feature: more attribute support

[secDre4mer]

Name of feature:

Support for reading / changing unsigned attributes

Pain or issue this feature alleviates:

Unsigned attributes can contain mutable information. E.g. adding a 2nd signature to a PKCS7 struct is done by adding an additional unsigned attribute that contains the PKCS7 for the secondary signature.

Why is this important to the project (if not answered above):

Reading and changing unsigned signatures is a valuable extension, especially since support for adding unsigned signatures at signing time already exists.

Is there documentation on how to use this feature? If so, where?

In what environments or workflows is this feature supported?

In what environments or workflows is this feature explicitly NOT supported (if any)?

Supporting links/other PRs/issues:

saferwall/pe#95

💔Thank you!

[CLAassistant]

All committers have signed the CLA.

[hslatman]

Hey @secDre4mer, thank you for opening the PR. I'll have a look at this soon.

I'm curious about the Copy function name / signature. It seems like the goal is to get an exact copy of an existing p7 struct, but then with specific unsigned attributes set? Maybe it would be more logical to define it as a method on the p7 itself, and return a new instance? Or with a more explicit name, like CopyWithUnsignedAttributes?

[secDre4mer]

Hey @hslatman , yes, you've described the use case well.

Maybe it would be more logical to define it as a method on the p7 itself, and return a new instance?

Defining this on the struct itself would make sense IMO, and returning a full PKCS7 struct makes sense. The raw content can then be queried anyway with PKCS7.Content.

Or with a more explicit name, like CopyWithUnsignedAttributes?

Maybe we can combine this? Like: Make Copy into (PKCS7).ModifyUnsignedAttributes(newAttributes ...Attribute) *PKCS7?

One other issue with the current API, now that I'm looking at it: There's no way to iterate over all attributes (signed or unsigned) yet. Should I add some functions for this?

[secDre4mer]

Added CopyWithUnsignedAttributes as suggested by you. Also added a Marshal function that can be used to turn a PKCS7 struct back into an ASN1 byte struct.

[LordNoteworthy]

Thank @secDre4mer for the update !

What do you think @hslatman ?