Informational Add-on for HTTP over the Secure Sockets Layer (SSL) Protocol and/or the Transport Layer Security (TLS) Protocol
draft-hoehlhubmer-https-upd-00

Network Working Group                                     W. Hoehlhubmer
Internet-Draft                                               Nov 4, 2013
Category: Best Current Practice
Intended status: Standards Track
Expires: May 4, 2014

                  Informational Add-on for HTTP over
            the Secure Sockets Layer (SSL) Protocol and/or
             the Transport Layer Security (TLS) Protocol
                    draft-hoehlhubmer-https-upd-00

Abstract

   This document describes an Add-on as a good practice for websites
   providing encrypted connectivity.

Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [RFC2119].

Status of this Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on April 24, 2014.

Copyright Notice

   Copyright (c) 2013 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents

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   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Implementing of this Add-on . . . . . . . . . . . . . . . . .   3
   2.1.  Content of this Add-on  . . . . . . . . . . . . . . . . . .   3
   2.1.  Formating of this Add-on  . . . . . . . . . . . . . . . . .   4
   3.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   4
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .   4
   5.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   4
   6.  Recommendations . . . . . . . . . . . . . . . . . . . . . . .   4
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   5
   7.1.  Normative References  . . . . . . . . . . . . . . . . . . .   5
   7.2.  Informative References  . . . . . . . . . . . . . . . . . .   5
   7.2.1.  Informative References (Cipher Suites)  . . . . . . . . .   6
   8.  Discussions . . . . . . . . . . . . . . . . . . . . . . . . .   6
   Appendix A.  Script Examples  . . . . . . . . . . . . . . . . . .   6
   Appendix B.  Add-on Sample Content  . . . . . . . . . . . . . . .   8
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .  10

1. Introduction

   Encrypted connections are not limited to just one encryption
   algorithm.

   A few encryption algorithms, a short and incomplete complete list:
   
   (1) Advanced Encryption Standard (AES)
   (2) Data Encryption Standard (DES, 3DES)
   (3) Ron's Code 4 (RC4)

   As an example a list of some kinds of the Camellia encryption
   algorithm (names taken from OpenSSL help [OPENSSL]):

   (1) camellia-128-cbc: 128-bit Camellia encryption in CBC mode
   (2) camellia-128-ecb: 128-bit Camellia encryption in ECB mode
   (3) camellia-192-cbc: 192-bit Camellia encryption in CBC mode
   (4) camellia-192-ecb: 192-bit Camellia encryption in ECB mode
   (5) camellia-256-cbc: 256-bit Camellia encryption in CBC mode
   (6) camellia-256-ecb: 256-bit Camellia encryption in ECB mode

   Only the X.509 Certificates are static,  all other informations
   depend on the capabilities of the used web browser.

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   Because not every browser allows you to view all these informations,
   it is a good practice placing an Uniform Resource Locator (URL)
   to this informations on the main page of the website.

   With most browsers you can view the used X.509 certificates of the
   actual session,  but have no direct comparison if they are the
   correct ones.  The X.509 certificates which are shown by the browser
   and these from this Add-on MUST match;  other ways there is going on
   a man-in-the-middle attack.

2.  Implementing this Add-on

   This Add-on is just one page of the website.  Its content MUST be 
   completely generated on server side.  For doing so see the sample
   scripts at Appendix A.  Presenting the content in sorted order is
   OPTIONAL.

2.1.  Content of this Add-on

   The informations MUST be the following:

   (1) The actual date and time in [RFC2822] format,
       that MUST NOT differ more than 5 seconds from actual date/time

   (2) The cipher specification name

   (3) Number of cipher bits (actually used)
   (4) Number of cipher bits (possible)

   (5) The SSL Protocol version: SSLv2, SSLv3, TLSv1, TLSv1.1, TLSv1.2,
                                 ...

