# [Q] 128-bit symmetric encryption.

Daniel Carrera dcarrera@math.umd.edu
Sat May 31 06:47:02 2003

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Hello,

I'm trying to figure out "how strong" 128-bit symmetric encryption is.  Tel=
l me=20
if I got it right:

For a good algorithm, the only possible attack is brute force.  From an ear=
lier=20
discussion, we can (roughly) estimate that it might take 50,000 computers a=
t=20
2GHz one year to break 64-bit encryption.  Now, 128-bit encryption should t=
ake=20
2^64 times more computing power to break.

In other words, if I had a trillion computers each going a 1 TeraHertz, it=
=20
would take them mover 1.8 billion years to break it.

In conclusion, breaking 128-bit encryption by brute force is impossible.

Is this correct?

Note:  I am not saying anything about security.  I know that there are many=
=20
other possible attacks.  I know that the algorithm itself might be broken s=
o=20
that brute force is not necessary.  That's not what I'm asking about. =20
Ultimately, I want to conclude that there is no point in using more than=20
128-bits in symmetric algorithmw.

Is this correct?

Thanks for the help.
--=20
Daniel Carrera         | OpenPGP fingerprint:
Graduate TA, Math Dept | 6643 8C8B 3522 66CB D16C D779 2FDD 7DAC 9AF7 7A88
UMD  (301) 405-5137    | http://www.math.umd.edu/~dcarrera/pgp.html

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