Re: Query reg. using certificates bigger than 4k for EAP-TLS

[Jan Just Keijser]

Hi Vishal,

On 20/10/21 13:34, Vishal Sinha wrote:

Hi Matt

The certificate is not large as such. But since it's a chain, the 
overall size crosses 4k. We used BIO_set_write_buffer_size() API to 
increase the size from 4k to 8k of the BIO buffer in SSL context.





just out of curiosity: does this issue occur with pppd with EAP-TLS 
support (which I originally added) ? if so, which version of the pppd 
code are you using or which version of the ppp-eap-tls patch?


If you *are* using pppd to do the EAP-TLS handshake then let me try to 
replicate your particular issue.


HTH,

JJK



On Wed, Oct 20, 2021 at 3:26 PM Vishal Sinha > wrote:


Hi

We are using openssl 1.1.1c version on our client and server.
Client and Server are doing EAP-TLS authentication using
certificates which are more than 4k in size (using 1 root CA and 2
intermediate CAs). We noticed that the server is not able to
handle it gracefully due to insufficient buffer size during SSL
handshake and hence authentication fails. To solve this issue, we
increased the buffer size to 8k programmatically and
authentication passed. Is there any other way to solve this problem?

Regards
Vishal

Re: Query reg. using certificates bigger than 4k for EAP-TLS

[Benjamin Kaduk via openssl-users]

I'm also a bit confused at how this became the limiting factor for the 
application
in question.

https://datatracker.ietf.org/doc/html/draft-ietf-emu-eaptlscert-08 has some
discussion of how large certificates can cause issues for EAP (as well as some
guidance to EAP deployments as to how to reduce the scale of the issues), which
suggests that most of the time there is already some buffering going on at
a 1-2k chunk size just based on the limits of the EAP exchange's MTU.  (The
parties in the exchange have to transmit one chunk at a time and get an ACK
back before transmitting the next chunk, and once that handshake flight is
finished the process is reversed with the other party sending a chunk at a 
time.)
A BIO-layer buffer would be between that and the libssl handshake buffering,
and as you describe, it should still get the data through, just maybe with
a slight inefficiency.

-Ben

On Wed, Oct 20, 2021 at 02:30:19PM +0100, Matt Caswell wrote:
> Your scenario is still not quite clear to me.
> 
> It sounds like you are using a BIO_f_buffer() BIO to buffer data. This is on
> the server side right? Are you encountering this problem for server writes?
> Since you are talking about the certificate chain, I assume you are
> referring to the server writing that chain.
> 
> libssl itself also uses a BIO_f_buffer() internally for writes during the
> handshake. It's not clear to me whether you are referring to the internal
> libssl buffering BIO, or one that you have created?
> 
> Either way, the effect of the buffering BIO during writes is that a 4k
> buffer is used by default. If data is written that is less than 4k in length
> then it is held in the buffer until either the BIO is "flushed" or the
> buffer is filled. In the event the buffer gets filled then it is
> automatically flushed, and any remaining data gets buffered.
> 
> The only effect of changing the buffer size should be to decrease the
> frequency that the buffer gets filled and automatic flushes occur. It sounds
> like by trying to increase the buffer size you are seeking to avoid "parial"
> writes where only part of the data is flushed and the remainder is held back
> for sending later when the buffer is next filled or flushed. This should not
> normally make any difference to the correct operation of the protocol
> (except for efficiency) although it does depend on what happens "downstream"
> of the buffering bio and how partial writes get sent to the peer.
> 
> It sounds like things are not quite working correctly for you when "partial"
> writes occur. This sounds like a potential problem in the BIO chain
> downstream of libssl (i.e. in your application).
> 
> Matt
> 
> On 20/10/2021 12:34, Vishal Sinha wrote:
> > Hi Matt
> > 
> > The certificate is not large as such. But since it's a chain, the
> > overall size crosses 4k. We used BIO_set_write_buffer_size() API to
> > increase the size from 4k to 8k of the BIO buffer in SSL context.
> > 
> > Regards
> > Vishal
> > 
> > 
> > On Wed, Oct 20, 2021 at 3:26 PM Vishal Sinha  > > wrote:
> > 
> > Hi
> > 
> > We are using openssl 1.1.1c version on our client and server. Client
> > and Server are doing EAP-TLS authentication using certificates which
> > are more than 4k in size (using 1 root CA and 2 intermediate CAs).
> > We noticed that the server is not able to handle it gracefully due
> > to insufficient buffer size during SSL handshake and hence
> > authentication fails. To solve this issue, we increased the buffer
> > size to 8k programmatically and authentication passed. Is there any
> > other way to solve this problem?
> > 
> > Regards
> > Vishal
> > 

Re: Query reg. using certificates bigger than 4k for EAP-TLS

[Matt Caswell]

Your scenario is still not quite clear to me.

