Re: [TLS] TLS 1.3, how to close the read side of a connection?

[Christopher Wood]

+1

On Mar 8, 2018, 12:56 PM -0500, Tony Putman , wrote:
> Fully agree. Defer it until there is a need.
> -- Tony
>
> From: TLS [mailto:tls-boun...@ietf.org] On Behalf Of David Schinazi
> Sent: 08 March 2018 17:48
> To: Tony Putman
> Cc: tls@ietf.org
> Subject: Re: [TLS] TLS 1.3, how to close the read side of a connection?
>
> Hi Tony,
>
> I agree with you, TLS should not have requirements on the underlying 
> transport.
> If there is a use case that would require endpoints have a way to signal to 
> the peer that they're done reading, I would suggest writing a draft about a 
> new close_request alert.
> I personally don't think this needs to be in the main TLS 1.3 spec, though.
>
> Thanks,
> David
>
>
>
> On Mar 8, 2018, at 02:23, Tony Putman  wrote:
>
> David,
>
> I think this is a valid concern. It's been commented on 
> (https://www.ietf.org/mail-archive/web/tls/current/msg25579.html) that the 
> draft has NO requirements on the underlying transport. There are potentially 
> other transports for TLS (such as being worked by the ATLAS WG) which may not 
> have a way to terminate the transport.
>
> At a minimum this must be addressed in DTLS, but it seems to me that the 
> addition of a close_request alert is a small matter which would benefit both 
> protocols. Of course, this could be added at a later date if/when the need 
> arises.
>
> Regards,
> Tony
>
> From: TLS [mailto:tls-boun...@ietf.org] On Behalf Of Xuelei Fan
> Sent: 07 March 2018 20:54
> To: David Schinazi
> Cc: tls@ietf.org
> Subject: Re: [TLS] TLS 1.3, how to close the read side of a connection?
>
> Hi David,
>
> The case I can think of now is the START TLS protocols (Opportunistic TLS).  
> But looks like these protocols need to use an existing plain-text socket, and 
> then establish a TLS connection over it, and will never go back to plain-text 
> again.  Maybe, for START TLS protocols, closing TLS connection just implies 
> close the underlying TCP socket in practice.  We don't do that previously as 
> we don't know how the  plain-text socket can be used in practice in the 
> follow on processes after TLS get closed (while socket still alive).   If an 
> application gets indication that the TLS connection get closed, it can use 
> the cleanup socket.  So it does not actually need to understand the TLS 
> specifics.
>
> I'm a little bit hesitate if there is a reality user case for such 
> requirement.  Maybe, I can just close the socket, and see what the 
> compatibility impact could be.
>
> Thanks,
> Xuelei
>
> On Wed, Mar 7, 2018 at 12:21 PM, David Schinazi  wrote:
> Hi Xuelei,
>
> Can you elaborate on what proxy protocol you're using that can reuse the TCP 
> connection for follow on connections, and what semantics it has?
> As far as I know, SOCKS and HTTP CONNECT don't support this.
> Additionally, the close_notify alerts are sent encrypted so the proxy 
> wouldn't be able to tell that applications are done with TLS.
>
> Thanks,
> David
>
>
>
>
> On Mar 7, 2018, at 11:24, Xuelei Fan  wrote:
>
> Hi David,
>
> This issue happens when the TLS connection is established/layered on an 
> existing TCP connection.  For example:
> 1. A client connects to a proxy
> 2. The client establishes a TLS 1.3 connection to a server via the proxy.
> 3. The  server delivers 2+ records  to the client.
> 4. The client receives the 1st record, and intends to close the TLS connection
>
> As the  existing TCP connection may be used for follow on connections, it 
> might not be a solution to close the TCP connection directly.  And the client 
> would better cleanup the data delivered by the server.   Otherwise, the data 
> may be used by the next follow on connection and may cause unknown issues.
>
> Then the question comes to me: how does the client close the TLS connection? 
> Closing the TCP connection may be not desired as it does not really have a 
> TCP connection to the server.  It would be nice to close the TLS connection 
> but keeping the TCP connection alive.
>
> Looks like there is no way to close the read side of a TLS connection in TLS 
> layer per the current TLS 1.3 specification.  The close_notify is used to 
> indicate the closure of client write side, but not the server write side.  If 
> the client sends the close_notify for read side closure, after receiving the 
> close_notify the server side will not receive data, but may still send data.  
> Even if the server side stop sending data, the client side does not actually 
> know how may data has been delivered by the server, and how to clean up the 
> TLS channel.
>
> For such cases in TLS 1.2, the client can send a  close_notify alert and then 
> wait for the server close_notify alert, and all of the intermediate data is 
> discarded.  There are still some problems, but in theory the client can 
> cleanup the TCP channel.
>
> In the TLS 1.3 specification, it says:
>
>   If the application protocol 

Re: [TLS] TLS 1.3, how to close the read side of a connection?

