Can I have SSL for peer authentication only? (and not for data encryption)

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Can I have SSL for peer authentication only? (and not for data encryption)

Urjit Gokhale
Hi all,
 
I am planning to use SSL for the communication between my client and server. The idea is to use SSL *mainly* for peer authentication and validation (Both server and client authentication by means of certificates). Regarding the data encryption, I would like to have it as an optional feature.
 
The motivation behind this desirable feature is that in a particular environment, I am not really worried about the data, but the client talking to my server. I would like to give up on encryption in favor of performance.
 
So the questions are:
1) Is it possible to use SSL only for the sake of peer authentication + validation and transfer un-encrypted data over this channel ?
 
2) Would sacrificing on encryption *really* improve the performance ?
 
Thanks,
 
~ Urjit
 
PS: This is my first mail to this list. So, in case, you think that my questions are out of the scope of this group, or you know of some other group which can yield me better answers, could you please point me to such groups ?
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Re: Can I have SSL for peer authentication only? (and not for data encryption)

Alain Damiral
Hi and welcome,

I haven't thought hardly about what you're trying to do but my first
intuition tells me that encryption also has some part to play in
authentication that you're missing. My knowledge of SSL is limited but I
think it is safe to say that private/public key (assymetric) encryption
is used to guarantee certificate authenticity, and to agree on the
secret (symetric) key that will be used for the actual communication.

If you use no secret key, you have no guarantee that the guy you're
talking with really is the same guy that you did your handshake with
(who showed you his certificate and knows the shared secret). So even if
you don't want your data encrypted, there must be some signature for
each message sent to guarantee authenticity, based on that shared secret.

So if what I said is correct, even if you don't use encryption you will
still need a signature of each message - probably in the form of a
cryptographic hash based on the shared secret. I'm really not sure that
such an operation is significantly cheaper than symmetric encryption.



Urjit Gokhale wrote:

> Hi all,
>  
> I am planning to use SSL for the communication between my client and
> server. The idea is to use SSL *mainly* for peer authentication and
> validation (Both server and client authentication by means of
> certificates). Regarding the data encryption, I would like to have it
> as an optional feature.
>  
> The motivation behind this desirable feature is that in a particular
> environment, I am not really worried about the data, but the client
> talking to my server. I would like to give up on encryption in favor
> of performance.
>  
> So the questions are:
> 1) Is it possible to use SSL only for the sake of peer authentication
> + validation and transfer un-encrypted data over this channel ?
>  
> 2) Would sacrificing on encryption *really* improve the performance ?
>  
> Thanks,
>  
> ~ Urjit
>  
> PS: This is my first mail to this list. So, in case, you think that my
> questions are out of the scope of this group, or you know of some
> other group which can yield me better answers, could you please point
> me to such groups ?


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Re: Can I have SSL for peer authentication only? (and not for data encryption)

Bernhard Fröhlich-2
In reply to this post by Urjit Gokhale
Urjit Gokhale wrote:

> Hi all,
>  
> I am planning to use SSL for the communication between my client and
> server. The idea is to use SSL *mainly* for peer authentication and
> validation (Both server and client authentication by means of
> certificates). Regarding the data encryption, I would like to have it
> as an optional feature.
>  
> The motivation behind this desirable feature is that in a particular
> environment, I am not really worried about the data, but the client
> talking to my server. I would like to give up on encryption in favor
> of performance.
>  
> So the questions are:
> 1) Is it possible to use SSL only for the sake of peer authentication
> + validation and transfer un-encrypted data over this channel ?
>  
> 2) Would sacrificing on encryption *really* improve the performance ?
Maybe this would be possible using the NULL cipher combined with DH
authentication...
But if your problem is only performance I don't think it's worthwhile to
worry about bulk encryption. Bulk encryption uses symetric ciphers that
are cheap compared to the public key algorithms needed for
authentication. It may be a concern if you want to reach transfer rates
bigger than let's say 10 MByte/s, but encryping traffic on a typical
internet connection will not keep your CPU really busy (assuming you're
using a not too old desktop PC).

