Anais - Engenharia de Redes de Comunicação - UnB

the requirements, the document cannot be considered valid.
Figure 2 shows the structure of a signed document for a hypothetic contract between
university “A” and company “B”. In this example, the document must be signed
by two people from the university, a Financial Manager and a Department Supervisor,
and one person from the company, the company Director. These constraints are specified
using the Role attribute type, which is defined in ISO/IEC 9594-8 [ITU-T 2008b]. The
Role shall have the same value in the authorization requirements and the signatory’s AC.
Figure 3 shows the ASN1 representation of the Authorization Requirements attribute for
this specific example. Since, for now, there are no OIDs defined for the types Authorization
Requirements and RequiredCounterSigEntry, these appear only as sequences in the
represented structure.
signs
Authorization Requirements
RequiredCounterSigEntry
Creator Signature
signerAttributes
Signed Attributes
Contract
Role: “Director”
Authorization
Requirements
...
RequiredCounterSigEntry
signerAttributes
Unsigned Attributes
Role: “Financial Manager”
1st Countersignature
2nd Countersignature
RequiredCounterSigEntry
3rd Countersignature
...
contains
matches AC attribute
signerAttributes
Role: “Department Supervisor”
signs
University A
PKC
AC
PKC
AC
PKC
AC
Company B
Department
Supervisor
Finacial
Manager
Director
Figure 2. Contract Signature
5. Discussion
It may seem natural to specify the identity and the authorization constraints of required
signatories directly in the document’s text. This may even be appropriate if those constraints
are meant to be checked manually. However, automated validation of the signatories’
identity and authorization becomes very tricky when the constraints are specified in
401