Hi Jeff,
Thanks for the reply. I don’t want to enable SSLv2, but would like to support
SSLv3, TLS 1.0. Code where I am creating the SSL context and setting the
options looks as shown below
ssl_ctx = SSL_CTX_new(SSLv23_client_method());
if (ssl_ctx != NULL)
SSL_CTX_set_options(ssl_ctx,SSL_OP_ALL|SSL_OP_NO_SSLv2);
...... ...... ...... ...... ...... ......
...... ...... ...... ...... ......
When I try to connect to a server that supports only SSLv3, client does not
fallback, rather it fails with an alert "protocol version". Because client
sends client hello with protocol version of TLS 1.0, that server does not
support. Is this the right behavior? Or should I modifiy the client app to try
with lower protocol version when I receive this alert. My understanding is
OpenSSL stack will not perform any fallback. It is up to applications to handle
it.
Regards
Jaya
-----Original Message-----
From: [email protected] [mailto:[email protected]]
On Behalf Of Jeffrey Walton
Sent: Monday, October 29, 2012 11:05 PM
To: [email protected]
Subject: Re: Need inputs/suggestions on SSL/TLS protocol version fallback
mechanism.
> SSL_CTX_set_options, should I indicate protocols using this function?.
Before you do that, please realize TLS 1.0 is the least broken of the protocols
you are trying to enable. You really want all TLS 1.2 clients, but its not
widely implemented in clients and servers. I can tell you that a number of
organizations will not want an SSL2/SSL3 clients accessing their corporate data.
Differences Between SSLv2, SSLv3, and TLS, www.yaksman.org/~lweith/ssl.pdf
Analysis of the SSL 3.0 Protocol, www.schneier.com/paper-ssl.html.
Jeff
On Mon, Oct 29, 2012 at 10:27 AM, Bhat, Jayalakshmi Manjunath
<[email protected]> wrote:
> Hi Charles,
>
> Thank you for the reply. I am not setting any option using
> SSL_CTX_set_options, should I indicate protocols using this function?.
>
> From: [email protected]
> [mailto:[email protected]] On Behalf Of Charles Mills
> Sent: Monday, October 29, 2012 7:40 PM
> To: [email protected]
> Subject: RE: Need inputs/suggestions on SSL/TLS protocol version
> fallback mechanism.
>
> Do you call SSL_CTX_set_options() with bit flags (SSL_OP_ALL,
> SSL_OP_NO_SSLv3, etc.) to indicate the protocols you are willing to accept?
>
> BTW, openssl-users (not –dev) is the proper forum for this sort of
> questions.
>
> From: [email protected]
> [mailto:[email protected]] On Behalf Of Bhat,
> Jayalakshmi Manjunath
> Sent: Monday, October 29, 2012 5:27 AM
> To: [email protected]; [email protected]
> Subject: Need inputs/suggestions on SSL/TLS protocol version fallback
> mechanism.
>
> I have a client application that uses SSL23_client_method(). When the
> client is getting connected to server that supports TLS 1.0 there are no
> issues.
> When the client is getting connected to server that supports only
> SSLv3.0, connection is getting aborted with protocol number error.
>
> I have couple of question around this issue.
>
> 1. If I like to support the fallback mechanism, I need to implement
> the same in the client application. SSL client state machine in
> OpenSSL does not implement any fallback.
>
> 2. I did not see any recommendation in SSL/TLS RFC to implement the
> fallback mechanism. I wanted to know are there any side effects in
> OpenSSL library if fallback mechanism is implemented.
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