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CryptEncodeObjectEx function

The CryptEncodeObjectEx function encodes a structure of the type indicated by the value of the lpszStructType parameter. This function offers a significant performance improvement over CryptEncodeObject by supporting memory allocation with the CRYPT_ENCODE_ALLOC_FLAG value.

Syntax


BOOL WINAPI CryptEncodeObjectEx(
  _In_     DWORD dwCertEncodingType,
  _In_     LPCSTR lpszStructType,
  _In_     const void *pvStructInfo,
  _In_     DWORD dwFlags,
  _In_     PCRYPT_ENCODE_PARA pEncodePara,
  _Out_    void *pvEncoded,
  _Inout_  DWORD *pcbEncoded
);

Parameters

dwCertEncodingType [in]

The certificate encoding type and message encoding type to use to encode the object. This parameter can be a combination of one or more of the following values.

ValueMeaning
PKCS_7_ASN_ENCODING
65536 (0x10000)

Specifies PKCS 7 message encoding.

X509_ASN_ENCODING
1 (0x1)

Specifies X.509 certificate encoding.

 

lpszStructType [in]

A pointer to an object identifier (OID) that defines the structure type. If the high-order word of the lpszStructType parameter is zero, the low-order word specifies an integer identifier for the type of the specified structure. Otherwise, this parameter is a pointer to a null-terminated string that contains the string representation of the OID.

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

pvStructInfo [in]

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

dwFlags [in]

Specifies options for the encoding. This parameter can be zero or a combination of one or more of the following values.

ValueMeaning
CRYPT_ENCODE_ALLOC_FLAG
32768 (0x8000)

The called encoding function allocates memory for the encoded bytes. A pointer to the allocated bytes is returned in pvEncoded.

CRYPT_ENCODE_ENABLE_PUNYCODE_FLAG
131072 (0x20000)

This flag is applicable for enabling Punycode encoding of Unicode string values. For more information, see Remarks.

Windows Server 2008, Windows Vista, Windows Server 2003, and Windows XP:  This flag is not supported.

CRYPT_UNICODE_NAME_ENCODE_DISABLE_CHECK_TYPE_FLAG
1073741824 (0x40000000)

This flag is applicable when encoding X509_UNICODE_NAME, X509_UNICODE_NAME_VALUE, or X509_UNICODE_ANY_STRING. If this flag is set, the characters are not checked to determine whether they are valid for the specified value type.

CRYPT_UNICODE_NAME_ENCODE_ENABLE_T61_UNICODE_FLAG
2147483648 (0x80000000)

This flag is applicable when encoding X509_UNICODE_NAME. If this flag is set and all the Unicode characters are <= 0xFF, the CERT_RDN_T61_STRING is selected instead of the CERT_RDN_UNICODE_STRING.

CRYPT_UNICODE_NAME_ENCODE_ENABLE_UTF8_UNICODE_FLAG
536870912 (0x20000000)

This flag is applicable when encoding an X509_UNICODE_NAME. When set, CERT_RDN_UTF8_STRING is selected instead of CERT_RDN_UNICODE_STRING.

CRYPT_UNICODE_NAME_ENCODE_FORCE_UTF8_UNICODE_FLAG
268435456 (0x10000000)

This flag is applicable when encoding an X509_UNICODE_NAME. When set, CERT_RDN_UTF8_STRING is selected instead of CERT_RDN_PRINTABLE_STRING for directory string types. Also, this flag enables CRYPT_UNICODE_NAME_ENCODE_ENABLE_UTF8_UNICODE_FLAG.

 

pEncodePara [in]

A pointer to a CRYPT_ENCODE_PARA structure that contains encoding information. This parameter can be NULL.

If either pEncodePara or the pfnAlloc member of pEncodePara is NULL, then LocalAlloc is used for the allocation and LocalFree must be called to free the memory.

If both pEncodePara and the pfnAlloc member of pEncodePara are not NULL, then the function pointed to by the pfnAlloc member of the CRYPT_ENCODE_PARA structure pointed to by pEncodePara is called for the allocation. The function pointed to by the pfnFree member of pEncodePara must be called to free the memory.

pvEncoded [out]

A pointer to a buffer to receive the encoded structure. The size of this buffer is specified in the pcbEncoded parameter. 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 the buffer for memory allocation purposes. For more information, see Retrieving Data of Unknown Length.