[Tony Putman]

Fully agree. Defer it until there is a need.
-- Tony

From: TLS [mailto:tls-boun...@ietf.org] On Behalf Of David Schinazi
Sent: 08 March 2018 17:48
To: Tony Putman
Cc: tls@ietf.org
Subject: Re: [TLS] TLS 1.3, how to close the read side of a connection?

Hi Tony,

I agree with you, TLS should not have requirements on the underlying transport.
If there is a use case that would require endpoints have a way to signal to the 
peer that they're done reading, I would suggest writing a draft about a new 
close_request alert.
I personally don't think this needs to be in the main TLS 1.3 spec, though.

Thanks,
David



On Mar 8, 2018, at 02:23, Tony Putman 
> wrote:

David,

I think this is a valid concern. It's been commented on 
(https://www.ietf.org/mail-archive/web/tls/current/msg25579.html) that the 
draft has NO requirements on the underlying transport. There are potentially 
other transports for TLS (such as being worked by the ATLAS WG) which may not 
have a way to terminate the transport.

At a minimum this must be addressed in DTLS, but it seems to me that the 
addition of a close_request alert is a small matter which would benefit both 
protocols. Of course, this could be added at a later date if/when the need 
arises.

Regards,
Tony

From: TLS [mailto:tls-boun...@ietf.org] On Behalf Of Xuelei Fan
Sent: 07 March 2018 20:54
To: David Schinazi
Cc: tls@ietf.org
Subject: Re: [TLS] TLS 1.3, how to close the read side of a connection?

Hi David,

The case I can think of now is the START TLS protocols (Opportunistic TLS).  
But looks like these protocols need to use an existing plain-text socket, and 
then establish a TLS connection over it, and will never go back to plain-text 
again.  Maybe, for START TLS protocols, closing TLS connection just implies 
close the underlying TCP socket in practice.  We don't do that previously as we 
don't know how the  plain-text socket can be used in practice in the follow on 
processes after TLS get closed (while socket still alive).   If an application 
gets indication that the TLS connection get closed, it can use the cleanup 
socket.  So it does not actually need to understand the TLS specifics.

I'm a little bit hesitate if there is a reality user case for such requirement. 
 Maybe, I can just close the socket, and see what the compatibility impact 
could be.

Thanks,
Xuelei

On Wed, Mar 7, 2018 at 12:21 PM, David Schinazi 
> wrote:
Hi Xuelei,

Can you elaborate on what proxy protocol you're using that can reuse the TCP 
connection for follow on connections, and what semantics it has?
As far as I know, SOCKS and HTTP CONNECT don't support this.
Additionally, the close_notify alerts are sent encrypted so the proxy wouldn't 
be able to tell that applications are done with TLS.

Thanks,
David




On Mar 7, 2018, at 11:24, Xuelei Fan 
> wrote:

Hi David,

This issue happens when the TLS connection is established/layered on an 
existing TCP connection.  For example:
1. A client connects to a proxy
2. The client establishes a TLS 1.3 connection to a server via the proxy.
3. The  server delivers 2+ records  to the client.
4. The client receives the 1st record, and intends to close the TLS connection

As the  existing TCP connection may be used for follow on connections, it might 
not be a solution to close the TCP connection directly.  And the client would 
better cleanup the data delivered by the server.   Otherwise, the data may be 
used by the next follow on connection and may cause unknown issues.

Then the question comes to me: how does the client close the TLS connection? 
Closing the TCP connection may be not desired as it does not really have a TCP 
connection to the server.  It would be nice to close the TLS connection but 
keeping the TCP connection alive.

Looks like there is no way to close the read side of a TLS connection in TLS 
layer per the current TLS 1.3 specification.  The close_notify is used to 
indicate the closure of client write side, but not the server write side.  If 
the client sends the close_notify for read side closure, after receiving the 
close_notify the server side will not receive data, but may still send data.  
Even if the server side stop sending data, the client side does not actually 
know how may data has been delivered by the server, and how to clean up the TLS 
channel.

For such cases in TLS 1.2, the client can send a  close_notify alert and then 
wait for the server close_notify alert, and all of the intermediate data is 
discarded.  There are still some problems, but in theory the client can cleanup 
the TCP channel.

