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On Thursday afternoon I gave my talk 'Everything you need to know about cryptography in 1 hour' at BSDCan'10. Two HNers (as far as I know -- there might be more?) came to hear me speak, but several other people here have said that they would like to see talk but couldn't attend; so here's my talk slides.

I understand that a recording will go online somewhere at some point, but I'm not entirely sure of the details about that.

Since I've only the slides, I have a question about the following point:

> DON’T: Put FreeBSD-8.0-RELEASE-amd64-disc1.iso and CHECKSUM.SHA256 onto the same FTP server and think that you’ve done something useful.

I take it the FTP got compromised and people simply regenerated the checksum for a modified image?

Wouldn't signing the checksum file solve the problem? Using different FTP servers for distributing the image and the checksums makes mirroring probably difficult.

I take it the FTP got compromised and people simply regenerated the checksum for a modified image?

I'm not aware of any problems with FreeBSD FTP mirrors being compromised recently. I wanted an example of data-adjacent-to-hash and most of the audience was FreeBSD people, so I figured that I'd go with an example close to home.

Wouldn't signing the checksum file solve the problem?

Yes. Or just relying on the FreeBSD release announcements, which contain SHA256 hashes and are signed.

Thanks Colin. Very informative.

Why did you choose to publish your slides in PDF when PDF documents are a main tool for security attacks?

Update: If PDFs are a major source of security attacks, and author cares about security, and author publishes document in PDF form, then why would you downvote this question?

Because it's a completely nonsensical question.

If balaclavas are used in bank robberies, and you care about the safety of your money, why would you wear a balaclava on a mountain climbing expedition?

PDFs are not a tool for security attacks because they are PDFs, they are a tool for security attacks because of vulnerabilities in Adobe Reader. Any given PDF is not a danger, only PDFs with exploits are dangerous.

And including a buffer overflow exploit, rootkit and phone-home code isn't something you're going to do accidentally while publishing your talk slides, is it?

I do not have the power to downvote, and I hate when people downvote because of disagreement but do not explain their stance -- I learn nothing from it; I can give you my perspective on your comment. (It would be nice to have a personal downvote message feature or something; the anonymity helps us avoid embarrassment, I guess.)

First, your point is irrelevant. Whatever the medium, this discussion is about cryptography. There is not a real case of hypocrisy here. Cryptography is certainly related to security, but as far as I can tell, that is not the thrust of this discussion.

Second, while the technology can be abused, as you point out, that is a far cry from this particular author abusing it and using it as a security attack. The author's PDF is fine.

I am not agreeing or disagreeing with you, btw.

In other words, I can see that this comment was downvoted because it did not meaningfully add to the discussion. I usually see downvotes on posts that include offtopic personal axe grinding. I may receive the same, myself, for this post, but I just wanted to help you avoid it in the future.

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