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Why Johnny Can't Encrypt: A Usability Evaluation of PGP 5.0 (1999)
Seminal 1999 USENIX study finds most novice users cannot correctly sign and encrypt email with PGP 5.0 in 90 minutes.
Whitten and Tygar's USENIX Security Symposium paper evaluates whether cryptography novices can use PGP 5.0 effectively, using cognitive walkthrough analysis and a laboratory user test. The majority of test participants failed to successfully sign and encrypt a message within 90 minutes, despite PGP 5.0 having a well-regarded graphical interface. The authors argue that security requires usability standards beyond those of general consumer software and propose domain-specific UI design principles for security. The paper is a foundational reference in usable security research.
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The gpg.fail aftermath: On responsible disclosure, GPG, and the state of security in 2026 [32:37]
A conference talk recounts GPG vulnerability disclosures, notes several GnuPG flaws remain unpatched, and demonstrates novel bugs live.
A researcher who disclosed multiple GnuPG vulnerabilities before 39c3 in December 2025 reports that several flaws, including one allowing spoofed PGP signatures, remain unpatched. Memory corruption in the basic PGP message parser was properly fixed, but GnuPG maintainer Werner Koch declared a widely-used feature 'harmful' instead of patching it. The talk presents additional novel GPG vulnerabilities and commentary on responsible disclosure and LLMs in security.
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Re: Retrospective by 'gpg.fail' authors
Peter Gutmann replies to gpg.fail retrospective, pointing to PGP's arbitrary packet format as root of many past vulnerabilities.
Peter Gutmann posted a follow-up on oss-security referencing an Hacker News discussion of the gpg.fail authors' retrospective. The thread argues that a recurring source of severe PGP vulnerabilities is the format's permissive packet system, where a PGP message is a practically arbitrary stream of packets. This is discussion and retrospective analysis rather than a new disclosure.
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