[SSL-Talk List FAQ] Secure Sockets Layer Discussion List FAQ v1.1.1

From: Shannon Appel (SAppel_at_consensus.com)
Date: 08/09/03

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    Content-type: text/x-usenet-FAQ;
        title="[SSL-Talk List FAQ] Secure Sockets Layer Discussion List FAQ v1.1.1"
    Archive-name: computer-security/ssl-talk-faq
    Posting-Frequency: monthly
    Last-modified: Nov 16 12:00:00 PST 1998
    Version: 1.1.1 (text) Mon Nov 16 12:00:00 PST 1998
    URL: http://www.consensus.com/security/ssl-talk-faq.html
    Copyright-Notice: (c) Copyright 1996-1998 by Consensus Development Corporation -- All Rights Reserved

                                  SSL-Talk FAQ
                Secure Sockets Layer Discussion List FAQ v1.1.1

                          Mon Nov 16 12:00:00 PST 1998

                               FAQ Maintained by:
                      Shannon Appel <SAppel@consensus.com>
                        Consensus Development Corporation

             The latest edition of this FAQ can always be found at:

      Copyright (c) 1996-1998 Consensus Development Corporation - All Rights

        Due to the November 15, 1998 dissolution of the SSL-Talk mailing
        list, this will be the last version of this FAQ in its current form.
        It will be replaced by a more general TLS & SSL FAQ in the near
        future that is not tied to any mailing list or newsgroup.

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        Many people have in the past provided feedback and corrections; we
        thank them for their input.

        In particular, many thanks to:

            Christopher Allen <ChristopherA@consensus.com>
            Shannon Appel <SAppel@consensus.com>
            Nelson Bolyard <NelsonB@netscape.com>
            Tim Dierks <TimD@consensus.com>
            Eric Greenberg <ericg@netscape.com>
            Charles Neerdaels <chuckn@netscape.com>
            Bruce Schneier <schneier@counterpane.com>
            Tom Weinstein <tomw@netscape.com>
            Jonathan Zamick <JonathanZ@consensus.com>

        Remaining ambiguities, errors, and difficult-to-read passages are
        not their fault. :)


        1) THE SSL-TALK LIST
            6.1) NETSCAPE QUESTIONS
            6.2) MICROSOFT QUESTIONS
            7.1) SSLREF QUESTIONS
            7.2) SSL PLUS QUESTIONS
            7.3) SSLEAY QUESTIONS



    This section contains information about the SSL-Talk list.

    1.1) What is the SSL-Talk List?

        The SSL-Talk List was an email list intended for discussion of the
        technical issues of implementing the SSL protocol. It ceased to exist
        on November 15, 1998.

        Past discussions included issues of software development,
        cryptanalysis of the protocol and of its various implementations,
        testing, interoperability, the applicability of SSL to additional
        TCP-based applications, infrastructure growth questions, etc.

    1.1.1) Do archives of the SSL-Talk List exist?

        Yes. An archive is maintained at:

        It covers the list from 1995-1998 and is filled with useful
        We are not aware of any plain text archives of the list.

    1.2) What is SSL?

        SSL is the Secure Sockets Layer protocol. Version 2.0 originated by
        Netscape Development Corporation, and version 3.0 was designed with
        public review and input from industry, and is defined at

    1.2.1) What is TLS?

        TLS is the Transport Layer Security protocol. It is effectively SSL
        3.1 and was submitted to the IETF standards committee for change
        control in 1996. It should be close to release.

    1.3) Has netscape replaced the SSL-Talk mailing list?

        Yes. Netscape, the host of the old ssl-talk mailing list, has
        replaced it with a newsgroup.
        The newsgroup netscape.dev.ssl is now available via two means:

        a) from <snews://secnews.netscape.com/>
        Note: snews is nntp over SSL. Supported in Communicator 4.x.

        b) from

    1.4) Are there any other SSL mailing lists?

        Some people prefer mailing lists to newsgroups. Fortunately, several
        other mailing lists exist to discuss SSL.


        This is a mailing list specifically geared toward application
        developers who are incorporating SSL or TLS into their products. It
        is hosted by Consensus Development, a division of Certicom, who has
        helped to develop the TLS specifications. To join, send a message to:


        THE SSL LIST

        As with the older SSL-Talk mailing list, the purpose of this
        mailing list is to discuss any SSL & TLS related issues. It covers
        the whole spectrum of issues, from beginners on up and is more
        oriented toward users of SSL-enabled applications. To subscribe
        simply send e-mail to:



        This is a list concerning SSLeay, a public implementation of SSL. To
        subscribe send mail to:


        The command "subscribe ssl-users" must appear in the body of the

        This is a mailing list dedicated to the writing of the TLS
        specification for the IETF. To subscribe, send a message to:



    This section contains general information on SSL and the SSL

    2.1) What is the current version of the SSL protocol?

