Bulletproof TLS Newsletter 
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.
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Two zeros bypass Java’s ECDSA signature check
28 Apr 2022
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.
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