   (6) If cipher is an export cipher: false, true
   (7) If secure renegotiation is supported: false, true

   (8) Algorithm used for the public key of server's certificate
   (9) Algorithm used for the signature of server's certificate
   (10) Issuer DN of server's certificate
   (11) Subject DN in server's certificate
   (12) The serial of the server certificate
   (13) The version of the server certificate
   (14) Validity of server's certificate (start time)
   (15) Validity of server's certificate (end time)

   (16) Client certificate verification:
        NONE, SUCCESS, GENEROUS or FAILED:reason

   (17) SSL compression method negotiated: NULL when disabled

   For connections where X.509 certificates are used for authentication
   these informations are RECOMMENDED:
   

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   (18) Algorithm used for the public key of client's certificate
   (19) Algorithm used for the signature of client's certificate
   (20) Issuer DN of client's certificate
   (21) Subject DN in client's certificate
   (22) The serial of the client certificate
   (23) The version of the client certificate
   (24) Validity of client's certificate (start time)
   (25) Validity of client's certificate (end time)
   (26) Number of days until client's certificate expires

   This information MAY be given:

   (27) The hex-encoded SSL session id

   These OPTIONAL informations depend on the used software:

   (28) The SSL-module program version: e.g. Apache mod_ssl version
   (29) The SSL program version: e.g. OpenSSL version

   See Appendix B for a sample content.

2.2.  Formating of this Add-on

   I RECOMMEND to present this information simple.  You MAY use HTML,
   but you MUST NOT make use of any client side scripting:
     e.g.  Javascript.

   Any design or formatting, also the translation to another language
   as English is allowed.

   Simple plain ASCII-Text is fine, too.

3.  IANA Considerations

   There are no requests for IANA actions in this document.

4.  Security Considerations

   When implementing this information as a popup window in the browser,
   this information MUST also be available with enabled popup-blocker.

   The Implementation MUST NOT use any scripts, that run on client side:
   e.g. Javascript, ...

   There SHOULD also be no references to other websites inside this
   Add-on page.

5.  Acknowledgements

6.  Recommendations

   I recommend using a standardized URL,  for more see Section 8.

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7.  References

7.1.  Normative References

   [HTTPTLS]  Rescorla, E., "HTTP over TLS", RFC 2818, May 2000.

   [PKIX]     Housley, R., Polk, W., Ford, W. and D. Solo, "Internet
              X.509 "Public Key Infrastructure Certificate and
              Certificate Restoration List (CRL) Profile", RFC 3280,
              April 2002.

   [SSLv3]    Freier, A., Karlton, P., and P. Kocher, "The Secure
              Sockets Layer (SSL) Protocol Version 3.0", RFC 6101,
              August 2011.

   [TLSv1]    Dierks, T. and C. Allen, "The TLS Protocol Version 1.0",
              RFC 2246, January 1999.

   [TLSv1.1]  Dierks, T. and E. Rescorla, "The Transport Layer Security
              (TLS) Protocol Version 1.1", RFC 4346, April 2006.

   [TLSv1.2]  Dierks, T. and E. Rescorla, "The Transport Layer Security
              (TLS) Protocol Version 1.2", RFC 5246, August 2008.

   [URL]      Berners-Lee, T., Masinter, L., and M. McCahill, "Uniform
              Resource Locators (URL)", RFC 1738, December 1994.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.
    
   [RFC2822]  Resnick, P., Ed., "Internet Message Format", RFC 2822,
              April 2001.

7.2.  Informative References

   [CAMELLIA] Matsui, M., Nakajima, J., and S. Moriai, "A Description
              of the Camellia Encryption Algorithm", RFC 3713,
              April 2004.

   [CGI]      Robinson, D. and K. Coar, "The Common Gateway Interface
              (CGI) Version 1.1", RFC 3875, October 2004.

   [HTML2.0]  Berners-Lee, T. and D. Connolly, "Hypertext Markup
              Language - 2.0", RFC 1866, November 1995.

   [MD5]      Rivest, R., "The MD5 Message-Digest Algorithm", RFC 1321,
              April 1992.

   [SHA1]     Eastlake 3rd, D. and P. Jones, "US Secure Hash
              Algorithm 1 (SHA1)", RFC 3174, September 2001.