        The current version is SSL 3.0, as documented at

        Errata to the SSL 3.0 Specification is periodically posted on
        the SSL discussion list, and is available at

        Netscape has submitted SSL 3.0 to the IETF-TLS Working Group
        as an Internet Draft (see the section 4.5 of this FAQ for more
        info on TLS). This will be TLS 1.0:

        The previous version of SSL, version 2.0 is documented at

    2.2) Where can I get a "management overview" of SSL and web security?

        There is a brief introduction on how Netscape uses public key
        cryptography in the SSL protocol called "Using Public Key
        Cryptography" at

        An overview on certificates and VeriSign's Digital IDs is at

        General information on Netscape security can be found in a
        set of web pages called "Network Security Solutions", at:

    2.3) Where can I get a more in-depth look at SSL and web security?

        The online version of the technical specifications for the SSL 3.0
        protocol is at

        A PostScript version is also available at

        A FAQ for SSLeay, a freeware implementation which support SSL 2.0,
        SSL 3.0, and TLS 1.0, is available at

        A rather broad list of public key related documents, with a focus on
        certificates and standards can be found at

    2.4) What software supports SSL 2.0 and SSL 3.0?

        A list of web servers that support SSL 3.0 can be found using the
        powersearch at:

        SSL is not just for web servers and is supported by numerous other
        internet clients and servers.

    2.5) What are the laws regarding the import and export of cryptography in
    various countries?

        There is an impressive "International Law Crypto Survey" of
        cryptographic laws and regulations throughout the world at

        RSA Data Security, Inc. offers an Acrobat version of their
        "Frequently Asked Questions: Export" at

        Other information on US export issues can be found on
        the Electronic Frontier Foundation's web site at

        Canadian export issues are covered at



    This section contains information on how the SSL protocol interacts
    with proxy servers, security gateways, and firewalls.

    3.1) What is a proxy server?

        A proxy server is a computer program that resides on your firewall
        and acts as a conduit between your computer and the broader
        Internet. In addition to acting as network guardian and logging
        traffic, a proxy server can also provide an enterprise cache for
        files as well as replication and site-filtering services.

        Any application which needs to communicate through a proxy has to
        negotiate with the proxy first before continuing through the
        firewall. Netscape Navigator works with many different types of
        proxies (such as the CERN proxy server and their own Netscape Proxy
        Server) and gateways that use the SOCKS protocol.

        One problem with SSL-based traffic is that it does not allow
        caching and replication with proxy servers. For a proxy server to
        support SSL it must either support SOCKS (a protocol independent
        proxy mechanism), or use a special SSL Tunneling protocol. The
        Netscape Proxy Server supports both SOCKS and the SSL Tunneling

    3.2) How does SSL work through (application level) firewalls,
    gateways and proxy servers?

        SSL was designed to provide security between client and server and
        to avoid any kind of 3-way man-in-the-middle attack. Thus SSL cannot
        be proxied through traditional application level firewalls (such as
        the CERN proxy server) because SSL considers a proxy server to be a

        The simplest alternative to this problem is to use a packet
        filtering firewall. You set it up to open a reserved and trusted
        port for the SSL+HTTP or SSL+NNTP services (443 or 563 respectively)
        allowing all traffic on those ports to be passed through
        unrestricted. The risk with this solution is that an internal
        attacker could attempt to use these trusted ports without using SSL
        and there is no way for the firewall to know.

        SSL also can work with gateways that support the SOCKS protocol, a
        protocol independent proxy mechanism. SOCKS is a generic byte
        forwarding gateway between client and server and generally works
        at the socket level. If all you want is TCP/UDP restrictions based on
        client IP or server IP, SOCKS works fine.

        However, most non-SSL HTTP proxies work at the protocol level and
        have the ability to understand header information related to the
        protocol. This goes beyond SOCKS to allow the firewall administrator
        to use the header information for filtering and/or monitoring the
        traffic. Also, SOCKS does not offer the firewall administrator
        enough information about the request to let it decide whether to
        allow it and whether to log the request.

        A more secure approach is to use a firewall that supports the SSL
        Tunneling CONNECT extension method as described in the Internet


        In SSL Tunneling, the client initiates an SSL connection via normal
        HTTP then handshakes and creates a secure connection to the server
        via a byte-forwarding tunnel. The proxy has access to the
        client-proxy request headers, but the session is encrypted. Once
        the handshake occurs, the proxy acts just like a SOCKS gateway. This
        allows the firewall to monitor the requests, but not the traffic.

        The biggest difference between the two methods is that when using
        SOCKS, DNS resolution is the responsibility of the client, whereas
        when requests are forwarded through a proxy, DNS resolution is the
        responsibility of the proxy.

