CryptExportPKCS8 function (wincrypt.h)

Article
07/27/2022

[The CryptExportPKCS8 function is no longer available for use as of Windows Server 2008 and Windows Vista. Instead, use the PFXExportCertStoreEx function.]

The CryptExportPKCS8 function exports the private key in PKCS #8 format. The function is superseded by CryptExportPKCS8Ex, which also may be altered or unavailable in subsequent versions.

Syntax

BOOL CryptExportPKCS8(
  [in]            HCRYPTPROV hCryptProv,
  [in]            DWORD      dwKeySpec,
  [in]            LPSTR      pszPrivateKeyObjId,
  [in]            DWORD      dwFlags,
  [in, optional]  void       *pvAuxInfo,
  [out, optional] BYTE       *pbPrivateKeyBlob,
  [in, out]       DWORD      *pcbPrivateKeyBlob
);

Parameters

[in] hCryptProv

An HCRYPTPROV variable that contains the cryptographic service provider (CSP). This is a handle to the CSP obtained by calling CryptAcquireContext.

[in] dwKeySpec

A DWORD variable that contains the key specification. The following dwKeySpec values are defined for the default provider.

Value	Meaning
AT_KEYEXCHANGE	Keys used to encrypt/decrypt session keys.
AT_SIGNATURE	Keys used to create and verify digital signatures.

[in] pszPrivateKeyObjId

An LPSTR variable that contains the private key object identifier (OID).

[in] dwFlags

This parameter should be zero if pbPrivateKeyBlob is NULL and 0x8000 otherwise.

[in, optional] pvAuxInfo

This parameter must be set to NULL.

[out, optional] pbPrivateKeyBlob

A pointer to an array of BYTE structures to receive the private key to be exported.

The private key will contain the information in a PKCS #8 PrivateKeyInfo Abstract Syntax Notation One (ASN.1) type found in the PKCS #8 standard.

For memory allocation purposes, you can get the size of the private key to be exported by setting this parameter to NULL. For more information, see Retrieving Data of Unknown Length.

[in, out] pcbPrivateKeyBlob

A pointer to a DWORD that may contain, on input, the size, in bytes, of the memory allocation needed to contain the pbPrivateKeyBlob. If pbPrivateKeyBlob is NULL, this parameter will return the size of the memory allocation needed for a second call to the function. For more information, see Retrieving Data of Unknown Length.

Return value

If the function succeeds, the function returns nonzero.

If the function fails, it returns zero. For extended error information, call GetLastError.

The following error codes are specific to this function.

Return code	Description
ERROR_UNSUPPORTED_TYPE	An export function that can be installed or registered could not be found.
ERROR_MORE_DATA	If the buffer specified by the pbPrivateKeyBlob 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, in the variable pointed to by the pcbPrivateKeyBlob parameter.

If the function fails, GetLastError may return an ASN.1 encoding/decoding error. For information about these errors, see ASN.1 Encoding/Decoding Return Values.

Remarks

This function is only supported for asymmetric keys.

Requirements

Requirement	Value
Minimum supported client	Windows XP [desktop apps only]
Minimum supported server	Windows Server 2003 [desktop apps only]
Target Platform	Windows
Header	wincrypt.h
Library	Crypt32.lib
DLL	Crypt32.dll