In the TLS 1.3 specification, it says:


   If the application protocol using TLS provides that any data may be

   carried over the underlying transport after the TLS connection is

   closed, the TLS implementation MUST receive a "close_notify" 

Re: [TLS] TLS 1.3, how to close the read side of a connection?

[Tony Putman]

David,

I think this is a valid concern. It's been commented on 
(https://www.ietf.org/mail-archive/web/tls/current/msg25579.html) that the 
draft has NO requirements on the underlying transport. There are potentially 
other transports for TLS (such as being worked by the ATLAS WG) which may not 
have a way to terminate the transport.

At a minimum this must be addressed in DTLS, but it seems to me that the 
addition of a close_request alert is a small matter which would benefit both 
protocols. Of course, this could be added at a later date if/when the need 
arises.

Regards,
Tony

From: TLS [mailto:tls-boun...@ietf.org] On Behalf Of Xuelei Fan
Sent: 07 March 2018 20:54
To: David Schinazi
Cc: tls@ietf.org
Subject: Re: [TLS] TLS 1.3, how to close the read side of a connection?

Hi David,

The case I can think of now is the START TLS protocols (Opportunistic TLS).  
But looks like these protocols need to use an existing plain-text socket, and 
then establish a TLS connection over it, and will never go back to plain-text 
again.  Maybe, for START TLS protocols, closing TLS connection just implies 
close the underlying TCP socket in practice.  We don't do that previously as we 
don't know how the  plain-text socket can be used in practice in the follow on 
processes after TLS get closed (while socket still alive).   If an application 
gets indication that the TLS connection get closed, it can use the cleanup 
socket.  So it does not actually need to understand the TLS specifics.

I'm a little bit hesitate if there is a reality user case for such requirement. 
 Maybe, I can just close the socket, and see what the compatibility impact 
could be.

Thanks,
Xuelei

On Wed, Mar 7, 2018 at 12:21 PM, David Schinazi 
> wrote:
Hi Xuelei,

Can you elaborate on what proxy protocol you're using that can reuse the TCP 
connection for follow on connections, and what semantics it has?
As far as I know, SOCKS and HTTP CONNECT don't support this.
Additionally, the close_notify alerts are sent encrypted so the proxy wouldn't 
be able to tell that applications are done with TLS.

Thanks,
David



On Mar 7, 2018, at 11:24, Xuelei Fan 
> wrote:

Hi David,

This issue happens when the TLS connection is established/layered on an 
existing TCP connection.  For example:
1. A client connects to a proxy
2. The client establishes a TLS 1.3 connection to a server via the proxy.
3. The  server delivers 2+ records  to the client.
4. The client receives the 1st record, and intends to close the TLS connection

As the  existing TCP connection may be used for follow on connections, it might 
not be a solution to close the TCP connection directly.  And the client would 
better cleanup the data delivered by the server.   Otherwise, the data may be 
used by the next follow on connection and may cause unknown issues.

Then the question comes to me: how does the client close the TLS connection? 
Closing the TCP connection may be not desired as it does not really have a TCP 
connection to the server.  It would be nice to close the TLS connection but 
keeping the TCP connection alive.

Looks like there is no way to close the read side of a TLS connection in TLS 
layer per the current TLS 1.3 specification.  The close_notify is used to 
indicate the closure of client write side, but not the server write side.  If 
the client sends the close_notify for read side closure, after receiving the 
close_notify the server side will not receive data, but may still send data.  
Even if the server side stop sending data, the client side does not actually 
know how may data has been delivered by the server, and how to clean up the TLS 
channel.

For such cases in TLS 1.2, the client can send a  close_notify alert and then 
wait for the server close_notify alert, and all of the intermediate data is 
discarded.  There are still some problems, but in theory the client can cleanup 
the TCP channel.

In the TLS 1.3 specification, it says:


   If the application protocol using TLS provides that any data may be

   carried over the underlying transport after the TLS connection is

   closed, the TLS implementation MUST receive a "close_notify" alert

   before indicating end-of-data to the application-layer.

For client read side in above case, it means that the server side MUST deliver 
a close_notify.  But it does not say if a client initiates the TLS closure, how 
could the client indicates the server for a close_notify alert.

Thanks for the suggestion of TCP RST option.  I will evaluate if TCP options 
can help.

Thanks & Regards,
Xuelei Fan


On Wed, Mar 7, 2018 at 10:19 AM, David Schinazi 
> wrote:
Hi Xuelei,

Do you have an example for when you would need to gracefully close the read 
side?
If you're downloading a 10GB video and the user cancels the download, you can 
simply tear down the TCP connection by sending a 

Re: [TLS] TLS 1.3, how to close the read side of a connection?