        The are three additional things that the SSL Tunneling mechanism
        does with the proxy server that do not happen when using SOCKS:

            * The client sends a "user agent" message (for example,

            * The proxy can send to the client an authorization request
              allowing the administrator to use passwords to control external
              Internet access.

            * The standard is more easily extensible. For example, the client
              could, in theory, send the URL being requested (or anything
              else) to the firewall. However, there is no standard to support
              this behavior and as far as we know there are no products which
              do it.

        The Netscape Proxy Server supports the SSL Tunneling CONNECT
        extension method for tunneling SSL, and the use of the proxy is
        described in

        Another solution, also available using the Netscape Proxy Server, is
        that the proxy server can spoof SSL on behalf of the internal client.
        The proxy will initiate SSL between itself and other servers on the
        Internet, but be unsecure inside the firewall between the proxy
        server and the client.

        This compromise means that client authentication is not possible;
        only server authentication of the remote sites is available.
        However, you gain the ability for client authentication between the
        client and the proxy. The administrator must decide which is more
        important, until such time as a better solution arises. The
        description of this feature of the Netscape Proxy Server is at


        Reverse proxies are a solution for serving secure content inside
        a firewall to outside clients. For the Netscape Proxy Server
        this is described at


        It is possible for a proxy server to hold both client and server
        keys for its internal clients. This allows SSL sessions to be
        carried out twice: once between the client and proxy server, and
        again between the proxy server and the secure server. Thus, the
        proxy server can to listen in on the conversation without having the
        private keys of external servers. Clearly this isn't reasonable for
        the general internet, but it is a viable solution for corporate
        requirements inside a firewall.

        Netscape Proxy Server 3.5 supports this feature. It can be used as
        described above, or simply to create a secure tunnel between sites
        across an insecure network. This is really multiple sessions of SSL,
        not an end-to-end secure connection.

        This means that 3.5 has full SSL support as opposed to just SSL
        tunneling. It can therefore do client authentication and serve
        documents like a secure server, or request documents like an
        SSL-enabled client. SSL doesn't allow recursive encryption, so by
        using it this way you lose the transparency of the proxy and get
        multiple segments of secure connections, rather than a single
        end-to-end connection.

    3.3) Since SSL is supposed to withstand replay attacks, does this
    preclude proxy servers from caching the data?

        A proxy server must pass SSL directly through without caching.

    3.4) What ports does SSL use?

        Theoretically SSL can transparently secure any TCP-based protocol
        running on any port if both sides know the other side is using SSL.
        However, in practice, separate port numbers have been reserved for
        each protocol commonly secured by SSL -- this allows packet
        filtering firewalls to allow such secure traffic through.

        As of October 1998, SSL has the following port numbers reserved
        with the Internet Assigned Numbers Authority (IANA), a part of the
        Internet Engineering Task Force (IETF):

            Keyword Decimal Description
            ------- ------- -----------
            nsiiops 261/tcp IIOP Name Service over TLS/SSL
            https 443/tcp http protocol over TLS/SSL
            ddm-ssl 448/tcp DDM-SSL
            smtps 465/tcp smtp protocol over TLS/SSL
            nntps 563/tcp nntp protocol over TLS/SSL
            sshell 614/tcp SSLshell
            ldaps 636/tcp ldap protocol over TLS/SSL
            ftps-data 989/tcp ftp protocol, data, over TLS/SSL
            ftps 990/tcp ftp, control, over TLS/SSL
            telnets 992/tcp telnet protocol over TLS/SSL
            imaps 993/tcp imap4 protocol over TLS/SSL
            ircs 994/tcp irc protocol over TLS/SSL
            pop3s 995/tcp pop3 protocol over TLS/SSL

        A listing of all IANA port assignments can currently be found at

    3.5) Do you have any information on sftp?

        SSL FTP has been assigned port 990 under the name ftps.



    This section contains more detailed information on the SSL protocol.

    4.1) Does SSL protect users from replay attack by eavesdroppers or
    message interceptors?

        Yes. The client and the server each provide part of the random data
        used to generate the keys for a connection. (The random portions of
        the connection that initiate a session, drawn from both the client
        and the server, are used to generate the master secret associated
        with that session.) Additionally, each record is protected with a
        MAC (Message Authentication Code) that contains a sequence number for
        the message.

    4.2) Isn't encrypt-only SSL open to "man-in-the-middle" attacks?

        Yes, even though SSL 3.0 defines an encrypt-only cipher suite (the
        SSL_DH_anon_WITH_DES_CBC_SHA cipher suite), there are many possible
        attacks against it, and some recommend against using it. SSL *MUST*
        have strong server authentication or it becomes open to some attacks.
        Netscape's browser and server products do not presently support
        encrypt-only cipher suites for this reason.

