Privacy – Pomcor

Overview of ISO/IEC 18013-5: Innovations and Vulnerabilities in the mDL Standard

Two weeks ago I gave a talk about the mobile driver’s license standard at IIW XXXVII, the 37th meeting of the Internet Identity Workshop, which took place as usual at the Computer History Museum in Mountain View.

One of the great things about IIW is that the agenda is created each day. That makes it possible for people interested in the same topic to merge their sessions. When I announced the session that I wanted to convene, Andrew Hughes “hijacked my session”, as he said, to present a progress update on the series of ISO driving license standards, which was a perfect introduction to the details of part 5 of the series that I discussed in the second half of the session. Andrew is a member of the committee that wrote ISO/IEC 18013-5, and other committee members came to the combined session. The notes of the session, taken by Dan Bachenheimer, will eventually be in the Book of Proceedings, and can now be found here. My slides were based in part on an early draft of a chapter of a book on Foundations of Cryptographic Authentication that I am coauthoring with Sukhi Chuhan and Veronica Wojnas.

The mDL standard has many interesting innovations and privacy features.

One innovation, explained in slide 26, is the inclusion of self-asserted (device-signed) and certified (issuer-signed) data elements in the same credential. One wouldn’t expect to find self-asserted claims in a driver’s license, and Section 8.3.2.1.2.2 explicitly says that the structure containing the device-signed elements may be empty. But the mDL standard is in fact a general purpose standard for mobile credentials, which competes with verifiable credentials as discussed in this UL white paper.

Both kinds of data elements are retrieved in an encrypted session established by an ECDH key agreement where both parties use ephemeral key pairs and therefore neither party is authenticated. After the session has been established, the mobile device that carries the credential authenticates as a side-effect of signing the list of self-asserted data elements requested by the reader, whether or not it is empty!

Another innovation, explained in slide 28, is a clever use of an asymmetric key pair to produce a repudiable symmetric signature (an “ECDH-agreed MAC”), and a third innovation, explained in slide 29, is a clever adaptation of OpenID Connect to a use case where it would not seem to be applicable.

Privacy features include declaration by the relying party of the intent to retain some of the data elements, data minimization using selective disclosure, and proof of age without revealing the birthdate by means of age attestations.

Selective disclosure is implemented by means of cryptographic hashing, as explained in slide 11. Full unlinkability (protection against tracking by collusion of the issuer and the relying parties) is not provided, but selective disclosure based on hashing combined with age attestations provides the key benefits of data minimization and proof of age in a simpler way than anonymous credentials. Alternative implementations of selective disclosure, based on hash functions or proofs of knowledge, are described in slides 12-23.

On the other hand, the mDL standard also has privacy drawbacks and vulnerabilities to unauthorized access and man-in-the-middle attacks. The vulnerabilities are discussed in slides 30-39, with an example of a man-in-the-middle attack shown in slide 37. They are also discussed in Section 13.1.9 of the book chapter, along with proposed mitigations in the current or future versions of the standard. Privacy is discussed in slides 40-42 and in Section 13.1.10 of the book chapter.

The vulnerabilities and the privacy drawbacks have two independent root causes.

A Brief Overview of Cryptographic Authentication with a Discussion of Three Hot Topics

Updated August 8 2023

I have just revamped the cryptographic authentication page of the Pomcor site to reflect two major changes that are happening in internet identity and authentication:

It is now clear that traditional MFA is vulnerable to MITM phishing attacks and cryptographic authentication is the solution. But the technology that the industry has bet on as a replacement, FIDO authentication, faces user experience (UX) challenges that have been impeding adoption.
Governments are trying to issue digital credentials usable instead of physical credentials, and some are experimenting with verifiable credentials and self-sovereign identifiers. But a UL white paper has noted that the ISO/IEC 18013-5 standard, although entitled “Mobile driving licence (mDL) application”, can be used to define any kind of credential and is in direct competition with verifiable credentials. And the arguably most successful government app in the world, the Diia app of Ukraine, described in a presentation to the Canadian CIO Strategy Council shown in this YouTube video, uses neither verifiable credentials nor the ISO/IEC 18013-5 standard.

