Why I use low-level function to decode an enveloped-data is so slo

From: yang (yy_bj_at_hotmail.com)
Date: 05/25/05 

Date: Tue, 24 May 2005 23:06:01 -0700

Hi,
    I want to use some low-level functions to decode an enveloped-data,but I
find it is so slowly.The function of msgupate runs about 3 min, MS outlook
decrypt the whole email about 30s.Why?
   The program like this:

hMsg = CryptMsgOpenToDecode(
   PKCS_7_ASN_ENCODING | X509_ASN_ENCODING, // Encoding type
   0, // Flags
   0, // Message type (get from msg.)
   0, // Cryptographic provider
   NULL, // Recipient info
   NULL); // Stream info

fResult = CryptMsgUpdate(
  hMsg, // Handle to the message
  pbEncryptedBlob, //
Pointer to the encoded blob
  cbEncryptedBlob, //
Size of the encoded blob
  TRUE);
// Last call

Thank you very much for your reply.

yang 

-- 
Help