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NCryptDecrypt function (ncrypt.h)

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The NCryptDecrypt function decrypts a block of encrypted data.

Syntax

SECURITY_STATUS NCryptDecrypt(
  [in]           NCRYPT_KEY_HANDLE hKey,
  [in]           PBYTE             pbInput,
  [in]           DWORD             cbInput,
  [in, optional] VOID              *pPaddingInfo,
  [out]          PBYTE             pbOutput,
  [in]           DWORD             cbOutput,
  [out]          DWORD             *pcbResult,
  [in]           DWORD             dwFlags
);

Parameters

[in] hKey

The handle of the key to use to decrypt the data.

[in] pbInput

The address of a buffer that contains the data to be decrypted. The cbInput parameter contains the size of the data to decrypt. For more information, see Remarks.

[in] cbInput

The number of bytes in the pbInput buffer to decrypt.

[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. This parameter is only used with asymmetric keys and must be NULL otherwise.

[out] pbOutput

The address of a buffer that will receive the decrypted data produced by this function. The cbOutput parameter contains the size of this buffer. For more information, see Remarks.

If this parameter is NULL, this function will calculate the size needed for the decrypted data 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 DWORD 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 decrypted data.

[in] dwFlags

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

If the key is an asymmetric key, this can be one of the following values.

Value Meaning
NCRYPT_NO_PADDING_FLAG
 No padding was used when the data was encrypted. The pPaddingInfo parameter is not used.
NCRYPT_PAD_OAEP_FLAG
 The Optimal Asymmetric Encryption Padding (OAEP) scheme was used when the data was encrypted. The pPaddingInfo parameter is a pointer to a BCRYPT_OAEP_PADDING_INFO structure.
NCRYPT_PAD_PKCS1_FLAG
 The data was padded with a random number to round out the block size when the data was encrypted. The pPaddingInfo parameter is not used.
 

The following value can be used for any key.

Value Meaning
NCRYPT_SILENT_FLAG
 Requests that the key service provider (KSP) not display any user interface. If the provider must display the UI to operate, the call fails and the KSP should set the NTE_SILENT_CONTEXT error code as the last error.

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.

Return code Description
ERROR_SUCCESS
 The function was successful.
NTE_BAD_FLAGS
 The dwFlags parameter contains a value that is not valid.
NTE_BUFFER_TOO_SMALL
 The size specified by the cbOutput parameter is not large enough to hold the decrypted data.
NTE_INVALID_HANDLE
 The hKey parameter is not valid.
NTE_INVALID_PARAMETER
 One or more parameters are not valid.
NTE_PERM
 The key identified by the hKey parameter cannot be used for decryption.

Remarks

The pbInput and pbOutput parameters can point to the same buffer. In this case, this function will perform the decryption in place.

A service must not call this function from its StartService Function. If a service calls this function from its StartService function, a deadlock can occur, and the service may stop responding.

Requirements

Requirement Value
Minimum supported client Windows Vista [desktop apps | UWP apps]
Minimum supported server Windows Server 2008 [desktop apps | UWP apps]
Target Platform Windows
Header ncrypt.h
Library Ncrypt.lib
DLL Ncrypt.dll

See also

NCryptEncrypt