Re: NetScape's dependence upon RSA down for the count!
jbass@dmsd.com writes:
client -> filter Client sends packet with K(c) filter -> Server filter forwards packet with K(f) filter <- Server Server sends encrypts with K(f) client <- filter filter re-encrypts with K(c)
As the protocol progresses the filter also uses the master key, and follows the renegotiation as the master key expires.
Yeah, but in order for this to work, the fake server needs to know netscape.com's private (secret) key, no?
-jon
No ... the public part of any server private key is held by the filter and not returned to the client. The client only encrypts with public keys provided by the filter. The Server only encrypts with public keys provided by the filter. The filter has cleartext of the entire session. John
jbass@dmsd.com writes:
client -> filter Client sends packet with K(c) filter -> Server filter forwards packet with K(f) filter <- Server Server sends encrypts with K(f) client <- filter filter re-encrypts with K(c)
As the protocol progresses the filter also uses the master key, and follows the renegotiation as the master key expires.
Yeah, but in order for this to work, the fake server needs to know netscape.com's private (secret) key, no?
-jon
No ... the public part of any server private key is held by the filter and not returned to the client. The client only encrypts with public keys provided by the filter. The Server only encrypts with public keys provided by the filter. The filter has cleartext of the entire session.
What you have described is the classic 'man in the middle' attack. Netscape claims that SSL V.3 is immune to the MITM attack in appendix D.4 of the SSL V.3 spec. You will need to get the 'filter' (MITM) key signed by Verisign. Or hack Verisign's server-key-signing key. BTW your 'offer' is silly- this is not a trivial amount of work, and you would not deserve any credit for coming up with so ordinary an attack. Write the code yourself, or pay the market rate for it. -- Eric Murray ericm@lne.com ericm@motorcycle.com http://www.lne.com/ericm PGP keyid:E03F65E5 fingerprint:50 B0 A2 4C 7D 86 FC 03 92 E8 AC E6 7E 27 29 AF
On Sat, 30 Sep 1995, Eric Murray wrote:
What you have described is the classic 'man in the middle' attack. Netscape claims that SSL V.3 is immune to the MITM attack in appendix D.4 of the SSL V.3 spec.
I think you're misunderstanding the claim somewhat - what D.4 does is warn implementors that they should perform some means of associating hostnames and certificates. You can't just use SSL out of the box without doing anything in the application to check. My currently recommended approach is to enforce the verisign requirement that all valid hostnames for the server be included in the certificate as CN values. This allows the check to be made below the application layer. Unfortunately a lot of currently issued certificates are non-compliant (even Verisign and netscape :-); any fully automated implementation needs a static table of hostnames aliases- interactive applications can display certificates for manual review.
You will need to get the 'filter' (MITM) key signed by Verisign. Or hack Verisign's server-key-signing key.
This is not really much protection. Getting hold of any key is much easier than getting a specific key, and don't forget there are a number of vulnerable keys floating around until their expiration dates pass. This attack has been known about for a long time, and is too obvious to be really interesting; I implemented a demonstration of the attack as part of developing a protection. If anybody is interested I can mail them my report. The variant of the attack I implemented is useless for anything but demonstration purposes, or I'd ask sameer for a T-shirt. The external fix is a bit more useful, but there doesn't seem to be a patchnetscape alias :-) Simon
participants (3)
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Eric Murray -
jbass＠dmsd.com -
Simon Spero