    4.3) When did MD5 get "disavowed"?

        It hasn't been truly "disavowed", but weaknesses have been
        discovered such that some people believe that an alternative should
        be found. These weaknesses were found by Dr. Hans Dobbertin
        <dobbertin@skom.rhein.de> of the German Information Security Agency
        in a paper called "Cryptanalysis of MD5 Compress" dated May 2, 1996.
        A postscript version of the paper is at

        SSL uses MD5 in combination with SHA for all negotiation. It also
        uses MD5 alone in most negotiated cipher suites. However, in these
        cases it is used with the HMAC construction, which strengthens it
        such that there are no known problems with this construction.

        It has been proposed with TLS to start phasing out all use of MD5.

    4.4) The record protocol sits underneath the other protocols, right?
    It appears that information can be sent only in blocks. Does
    there have to be a one-to-one mapping between write() calls on the
    client/server and SSL records? Is there some other blocking
    taking place when user data is being sent?

        The record layer takes a data stream from the higher layers and
        fragments it into records. If the write is longer than 2^14 bytes
        (with headers), the record layer will generate multiple records.
        Multiple writes can be condensed into a single record.

    4.5) It appears that there is no way in the SSL protocol to
    resynchronize blocks if they get out of synch. Is that true?

        Yes. SSL relies on an underlying reliable protocol to assure that
        bytes are not lost or inserted. There was some discussion of
        reengineering the future TLS protocol to work over datagram
        protocols such as UDP, however TLS 1.0 does not support this.

    4.6) Why does SSL3 have Diffie-Hellman encryption at all? What good is
    it? Exchanging random numbers that are encrypted with the server's (or
    client's) public key would seem to be an adequate way of getting the
    secret bits across. Why have DH as well?

        Anonymous DH key exchange doesn't require the use of certificates.
        Ephemeral DH allows you to use signing-only certificates, and it
        protects the session from future compromise of the server's private
        key. Another advantage of DH is that the patent expired in 1997.

    4.7) What is TLS? What happened at these meetings? Has anything come
    out of them yet?

        TLS is the Transport Layer Security Working Group of the IETF
        (Internet Engineering Task Force). It is the working group
        responsible for moving transport layer protocols such as SSL
        through the standards tracks.

        IETF working groups do most of their activities through mailing
        lists and thrice-annual IETF meetings. The first official IETF-TLS
        Working Group meeting was June 1996 in Montreal. (Before then it was
        an unofficial BOF "birds of a feather" group.)

        The home page for the IETF-TLS Working Group is at

        The discussion list for IETF-TLS is at IETF-TLS@CONSENSUS.COM. You
        subscribe and unsubscribe by sending to IETF-TLS@CONSENSUS.COM with
        subscribe or unsubscribe in the SUBJECT of the message. Archives of
        the list are at

        Minutes are available for a number of past IETF-TLS meetings.
        August 1998:
            Not currently available
        March 1998:

        December 1997:

        April 1997:

        December 1996:

        June 1996:

        May 1996:

        A number of internet-draft documents have been submitted to the
        IETF-TLS Working Group.

        The TLS Protocol 1.0 (Current Version 06):

        Addition of Kerberos Cipher Suites to Transport Layer
        Security (TLS):

        ECC Cipher Suites for TLS

        HTTP over SSL:

        An Internet AttributeCertificate Profile for Authorization

        TLS extensions for AttributeCertificate based authorization

        The following internet drafts are expired, but are of historical

        Addition of Shared Key Authentication to Transport Layer
        Security (TLS):
                (16885 bytes, expires May '97)

        Modifications to the SSL protocol for TLS:
            <draft-ietf-tls-ssl-mods-00.txt> (9271 bytes, expires May '97)

        Secure FTP over SSL:
                (14238 bytes, expires June '97)

        SSH Transport Layer Protocol (originally
                (44411 bytes, expired December '96)

    4.8) What is the purpose of pad1 and pad2, and why were the numbers 0x36
    and 0x5c chosen?

        The purpose of the construction of a "keyed-MAC" in the form of
        HASH(K,pad2,HASH(K,pad1,text)). It was proposed by the cryptographer
        Hugo Krawczyk of IBM as a much more secure alternative to traditional
        MACs. In a paper last year he demonstrated a proof that even if the
        hash function was relatively weak (as MD5 has since proven itself to
        be) the addition of the secret key in the function makes it
        significantly more secure. The particular method proposed by
        Krawczyk is now known as an HMAC.

