C. Scott Ananian wrote:
On Wed, 15 Dec 2004, Tim Dierks wrote:
Here's an example, although I think it's a stupid one, and agree with
[...]
I send you a binary (say, a library for doing AES encryption) which
you test exhaustively using black-box testing.
The black-box testing would obviously be the mistake. How can you tell
that the library doesn't start sending plain-text for messages which
start with a particular magic bytes, or some other evilness? You can't
hope to test *all* messages. The word 'exhaustively' is where your
example goes wrong.
I'll play Ben's part and claim that if you can provide a library which
will *only* be checked using black-box testing, it's much easier to skip
the whole MD5 aspect and have it use a covert channel (leak key bits in
padding or some such) or transmit plain-text after the first 100M of
data encrypted or some such. There are lots of easy ways to get your
maliciousness past a black-box test. The use of MD5 (a relatively
*hard* way to be malicious) doesn't appreciably change the threat.
Exactly so, thankyou.
Cheers,
Ben.
--
http://www.apache-ssl.org/ben.html http://www.thebunker.net/
"There is no limit to what a man can do or how far he can go if he
doesn't mind who gets the credit." - Robert Woodruff
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