If dwFlags contains the CRYPT_ENCODE_ALLOC_FLAG flag, pvEncoded is not a pointer to a buffer but is the address of a pointer to the buffer. Because memory is allocated inside the function and the pointer is stored in pvEncoded, pvEncoded cannot be NULL.

pcbEncoded [in, out]

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

When dwFlags contains the CRYPT_ENCODE_ALLOC_FLAG flag, pcbEncoded is the address of a pointer to the DWORD value that is updated.

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

Returns nonzero if successful or zero otherwise.

For extended error information, call GetLastError. The following table shows some possible error codes that can be returned from GetLastError when CryptEncodeObjectEx fails.

Return codeDescription
CRYPT_E_BAD_ENCODE

An error was encountered while encoding.

ERROR_FILE_NOT_FOUND

An encoding function could not be found for the specified dwCertEncodingType and lpszStructType.

ERROR_MORE_DATA

If the buffer specified by the pvEncoded 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.

Remarks

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.

CryptEncodeObjectEx first looks for an installable extended encoding function. If no extended encoding function is found, the old, nonextended, installable function is located.

When direct IA5String encoding of the object is not possible, you can specify Punycode encoding by setting the dwFlag parameter to the CRYPT_ENCODE_ENABLE_PUNYCODE_FLAG value. Setting the CRYPT_ENCODE_ENABLE_PUNYCODE_FLAG flag has different effects based on the structure type being encoded as specified by the value of the lpszStructType parameter.

Each constant in the list below has an associated structure type that is pointed to by the pvStructInfo parameter. The structure pointed to, directly or indirectly, has a reference to a CERT_ALT_NAME_ENTRY structure.

  • X509_ALTERNATE_NAME
  • szOID_AUTHORITY_INFO_ACCESS
  • X509_AUTHORITY_INFO_ACCESS
  • X509_AUTHORITY_KEY_ID2
  • szOID_AUTHORITY_KEY_IDENTIFIER2
  • szOID_CRL_DIST_POINTS
  • X509_CRL_DIST_POINTS
  • szOID_CROSS_CERT_DIST_POINTS
  • X509_CROSS_CERT_DIST_POINTS
  • szOID_ISSUER_ALT_NAME
  • szOID_ISSUER_ALT_NAME2
  • szOID_ISSUING_DIST_POINT
  • X509_ISSUING_DIST_POINT
  • szOID_NAME_CONSTRAINTS
  • X509_NAME_CONSTRAINTS
  • szOID_NEXT_UPDATE_LOCATION
  • OCSP_REQUEST
  • zOID_SUBJECT_ALT_NAME
  • szOID_SUBJECT_ALT_NAME2

The CRYPT_ENCODE_ENABLE_PUNYCODE_FLAG flag, in conjunction with the value of the dwAltNameChoice member of the CERT_ALT_NAME_ENTRY structure, determines the manner in which strings are encoded.

dwAltNameChoiceEffect
CERT_ALT_NAME_DNS_NAMEIf the host name contains Unicode characters outside of the ASCII character set, the host name is first encoded in Punycode and then encoded as an IA5String string.
CERT_ALT_NAME_RFC822_NAMEIf the host name portion of the email address contains Unicode characters outside of the ASCII character set, the host name portion of the email address is encoded in Punycode. The resultant email address is then encoded as an IA5String string.
CERT_ALT_NAME_URLIf the server host name of the URI contains Unicode characters outside of the ASCII character set, then the host name portion of URI is encoded in Punycode. Then the resultant URI is escaped, and the URL is then encoded as an IA5String string.

 

Each constant in the list below has an associated structure type that is pointed to by the pvStructInfo parameter. The structure pointed to, directly or indirectly, has a reference to a CERT_HASHED_URL structure.

