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Comment: Re:What about a re-implementation... (Score 1) 278

by blueg3 (#46760067) Attached to: OpenBSD Team Cleaning Up OpenSSL

...you can receive that passphrase into a char array on the stack, use it, and zero it out immediately. Poof, gone in microseconds.

Only if you've set that part of your stack to locked. Otherwise it could get paged out to disk. Thanks to the fun of timing on computers, the amount of actual time that passes between "receive [into memory]" and "zero out" is arbitrarily long.

Comment: Re:What about a re-implementation... (Score 1) 278

by blueg3 (#46759981) Attached to: OpenBSD Team Cleaning Up OpenSSL

So if C is so bad why should we trust the languages that are implemented in it? You do realize that most of these "safe" languages are written in C, right?

I'm just going to link to a previous comment where I answered the same question.

TLDR: Languages aren't "written in" anything, and the language the compiler is written in has no bearing on the capabilities of the language it compiles. (We're all Turing complete here.)

Comment: Re:It's not just the implementation (Score 1) 444

by blueg3 (#46725319) Attached to: Heartbleed Coder: Bug In OpenSSL Was an Honest Mistake

For one, you need to be able to correlate your requests with the other party's responses in a way that is non-replayable (regardless of the encryption used).

The payload is of variable length so that heartbeats can be used for path MTU discovery.

Just because someone "sees no reason" for a design decision doesn't mean there is no reason.

The heartbeat spec isn't necessarily a great design, but it's by no means the problem. If you can't implement what is essentially ping that passes two variable length data fields, what hope do you have of being able to implement anything useful?

Comment: Re:for a library... (Score 2) 444

by blueg3 (#46721973) Attached to: Heartbleed Coder: Bug In OpenSSL Was an Honest Mistake

And what languages are these languages themselves written in?

Languages aren't written in anything. (Though, the specification for a language could be written in English, for instance.) Compilers and interpreters are written in a language.

and if those languages are dangerous to directly write apps in, then surely they must be equally dangerous to write the compilers and platforms on which your non-VM language runs.

A program isn't run by a compiler, it's compiled by a compiler. There's a pretty significant difference.

There's also a significant difference between writing an application in C and writing an application in a language that is compiled by a compiler written in C. For one, the compiler has a much smaller attack surface. There is a lot less code in the compiler than there is in the set of applications written in that language. For another, vulnerabilities aren't magically transitive like that. Imagine a language, M, that is just like C, but it is impossible to create a buffer overrun. The M compiler is written in C. It contains a buffer overrun bug. That doesn't magically make M source code compiled with this compiler also contain a buffer overrun. To say it another way: the features of the language the compiler is written in don't really matter for the security of a compiled application, it's the quality of the implementation of the compiler -- the compiler needs to produce a binary that actually has the properties of the language it's compiling for.

At some point you're working with something written in C, C++ or assembler

No, you're not. Traditionally, a compiler is written in the same language that it compiles: so a C++ compiler is written in C++ and a Forth compiler is written in Forth. (Realistically, most are now written in C as a component of GCC.)

Comment: Re:It's not just the implementation (Score 4, Informative) 444

by blueg3 (#46721753) Attached to: Heartbleed Coder: Bug In OpenSSL Was an Honest Mistake

As others have indicated, the primary stated use of heartbeat is for DTLS, which is not over TCP.

The payload length is not actually superfluous. The packet has an arbitrary amount of both payload and padding, of which only the payload is echoed to the sender. Roughly: { uint16 payload_len; char payload[]; char padding[]; } The intent of payload_len is to tell you which of the bytes following it are payload rather than padding. Of course, you need to check that it's less than the remaining data in the packet. (Per the spec, at least 16 less -- at least 16 bytes of random padding are required.)

Comment: Re:Modern audiophiles are no different. (Score 2) 469

He didn't say they weren't different. He said people think that vinyl is "more genuine" or "more accurate" than digital. Genuine is a weasel word -- it's ill-defined. (Probably the most reasonable definition here is "closest to how the creator of the music intended for you to hear it". But, I digress. It's hard to measure.) Vinyl is certainly less accurate than a good digital representation.

It can be different, though, because it introduces flaws that the digital representation doesn't have. Maybe those flaws make the music "better" in some sense, but not "more accurate".

Comment: Re:Huh? (Score 4, Informative) 243

by blueg3 (#46621851) Attached to: Dropbox's New Policy of Scanning Files For DMCA Issues

He wasn't making an analogy between how you find a hash collision and how you win the lottery -- only comparing the odds.

Dropbox uses SHA-256 hashes. I'm assuming this is what they use for this feature, since it's what they use internally for file identification and deduplication. They actually hash 2 MB file chunks, which means that any file more than 2 MB produces multiple hashes (one per chunk, naturally).

The "many chances of winning" you're referring to here is the birthday collision problem. A good, rough approximation is that for an N-bit hash, while the number of different hashes is 2^N, the number you can generate before risking a collision is about 2^(N/2). So, with SHA-256, we run no significant risk of collision until we've generated around 2^128 ~= 10^38 hashes.

The total amount of data stored worldwide is on the order of 1 ZB. That's room enough for about 10^15 2-MB chunks. Of course, some of our files might be smaller than this 2 MB chunk size, enabling us to be more efficient with storage. We might be able to get somewhere around 10^20 different files in there.

That's a strange and untenable use of all of the world's storage, and it still puts us about 18 orders of magnitude short of being able to risk a SHA-256 collision. If you had this giant set of a ton of different files, the probability of a collision existing is about 1 in 10^37.

So, short of a flaw in SHA-256, you can assume that a hash collision will never happen. We know of no such flaws. (If we do, it will almost certainly be the case that the collision only occurs because one of the two files was specifically manipulated to produce the collision.)

On the other hand, the odds of winning the lottery are rarely worse than 1 in 10^9.

"Love is an ideal thing, marriage a real thing; a confusion of the real with the ideal never goes unpunished." -- Goethe

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