[Cryptography] RSA equivalent key length/strength
Tero Kivinen
kivinen at kivinen.iki.fi
Mon Sep 16 10:42:14 EDT 2013
ianG writes:
> On 14/09/13 18:53 PM, Peter Fairbrother wrote:
> > But, I wonder, where do these longer equivalent figures come from?
>
> http://keylength.com/ (is a better repository to answer your question.)
I assume that web site only takes account of time, it does not base
its calculations to cost of doing cracking, which would also include
the space needed to do the actual calculations.
Old paper from year 2000 which takes also space calculations in to
account
http://www.emc.com/emc-plus/rsa-labs/historical/a-cost-based-security-analysis-key-lengths.htm
says that to crack 1620 bit RSA key you need 10^10 years, with 158000
machines each having 1.2*10^14 bytes (120 Tb) of memory (year 2000 $10
trillion estimate).
Cost of that amount of memory today would still be quite high (at
$3-$10 per GB, the price would be hundreds of thousands - over million
dollars per machine).
Most of key size calculations in the net only take account the time
needed, not the space at all, thus they assume that memory is free.
For symmetric crypto cracking that is true, as you do not need that
much of memory, for public keys that is not true for some of the
algoritms.
--
kivinen at iki.fi
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