Bulletproof TLS Newsletter

Two zeros bypass Java’s ECDSA signature check

28 April 2022

Bulletproof TLS Newsletter is a free periodic newsletter bringing you commentary and news surrounding SSL/TLS and Internet PKI, designed to keep you informed about the latest developments in this space. Received monthly by more than 50,000 subscribers. Maintained by Hanno Böck.

BROUGHT TO YOU BY OUR SPONSOR
Application Security Across Top 1 Million Sites Curious about the state of application security across the top 1 million web sites? Read this report for cybersecurity analysis outlining trends in HTTPS, Certificate Authority, Permissions Policy and more. VENAFI

A security vulnerability in Java’s ECDSA implementation allows creating a signature that would always be evaluated as valid. Neil Madden, who discovered the flaw, called it a psychic signature.

ECDSA signatures consist of two values, usually called r and s. The issue is that ECDSA signature validation compares r to the product of the inverse of s multiplied with other values. Depending on how the inverse of s is calculated, the inverse of zero may also be evaluated to zero.

In Java this is the case, so zero gets compared to zero—independent of the message to be validated. Thus a signature where the r and s values are set to zero will always pass.

This is generally a known property of ECDSA. It is therefore required to check that the r and s values are not zero, which is supposed to be the first step of the signature verification algorithm. However, Java failed to implement that check.

Madden noted in a later blog post that two zeros are not the only way to bypass the signature check.

The vulnerability was introduced in Java version 15, where the previous ECDSA implementation written in C++ was replaced by one written in native Java. Oracle fixed the vulnerability in its April update, and the vulnerability was assigned the ID CVE-2022-21449. OpenJDK, the open-source distribution of Java, also published an advisory.

It is noteworthy that this vulnerability was not caught earlier. Neil Madden points out that Project Wycheproof, a cryptographic test suite published by Google, would have caught this vulnerability.

Subscribe to the Bulletproof TLS Newsletter

This subscription is just for the newsletter; we won't send you anything else.

Short news

Here are some things that caught our attention since the previous newsletter:

Interesting jobs

Here are some interesting jobs we've come across in the last month:

If you know of similar jobs that our readers might be interested in, for example cryptography, TLS, or PKI, let us know and we may add them to future newsletters.

Books and Resources

And here is a free book we think you might find interesting:

Designed by Ivan Ristić, the author of SSL Labs, Bulletproof TLS and PKI, and Hardenize, our course covers everything you need to know to deploy secure servers and encrypted web applications.

Remote and trainer-led, with small classes and a choice of timezones.

Join over 1,500 students who have benefited from more than a decade of deep TLS and PKI expertise.

Find out More