Howard Chu wrote:

Philip Guenther wrote:

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On Mon, 30 Apr 2007, Howard Chu wrote:

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guenther+ldapdev@sendmail.com wrote:

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• 'allow' checks the identity of the server vs its cert (per RFC 4513, section 3.1.3) and will terminate the connection if they don't match
• 'try' is the same as 'demand' and 'hard'

Not quite. With both "allow" and "try" it's OK if the server provides no certificate.

That's true of 'demand' and 'hard' as well. The only difference between 'try' and 'demand' in the code is that the latter passes SSL_CTX_set_verify() the SSL_VERIFY_FAIL_IF_NO_PEER_CERT flag, but that flag has NO EFFECT on SSL clients. This is documented on the SSL_CTX_set_verify() manpage and confirmed by grepping the openssl source for it.

If you don't believe me, I suggest you try configuring your server to accept the ADH suites (don't forget to set TLSDHParamFile to /dev/null) and give ldapsearch a whirl with LDAPTLS_REQCERT=hard LDAPTLS_CIPHER_SUITE=ADH-AES256-SHA

in your environment. That's what I did.

When this text was written, there was no support for anonymous cipher suites. So the meaning of the text is: assuming a cipher suite that actually uses certificates, the client would proceed even if the server didn't provide a cert. It's entirely possible that this circumstance has been overcome by other developments. Most likely this hasn't been a valid use case for quite a long time. But it has nothing to do with Diffie-Hellman key exchanges...

Aside from clarifying that we're assuming the use of X.509 certificates in the first place, this text is correct. I note that GnuTLS also works with OpenPGP keys, but I've never tested that here. Anyway, the current description is also accurate for GnuTLS.