  • szOID_BIOMETRIC_EXT
  • X509_BIOMETRIC_EXT
  • szOID_LOGOTYPE_EXT
  • X509_LOGOTYPE_EXT

When encoding the CERT_HASHED_URL structure value, if the server host name of the URI contains Unicode characters outside of the ASCII character set, and the CRYPT_ENCODE_ENABLE_PUNYCODE_FLAG is set, the host name portion of URI is encoded in Punycode. Then the resultant URI is escaped, and the URL is then encoded as an IA5String string.

Each X509_UNICODE_NAME constant in the list below has an associated structure type that is pointed to by the pvStructInfo parameter.

  • X509_UNICODE_NAME

If the pszObjId member of the CERT_RDN_ATTR structure is set to szOID_RSA_emailAddr and the email address in the Value member contains Unicode characters outside of the ASCII character set, the host name portion of the email address is encoded in Punycode. Then the resultant email address is then encoded as an IA5String string.

In all cases, the Punycode encoding of the host name is performed on a label-by-label basis.

Examples

The following example shows initializing and encoding an X509_NAME structure using CryptEncodeObjectEx. For an example that includes the complete context for this example, see Example C Program: ASN.1 Encoding and Decoding.


#include <windows.h>
#include <stdio.h>
#include <Wincrypt.h>
#pragma comment(lib, "crypt32.lib")


#define MY_TYPE (X509_ASN_ENCODING)

void main()
{

//#define moved

//--------------------------------------------------------------------
//   Declare and initialize local variables.

char *Cert_Sub_Name ="Test User Name";

//--------------------------------------------------------------------
// Initialize a single RDN structure.

CERT_RDN_ATTR rgNameAttr = 
{
   "2.5.4.3",                      // The OID
   CERT_RDN_PRINTABLE_STRING,      // Type of string
   (DWORD)strlen(Cert_Sub_Name)+1, // String length including
                                   //  the terminating null character
   (BYTE *)Cert_Sub_Name           // Pointer to the string 
};
//--------------------------------------------------------------------
// Declare and initialize a structure to include
// the array of RDN structures.

CERT_RDN rgRDN[] = 
{
   1,               // The number of elements in the array
   &rgNameAttr      // Pointer to the array
};

//--------------------------------------------------------------------
//  Declare and initialize a CERT_NAME_INFO 
//  structure that includes a CERT_RND.

CERT_NAME_INFO CertName = 
{
    1,          // The number of elements in the CERT_RND's array
    rgRDN
};

//--------------------------------------------------------------------
//  Declare additional variables.

DWORD cbEncoded;              // Variable to hold the
                              //  length of the encoded string
BYTE *pbEncoded;              // Variable to hold a pointer to the 
                              //  encoded buffer
//--------------------------------------------------------------------
// Call CrypteEncodeObjectEx to get 
// length to allocate for pbEncoded.

if( CryptEncodeObjectEx(
     MY_TYPE,        // The encoding/decoding type
     X509_NAME,    
     &CertName,
     0,                 
     NULL, 
     NULL,
     &cbEncoded))    // Fill in the length needed for
                     // the encoded buffer.
{
     printf("The number of bytes needed is %d \n",cbEncoded);
}
else
{
     printf("The first call to the function failed.\n");
     exit(1);
}

if( pbEncoded = (BYTE*)malloc(cbEncoded))
{
     printf("Memory for pvEncoded has been allocated.\n");
}
else
{
    printf("Memory allocation failed.\n");
    exit(1);
}

if(CryptEncodeObjectEx(
     MY_TYPE,
     X509_NAME,
     &CertName,
     0,
     NULL, 
     pbEncoded,
     &cbEncoded))
{
     printf("The structure has been encoded.\n");
}
else
{
     printf("Encoding failed.");
     exit(1);
}
// Free allocated memory when done.
// ...
if(pbEncoded)
{
    free(pbEncoded);
}



Requirements

Minimum supported client

Windows XP [desktop apps only]

Minimum supported server

Windows Server 2003 [desktop apps only]

Header

Wincrypt.h

Library

Crypt32.lib

DLL

Crypt32.dll

See also

Object Encoding and Decoding Functions
CryptDecodeObject
CryptDecodeObjectEx
CryptEncodeObject

 

 

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