[145798] in cryptography@c2.net mail archive
Re: RSA question
daemon@ATHENA.MIT.EDU (travis+ml-cryptography@subspacefie)
Thu Sep 2 13:03:32 2010
Date: Thu, 2 Sep 2010 08:49:07 -0700
From: travis+ml-cryptography@subspacefield.org
To: Bill Stewart <bill.stewart@pobox.com>
Cc: Justin Ferguson <jnferguson@gmail.com>, cryptography@metzdowd.com
Mail-Followup-To: Bill Stewart <bill.stewart@pobox.com>,
Justin Ferguson <jnferguson@gmail.com>, cryptography@metzdowd.com
In-Reply-To: <6.2.1.2.1.20100831231715.02e7a530@pop.sonic.net>
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On Tue, Aug 31, 2010 at 11:27:39PM -0700, Bill Stewart wrote:
> It's possible that=20
> under some conditions, trying to brute-force the RSA is more efficient=20
> than simply brute-forcing the symmetric key
As of 2003, RSA said:
1024 bit RSA ~=3D 80 bit symmetric
2048 bit RSA ~=3D 112 bit symmetric
3072 bit RSA ~=3D 128 bit symmetric
So PK is usually weaker than the symmetric part of a hybrid scheme.
I hear that NIST Key Mgmt guideline (SP 800-57) suggests that the RSA
key size equivalent to a 256 bit symmetric key is roughly 15360 bits.
I haven't actually checked this reference, so I don't know how they
got such a big number; caveat emptor.
I have no idea what the state of, say, AES brute forcing is, so I
don't know the ratio from AES key size to ideal symmetric cipher key
sizes. I'm guessing it's pretty close to 1, but would love to hear
if it's not.
--=20
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program doesn't understand. | http://www.subspacefield.org/~travis/=20
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