Re: [Cfrg] possibly dumb question about the opus codec and padding
"Scott Fluhrer (sfluhrer)" <sfluhrer@cisco.com> Wed, 06 June 2012 16:55 UTC
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Date: Wed, 06 Jun 2012 09:55:00 -0700
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Thread-Topic: [Cfrg] possibly dumb question about the opus codec and padding
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From: "Scott Fluhrer (sfluhrer)" <sfluhrer@cisco.com>
To: Russ Housley <housley@vigilsec.com>, Stephen Farrell <stephen.farrell@cs.tcd.ie>
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Cc: cfrg@irtf.org
Subject: Re: [Cfrg] possibly dumb question about the opus codec and padding
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On the other hand, if a stream cipher is so weak that it can be broken with a bit of known plaintext, I'm pretty confident that we shouldn't use that stream cipher in any case. -----Original Message----- From: cfrg-bounces@irtf.org [mailto:cfrg-bounces@irtf.org] On Behalf Of Russ Housley Sent: Wednesday, June 06, 2012 11:58 AM To: Stephen Farrell Cc: cfrg@irtf.org Subject: Re: [Cfrg] possibly dumb question about the opus codec and padding I'd encourage the documentation of the concerns with known plaintext (the zero pad) and a poor stream cipher. It seems like a simple sentence or two in the Security Considerations section. Russ On Jun 6, 2012, at 10:54 AM, Stephen Farrell wrote: > > Hiya, > > I'm reviewing the opus codec spec [1] for this week's > IESG telechat. > > On p20, they say to zero out padding bits to avoid a covert > channel. > > Now I don't know how often that might happen, nor for how > many bits (its a complicated beast;-) but I wondered if > there's a possible problem there if the resulting encoded > bits are stream-enciphered with a not-quite-good-enough > cipher and for whatever reason there's a lot of padding. > > I could ask 'em to say "pad randomly if these may be > stream enciphered since you can hide the covert channel > in the ciphertext nicely in any case" but it may be > hard to know from within the codec if a stream cipher > will be used elsewhere in the stack. Or, perhaps I > could suggest they add a warning that these zero'd > padding bits would be problematic if you use a crap > stream cipher, but then that's motherhood/apple-pie > and would be ignored, buried as it is within the bowels > of a 331 page spec. > > Any thoughts? (Most usefully before 1530 UTC tomorrow:-) > > Ta, > S. > > [1] http://tools.ietf.org/html/draft-ietf-codec-opus-14 _______________________________________________ Cfrg mailing list Cfrg@irtf.org http://www.irtf.org/mailman/listinfo/cfrg
- [Cfrg] possibly dumb question about the opus code… Stephen Farrell
- Re: [Cfrg] possibly dumb question about the opus … Jon Callas
- Re: [Cfrg] possibly dumb question about the opus … Russ Housley
- Re: [Cfrg] possibly dumb question about the opus … Scott Fluhrer (sfluhrer)
- Re: [Cfrg] possibly dumb question about the opus … Hal Finney
- Re: [Cfrg] possibly dumb question about the opus … Stephen Farrell
- Re: [Cfrg] possibly dumb question about the opus … Jon Callas
- Re: [Cfrg] possibly dumb question about the opus … Stephen Farrell
- Re: [Cfrg] possibly dumb question about the opus … David Wagner
- Re: [Cfrg] possibly dumb question about the opus … Jon Callas
- Re: [Cfrg] possibly dumb question about the opus … Steven Bellovin
- Re: [Cfrg] possibly dumb question about the opus … David Wagner
- Re: [Cfrg] possibly dumb question about the opus … Stephen Farrell
- Re: [Cfrg] possibly dumb question about the opus … David McGrew
- Re: [Cfrg] possibly dumb question about the opus … David McGrew
- Re: [Cfrg] possibly dumb question about the opus … Steven Bellovin