More 40-bit RC4 nonsense
-----BEGIN PGP SIGNED MESSAGE----- If I recall correctly, the first byte out of the RC4 stream has about a 40% chance of being the first byte of the key. Thus, if the 40-bit "secret" part of the key is the _beginning_ of the full 128-bit key, then the keyspace is effectively reduced by about seven bits, meaning that I would be able to crack a key on my PC in a couple of days or so. Of course, if the "clear" 88 bits went first, there would be no advantage whatsoever. The SSL document very carefully does not say how they combine the two key parts to form the 128-bit key. Does anyone know? Raph -----BEGIN PGP SIGNATURE----- Version: 2.6 iQCVAwUBLu3cI/4BfQiT0bDNAQEToQQAtcy2v0sBd+g5GBrm+Pa1AykqS4tTctfu EYga7kPry4wvGmI7/HpD+SVVDQRcJe+O9CxH9cpvRgBRIBhyvsFXVBSTW0OTJgXb 1bYh5qerD5J/gXAs0XWIp0+Hj8GqeTIRkFTseU4MDcDfQ7tOSEFvul97iSNYIytX AMkmAEmMXxU= =S80T -----END PGP SIGNATURE-----
Raph Levien writes:
If I recall correctly, the first byte out of the RC4 stream has about a 40% chance of being the first byte of the key. Thus, if the 40-bit "secret" part of the key is the _beginning_ of the full 128-bit key, then the keyspace is effectively reduced by about seven bits, meaning that I would be able to crack a key on my PC in a couple of days or so. Of course, if the "clear" 88 bits went first, there would be no advantage whatsoever. The SSL document very carefully does not say how they combine the two key parts to form the 128-bit key. Does anyone know?
Why did the NSA require that an application using the Sapphire Stream Cipher be limited to a _32-bit_ session key instead of the well-known _40-bit_ limit for RC4? I wonder if there are other key bit leaks that cover the other 60%? Hmmm....
On Dec 13, 2:59pm, Michael Johnson wrote:
Why did the NSA require that an application using the Sapphire Stream Cipher be limited to a _32-bit_ session key instead of the well-known _40-bit_ limit for RC4? I wonder if there are other key bit leaks that cover the other 60%?
It could also be because they've made an investment in custom hardware to "crack" RC4 by justifying it in terms of the volume which will result from the special export status, whereas the volume of sapphire use they are expecting is lower and so they'll be using off-the-shelf systems to decrypt any streams seen from it. Ian.
participants (3)
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Ian Farquhar -
mpjohnso＠nyx10.cs.du.edu -
raph＠netcom.com