可信时间戳 - 了解格式（rfc3161）

TimeStampReq ::= SEQUENCE  {
   version                      INTEGER  { v1(1) },
   messageImprint               MessageImprint,
     --a hash algorithm OID and the hash value of the data to be

     --time-stamped
   reqPolicy             TSAPolicyId              OPTIONAL,
   nonce                 INTEGER                  OPTIONAL,
   certReq               BOOLEAN                  DEFAULT FALSE,
   extensions            [0] IMPLICIT Extensions  OPTIONAL  }

   MessageImprint ::= SEQUENCE  {
        hashAlgorithm                AlgorithmIdentifier,
        hashedMessage                OCTET STRING  }