CryptEncodeObject function (wincrypt.h)

The CryptEncodeObject function encodes a structure of the type indicated by the value of the lpszStructType parameter. The use of CryptEncodeObjectEx is recommended as an API that performs the same function with significant performance improvements.


BOOL CryptEncodeObject(
  [in]      DWORD      dwCertEncodingType,
  [in]      LPCSTR     lpszStructType,
  [in]      const void *pvStructInfo,
  [out]     BYTE       *pbEncoded,
  [in, out] DWORD      *pcbEncoded


[in] dwCertEncodingType

Type of encoding used. It is always acceptable to specify both the certificate and message encoding types by combining them with a bitwise-OR operation as shown in the following example:


Currently defined encoding types are:

Note  Either a certificate or message encoding type is required. X509_ASN_ENCODING is the default. If that type is indicated, it is used. Otherwise, if the PKCS7_ASN_ENCODING type is indicated, it is used.

[in] lpszStructType

A pointer to an OID defining the structure type. If the high-order word of the lpszStructType parameter is zero, the low-order word specifies the integer identifier for the type of the specified structure. Otherwise, this parameter is a long pointer to a null-terminated string.

For more information about object identifier strings, their predefined constants and corresponding structures, see Constants for CryptEncodeObject and CryptDecodeObject.

[in] pvStructInfo

A pointer to the structure to be encoded. The structure must be of a type specified by lpszStructType.

[out] pbEncoded

A pointer to a buffer to receive the encoded structure. When the buffer that is specified is not large enough to receive the decoded structure, the function sets the ERROR_MORE_DATA code and stores the required buffer size, in bytes, in the variable pointed to by pcbEncoded.

This parameter can be NULL to retrieve the size of this information for memory allocation purposes. For more information, see Retrieving Data of Unknown Length.

[in, out] pcbEncoded

A pointer to a DWORD variable that contains the size, in bytes, of the buffer pointed to by the pbEncoded parameter. When the function returns, the DWORD value contains the number of allocated encoded bytes stored in the buffer.

Note  When processing the data returned in the buffer, applications must use the actual size of the data returned. The actual size can be slightly smaller than the size of the buffer specified on input. (On input, buffer sizes are usually specified large enough to ensure that the largest possible output data fits in the buffer.) On output, the variable pointed to by this parameter is updated to reflect the actual size of the data copied to the buffer.

Return value

If the function succeeds, the return value is nonzero (TRUE).

If the function fails, the return value is zero (FALSE). For extended error information, call GetLastError. Some possible error codes are listed in the following table.

Return code Description
An error was encountered while encoding.
An encoding function could not be found for the specified dwCertEncodingType and lpszStructType.
If the buffer specified by the pbEncoded 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 pcbEncoded.

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


When encoding a cryptographic object using the preferred CryptEncodeObjectEx function, the terminating NULL character is included. When decoding, using the preferred CryptDecodeObjectEx function, the terminating NULL character is not retained.


For an example that uses this function, see Example C Program: Making a Certificate Request and Example C Program: ASN.1 Encoding and Decoding.


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

See also



Object Encoding and Decoding Functions