fix: fix MessageImprint.HashAlgorithm.Parameters

[Two-Hearts]

This PR fixes MessageImprint.HashAlgorithm.Parameters and added corresponding validation in TSA response based on RFC 3161.

The issue that this PR is trying to fix is:
Golang's asn1.RawValue has zero value with Tag 0, which is actually not a valid asn1 tag (https://luca.ntop.org/Teaching/Appunti/asn1.html).
The correct zero value of the struct should be asn1.NullRawValue with Tag 5. However, asn1.NullRawValue is not a valid asn1 object either. The valid struct, as added by this PR, should be:

asn1.RawValue{
     Tag: 5,
     FullBytes: []bytes{5, 0}  // tag and length
}

If running the below piece of code:

v1 := asn1.NullRawValue
fmt.Println("v1:", v1)

b, _:= asn1.Marshal(v1)
var v2 asn1.RawValue
asn1.Unmarshal(b, &v2)
fmt.Println("v2:", v2)

The printouts will be:

v1: {0 5 false [] []}
v2: {0 5 false [] [5 0]}   --> unmarshal returns the correct struct

(This is a known issue of golang encoding/asn1 package: golang/go#30414. The issue was closed without any code update though)

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[priteshbandi]

LGTM

[JeyJeyGao]

https://cs.opensource.google/go/go/+/master:src/encoding/asn1/asn1_test.go;l=1045-1068?q=NullRawValue&ss=go%2Fgo

Could you have a look at this test? Is it by design?

[Two-Hearts]

https://cs.opensource.google/go/go/+/master:src/encoding/asn1/asn1_test.go;l=1045-1068?q=NullRawValue&ss=go%2Fgo

Could you have a look at this test? Is it by design?

Yes, it is by design by the golang library, but that's not by design of RFC 3161. When a TSA request contains asn1.NullRawValue, the TSA response may contain the correct null raw value struct instead. And this would fail tspclient-go's response validation. Therefore, we need to make sure we send out the correct asn1 object in the request. @JeyJeyGao

[shizhMSFT]

LGTM with suggestions.

[shizhMSFT]

LGTM