Re: [secdir] review of draft-ietf-dnsext-dnssec-gost-05

Uri Blumenthal <uri@MIT.EDU> Fri, 08 January 2010 16:45 UTC

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Date: Fri, 08 Jan 2010 11:35:28 -0500
From: Uri Blumenthal <uri@MIT.EDU>
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References: <p06240810c76be77be756@[128.89.89.161]> <20100107222809.GA25747@shinkuro.com> <p06240818c76c1a38cbf8@[128.89.89.161]> <20100108144431.GB26259@shinkuro.com> <p06240812c76d0821dd1b@[10.20.30.158]>
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Subject: Re: [secdir] review of draft-ietf-dnsext-dnssec-gost-05
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I am in full agreement with the arguments Paul and Steve have made.

Keep GOST as MAY.

Quoting Paul Hoffman <phoffman@imc.org>rg>:
> To take it one step further: a signing algorithm that is easily 
> broken opens up a new attack vector. Imagine that all DNSSEC "client" 
> implementations (resolvers) need to support two algorithms, A and B. 
> If A and B are of actual equal strength, an attacker has an equal 
> problem. However, if B is found to have weaknesses that allows an 
> attacker to forge signatures, that attacker then can create a bogus 
> chain to a trust anchor using B in the entire path.
>
> It is for this reason that DNSSEC does not, for example, require that 
> resolvers MUST be able to validate RSA signatures with 256-bit keys. 
> However, by saying that resolvers MUST be able to validate anything 
> other than the widely-agreed-to algorithms, you are opening up such 
> an attack.
>
> GOST signatures use a hash algorithm that has a known academic 
> attack. Thus, even if the GOST asymmetric encryption algorithm is as 
> strong as RSA with the size of keys that people are using, the 
> overall signing algorithm may be weaker. This is *not* an argument 
> that Russia should not use GOST: they have made their own security 
> decisions based on the same knowledge that we have (and possibly 
> more). It is, however, an argument against making everyone else be 
> able to verify GOST signatures as if they were equivalent to other 
> mandatory-to-implement signature algorithms.
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