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   [OPENSSL]  OpenSSL Cryptography and SSL/TLS Toolkit at
              http://www.openssl.org/

7.2.1.  Informative References (Cipher Suites)

   [RFC3268]  Chown, P., "Advanced Encryption Standard (AES)
              Ciphersuites for Transport Layer Security (TLS)",
              RFC 3268, June 2002.

   [RFC4279]  Eronen, P., Ed., and H. Tschofenig, Ed., "Pre-Shared Key
              Ciphersuites for Transport Layer Security (TLS)",
              RFC 4279, December 2005.

   [RFC4492]  Blake-Wilson, S., Bolyard, N., Gupta, V., Hawk, C., and
              B. Moeller, "Elliptic Curve Cryptography (ECC) Cipher
              Suites for Transport Layer Security (TLS)", RFC 4492,
              May 2006.

   [RFC4785]  Blumenthal, U. and P. Goel, "Pre-Shared Key (PSK)
              Ciphersuites with NULL Encryption for Transport Layer
              Security (TLS)", RFC 4785, January 2007.

   [RFC5288]  Salowey, J., Choudhury, A., and D. McGrew, "AES Galois
              Counter Mode (GCM) Cipher Suites for TLS", RFC 5288,
              August 2008.

   [RFC5469]  Eronen, P., Ed., "DES and IDEA Cipher Suites for
              Transport Layer Security (TLS)", RFC 5469, February 2009.

   [RFC5489]  Badra, M. and I. Hajjeh, "ECDHE_PSK Cipher Suites for
              Transport Layer Security (TLS)", RFC 5489, March 2009.

   [RFC5932]  Kato, A., Kanda, M., and S. Kanno, "Camellia Cipher
              Suites for TLS", RFC 5932, June 2010.

8.  Discussions

   It MAY be good to have an standardized URL for this Add-on;
   e.g.  https://www.example.com/sslinfo/
   in case the word "ssl" is already part of the URL's subdomain:
   e.g. ssl.example.com  or www-ssl.example.com,  then
   https://ssl.example.com/info/ or https://www-ssl.example.com/info
   are also fine for this standardized URL.

Appendix A.  Script Examples

   Use the following script examples as a template for your
   implementation of this Add-on.

   The first two examples generate identical content, the third
   example presents the content of Section 2.1.  unsorted.

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Example 1.  CGI-script, used on Linux systems

   #!/bin/sh

   printf "Content-type: text/plain\n\n"

   printf "SSL informations: $(date --rfc-2822)\n"
   printf "================\n\n"

   if [ "$HTTPS" == "on" ]; then
     env | grep --regexp="^SSL_" | sort
   else
     printf "No SSL information available.\n"
   fi

Example 2.  PHP-script

   <?php

   header( "Content-type: text/plain" );

   print "SSL informations: " . date( "r" ) . "\r\n";
   print "================\r\n\r\n";

   if ( isset( $_SERVER['HTTPS'] ) && ( $_SERVER['HTTPS'] == "on" ) ) {
     $list = array( );
     $nmbrOfValues = 0;
     foreach ( $_SERVER as $key => $value ) {
       if ( substr( $key, 0, 4 ) == "SSL_" ) {
         $list[ $nmbrOfValues++ ] = $key . "=" . $value;
       }
     }
     sort( $list );   // sort content before printing ...
     for ( $iter = 0; $iter < $nmbrOfValues; $iter++ ) {
       print $list[ $iter ] . "\r\n";
     }
   }
   else {
     echo "No SSL information available.\r\n";
   }
   ?>

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Example 3.  CGI-script (a compiled C program)

   /* Compiles with GNU C compiler on Linux, Windows, ...
    *
    * When using Microsoft C/C++ in Windows, strftime format specifiers
    *   for timezone behave in a non-standard way;
    */

   #include <stdio.h>
   #include <stdlib.h>
   #include <string.h>
   #include <time.h>

