Re: A couple of newbie questions to sci.cypt.
From: Gregory G Rose (ggr_at_qualcomm.com)
Date: 08/21/03
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Date: 21 Aug 2003 07:28:31 -0700
In article <3f447c3e$0$24626$edfadb0f@dread14.news.tele.dk>,
KH <main@events.dk> wrote:
>1. Where the FAQ is the FAQ ? ;o)
Like all usenet FAQs, they are archived and can
be found at rtfm.mit.edu, in particular:
ftp://rtfm.mit.edu/pub/usenet-by-hierarchy/sci/crypt/
>2. Speaking cryptology in general. Am I correct to assume that its not the
>ciphertext but rather the algorithm that is the interesting part when
>presenting a new "crack this ciphertext"-thingie ?
Correct. Preferably a readable description of the
algorithm accompanied by source code. Ciphertext
challenges are forbidden by the FAQ.
>3. Is 1024-bit RSA double up security compared to 512-bit RSA ? (linear ???)
No. Assuming that it's cracked by factoring, the
current best complexity formula for factoring is
exp(log(n)^1/3*log(log(n))^2/3+O(1)). This is a
superpolylogarithmic subexponential function.
(Read it out loud.) Complexity is measured w.r.t.
the length of the modulus.
Anyway, comparing to an "equivalent" block cipher,
doubling the number of bits in the modulus does
significantly less than doubling the number of
bits in the "equivalent" keyspace of the block
cipher. Some would say that 512-bit RSA was
equvalent to a 64-bit security, while 1024-bit RSA
is equivalent to about 80-90 bits block cipher.
Either way, this is much more than linear w.r.t.
the number of bits in the modulus, but I suspect
you meant linear w.r.t. n (the modulus) itself.
Greg.
Greg.
-- Greg Rose INTERNET: ggr@qualcomm.com Qualcomm Australia VOICE: +61-2-9817 4188 FAX: +61-2-9817 5199 Level 3, 230 Victoria Road, http://people.qualcomm.com/ggr/ Gladesville NSW 2111 232B EC8F 44C6 C853 D68F E107 E6BF CD2F 1081 A37C
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