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| bio | website | |
|---|---|---|
| location | Sweden | |
| age | 40 | |
| visits | member for | 5 months |
| seen | 7 hours ago | |
| stats | profile views | 1 |
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7h |
awarded | Commentator |
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7h |
comment |
Recommended authenticated stream cipher for minimum overhead? @tylo Each trial should be independent since the we mix in new nonces to generate keys from. How do you figure the DoS attack here? I'm only blocking that particular IP for 5 seconds, and only for login. |
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1d |
comment |
Recommended authenticated stream cipher for minimum overhead? @tylo I understand, but isn't the necessary security of the HMAC also dependent on the protocol. If, for example, a failed HMAC checksum forces a re-negotiation of encryption and signing keys, then you'd basically have to randomly check keys until you get a valid HMAC. And that just gives you the ability to change the bits of a single packet. If the protocol blacklists someone for 5 seconds for violating a HMAC, you have a 50% chance to find a match within 340 years. Or am I doing the maths wrong? |
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2d |
comment |
Recommended authenticated stream cipher for minimum overhead? I know I shouldn't cross-post, but the type of answers differ widely, so I couldn't resist it. As for the running MAC, I already bundle a counter with the packet (in the encrypted data) to avoid replay attacks. I'm guessing that either: a) putting the counter in the encrypted data or b) adding the counter to the HMAC of c) keep a running hash would be fairly equivalent, or? |
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Jun 14 |
comment |
Recommended authenticated stream cipher for minimum overhead? What way would that be? |
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Jun 14 |
awarded | Editor |
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Jun 14 |
revised |
Recommended authenticated stream cipher for minimum overhead? clarified protocol |
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Jun 14 |
comment |
Recommended authenticated stream cipher for minimum overhead? @tylo I wasn't seriously suggesting a 1 byte HMAC. What I was wondering was what the good ways are of reducing the size of the extra data needed for integrity. From what I understand then some modes, like CCM offer different MAC sizes, (CCM has a smallest size of 4 bytes). Also, see my clarification regarding how the protocol works in terms of integrity checks. |
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Jun 14 |
comment |
Recommended authenticated stream cipher for minimum overhead? Yes, but the question is how to minimize the data needed for the fingerprinting. For example as a naive suggestion, one could envision extracting only part of the HMAC for smaller packets making some rule that for a packet of size n the HMAC is max n / 2 bytes long - by taking only that many bytes from the HMAC, starting from the end or front. |
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Jun 14 |
comment |
Recommended authenticated stream cipher for minimum overhead? @Thomas yes, of course AES-CTR is a stream cipher. In order to avoid trivial bit-flipping of the packets, some integrity checking is necessary. As I understand it there are several ways to put that on top a stream cipher without having a separate HMAC or similar as checksum. |
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Jun 14 |
asked | Recommended authenticated stream cipher for minimum overhead? |
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Dec 31 |
awarded | Supporter |
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Dec 31 |
awarded | Student |