[David Schinazi]

Hi Xuelei,

Can you elaborate on what proxy protocol you're using that can reuse the TCP 
connection for follow on connections, and what semantics it has?
As far as I know, SOCKS and HTTP CONNECT don't support this.
Additionally, the close_notify alerts are sent encrypted so the proxy wouldn't 
be able to tell that applications are done with TLS.

Thanks,
David


> On Mar 7, 2018, at 11:24, Xuelei Fan  wrote:
> 
> Hi David,
> 
> This issue happens when the TLS connection is established/layered on an 
> existing TCP connection.  For example:
> 1. A client connects to a proxy
> 2. The client establishes a TLS 1.3 connection to a server via the proxy.
> 3. The  server delivers 2+ records  to the client.
> 4. The client receives the 1st record, and intends to close the TLS connection
> 
> As the  existing TCP connection may be used for follow on connections, it 
> might not be a solution to close the TCP connection directly.  And the client 
> would better cleanup the data delivered by the server.   Otherwise, the data 
> may be used by the next follow on connection and may cause unknown issues.
> 
> Then the question comes to me: how does the client close the TLS connection? 
> Closing the TCP connection may be not desired as it does not really have a 
> TCP connection to the server.  It would be nice to close the TLS connection 
> but keeping the TCP connection alive.
> 
> Looks like there is no way to close the read side of a TLS connection in TLS 
> layer per the current TLS 1.3 specification.  The close_notify is used to 
> indicate the closure of client write side, but not the server write side.  If 
> the client sends the close_notify for read side closure, after receiving the 
> close_notify the server side will not receive data, but may still send data.  
> Even if the server side stop sending data, the client side does not actually 
> know how may data has been delivered by the server, and how to clean up the 
> TLS channel.
> 
> For such cases in TLS 1.2, the client can send a  close_notify alert and then 
> wait for the server close_notify alert, and all of the intermediate data is 
> discarded.  There are still some problems, but in theory the client can 
> cleanup the TCP channel.
> 
> In the TLS 1.3 specification, it says:
>
>If the application protocol using TLS provides that any data may be
>carried over the underlying transport after the TLS connection is
>closed, the TLS implementation MUST receive a "close_notify" alert
>before indicating end-of-data to the application-layer.
> 
> For client read side in above case, it means that the server side MUST 
> deliver a close_notify.  But it does not say if a client initiates the TLS 
> closure, how could the client indicates the server for a close_notify alert.
> 
> Thanks for the suggestion of TCP RST option.  I will evaluate if TCP options 
> can help.
> 
> Thanks & Regards,
> Xuelei Fan
> 
> 
> On Wed, Mar 7, 2018 at 10:19 AM, David Schinazi  > wrote:
> Hi Xuelei,
> 
> Do you have an example for when you would need to gracefully close the read 
> side?
> If you're downloading a 10GB video and the user cancels the download, you can 
> simply tear down the TCP connection by sending a RST.
> The benefit of having a graceful read close would be for the server to know 
> that the client application was done, but in the 10GB video example,
> I don't see what the server application would do with that information. Do 
> you have an example where the server would treat a graceful read close
> differently from a non-graceful close? In TLS 1.2 and prior, the client would 
> send a close_notify, the server would reply with a close_notify
> in the middle of the 10GB of application data. That actually doesn't provide 
> any gracefulness to the server application - the point of close_notify
> is to indicate that the data you're sending hasn't been truncated, and in 
> this example it does get truncated.
> 
> Thanks,
> David Schinazi
> 
> 
>> On Mar 7, 2018, at 09:51, Eric Rescorla > > wrote:
>> 
>> Well, this is like TCP in that respect. You send close_notify and then you 
>> either stop reading off of or close the TCP socket.
>> 
>> -Ekr
>> 
>> 
>> On Wed, Mar 7, 2018 at 9:40 AM, Xuelei Fan > > wrote:
>> Hi,
>> 
>> Per TLS 1.3 draft (Section 6.1, Closure Alerts), the close_notify alert is 
>> used to notify the recipient that the sender will not send any more messages 
>> on this connection.  And this does not have any effect on its read side of 
>> the connection.  I think it means that after sending the close_notify alert, 
>> it still can keep reading data from the peer; and after receiving the 
>> close_notify alert, it still can keep sending data to the peer.
>> 
>> The question comes to me is about how to close the read side of the 
>> connection.  If closing the 

Re: [TLS] TLS 1.3, how to close the read side of a connection?

