptEncrypt. This handle must be released when it is no longer needed by passing it to the BCryptDestroyKey function.

pbKeyObject
Type: PUCHAR

[out, optional] A pointer to a buffer that receives the key object. The cbKeyObject parameter contains the size of this buffer. The required size of this buffer can be obtained by calling the BCryptGetProperty function to get the BCRYPT_OBJECT_LENGTH property. This will provide the size of the key object for the specified algorithm.

This memory can only be freed after the phKey key handle is destroyed.

If the value of this parameter is NULL and the value of the cbKeyObject parameter is zero, the memory for the key object is allocated and freed by this function.

cbKeyObject
Type: ULONG

[in] The size, in bytes, of the pbKeyObject buffer.

If the value of this parameter is zero and the value of the pbKeyObject parameter is NULL, the memory for the key object is allocated and freed by this function.

pbSecret
Type: PUCHAR

[in]

Pointer to a buffer that contains the key from which to create the key object. The cbSecret parameter contains the size of this buffer. This is normally a hash of a password or some other reproducible data. If the data passed in exceeds the target key size, the data will be truncated and the excess will be ignored.

Note

We strongly recommended that applications pass in the exact number of bytes required by the target key.

cbSecret
Type: ULONG

[in] The size, in bytes, of the pbSecret buffer.

dwFlags
Type: ULONG

[in] A set of flags that modify the behavior of this function. No flags are currently defined, so this parameter should be zero.

Return value

Type: NTSTATUS

Returns a status code that indicates the success or failure of the function.

Return codes

Possible return codes include, but are not limited to, the following.

Return code	Description
STATUS_SUCCESS	The function was successful.
STATUS_BUFFER_TOO_SMALL	The size of the key object specified by the cbKeyObject parameter is not large enough to hold the key object.
STATUS_INVALID_HANDLE	The algorithm handle in the hAlgorithm parameter is not valid.
STATUS_INVALID_PARAMETER	One or more parameters are not valid.

Remarks

Depending on what processor modes a provider supports, BCryptGenerateSymmetricKey can be called either from user mode or kernel mode. Kernel mode callers can execute either at PASSIVE_LEVELIRQL or DISPATCH_LEVEL IRQL. If the current IRQL level is DISPATCH_LEVEL, the handle provided in the hAlgorithm parameter must have been opened by using the BCRYPT_PROV_DISPATCH flag, and any pointers passed to the BCryptGenerateSymmetricKey function must refer to nonpaged (or locked) memory.

Requirements

Header: Declared in bcrypt.h.

Library: Use bcrypt.lib.