It sounds like you are using a BIO_f_buffer() BIO to buffer data. This 
is on the server side right? Are you encountering this problem for 
server writes? Since you are talking about the certificate chain, I 
assume you are referring to the server writing that chain.


libssl itself also uses a BIO_f_buffer() internally for writes during 
the handshake. It's not clear to me whether you are referring to the 
internal libssl buffering BIO, or one that you have created?


Either way, the effect of the buffering BIO during writes is that a 4k 
buffer is used by default. If data is written that is less than 4k in 
length then it is held in the buffer until either the BIO is "flushed" 
or the buffer is filled. In the event the buffer gets filled then it is 
automatically flushed, and any remaining data gets buffered.


The only effect of changing the buffer size should be to decrease the 
frequency that the buffer gets filled and automatic flushes occur. It 
sounds like by trying to increase the buffer size you are seeking to 
avoid "parial" writes where only part of the data is flushed and the 
remainder is held back for sending later when the buffer is next filled 
or flushed. This should not normally make any difference to the correct 
operation of the protocol (except for efficiency) although it does 
depend on what happens "downstream" of the buffering bio and how partial 
writes get sent to the peer.


It sounds like things are not quite working correctly for you when 
"partial" writes occur. This sounds like a potential problem in the BIO 
chain downstream of libssl (i.e. in your application).


Matt

On 20/10/2021 12:34, Vishal Sinha wrote:

Hi Matt

The certificate is not large as such. But since it's a chain, the 
overall size crosses 4k. We used BIO_set_write_buffer_size() API to 
increase the size from 4k to 8k of the BIO buffer in SSL context.


Regards
Vishal


On Wed, Oct 20, 2021 at 3:26 PM Vishal Sinha > wrote:


Hi

We are using openssl 1.1.1c version on our client and server. Client
and Server are doing EAP-TLS authentication using certificates which
are more than 4k in size (using 1 root CA and 2 intermediate CAs).
We noticed that the server is not able to handle it gracefully due
to insufficient buffer size during SSL handshake and hence
authentication fails. To solve this issue, we increased the buffer
size to 8k programmatically and authentication passed. Is there any
other way to solve this problem?

Regards
Vishal

Re: Query reg. using certificates bigger than 4k for EAP-TLS

[Vishal Sinha]

Hi Matt

The certificate is not large as such. But since it's a chain, the overall
size crosses 4k. We used BIO_set_write_buffer_size() API to increase the
size from 4k to 8k of the BIO buffer in SSL context.

Regards
Vishal


On Wed, Oct 20, 2021 at 3:26 PM Vishal Sinha  wrote:

> Hi
>
> We are using openssl 1.1.1c version on our client and server. Client and
> Server are doing EAP-TLS authentication using certificates which are more
> than 4k in size (using 1 root CA and 2 intermediate CAs). We noticed that
> the server is not able to handle it gracefully due to insufficient buffer
> size during SSL handshake and hence authentication fails. To solve this
> issue, we increased the buffer size to 8k programmatically and
> authentication passed. Is there any other way to solve this problem?
>
> Regards
> Vishal
>

Re: Query reg. using certificates bigger than 4k for EAP-TLS

[Matt Caswell]

On 20/10/2021 10:56, Vishal Sinha wrote:
We are using openssl 1.1.1c version on our client and server. Client and 
Server are doing EAP-TLS authentication using certificates which are 
more than 4k in size (using 1 root CA and 2 intermediate CAs). We 
noticed that the server is not able to handle it gracefully due to 
insufficient buffer size during SSL handshake and hence authentication 
fails. To solve this issue, we increased the buffer size to 8k 
programmatically and authentication passed. Is there any other way to 
solve this problem?


Which buffer did you change? Do you have an example certificate that is 
shareable? Is it the certificate that is too large, or the whole chain?


Matt

Query reg. using certificates bigger than 4k for EAP-TLS

[Vishal Sinha]

Hi

We are using openssl 1.1.1c version on our client and server. Client and
Server are doing EAP-TLS authentication using certificates which are more
than 4k in size (using 1 root CA and 2 intermediate CAs). We noticed that
the server is not able to handle it gracefully due to insufficient buffer
size during SSL handshake and hence authentication fails. To solve this
issue, we increased the buffer size to 8k programmatically and
authentication passed. Is there any other way to solve this problem?

Regards
Vishal