        The particular construction that Netscape uses for SSL is based on
        the original internet-draft, and since that time it has been revised
        such that it XORs the pads rather than appending them -- a nice
        consequence of which is that pads are of the same size whether you
        use MD5 or SHA; it also allows for long keys and has some
        security advantages. This version may now be found as RFC 2104:


        In the proposals we've seen for the IETF-TLS Working Group the
        scheme SSL 3.0 uses will be replaced by the official RFC HMAC

        The particular pad bytes used are the ones defined in Krawczyk's
        original HMAC paper. We believe that they are relatively arbitrary.
        The salient property is that half the bits differ: the hamming
        distance between 0x36 and 0x5c is 4 out of a possible 8. We don't
        know if the fact that each of the pads also has a hamming weight of
        4 is significant or not.

    4.9) Are you aware of any SSL toolkits supporting client authentication?

        SSLRef 3.0 and SSL Plus both support SSL 3.0 client authentication.
        SSLeay supports SSL 2.0 and 3.0 client authentication as well as the
        proposed TLS standard for client authentication.

    4.10) What SSL implementations should I test against?

        There is no formal conformance testing, but Netscape does currently
        offer an interoperability test server that has been used to test
        conformance with many other implementations of SSL 3.0. This server
        is located at

        Another interoperability test server can be found at:
        VeriSign also has an "Authentic Site" program listing various sites
        that use SSL authentication. Also included is a test page that
        requires that you present a valid VeriSign client certificate.
        More information on the Authentic Site program is at

        Client authentication can be tested at:

    4.11) What is the difference between SSL 2.0 and 3.0?

        Security improvements:

        1. SSL 2.0 is vulnerable to a "man-in-the-middle" attack. An
        active attacker can invisibly edit the list of ciphersuite
        preferences in the hello messages to invisibly force both client and
        server to use 40-bit encryption. SSL 3.0 defends against this
        attack by having the last handshake message include a hash of all
        the previous handshake messages.

        2. SSL 2.0 uses a weak MAC construction, although post-encryption
        seems to stop attacks. This is fixed in 3.0.

        3. SSL 2.0 feeds padding bytes into the MAC in block cipher modes,
        but leaves the padding-length field unauthenticated, which could
        allow active attackers to delete bytes from the end of messages.
        This, too, is fixed in 3.0.

        4. In SSL 3.0, the Message Authentication Hash uses a full 128 bits
        of keying material, even when using an Export cipher. In SSL 2.0,
        Message Authentication used only 40 bits when using an Export

        Functionality improvements:

        1. In SSL 2.0, the client can only initiate a handshake at the
        beginning of the connection. In 3.0, the client can initiate a
        handshake routine, even in the middle of an open session. A server
        can request that the client start a new handshake. Thus, the
        parties can change the algorithms and keys used whenever they want.

        2. SSL 3.0 allows the server and client to send chains of
        certificates. This allows organizations to use a certificate
        hierarchy that is more than two certifications deep.

        3. SSL 3.0 has a generalized key exchange protocol. It allows
        Diffie-Hellman and Fortezza key exchanges and non-RSA certificates.

        4. SSL 3.0 allows for record compression and decompression.

        Backward compatibility:

        1. SSL 3.0 can recognize an SSL 2.0 client hello and fall back to
        SSL 2.0. An SSL 3.0 client can also generate an SSL 2.0 client
        hello with the version set to SSL 3.0, so SSL 3.0 servers will
        continue the handshake in SSL 3.0, and SSL 2.0 server will cause the
        client to fall back to SSL 2.0.


        1. SSL 3.0 separates the transport of data from the message layer.
        In 2.0, each packet contained only one handshake message. In 3.0, a
        record may contain part of a message, a whole message, or several
        messages. This requires different logic to process packets into
        handshake messages. Therefore, the formatting of the packets had to
        be completely changed.

        2. Cipher specifications, handshake messages, and other constants
        are different.



    This section contains information on certificates used by the SSL

    5.1) How does Netscape handle client certificates in Communicator 4.X?
    Navigator 3.X?

        Netscape describes their framework for web-based key generation and
        certificate issuing on their web pages at

    5.2) What is the format of the SSL certificates used by Netscape

        Netscape has documented their SSL 2.0 certificate format at

    5.3) I am distributing load on several different web servers and I
    don't want to have to have a different certificate for each. How can
    I do this?

        When establishing a secure connection in SSL, many SSL clients
        applications, including Netscape's Navigator, check the common name
        of the certificate against the name of the site in the URL. If it
        doesn't match, the client application warns the user. Thus the
        preferred format of a common name of an SSL server is a simple DNS
        name like "www.consensus.com".

        To support multiple servers you can use a round-robin DNS to send
        each request for "www.consensus.com" to different IP addresses. As
        Netscape Navigator does not check to see that the IP address matches
        the original domain name (reverse-IP), this will work for each
        round-robin server.