The revamped page includes a definition of the term cryptographic authentication that manages to encompass authentication with key pairs, public key certificates, anonymous credentials, symmetric key credentials and verifiable credentials. It also includes a classification of cryptographic credentials and authentication methods, a recapitulation of the benefits and challenges of cryptographic authentication, and a discussion of three ~~hot topics~~ unsettled issues:

How to use cryptographic authentication to actually provide effective protection against MITM phishing attacks.
How to let the user authenticate on multiple devices, and
How ~~to provide protection~~ to combine the cryptographic factor with additional factors for protection against theft of the device that carries the credential.

Airport Security in the Age of COVID-19

As the travel restrictions imposed to control the coronavirus pandemic are beginning to be relaxed in some parts of the world, it is time to start rethinking airport security in the age of COVID-19. Even if an effective vaccine is found for COVID-19, it will be out of the question to go back to long lines at security checkpoints and boarding gates, and the manual checking of identity documents and boarding passes.

In a provisional patent application that I coauthored with Karen Lewison before the pandemic and have now published, we proposed an automated method of verifying the identity of travelers that could be used in the post-pandemic world to speed up the security check and the boarding process, and to eliminate the face-to-face interaction with a security officer at the checkpoint and a flight attendant at the boarding gate. The method takes advantage of the high accuracy achieved by today’s deep neural networks for face recognition, while overcoming the privacy concerns raised by the collection and storage of facial images.

Here is a summary of the method.

A New Tool Against the Surge of Application Fraud

This blog post has been coauthored with Karen Lewison

In recent posts we have been concerned with online credit card fraud and how to fight it using cardholder authentication. In this post we are concerned with another kind of financial fraud, known as application fraud or new account fraud. Both kinds of fraud have been rising after the introduction of chip cards, for reasons mentioned by Elizabeth Lasher in her article The Surge of Application Fraud:

“Due to the high volume of data breaches, Social Security numbers, mailing addresses, passwords, health history, even the name of our first pet is all for sale on the Dark Web. When you combine this phenomenon with the economic pressure applied on fraudsters to find a new cash cow after chip and signature plugged a gap in card-present fraud in the US, there is a perfect storm.”

The term “application fraud” refers to the creation of a financial account, such as a bank account or a mortgage account, with the intention to commit fraud. Application fraud can be first-party fraud, where the account is opened under the fraudster’s own identity, or third-party fraud, where the fraudster uses a stolen identity. Here we are primarily concerned with the latter.

Will Cardholder Authentication Ever Come to the US?

This blog post has been coauthored with Karen Lewison

You may have heard that the EU is struggling to implement the Strong Customer Authentication (SCA) requirements of Payment Services Directive 2 (PSD2). The directive was issued four years ago, Regulatory Technical Standards (RTS) followed two years later, and the SCA requirements went into effect on September 14. But on October 16 the European Banking Authority (EBA) had to postpone enforcement until December 31, 2020, due to pushback from the National Competent Authorities (NCAs) of the EU member countries. In an opinion announcing the postponement, the EBA cited as a reason for the pushback the fact that 3-D Secure 2 (3DS2) is not ready.

The problems that the EBA is having with the SCA requirements have more to do with the bureaucratic formulation of the requirements in PSD2, than with the technical difficulty of providing strong security. We will discuss this in another post, but first we want to ask here whether cardholder authentication will ever come to the US.

An Omission-Tolerant Cryptographic Checksum

This is part 1 of a series on omission-tolerant integrity protection and related topics. A technical report on the topic is available on this site and in the IACR ePrint Archive.

Broadly speaking, an omission-tolerant cryptographic checksum is a checksum on data that does not change when items are removed from the data but makes it infeasible for an adversary to modify the data in other ways without invalidating the checksum.

We discovered the concept of omission-tolerant integrity protection while working on rich credentials. A rich credential includes subject attributes and verification data stored in a typed hash tree. We noted in an interim report that the root label of the tree could be viewed as an “omission-tolerant cryptographic checksum”. Prof. Phil Windley, who read the report, told us that he had not seen the concept before, and asked if we had invented it. We then added a section on typed hash trees and omission-tolerant integrity protection to the final report.

We’ve now written a new technical report that discusses omission-tolerant checksums and omission-tolerant integrity protection in a broader context than rich credentials. The main contributions of the new paper are a formal definition of omission-tolerant integrity protection, a method of computing an omission-tolerant checksum on a bit-string encoding of a set of key-value pairs, and a formal proof of security in an asymptotic security setting that uses the system parameterization concept introduced by Boneh and Shoup in their online book.

