Re: [fw-wiz] Security of HTTPS

From: Ng Pheng Siong (ngps_at_netmemetic.com)
Date: 11/28/04

  • Next message: Ng Pheng Siong: "Re: [fw-wiz] Security of HTTPS" 
    To: Frank Knobbe <frank@knobbe.us>
Date: Mon, 29 Nov 2004 00:15:45 +0800

    On Fri, Nov 26, 2004 at 06:58:44PM -0600, Frank Knobbe wrote:
    > On Tue, 2004-11-23 at 10:00, lordchariot@earthlink.net wrote:
    > > I wouldn't necessarily call it a MITM attack, but there are some products
    > > out there that intentionally decrypt an SSL connection. These type of
    > > products will take an SSL certificate as presented from the web site, and
    > > re-create a new one on-the-fly to present to the client browser. If the
    > > product's CA cert is loaded into the client, there aren't any certificate
    > > warnings. If not, then most people click through the cert warning anyway
    > > because they don't know any better.
    >
    > Yuck... that's too complicated. All such a product needs are the public
    > and private keys from the server. At run-time, it can sniff the public
    > key of the visiting client, and that's all that's required to follow an
    > SSL session up to and including the exchange of the session keys (after
    > which point the device can decrypt and monitor the full SSL session).
    > This is caused by an (I guess intentional) weakness in the SSL
    > handshaking.

    You're thinking of a device near the server. lordchariot is talking about a
    device near the client which doesn't have admin access to the server. He
    gave the example of virus/adware scanning, which is aimed at protecting the
    client.

    > (If I remember right, the skinny is that the client encrypts the
    > pre-master key and sends it to the server. The server [and client] then
    > generate the master key which is used to generate the session key. The
    > "weakness" imho is that there is no transfer of encrypted key material
    > from the server to the client, which would require the clients secret
    > key to decrypt. Thus, by having the clients public key, and the servers
    > public and private key, an observer can follow the negotiation and
    > arrive with the same session key materials as the server. Or perhaps
    > that is a feature :)

    In SSL/TLS, the client certificate request is optional, and its typical
    use, HTTPS, does not require client certificates, so there is no client
    public/private key here that can be used to "transfer encrypted key
    material".

    Cheers. 

    -- 
Ng Pheng Siong <ngps@netmemetic.com> 
http://sandbox.rulemaker.net/ngps -+- M2Crypto, ZServerSSL for Zope, Blog
http://www.sqlcrypt.com -+- Database Engine with Transparent AES Encryption
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