>  
> Thanks,
>  
> ~ Urjit
>  
> PS: This is my first mail to this list. So, in case, you think that my
> questions are out of the scope of this group, or you know of some
> other group which can yield me better answers, could you please point
> me to such groups ?

Hope it helps.
Ted
;)

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Re: Can I have SSL for peer authentication only? (and not for data encryption)

Richard Koenning
Bernhard Froehlich wrote:

> Maybe this would be possible using the NULL cipher combined with DH
> authentication...

(The official NULL cipher suites use RSA authentication.) The answer to
the first question of the OP is yes, use a NULL cipher suite.

> But if your problem is only performance I don't think it's worthwhile to
> worry about bulk encryption. [...]

I agree to this. Anyway, it is not much effort to make the cipher suite
used by the application configurable; comparing a NULL cipher suite with
an e.g. AES-128 cipher suite gives in short time the answer to the OP's
second question.
Ciao,
Richard
--
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Fujitsu Siemens Computers GmbH
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Re: Can I have SSL for peer authentication only? (and not for data encryption)

Kyle Hamilton
In reply to this post by Alain Damiral
Brief primer on SSL/TLS:

1) Server has a public and private key pair.  Optionally, the client
has a public and private key pair.  Any public key is authenticated by
a 'certificate', which is a set of data attached to the public key,
the entirety of which has a hash encrypted by the private key of a
trusted third party.
2) [Different versions of the protocol modify this part; this is a
10,000 foot view] On connection, server sends client its certificate
(and perhaps a random number encrypted with its private key that the
client can decrypt with the public key in the certificate).  Client
decrypts the random number, generates its own random number, and
encrypts that with the server's public key (perhaps combining it with
the server's random number in some fashion), and sends it back.  [this
assumes that the client trusts the signer of the certificate.]
3) Server decrypts what the client sent, removes its own randomness,
and uses this as the generator for the base key for the session.  (if
the client sends information that the server can't decrypt, then the
server doesn't have the private key for the certificate that it has
presented.)  The client already has this knowledge, so it has already
generated this key.
4) Server can optionally ask the client to authenticate itself, by
essentially performing the exchange in reverse.
5) In this exchange, there is also a list of "cipher suites" that are
acceptable to each side.  The cipher suite chosen is the
highest-security one that both sides support.  (Highest-security means
'highest bulk cipher bit security'.)  The generated keys (from step 3)
are used for bulk cipher encryption, as well as being the means of
encrypting the message authentication code for verification.
6) It's possible (and, indeed, legally necessary in France) for there
to be no bulk cipher applied; in this case, the generated key material
from step 3 is used only for message authentication, to show that it
actually came from the other side and wasn't injected into the TCP
stream.

The hashing occurs regardless of whether there's a bulk cipher in use.
 A bulk cipher only adds a little bit of overhead to the end, just
before the data is transmitted and as soon as the data is received.

In France (unless the laws have changed) it's illegal to use
cryptography to encrypt data payload, but not illegal to use
cryptography as a means of identification.  This is, if I understand
Netscape's and the IETF's motives correctly, the only reason why the
NULL cipher suites exist in the SSL/TLS specifications.

-Kyle H
...who now waits for other people to nitpick over the details of his
explanation, since it's based primarily on SSL2 and 3, and not TLS.

On 1/24/06, Alain Damiral <[hidden email]> wrote:

