der: implementing other tag classes than Context-Specific

[ghost]

Hello,

first of all thanks for the crate.

I need to parse (and also write) serialized asn1 sequences, where the tags are given as application tag classes, i.e.:

InitiateSession ::= [APPLICATION 0] IMPLICIT SEQUENCE {
    sid-a                [APPLICATION 10] IMPLICIT OCTET STRING (SIZE(8..32)),
    login-protocol-list  [APPLICATION 11] IMPLICIT OCTET STRING,
    system-use-text      [APPLICATION 31] IMPLICIT UTF8String (SIZE(1..512)) OPTIONAL,
    server-msg-buf-size  [APPLICATION 32] IMPLICIT OCTET STRING (SIZE(2..2)) OPTIONAL
}

I do not think this is already possible with this library? I only found the distinguishing between context-specific and universal tags when you want to encode a struct (with derives) to der. Are there plan to implement that?

formats/der/derive/src/tag.rs

Line 13 in b20d644

pub(crate) enum Tag {

[tarcieri]

We don’t currently have plans to implement this, and generally implement features as needed by the cryptographic formats implemented in this repo.

What format are you trying to implement?

[ghost]

I am trying to implement that in DER format.

[tarcieri]

I was asking the name of the protocol you are trying to implement, i.e. where is that schema defined, and what protocol is it a message for?

[ghost]

Ah - sorry. Misunderstood. We use X.509 and custom ones. But in X.509 you do not have application tags, I think. So maybe this is the wrong place, if you only implement features needed for cryptographic formats.

But anyway - thanks for the fast response. I'll close the issue then.

[tarcieri]

We’re happy to accept PRs for additional functionality that goes beyond the formats we’re actively implementing. It’s just not something we’re planning on implementing ourselves any time soon

[zkonge]

I think the issue is still valuable because of the kerberos protocol requirement.

The remarkable thing is that it needs the APPLICATION as toplevel attribute, not field level.

[dishmaker]

The remarkable thing is that it needs the APPLICATION as toplevel attribute, not field level.

Here's an example of top-level tag:

formats/der/tests/derive.rs

Lines 556 to 562 in fd9b041

	/// EU Tachograph certificate
	pub type TachographCertificate<'a> = ApplicationImplicit<33, TachographCertificateInner<'a>>;
	/// EU Tachograph certificate inner sequence
	#[derive(Sequence)]
	#[asn1(tag_mode = "IMPLICIT")]
	pub struct TachographCertificateInner<'a> {