I have not said much in this blog about omission-tolerant integrity protection, and there is a lot to say: how an omission-tolerant checksum can be used to implement selective disclosure of subject attributes in public key certificates; how public key certificates with selective disclosure could easily provide security and privacy for client authentication in TLS; what’s special about Boneh and Shoup’s system parameterization concept and how we use it in our definitions and proofs; how can a typed hash tree provide omission-tolerant integrity protection whereas a Merkle tree cannot; and a number of narrower but no less interesting topics. This is the first of a series of posts on these topics.

Pomcor Contributes Biometrics Chapter to HCI and Cybersecurity Handbook

Karen Lewison and I have contributed the chapter on Biometrics to the book Human-Computer Interaction and Cybersecurity Handbook, published by Taylor & Francis in the CRC Press series on Human Factors and Ergonomics. The editor of the paper, Abbas Moallem, has received the SJSU 2018 Author and Artist Award for the book.

Biometrics is a very complex topic because there are many biometric modalities, and different modalities use different technologies that require different scientific backgrounds for in-depth understanding. The chapter focuses on biometric verfication and packs a lot of knowledge in only 20 pages, which it organizes by identifying general concepts, matching paradigms and security architectures before diving into the details of fingerprint, iris, face and speaker verification, briefly surveying other modalities, and discussing several methods of combining modalities in biometric fusion. It emphasizes presentation attacks and mitigation methods that can be used in what will always be an arms race between impersonators and verifiers, and discusses the security and privacy implications of biometric technologies.

Feedback or questions about the chapter would be very welcome as comments on this post.

New Conference to Address the Human Aspects of Cybersecurity and Cryptography

Human factors are an essential aspect of cybersecurity. Take for example credit card payments on the web. A protocol for reducing fraud by authenticating the cardholder, 3-D Secure, was introduced by VISA in 1999 and adopted by other payment networks, but has seen limited deployment because of poor usability. Now 3-D Secure 2.0 attempts to reduce friction by asking the merchant to share privacy-sensitive customer information with the bank and giving up on cardholder authentication for transactions deemed low-risk based on that data. A protocol with better usability would provide better security without impinging on cardholder privacy.

But human factors are not limited to the usability of cybersecurity defenses. In biometric authentication, human factors are the very essence of the defense. Human factors are also of the essence in cybersecurity attacks such as phishing and social engineering attacks, and play a role in enabling or spreading attacks that exploit technical vulnerabilities.

The 1st International Conference on HCI for Cybersecurity, Privacy and Trust (HCI-CPT) recognizes the multifaceted role played by human factors in cybersecurity, and intends to promote research that views Human-Computer Interaction (HCI) as “a fundamental pillar for designing more secure systems”. A call for participation can be found here.

Storing Cryptographic Keys in Persistent Browser Storage

This blog post is a companion to a presentation made at the 2017 International Cryptographic Module Conference and refers to the presentation slides, revised after the conference. Karen Lewison is a co-author of the presentation and of this blog post.

Slide 2: Key storage in web clients

Most Web applications today use TLS, thus relying on cryptography to provide a secure channel between client and server, and to authenticate the server to the client by means of a cryptographic credential, consisting of a TLS server certificate and its associated private key. But other uses of cryptography by Web applications are still rare. Client authentication still relies primarily on traditional username-and-password, one-time passwords, proof of possession of a mobile phone, biometrics, or combinations of two or more of such authentication factors. Web payments still rely on a credit card number being considered a secret. Encrypted messaging is on the rise, but is not Web-based.

A major obstacle to broader use of cryptography by Web applications is the problem of where to store cryptographic keys on the client side. Continue reading “Storing Cryptographic Keys in Persistent Browser Storage”

What kind of “encrypted fingerprint template” is used by MasterCard?

In a press release, MasterCard announced yesterday an EMV payment card that features a fingerprint reader. The release said that two trials have been recently concluded in South Africa and, after additional trials, a full roll out is expected this year.

In the United States, EMV chip cards are used without a PIN. The fingerprint reader is no doubt intended to fill that security gap. But any use of biometrics raises privacy concerns. Perhaps to address such concerns, the press release stated that a fingerprint template stored in the card is “encrypted”.

That’s puzzling. If the template is encrypted, what key is used to decrypt it before use?