> Hi and welcome,
>
> I haven't thought hardly about what you're trying to do but my first
> intuition tells me that encryption also has some part to play in
> authentication that you're missing. My knowledge of SSL is limited but I
> think it is safe to say that private/public key (assymetric) encryption
> is used to guarantee certificate authenticity, and to agree on the
> secret (symetric) key that will be used for the actual communication.
>
> If you use no secret key, you have no guarantee that the guy you're
> talking with really is the same guy that you did your handshake with
> (who showed you his certificate and knows the shared secret). So even if
> you don't want your data encrypted, there must be some signature for
> each message sent to guarantee authenticity, based on that shared secret.
>
> So if what I said is correct, even if you don't use encryption you will
> still need a signature of each message - probably in the form of a
> cryptographic hash based on the shared secret. I'm really not sure that
> such an operation is significantly cheaper than symmetric encryption.
>
>
>
> Urjit Gokhale wrote:
>
> > Hi all,
> >
> > I am planning to use SSL for the communication between my client and
> > server. The idea is to use SSL *mainly* for peer authentication and
> > validation (Both server and client authentication by means of
> > certificates). Regarding the data encryption, I would like to have it
> > as an optional feature.
> >
> > The motivation behind this desirable feature is that in a particular
> > environment, I am not really worried about the data, but the client
> > talking to my server. I would like to give up on encryption in favor
> > of performance.
> >
> > So the questions are:
> > 1) Is it possible to use SSL only for the sake of peer authentication
> > + validation and transfer un-encrypted data over this channel ?
> >
> > 2) Would sacrificing on encryption *really* improve the performance ?
> >
> > Thanks,
> >
> > ~ Urjit
> >
> > PS: This is my first mail to this list. So, in case, you think that my
> > questions are out of the scope of this group, or you know of some
> > other group which can yield me better answers, could you please point
> > me to such groups ?
>
>
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Re: Can I have SSL for peer authentication only? (and not for data encryption)

Alain Damiral
Kyle Hamilton wrote:

>
>In France (unless the laws have changed) it's illegal to use
>cryptography to encrypt data payload, but not illegal to use
>cryptography as a means of identification.  This is, if I understand
>Netscape's and the IETF's motives correctly, the only reason why the
>NULL cipher suites exist in the SSL/TLS specifications.
>
>  
>
>@openssl.org
>  
>
It's hard to find intelligible up to date information on that matter but
things have changed since june 2004 (Loi n°2004-575). It seems that as
long as the "provider" of encryption is known you're pretty much free to
do whatever you want. But you get punished harder if you're using
encryption for naughty criminal stuff. I found nothing about limits on
key sizes.


--
Alain Damiral,

I hope this message makes me look like a very intelligent person

Université Catholique de Louvain - student
alain.damiral'at'student.info.ucl.ac.be

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Re: Can I have SSL for peer authentication only? (and not for data encryption)

Katie Lucas
In reply to this post by Urjit Gokhale
On Tue, Jan 24, 2006 at 06:44:30PM +0530, Urjit Gokhale wrote:
> Hi all,
>

> I am planning to use SSL for the communication between my client and
>server. The idea is to use SSL *mainly* for peer authentication and
>validation (Both server and client authentication by means of
>certificates). Regarding the data encryption, I would like to have it
>as an optional feature.
 

> 1) Is it possible to use SSL only for the sake of peer
>authentication + validation and transfer un-encrypted data over this
>channel ?

How about; you open the sockets using your socket level
interface. Then you attach SSL constructs to both ends, but with the
"don't close this option".

They connect, authenticate each other. You can then use the connection
objects to get the peer certificates (you need to do this because the
connection will succeed if the client doesn't offer a certificate,
whereas you're after BOTH parties being authenticated). If both ends
get a validated certificate presented, the connection is authenticated.

Close the SSL layer, which will leave you with two natice connected
sockets to talk over.
 
> 2) Would sacrificing on encryption *really* improve the performance ?

We're sending video data, so your mileage may vary, but SSL's
symmetric encryption is far faster than the network can move the data
and the overhead of TLS is non-noticable for those volumes of
data.

Yes, it'll remove some strain from your machine, but next year's CPUs
will remove that strain from notice.




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Re: Can I have SSL for peer authentication only? (and not for data encryption)

Kyle Hamilton
On 2/2/06, Katie Lucas <[hidden email]> wrote:
> On Tue, Jan 24, 2006 at 06:44:30PM +0530, Urjit Gokhale wrote:
> > Hi all,
> >
>
> > I am planning to use SSL for the communication between my client and
> >server. The idea is to use SSL *mainly* for peer authentication and
> >validation (Both server and client authentication by means of
> >certificates). Regarding the data encryption, I would like to have it
> >as an optional feature.

