The State of Anonymous Credentials (discussion)

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Session Topic: Attribute-Based-Credentials

Wednesday 3J

Convener: Andrew

Notes-taker: Hugh Pyle

Discussion notes, key understandings, outstanding questions, observations, and, if appropriate to this discussion: action items, next steps:

Lots more attendees to this session than expected for an esoteric crypto topic. So we started with a round of intros & asking why people are interested in the topic.

Andrew (convener): math background & voting systems. Previously: AskForIt startup. Interest areas including proving something while anonymous.

Greg - One use case is to have lots of "demo" accounts, or personas; interested in controls & management to how things become linked together.

Mads – WAYF, Denmark. Have deployed a hub & spoke attribute-federation system, but WAYF actively don't want to know everything about the users; would like to be able to deliver similar functionality, filter attributes for disclosure to various RPs, & mechanisms for users to grant usage-consent without disclosing the PII values to the hub.

Steve - VMware, access management. Balance marketing desire for tracking/login. Access control & authentication credentials

Morten - Alexandra Institute. Security & identity management work. 25years ago was young crypto nerd -> then book about anonymous credentials (Stefan Brands, etc). Thought maybe we would have a truly private internet by now, but still waiting!

Jin - McKesson - has some understanding of uProve. Use case for patient accessing healthcare, with limited disclosure as needed for service provision

Terry - interest in this stuff.

Kazue - NEC - cryptographer. Worked on group signature schemes & anonymous authentication. Has worked through approaches of: standardization, documents. Also working with ABC4trust.

Berit - Alexandra Institute. Background in math, cryptography, but not practitioner for some years. Interested in the gap between research & commercial applications,

Jim - independent - involved in the ID ecosystem steering group.

Paul - NIST - part of NSTIC program office. Business sponsor of Identity Broker. Citizen access to federal applications. Should eliminate trackability etc but don't think it does today. Want to move to something production-ready & commercially available.

William - Google identity team; Some identifiers for purposes of login mainly.

Steve - interested in pseudonymous-by-default

Mary - Google same team as William. Main applications are in federation protocols.

Reiner - independent consulting. Interested in alternatives to anonymous credentials; did a survey for kantara. How can we achieve same goals? - the Canadian late-binding model; or a mirror-like model to anon credentials, = anonymous service providers or relying parties

One problem is how to get these things started. For example, how to build into SAML.

Hugh - Qredo - software startup, building a new platform for applications of personal data; interested in use cases for rapid consumer adoption. Some seem to be around single or few attributes in retail environment.

Bill - New Zealand - ministry of education; worked with government central identity management


Q: uProve: active, alive, working?

birg should be running beginning next year
mixed signs from MSFT
discontinued Java implementation? Nothing happening for long periods?
decent license though, Microsoft explicitly permissive.

idemix (IBM's identity mixer):...?

weird license, should be cautious as a commercial enterprise

uprove issuing certs every time

idemix re-using, so more efficient in real uses.

upro? mybe, if want to release multiple attributes -> slow

talked to ronne bjernst (sp?) from Microsoft
ZKP versus group signature protocols

Q: are they doing ZKP really?

Andrew: math for idemix is.

Uprove uses *blind* signatures (Brands). If want to bind multiple

attributes they may become complicated.

ABC4trust (EU projects) use idemix?

First thing ABC4trust has a harmonized (pluggable) API for multiple systems with uProve and idemix as two.

Some politics maybe for IP issues

Sweden project - Soderhamn - smartcard with identity - education setting

prove that you had been in classes -> track when gave feedback
secure for purpose (no false voting) but retaining privacy

Also there’s a similar project in Greece

Both proof of concept projects

Additionally there is an ISO standardization effort -> quite early, working on a study period

Head is from IBM Zurich

Will probably take 3-4 years before standards can be ready

Other? Different cryptosystems, other implementations??

Group sig libraries? ->

hard to find a library that implements these things
MIRACL? & few others with primitives, not end-to-end

Reiner has proposed blinding of the IDP

Q (NIST): re idemix, is it using SAML or ...?

A: Some addendum, quite vague
Q: Next step -> profiling so can be deployed in identity systems that support these standards
Existing standards assume traditional PKI
Broker model

Morten: Looking for blindable single-use certificates

for use cases that are traditionally solved in other ways

Hugh -> blinded tokens for service access

Reiner - hopeful - layers, that's the way stuff evolves

e.g. Gateway / add software layer for access to existing infrastructure
plus need a back-channel
e.g. need to send user email


attach a coin to request

Reiner -> need a pseudonymous recipient address


Q: Jim:

anonymous/pseudonymous with respect to which parts of the transaction?

Mostly we say that with respect to relying parties

but there are lots of others - IDPs, attribute-providers, etc.

e.g. over21, usually need other information than that

intermediaries are an efficient way of solving the problem

probably want an intermediary in order to provide blinding of who is using these attributes from the authoritative source of them

morten: thing is to do the blinding yourself.

then any intermediary doesn't have the tracking of usage and so on.

Jim: more about being able to abstract some of the information

Hugh -> use scenarios? e.g. age plus photo, where photo is the "recognizer" for F2F

Morten: ZKP attributes - meaning, provable attributes, with the RP unable to pass those attributes to a third party

But: for example, liquor purchase, want to be able to prove to authorities that the user was verified

Reiner: Systems build this as a role for discloser ("designated opener"), able to unlock under special circumstances

Morten: The opener - interesting but some potential for misuse depending on your scenarios

Kazue: everyone has different needs

but the crypto is different based on everyone's needs
that's part of the problem comparing with e.g. SAML

Andrew: does that need advances in the cryptography? for standardization?

Kazue: where's the instance to implement?


Nist: working on at least three use cases

one will be made public once solve it
(that won't happen immediately though...)
hub approach --> identity & attribute - implementing parts of this
another: with msft & uprove, some work
another: recently awarded, hub model, trying to keep subject privacy

So there are at least three attribute hubs? demonstrates a real demand for these things

USA / nist described
Denmark - part of ProAc - researching options
UK - IDESG / Cabinet Office digital services - private-sector IDPs, local & central gov RPs

at varying states of development

shows that use cases are valuable


single credential to use services from multiple US-government RPs
attributes shared with consent
multiple IDPs incl private sector

good at blinding the identity, but nothing yet in place for the attributes
Signed & encrypted from IDP to hub -> strips -> repackages for the RP
Want to maintain that level of blinding for all the PII attributes

Reiner: alternative is to have end-to-end from IDP to provider

as long as the IDP has no knowledge who they're encrypting for
attributes passed through because encrypted

UK: assertions are signed across the hub

so the hub can't change - but can see the attributes as they pass the hub

Morten: Canadian system had a similar

late-binding model
blinded token
Reiner: paper see link:

nice thing about end-to-end is that in the SAML world that's minimally invasive

Q: (Reiner) if don't use smartcards as the credentials, what can you use? ubikey? mini-HSM -

nice, not really "anonymous" in the sense of unlinkable show;
device holds a secret key; generates keypair, encrypts the private key & sends to RP
So quite simple, and unlinked across RPs