        Netscape's Navigator will also allow for some simple pattern
        matching. Netscape has documented a number of different possibilities
        in their SSL 2.0 Certificate Format web pages at:

        Note, however, none of these regular expression/pattern matching
        choices are accepted by VeriSign. In the past they have accepted
        server certificate common names with regular expressions, but these
        are no longer allowed.

        Other CAs may have different policies regarding use of regular
        expressions in common names.

    5.4) When comparing a URL against the common name of the certificate,
    why don't you do a reverse-DNS lookup?

        DNS is not a secure name service, and trying to treat it like one
        could be a security hole. The purpose of checking the common name
        against the URL is to make sure that at least the user's expectation
        of what site the user is visiting is not compromised.

    5.5) Does Netscape require hierarchical naming (that is, distinguished
    names) for its certificates?

        Yes, Netscape requires distinguished names.

    5.6) Where can I get more information on certificates?

        PKIX is an IETF working group dedicated to providing standards
        for an X509-based PKI. You can find their charter at:
        VeriSign, the default CA (Certificate Authority) used by Netscape
        and most other WWW browsers has a FAQ at:

        Entrust has a primer on Web Security with an emphasis on
        Certificate Authorities at:

        There is also a good resource of links to a variety of certificate
        technical and policy issue sites available at:

    5.7) What other CAs exist besides VeriSign?

        We know of these CAs:

            Thawte Consulting <http://www.thawte.com/certs/>
            COST Computer Security Technologies <http://www.cost.se/>
            CompuSource <http://www.compusource.co.za/id/personal/>
            XCert <http://www.xcert.com>

        Numerous other CAs now exist; additional links will be included in
        the replacement TLS/SSL FAQ intended for the future.
    5.8) How do I set up my own Certificate Authority?

        There is some support for creating your own CA in SSLeay; there is
        information on how to integrate it with Netscape available at:

        Several specific products also exist; additional links will be
        included in the replacement TLS/SSL FAQ intended for the future.

    5.9) What criteria should I use in deciding between one CA and another?

        The purpose of a Certificate Authority is to bind a public key to
        the common name of the certificate, and thus assure third parties
        that some measure of care was taken to ensure that this binding
        is valid. A measure of a Certificate Authority is their "Policy
        Statement" which states what measures they take for each class of
        certificate they offer to ensure that this binding of identity
        with public key is valid.

    5.10) What are Attribute Certificates?

        Attribute Certificates are a new type of certificate proposed by
        Netscape. These are signed objects that assert additional properties
        about a particular identity certificate.

        An attribute cert has no associated key pair and consequently cannot
        be used to establish identity. Informally, one can think of them as
        a mechanism for extending the attributes of an identity certificate
        without requiring that the identity certificate be reissued.

        More details of the proposal are at



    This section offers specific implementation details of different SSL
    clients and servers that are not specific to the protocol.



    This is not an official statement by Netscape, and Netscape has not
    reviewed this for accuracy. For additional information, please see:


    6.1.1) I just downloaded a new version of Netscape's browser, and it
    doesn't have 128-bit encryption. What version(s) of the browser have
    128-bit encryption?

        All versions of Netscape Navigator and Communicator, except "Preview
        Release" versions, are available in two flavors: a "domestic" flavor
        with 128-bit encryption for use in the USA and Canada, and an
        "export" or "international" flavor with only 40-bit encryption.
        (There is also a third flavor of Communicator 4.x available for use
        in France.) Preview releases are only available in the export flavor.
        To get 128-bit encryption, you must download the U.S. flavor.

    6.1.2) I just downloaded a newly released version of Netscape's browser
    and my bank's server tells me my browser does not have adequate
    security. What's wrong?

        Here are the likely explanations for this:

        a) You have downloaded an "export" flavor of the browser with only
        40-bit encryption, but your bank requires that you use the "domestic"
        flavor of the browser with 128-bit encryption. In this case, you must
        download the domestic 128-bit version.

        b) Your bank's server keeps a list of the browser versions with which
        it will work, and that list has not yet been updated to include the
        very latest version(s) of Netscape's browser. In this case, please
        ask your bank to add the newest version of Netscape's browser to
        their server's list of acceptable versions. Note that many banks will
        not accept "Preview Release" versions because they do not contain
        domestic (128-bit) encryption.

    6.1.3) I downloaded a version of Netscape's browser that is newer than
    version 4.05. Now, when I go to certain https web sites that used to
    work for me (like my bank) I get an error message telling me that
    "Netscape has received bad data from the server." I've been told the
    problem is with SSL v3 in my new browser, and that I should disable
    SSL v3 in my browser. What's wrong with SSL v3 in these new browsers?
    Should I disable it?