This is already possible with the NULL cipher suite.

> > 1) Is it possible to use SSL only for the sake of peer
> >authentication + validation and transfer un-encrypted data over this
> >channel ?

Yes.  Remember that SSL/TLS also provides an integrity check to ensure
that a session hasn't been hijacked.  If this is important to your
application, don't shut down the SSL layer as Ms. Lucas suggests.

>
> How about; you open the sockets using your socket level
> interface. Then you attach SSL constructs to both ends, but with the
> "don't close this option".
>
> They connect, authenticate each other. You can then use the connection
> objects to get the peer certificates (you need to do this because the
> connection will succeed if the client doesn't offer a certificate,
> whereas you're after BOTH parties being authenticated). If both ends
> get a validated certificate presented, the connection is authenticated.
>
> Close the SSL layer, which will leave you with two natice connected
> sockets to talk over.
>
> > 2) Would sacrificing on encryption *really* improve the performance ?
>
> We're sending video data, so your mileage may vary, but SSL's
> symmetric encryption is far faster than the network can move the data
> and the overhead of TLS is non-noticable for those volumes of
> data.
>
> Yes, it'll remove some strain from your machine, but next year's CPUs
> will remove that strain from notice.
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Re: Can I have SSL for peer authentication only? (and not for data encryption)

Alain Damiral
In reply to this post by Katie Lucas

>>1) Is it possible to use SSL only for the sake of peer
>>authentication + validation and transfer un-encrypted data over this
>>channel ?
>>    
>>
>
>How about; you open the sockets using your socket level
>interface. Then you attach SSL constructs to both ends, but with the
>"don't close this option".
>
>They connect, authenticate each other. You can then use the connection
>objects to get the peer certificates (you need to do this because the
>connection will succeed if the client doesn't offer a certificate,
>whereas you're after BOTH parties being authenticated). If both ends
>get a validated certificate presented, the connection is authenticated.
>
>Close the SSL layer, which will leave you with two natice connected
>sockets to talk over.
>
>  
>
But with no cryptographic digest you have no guarantee that the data you
receive provides from the person who showed his certificate. I think it
would be vulnerable to a man in the middle type of attack.

I suppose a digest is still included when using the null cipher with
OpenSSL... ?

--
Alain Damiral

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Re: Can I have SSL for peer authentication only? (and not for data encryption)

Katie Lucas
On Thu, Feb 02, 2006 at 05:09:42PM +0100, Alain Damiral wrote:

>
> >>1) Is it possible to use SSL only for the sake of peer
> >>authentication + validation and transfer un-encrypted data over this
> >>channel ?
> >>  
> >>
> >
> >How about; you open the sockets using your socket level
> >interface. Then you attach SSL constructs to both ends, but with the
> >"don't close this option".
> >
> >They connect, authenticate each other. You can then use the connection
> >objects to get the peer certificates (you need to do this because the
> >connection will succeed if the client doesn't offer a certificate,
> >whereas you're after BOTH parties being authenticated). If both ends
> >get a validated certificate presented, the connection is authenticated.
> >
> >Close the SSL layer, which will leave you with two natice connected
> >sockets to talk over.
> >
> >
> >
> But with no cryptographic digest you have no guarantee that the data you
> receive provides from the person who showed his certificate. I think it
> would be vulnerable to a man in the middle type of attack.

Only if they can spoof the IP streams...

At the point the SSL connection says "yep. Everything's OK", it's
already done the challenges and responses so it's all ready to go --
this is as long as you don't include the null cipher, so the initial
comms are encrypted.

Closing the SSL connection means turning off the encryption later on,
so it can still be used initially for the certificate verification.




