One form of attack on secure communications is "man-in-the-middle". The Internet is constructed from many routers, which pass data on to each other in order to create a path from IBrowse² to the web server. Assuming one of these routers was compromised, it could tap into the communication between you and the web server. Going back to how the SSL connection are created, the following could happen: |
- IBrowse² will initiate the connection to the web server.
- IBrowse² will send which version of the SSL protocol it wishes to communicate with.
- The compromised router intercepts this message, and sends on to the web server a fake message saying that IBrowse² only supports SSLv2.
- IBrowse² will send a list of cipher suites it supports.
- The compromised router intercepts this message, and sends on to the web server a fake message that IBrowse² only supports a weak cipher suite, e.g. EXP-RC4-MD5, which is easy to crack these days.
- The web server will respond with the version of the SSL protocol it supports, which will be SSLv2 as that is all that the compromised router sent when it intercepted the original IBrowse² communication.
- The web server will respond with the weak cipher suite as that was the only cipher suite the compromised router sent when it intercepted the original IBrowse² communication.
- The data will be transferred between the web server and IBrowse² (via the compromised router), using the weak cipher suite. This then gives the compromised router the chance to log the communications and later crack the weak encryption.
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The sole purpose of the SSLv2, SSLv3 and TLSv1 protocols is to stop this kind of activity from taking place and there are various procedures in the SSL protocols to combat this. As SSLv3 is a progression from SSLv2, it has further improvements in the protocol to protect against these kinds of spoof attempts. The SSL version does not directly relate to the strength of the encryption used, but allows IBrowse² and the web server to find the strongest common cipher they both can use. SSLv3 also introduces stronger encryptions, simply as they were not originally available for various reasons, when the original SSLv2 protocol was designed. |
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For more information about SSLv3, visit http://wp.netscape.com/eng/ssl3/. For more information about OpenSSL, visit http://www.openssl.org |
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