        Newer versions of Netscape's browsers enforce the legal export
        control requirements of the SSL v3 specification and will not work
        with servers that violate the export control provisions of the SSL v3

        Some SSL servers do not properly follow the SSL v3 specification's
        requirements for the U.S. Government's export control regulations.
        Netscape's server products, and most other brands of server products,
        conform to the specification, but a few others do not.

        We strongly advise you to NOT disable SSL v3 in your browser. If you
        do disable SSL v3, you lose the extra security protections of SSL v3
        with ALL the https web sites you visit. By keeping SSL v2 and v3
        enabled in your browser, you get the best protection each site can

        Please ask the failing web site to upgrade to conforming servers.

        Web sites whose servers violate the specification have several
        options at their disposal, including falling back on the less secure
        SSL v2, by disabling the non-conformant SSL v3 in their servers, or
        replacing their servers with servers that conform to the SSL v3 spec.

    6.1.4) Do Netscape's browsers cache data on disk that has been received
    via https?

        Navigator 3.0 and Communicator 4.x have an option to allow on-disk
        caching of data fetched over SSL connections. The default setting is
        to not cache https data on disk.

        In Navigator 2.0, documents fetched using SSL were cached in the same
        way as non-SSL documents. You could use the "Pragma: no-cache" HTTP
        header to disable caching for a particular page.

        In Navigator 1.0, documents fetched with SSL were not cached on disk.

    6.1.5) Is the cached data encrypted using some key?

        No, Navigator and Communicator do not encrypt documents that are
        stored in the cache.

    6.1.6) Does Netscape use "regular" RSA libraries (such as BSAFE) or
    "custom" RSA code? More specifically, is Netscape using BSAFE 3.0?

        Netscape is a BSAFE source licensee. Much of the code in BSAFE 3.0
        has been integrated into Netscape's products. However, the BSAFE API
        is not available to plugins.

    6.1.7) Are the 512-bit RSA keys used by exportable servers generated on
    the fly by Netscape's servers? How often are they changed?
    Does the Netscape server take care of changing them automatically?

        In Netscape's server products, if the server's public key is longer
        than 512 bits, the server generates a temporary 512-bit export key at
        start-up time. This key is regenerated only when the server is

    6.1.8) How can additional root CA certificates be added to the
    browser's certificate database?

        Root keys for CA (Certificate Authority) certificates may be loaded
        using an SSL connection to a previously unknown CA. Please see:


        for more information. Also, new releases of the Navigator have added
        additional CA root keys.

    6.1.9) What X.509v3 certificate extensions are supported by the various
    versions of Netscape browsers?

        Please see <http://home.netscape.com/eng/security/certs.html>.

    6.1.10) The Help Information for Netscape's Enterprise server indicates
    that the server supports 6 ciphers for SSL 2.0 and 6 ciphers for SSL
    3.0. However, the Encryption|Security Preferences menu in the server
    Manager displays only 2 choices for SSL 2.0 and 3 choices for SSL 3.0.
    How can I select the other choices?

        The Enterprise server is available in two flavors, the "domestic"
        flavor with 128-bit encryption for use in the USA and Canada, and the
        "export" or "international" flavor with only 40-bit encryption. If
        you do not have all the ciphers, then you have the export flavor of
        the server. If you want to use the others, you must use the domestic
        (non-export) flavor.

    6.1.11) When will Netscape support SSL sockets for Java browser applets?

        There are presently no announced plans to do so.



    The text for sub-section 6.2 was grabbed from various documents
    found at


    6.2.1) Which of Microsoft's products will support SSL?

        Internet Explorer 3.0 provides support for SSL versions 2.0 and 3.0
        and for Private Communication Technology (PCT) version 1.0. It will
        include support for the Transport Layer Security Protocol (TLS),
        which is being considered by IETF.

    6.2.2) Which Microsoft products support Client Authentication?

        Client authentication as implemented by Microsoft Internet Explorer
        3.0 is interoperable with popular Web servers that support secure
        sockets layer (SSL) 3.0 client authentication.

        Internet Information Server 3.0 supports client authentication using
        standards-based X.509 version 3 certificates. Webmasters can easily
        add client authentication to their Web sites by creating an Active
        Server Pages (ASP) application.



    This section offers specific details of different SSL development
    toolkits that are not specific to the protocol.



    This subsection contains information on SSLRef 3.0 which was
    codeveloped by Netscape Communications Corp. of Mountain View,
    California <http://home.netscape.com/> and Consensus Development
    Corporation of Berkeley, California <http://www.consensus.com/>.

    7.1.1) What is SSLRef 3.0?

        SSLRef 3.0 is a reference implementation of the SSL (Secure Sockets
        Layer) protocol. SSLRef 3.0 is intended to aid and accelerate
        developers' efforts to provide security within TCP/IP applications.
        It can also be used to qualify other implementations of version 3.0
        of the SSL protocol.