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Re: Can I have SSL for peer authentication only? (and not for data encryption)

Alain Damiral
Katie Lucas wrote:

>On Thu, Feb 02, 2006 at 05:09:42PM +0100, Alain Damiral wrote:
>  
>
>>But with no cryptographic digest you have no guarantee that the data you
>>receive provides from the person who showed his certificate. I think it
>>would be vulnerable to a man in the middle type of attack.
>>    
>>
>
>Only if they can spoof the IP streams...
>  
>
Why would anyone assume that they can't ? An attacker might even have
other means of messing around with IP adresses that would allow him to
achieve man in the middle without spoofing.



--
Alain Damiral

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Re: Can I have SSL for peer authentication only? (and not for data encryption)

Urjit Gokhale
In reply to this post by Kyle Hamilton
Hi all,
Thanks for all those mails.
I now understand that I can use NULL cipher suite to exchange data without
encryption.
I understand that on specifying NULL cipher suite, ssl will use RSA
authentication.

I believe that I will have to call SSL_CTX_set_cipher_list with second
argument as "NULL"
                   SSL_CTX_set_cipher_list(ctx, "NULL");
And then the application should be able to communicate using SSL_read() and
SSL_write().
Please correct me if I am wrong.

Now I have a source for a server application. The server goes through the
following function sequence:
===========
SSL_context =  SSL_CTX_new(SSLv23_method());
SSL_CTX_use_certificate_file(SSL_context, fnbuf, SSL_FILETYPE_PEM);
SSL_CTX_use_PrivateKey_file(SSL_context, fnbuf, SSL_FILETYPE_PEM);
SSL_CTX_check_private_key(SSL_context);

port->ssl = SSL_new(SSL_context);
SSL_set_fd(port->ssl, port->sock);
SSL_accept(port->ssl);

SSL_read(port->ssl, pkt->ptr, pkt->nrtodo);
===========
Now the questions I have here is:
1) Is the server using NULL cipher ?
2) If not, then which authentication and which cipher would it be using ?
3) If I want to force NULL cipher, do I give a call to
SSL_CTX_set_cipher_list() before I call SSL_new ?

If you want any more information in order to answer the above questions,
please do ask me.

Thanks,
~ Urjit

----- Original Message -----
From: "Kyle Hamilton" <[hidden email]>
To: <[hidden email]>
Sent: Thursday, February 02, 2006 9:37 PM
Subject: Re: Can I have SSL for peer authentication only? (and not for data
encryption)


On 2/2/06, Katie Lucas <[hidden email]> wrote:
> On Tue, Jan 24, 2006 at 06:44:30PM +0530, Urjit Gokhale wrote:
> > Hi all,
> >
>
> > I am planning to use SSL for the communication between my client and
> >server. The idea is to use SSL *mainly* for peer authentication and
> >validation (Both server and client authentication by means of
> >certificates). Regarding the data encryption, I would like to have it
> >as an optional feature.

This is already possible with the NULL cipher suite.

> > 1) Is it possible to use SSL only for the sake of peer
> >authentication + validation and transfer un-encrypted data over this
> >channel ?

Yes.  Remember that SSL/TLS also provides an integrity check to ensure
that a session hasn't been hijacked.  If this is important to your
application, don't shut down the SSL layer as Ms. Lucas suggests.

>
> How about; you open the sockets using your socket level
> interface. Then you attach SSL constructs to both ends, but with the
> "don't close this option".
>
> They connect, authenticate each other. You can then use the connection
> objects to get the peer certificates (you need to do this because the
> connection will succeed if the client doesn't offer a certificate,
> whereas you're after BOTH parties being authenticated). If both ends
> get a validated certificate presented, the connection is authenticated.
>
> Close the SSL layer, which will leave you with two natice connected
> sockets to talk over.
>
> > 2) Would sacrificing on encryption *really* improve the performance ?
>
> We're sending video data, so your mileage may vary, but SSL's
> symmetric encryption is far faster than the network can move the data
> and the overhead of TLS is non-noticable for those volumes of
> data.
>
> Yes, it'll remove some strain from your machine, but next year's CPUs
> will remove that strain from notice.
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RE: Can I have SSL for peer authentication only? (and not for data encryption)

