BCryptSignHash function (bcrypt.h)

The BCryptSignHash function creates a signature over data to be signed.

Syntax

NTSTATUS BCryptSignHash(
  [in]            BCRYPT_KEY_HANDLE hKey,
  [in, optional]  VOID              *pPaddingInfo,
  [in, optional]  PUCHAR            pbInput,
  [in]            ULONG             cbInput,
  [out, optional] PUCHAR            pbOutput,
  [in]            ULONG             cbOutput,
  [out]           ULONG             *pcbResult,
  [in]            ULONG             dwFlags
);

Parameters

[in] hKey

The handle of the private key to use to generate the signature.

[in, optional] pPaddingInfo

A pointer to a structure that contains padding information. The actual type of structure this parameter points to depends on the value of the dwFlags parameter. When dwFlags is 0, this parameter must be NULL.

[in, optional] pbInput

A pointer to a buffer that contains the input to be signed. The cbInput parameter contains the size of this buffer.

For many signature algorithms (DSA, RSA, ECDSA, HashML-DSA, etc.), the signature routine is defined to take the result of a hash function as input. In these algorithms, the original message to be signed must first be hashed, and the resultant hash value (pre-hash) is passed in the pbInput buffer.

However, some signature algorithms (pure ML-DSA, pure SLH-DSA, etc.) allow direct signing of arbitrary sized data. For these algorithms the pbInput buffer contains the input to be signed. Signer and verifier must agree on how to construct this input, but there is no requirement for a pre-hash to be involved. Signing a very large buffer directly may harm interoperability.

In either case, the pbInput buffer represents the input to be signed.

[in] cbInput

The size, in bytes, of the pbInput buffer.

[out, optional] pbOutput

The address of a buffer to receive the signature produced by this function. The cbOutput parameter contains the size of this buffer.

If this parameter is NULL, this function will calculate the size required for the signature and return the size in the location pointed to by the pcbResult parameter.

[in] cbOutput

The size, in bytes, of the pbOutput buffer. This parameter is ignored if the pbOutput parameter is NULL.

[out] pcbResult

A pointer to a ULONG variable that receives the number of bytes copied to the pbOutput buffer.

If pbOutput is NULL, this receives the size, in bytes, required for the signature.

[in] dwFlags

A set of flags that modify the behavior of this function. The allowed set of flags depends on the type of key specified by the hKey parameter.

This can be zero or one of the following values:

Return value

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

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

Remarks

This function performs the Signing operation of a digital signature scheme. It takes data to be signed and a private key, with additional parameters optionally specified by dwFlags and pPaddingInfo, and produces a signature which can later be verified with the corresponding public key.

To later verify that the signature is valid, call the BCryptVerifySignature function with a key containing the public key corresponding to the provided private key and identical data to be verified.

When using a supported algorithm provider, BCryptSignHash can be called either from user mode or kernel mode. Kernel mode callers can execute either at PASSIVE_LEVEL IRQL or DISPATCH_LEVEL IRQL. If the current IRQL level is DISPATCH_LEVEL, the handle provided in the hKey parameter must be derived from an algorithm handle returned by a provider that was opened with the BCRYPT_PROV_DISPATCH flag, and any pointers passed to the BCryptSignHash function must refer to nonpaged (or locked) memory.

To call this function in kernel mode, use Cng.lib, which is part of the Driver Development Kit (DDK). Windows Server 2008 and Windows Vista: To call this function in kernel mode, use Ksecdd.lib.

Requirements

See also

BCryptVerifySignature