This blog post explores how a Certificate Authority (CA) could maliciously issue a certificate with a valid signature but an impossibly distant expiration date, far beyond the CA's own validity period. This "fake future" certificate wouldn't trigger typical browser warnings because the signature checks out. However, by comparing the certificate's notAfter date with Signed Certificate Timestamps (SCTs) from publicly auditable logs, inconsistencies can be detected. These SCTs provide proof of inclusion in a log at a specific time, effectively acting as a timestamp for when the certificate was issued. If the SCT is newer than the CA's validity period but the certificate claims an older issuance date within that validity period, it indicates potential foul play. The post further demonstrates how this discrepancy can be checked programmatically using open-source tools.
The blog post details a formal verification of the standard long division algorithm using the Dafny programming language and its built-in Hoare logic capabilities. It walks through the challenges of representing and reasoning about the algorithm within this formal system, including defining loop invariants and handling edge cases like division by zero. The core difficulty lies in proving that the quotient and remainder produced by the algorithm are indeed correct according to the mathematical definition of division. The author meticulously constructs the necessary pre- and post-conditions, and elaborates on the specific insights and techniques required to guide the verifier to a successful proof. Ultimately, the post demonstrates the power of formal methods to rigorously verify even relatively simple, yet subtly complex, algorithms.
Hacker News users discussed the application of Hoare logic to verify long division, with several expressing appreciation for the clear explanation and visualization of the algorithm. Some commenters debated the practical benefits of formal verification for such a well-established algorithm, questioning the likelihood of uncovering unknown bugs. Others highlighted the educational value of the exercise, emphasizing the importance of understanding foundational algorithms. A few users delved into the specifics of the chosen proof method and its implications. One commenter suggested exploring alternative verification approaches, while another pointed out the potential for applying similar techniques to other arithmetic operations.
A VTuber's YouTube channel, linked to a Brand Account, was requested to verify ownership via phone number. Upon doing so, the channel's name and icon were permanently changed to match the Google account associated with the phone number, completely overwriting the VTuber's branding. YouTube support has been unhelpful, claiming this is intended behavior. The VTuber is seeking community support and attention to the issue, warning others with Brand Accounts to avoid phone verification, as it risks irreversible damage to their channel identity.
HN commenters were largely skeptical of the YouTuber's claims, suspecting they had misunderstood or misrepresented the situation. Several pointed out that YouTube likely wouldn't overwrite an existing Google account with a brand account's information and suggested the user had accidentally created a new account or merged accounts unintentionally. Some offered technical explanations of how brand accounts function, highlighting the separation between personal and brand channel data. Others criticized the YouTuber for not contacting YouTube support directly and relying on Reddit for technical assistance. A few commenters expressed general frustration with YouTube's account management system, but most focused on the plausibility of the original poster's story.
Summary of Comments ( 43 )
https://news.ycombinator.com/item?id=43285671
Hacker News users discuss the practicality and implications of the blog post's method for detecting malicious Sub-CAs. Several commenters point out the difficulty of implementing this at scale due to the computational cost and potential performance impact of checking every certificate against a large CRL set. Others express concerns about the feasibility of maintaining an up-to-date list of suspect CAs, given their dynamic nature. Some question the overall effectiveness, arguing that sophisticated attackers could circumvent such checks. A few users suggest alternative approaches like using DNSSEC and DANE, or relying on operating system trust stores. The overall sentiment leans toward acknowledging the validity of the author's points while remaining skeptical of the proposed solution's real-world applicability.
The Hacker News post "How to distrust a CA without any certificate errors" sparked a discussion with several insightful comments. Many commenters engaged with the core concept of the blog post, which explored how a Certificate Authority (CA) could potentially manipulate certificates without triggering typical browser warnings.
One commenter highlighted the difficulty in detecting this type of manipulation, emphasizing that the trust model inherently relies on the CA. They pointed out the unlikelihood of a user independently verifying the certificate chain, especially given the complexity involved. This reinforced the article's point about the potential vulnerability.
Another commenter discussed the "certificate pinning" technique, which involves hardcoding expected certificate information into an application. While effective against the specific attack described in the article, they acknowledged that it's not a widespread solution and introduces its own set of management challenges, such as the need to update pinned certificates regularly.
The conversation also touched upon the broader issues of trust and security in the digital landscape. One commenter expressed a general lack of trust in CAs, citing past incidents of compromised CAs and questionable practices. This sentiment resonated with other users who echoed concerns about the centralized nature of the CA system.
Some commenters suggested alternative approaches to enhance security. One idea involved using DNSSEC combined with DANE (DNS-based Authentication of Named Entities), allowing domain owners to specify which CAs are authorized to issue certificates for their domain. Another suggestion was to explore decentralized identity solutions, moving away from the reliance on centralized CAs altogether.
Several comments also delved into the technical details of the attack described in the article, with users discussing specific aspects of certificate validation and the potential implications for different browsers and operating systems. There was some debate about the practicality of the attack and the likelihood of it being exploited in the wild, with some arguing that the complexity involved would make it a less attractive option for attackers.
Overall, the comments section reflected a general understanding of the potential vulnerabilities associated with the current CA system and a desire for more robust and transparent security solutions. While no single solution emerged as a clear winner, the discussion provided valuable insights into the challenges and potential future directions of certificate management and online trust.