Ambarish Mitra
Urjit,

To answer your 2nd question, just immediately after SSL_accept and
SSL_connect on the server and client side respectively, you can use the
functions:
SSL_get_cipher (ssl), SSL_get_cipher_version (ssl)

These will give you the cipher and SSL version. A sample output can be:

SSL connection cipher:[EDH-RSA-DES-CBC3-SHA],version:[TLSv1/SSLv3]


-----Original Message-----
From: [hidden email]
[mailto:[hidden email]]On Behalf Of Urjit Gokhale
Sent: Wednesday, February 08, 2006 11:07 AM
To: [hidden email]
Subject: Re: Can I have SSL for peer authentication only? (and not for
data encryption)


Hi all,
Thanks for all those mails.
I now understand that I can use NULL cipher suite to exchange data without
encryption.
I understand that on specifying NULL cipher suite, ssl will use RSA
authentication.

I believe that I will have to call SSL_CTX_set_cipher_list with second
argument as "NULL"
                   SSL_CTX_set_cipher_list(ctx, "NULL");
And then the application should be able to communicate using SSL_read() and
SSL_write().
Please correct me if I am wrong.

Now I have a source for a server application. The server goes through the
following function sequence:
===========
SSL_context =  SSL_CTX_new(SSLv23_method());
SSL_CTX_use_certificate_file(SSL_context, fnbuf, SSL_FILETYPE_PEM);
SSL_CTX_use_PrivateKey_file(SSL_context, fnbuf, SSL_FILETYPE_PEM);
SSL_CTX_check_private_key(SSL_context);

port->ssl = SSL_new(SSL_context);
SSL_set_fd(port->ssl, port->sock);
SSL_accept(port->ssl);

SSL_read(port->ssl, pkt->ptr, pkt->nrtodo);
===========
Now the questions I have here is:
1) Is the server using NULL cipher ?
2) If not, then which authentication and which cipher would it be using ?
3) If I want to force NULL cipher, do I give a call to
SSL_CTX_set_cipher_list() before I call SSL_new ?

If you want any more information in order to answer the above questions,
please do ask me.

Thanks,
~ Urjit

----- Original Message -----
From: "Kyle Hamilton" <[hidden email]>
To: <[hidden email]>
Sent: Thursday, February 02, 2006 9:37 PM
Subject: Re: Can I have SSL for peer authentication only? (and not for data
encryption)


On 2/2/06, Katie Lucas <[hidden email]> wrote:
> On Tue, Jan 24, 2006 at 06:44:30PM +0530, Urjit Gokhale wrote:
> > Hi all,
> >
>
> > I am planning to use SSL for the communication between my client and
> >server. The idea is to use SSL *mainly* for peer authentication and
> >validation (Both server and client authentication by means of
> >certificates). Regarding the data encryption, I would like to have it
> >as an optional feature.

This is already possible with the NULL cipher suite.

> > 1) Is it possible to use SSL only for the sake of peer
> >authentication + validation and transfer un-encrypted data over this
> >channel ?

Yes.  Remember that SSL/TLS also provides an integrity check to ensure
that a session hasn't been hijacked.  If this is important to your
application, don't shut down the SSL layer as Ms. Lucas suggests.

>
> How about; you open the sockets using your socket level
> interface. Then you attach SSL constructs to both ends, but with the
> "don't close this option".
>
> They connect, authenticate each other. You can then use the connection
> objects to get the peer certificates (you need to do this because the
> connection will succeed if the client doesn't offer a certificate,
> whereas you're after BOTH parties being authenticated). If both ends
> get a validated certificate presented, the connection is authenticated.
>
> Close the SSL layer, which will leave you with two natice connected
> sockets to talk over.
>
> > 2) Would sacrificing on encryption *really* improve the performance ?
>
> We're sending video data, so your mileage may vary, but SSL's
> symmetric encryption is far faster than the network can move the data
> and the overhead of TLS is non-noticable for those volumes of
> data.
>
> Yes, it'll remove some strain from your machine, but next year's CPUs
> will remove that strain from notice.
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