   #ifdef __linux__
   #include <unistd.h>
   #endif

   int main( int argc, char* argv[ ], char** envp )
   {                               /* char* envp[ ] */
     char* psz;
     char szDateTime[ 80 ];

     time_t tnow = time( NULL );
     struct tm* tmnow = localtime( &tnow );

     strftime( szDateTime, sizeof( szDateTime ) - 4,
       "%a, %d %b %Y %H:%M:%S %z", tmnow );

     printf( "Content-type: text/plain\r\n\r\n" );

     printf( "SSL informations: %s\r\n", szDateTime );
     printf( "================\r\n\r\n" );

     if ( ( psz = getenv( "HTTPS" ) ) && ( strcmp( psz, "on" ) == 0 ) )
     {
       char** ppsz = envp;

       /* print content without sorting ... */
       while ( ppsz && *ppsz )
       { 
         if ( strncmp( *ppsz, "SSL_", 4 ) == 0 )
           printf( "%s\r\n", *ppsz );
         ppsz++;
       }
     }
     else
       printf( "No SSL information available.\r\n" );

     return 0;
   }

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Appendix B.  Add-on Sample Content

   The first example shows a complete Add-on sample content generated
     by one of the scripts in Appendix A,  the other example shows
     only that differs when using another browser.
   For meaning of the numbers in brackets see Section 2.1.

Example 1.  A complete sample content

   SSL informations: Thu, 01 Jan 1970 00:00:00 +0000               (1)
   ================

   SSL_CIPHER=AES256-SHA                                           (2)
   SSL_CIPHER_ALGKEYSIZE=256                                       (4)
   SSL_CIPHER_EXPORT=false                                         (6)
   SSL_CIPHER_USEKEYSIZE=256                                       (3)
   SSL_CLIENT_VERIFY=NONE                                          (16)
   SSL_COMPRESS_METHOD=NULL                                        (17)
   SSL_PROTOCOL=TLSv1                                              (5)
   SSL_SECURE_RENEG=true                                           (7)
   SSL_SERVER_A_KEY=rsaEncryption                                  (8)
   SSL_SERVER_A_SIG=sha1WithRSAEncryption                          (9)
   SSL_SERVER_I_DN=/C=--/O=SomeOrg/OU=SomeOrgUnit/CN=Root CA       (10)
   SSL_SERVER_I_DN_C=--                                            (10)
   SSL_SERVER_I_DN_CN=Root CA                                      (10)
   SSL_SERVER_I_DN_O=SomeOrg                                       (10)
   SSL_SERVER_I_DN_OU=SomeOrgUnit                                  (10)
   SSL_SERVER_M_SERIAL=01                                          (12)
   SSL_SERVER_M_VERSION=3                                          (13)
   SSL_SERVER_S_DN=/C=AT/CN=www.example.com                        (11)
   SSL_SERVER_S_DN_C=AT                                            (11)
   SSL_SERVER_S_DN_CN=www.example.com                              (11)
   SSL_SERVER_V_END=Dec 31 23:59:59 1970 GMT                       (15)
   SSL_SERVER_V_START=Jan 01 00:00:00 1970 GMT                     (14)
   SSL_SESSION_ID=000000000000000000000000000000000000000000000    (27)
   SSL_VERSION_INTERFACE=mod_ssl/2.2.15                            (28)
   SSL_VERSION_LIBRARY=OpenSSL/1.0.0-fips                          (29)

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Example 2.
   
   SSL informations: Thu, 01 Jan 1970 00:00:00 +0000
   ================
   ...
   SSL_CIPHER=RC4-MD5
   SSL_CIPHER_ALGKEYSIZE=128
   SSL_CIPHER_EXPORT=false
   SSL_CIPHER_USEKEYSIZE=128
   SSL_CLIENT_VERIFY=NONE
   SSL_COMPRESS_METHOD=NULL
   SSL_PROTOCOL=SSLv3
   SSL_SECURE_RENEG=false
   ...

Author's Address

   Walter Hoehlhubmer
   Lederergasse 47a
   A-4020 Linz
   Austria, EUROPE

   EMail: walter.h@mathemainzel.info

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