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A comment on Everything you need to know about cryptography in 1 hour, by Colin Percival. Parent comment

Re:Everything you need to know about cryptography in 1 hour,... by tptacek on Wednesday January 19, 2011 @12:08AM (#2118709)
We're getting near 20 questions territory here. I think I've made my point.
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Re:Everything you need to know about cryptography in 1 hour,... by swaits on Wednesday January 19, 2011 @01:05AM (#2118845)
Well, would you mind humoring us? The unwashed masses...
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Re:Everything you need to know about cryptography in 1 hour,... by tptacek on Wednesday January 19, 2011 @01:06AM (#2118851)
Just make sure your counters can't wrap and you don't have this problem, noting that attackers will do things to try to force your counters to wrap.
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Re:Everything you need to know about cryptography in 1 hour,... by cperciva on Wednesday January 19, 2011 @02:14AM (#2119004)
If you're talking about starting the AES-CTR counter at 2^64-x, that's a buggy AES-CTR implementation: AES-CTR counters always start at zero.
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Re:Everything you need to know about cryptography in 1 hour,... by tptacek on Wednesday January 19, 2011 @06:12AM (#2119430)
Jiminy. This is like saying "if you're talking about a CTR implementation tht forgets to make nonces unique, that's a buggy CTR implementation". Well, no shit, Colin.

This case has the added benefit of you being wrong (the counterspace always starts at zero, but that doesn't mean decryption or encryption does).

And: that's not all I'm talking about.

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Re:Everything you need to know about cryptography in 1 hour,... by cperciva on Wednesday January 19, 2011 @07:59AM (#2119599)
This is like saying "if you're talking about a CTR implementation tht forgets to make nonces unique, that's a buggy CTR implementation"

No, it isn't. The CTR counter is part of the implementation; the nonce is part of how CTR is used by the application.

(the counterspace always starts at zero, but that doesn't mean decryption or encryption does

If you're not encrypting starting from a counter of zero, you're not using a stream cipher. (Most likely, you're using a block storage cipher.)

And: that's not all I'm talking about.

Ok. I was just guessing, because you're claiming that an impossible bug exists and refusing to give any details.

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Re:Everything you need to know about cryptography in 1 hour,... by tptacek on Wednesday January 19, 2011 @08:02AM (#2119602)
You're drawing irrelevant distinctions here. If it was the case that you'd have to code your own entire implementation of the CTR mode of operation to have these bugs, I'd see your point.
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