To sign or not to sign: Practical vulnerabilities in GPG & friends

Might contain zerodays. https://gpg.fail/ From secure communications to software updates: PGP implementations such as *GnuPG* ubiquitously relied on to provide cryptographic assurances. Many applications from secure communications to software updates fundamentally rely on these utilities. Since these have been developed for decades, one might expect mature codebases, a multitude of code audit reports, and extensive continuous testing. When looking into various PGP-related codebases for some personal use cases, we found these expectations not met, and discovered multiple vulnerabilities in cryptographic utilities, namely in *GnuPG*, *Sequoia PGP*, *age*, and *minisign*. The vulnerabilities have implementation bugs at their core, for example in parsing code, rather than bugs in the mathematics of the cryptography itself. A vulnerability in a parser could for example lead to a confusion about what data was actually signed, allowing attackers without the private key of the signer to swap the plain text. As we initially did not start with the intent of conducting security research, but rather were looking into understanding some internals of key management and signatures for personal use, we also discuss the process of uncovering these bugs. Furthermore, we touch on the role of the OpenPGP specification, and the disclosure process.