On Sun, 26 Nov 2000, "Derek D. Martin" <[EMAIL PROTECTED]> wrote:
>
> > Benjamin Scott wrote:
> > > Ummm, I believe conventional wisdom says that with modern algorithms, session
> > > encryption keys longer then 100 bits or so is just a waste of resources. In
> > > fact, I just checked, and the FreeS/WAN website makes reference to this.
>
> I don't think that statement is true... GPG recommends a key length
> of 1024 bits, and suggests that keys larger than that probably don't
> really enhance security at all, but slow down decryption substantially
> (and use more CPU).
This is the length of an RSA (or Diffie/Hellman) public cryptography key,
and is not directly comparable to the symmetric "session key" of the
resulting session.
Recall the RSA (or DH) public/private key pair is used to encrypt and
exchange a (hopefully) random session key between the two parties.
An RSA key of length N is easier to crack than a symmetric session key
of length N. The reason is the RSA key obeys a formula that aids in the
cracking (you basically have to factor a number of order 2^N into two
prime numbers).
Current state of the art is:
An RSA key of order 2^1024 is "too hard" to factor,
A random symmetric session key of order 2^128 is "too hard" to guess
by brute force.
Karl
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