[David Schinazi]

Hi Xuelei,

Do you have an example for when you would need to gracefully close the read 
side?
If you're downloading a 10GB video and the user cancels the download, you can 
simply tear down the TCP connection by sending a RST.
The benefit of having a graceful read close would be for the server to know 
that the client application was done, but in the 10GB video example,
I don't see what the server application would do with that information. Do you 
have an example where the server would treat a graceful read close
differently from a non-graceful close? In TLS 1.2 and prior, the client would 
send a close_notify, the server would reply with a close_notify
in the middle of the 10GB of application data. That actually doesn't provide 
any gracefulness to the server application - the point of close_notify
is to indicate that the data you're sending hasn't been truncated, and in this 
example it does get truncated.

Thanks,
David Schinazi


> On Mar 7, 2018, at 09:51, Eric Rescorla  wrote:
> 
> Well, this is like TCP in that respect. You send close_notify and then you 
> either stop reading off of or close the TCP socket.
> 
> -Ekr
> 
> 
> On Wed, Mar 7, 2018 at 9:40 AM, Xuelei Fan  > wrote:
> Hi,
> 
> Per TLS 1.3 draft (Section 6.1, Closure Alerts), the close_notify alert is 
> used to notify the recipient that the sender will not send any more messages 
> on this connection.  And this does not have any effect on its read side of 
> the connection.  I think it means that after sending the close_notify alert, 
> it still can keep reading data from the peer; and after receiving the 
> close_notify alert, it still can keep sending data to the peer.
> 
> The question comes to me is about how to close the read side of the 
> connection.  If closing the read side silently, there are potential issues if 
> the application protocol using TLS provides that any data may be carried over 
> the underlying transport after the TLS connection is closed.  If sending a 
> close_notify alert, the peer may just treat is as close the its read side and 
> may keep write in its write side.  It does not actually close the read side 
> cleanly.  If keep waiting for the close_notify from the peer, the local may 
> have to wait until the peer happy to close its write side.  It does not sound 
> friendly to the local side.   From example, if I download a 10GB video via 
> TLS 1.3 over VPN, looks like there is no way to indicate the server that I 
> want to cancle in the middle of the downloading in TLS layer.  I may miss 
> something.  I did not find a solution about how to close the read side of TLS 
> 1.3 connections yet.  Please help if you have an idea!
> 
> It's not a problem in TLS 1.2 and prior versions, as the peer MUST respond 
> with a close_notify of its own after receiving a close_notify alert.
> 
> Thanks,
> Xuelei Fan
> 
> ___
> TLS mailing list
> TLS@ietf.org 
> https://www.ietf.org/mailman/listinfo/tls 
> 
> 
> 
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Re: [TLS] TLS 1.3, how to close the read side of a connection?

[Eric Rescorla]

Well, this is like TCP in that respect. You send close_notify and then you
either stop reading off of or close the TCP socket.

-Ekr


On Wed, Mar 7, 2018 at 9:40 AM, Xuelei Fan  wrote:

> Hi,
>
> Per TLS 1.3 draft (Section 6.1, Closure Alerts), the close_notify alert is
> used to notify the recipient that the sender will not send any more
> messages on this connection.  And this does not have any effect on its read
> side of the connection.  I think it means that after sending the
> close_notify alert, it still can keep reading data from the peer; and after
> receiving the close_notify alert, it still can keep sending data to the
> peer.
>
> The question comes to me is about how to close the read side of the
> connection.  If closing the read side silently, there are potential issues
> if the application protocol using TLS provides that any data may be carried
> over the underlying transport after the TLS connection is closed.  If
> sending a close_notify alert, the peer may just treat is as close the its
> read side and may keep write in its write side.  It does not actually close
> the read side cleanly.  If keep waiting for the close_notify from the peer,
> the local may have to wait until the peer happy to close its write side.
> It does not sound friendly to the local side.   From example, if I download
> a 10GB video via TLS 1.3 over VPN, looks like there is no way to indicate
> the server that I want to cancle in the middle of the downloading in TLS
> layer.  I may miss something.  I did not find a solution about how to close
> the read side of TLS 1.3 connections yet.  Please help if you have an idea!
>
> It's not a problem in TLS 1.2 and prior versions, as the peer MUST respond
> with a close_notify of its own after receiving a close_notify alert.
>
> Thanks,
> Xuelei Fan
>
> ___
> TLS mailing list
> TLS@ietf.org
> https://www.ietf.org/mailman/listinfo/tls
>
>
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