        SSLRef 3.0 consists of a software library, distributed as ANSI C
        source-code, that can be compiled on Windows 95/NT and Solaris
        platforms and then linked into TCP/IP application programs. SSLRef
        3.0 was also designed to be easily ported to a wide variety of
        other platforms and operating systems.

        More information on SSLRef can be found at

        If you are a US citizen you can download SSLRef 3.0 at

    7.1.2) How can I license SSLRef 3.0? What does it cost? With what

        The SSLRef 3.0 distribution includes a license for non-commercial
        use. For commercial licensing, send mail to <sslref@netscape.com>.

        The SSLRef 3.0 commercial license is Part Number 70-01128-00 and the
        price is $30,000. The license agreement is a flat one-time fee, not
        a recurring royalty.

        SSLRef 3.0 may not be exported. However, the encryption options in
        SSLRef 3.0 can be limited to make exportable products.

        SSLRef 3.0 does not include an RSA/BSAFE license for required
        cryptographic functions. Most users would use BSAFE.

            For BSAFE information contact RSA at



    This sub-section contains information specific to the SSL Plus: SSL
    3.0 Integration Suite(tm) software toolkit developed by Consensus
    Development Corporation of Berkeley, California

    7.2.1) What is the relationship between SSLRef and SSL Plus?

        SSLRef 3.0 was written by Netscape Development Corporation and
        Consensus Development Corporation. SSL Plus, a derivative of
        SSLRef 3.0, is fully supported and offers unique value-added

        SSL Plus 2.0 includes numerous updates to SSLRef 3.0, support, a
        VeriSign certificate request tool, and a "signer" file format for
        storing keys and certificates. It is qualified for additional
        platforms, and system integration services are available. When the
        TLS spec becomes official, SSL Plus will be upgraded to that new

        SSLRef 3.0 offers 4 ciphersuites:

          * RSA authenticated, unencrypted, with MD5

          * RSA authenticated with exportable RC4 encryption, and MD5

          * RSA authenticated with DES encryption, and SHA

          * Diffie-Hellman anonymous key exchange with DES encryption,
            and SHA

        SSL Plus 2.0 adds support for an additional 6 ciphersuites:

          * RSA authenticated, unencrypted, with SHA

          * RSA authenticated with non-exportable RC4 encryption, with
            MD5 or SHA
            (SSL_RSA_WITH_RC4_128_MD5 & SSL_RSA_WITH_RC4_128_SHA)

          * RSA authenticated with Triple-DES encryption, with SHA

          * Diffie-Hellman anonymous key exchange with RC4 encryption,
            with MD5
            (SSL_DH_anon_WITH_RC4_128_MD5 &

          * Diffie-Hellman anonymous key exchange with Triple-DES
            encryption and SHA
            (SSL_DH_anon_WITH_RC4_128_MD5 &

        For more information on SSL Plus features see

    7.2.2) What is the relationship between SSL Plus and SSLRef 2.0?

        There is no relationship between SSLRef 2.0 and SSL Plus -- SSL Plus
        was originally based on SSLRef 3.0 which was not based on SSLRef 2.0.

    7.2.3) How can I license SSL Plus?

        SSL Plus is available for commercial use only. Certicom will work
        with you to provide a license tailored to fit your company's business
        model, whether you prefer flat yearly licenses, royalty based payment
        or even one time buyouts.

        Since SSL Plus is a protocol toolkit, SSL Plus customers will also
        require a license for one of the standard crytographic libraries such
        as Certicom's Security Builder, or RSA's BSAFE.

        You can get more information about SSL Plus at
        <http://www.consensus.com/SSLPlus>, and about Certicom's Security
        Builder toolkit at <http://www.certicom.com/cSecure/sdk.htm>

        In addition, you can contact Consensus directly for more information
        on SSL Plus, including pricing, technical information, or more
        information about cryptographic library tools, at
        <mailto:sales@consensus.com> or at 510/649-3300.

    7.2.4) Is there any relationship between SSL Plus and Winsock 1.1 or
    Winsock 2.0? Which Winsock would you recommend using to test our
    SSL? Does it matter if Winsock 1.1 or 2.0 architecture is used?

        No -- SSL Plus is designed to be transport independent and work with
        both socket and stream styles of I/O. SSL Plus includes some
        examples of using WinSock 1.1 in the Win32 builds of our sample
        code. However, we recommend that you write your own callback code if
        you want better handling of your I/O than what our sample routines

    7.2.5) How does the data flow within the application, WinSock, SSL,
    TCP/IP stack layers?

        The short answer is that you insert SSL Plus between your I/O and
        your application code.

        Basically, you call SSL Plus instead of your read and write. SSL
        Plus does its stuff and calls your callback code to do the I/O. Data
        comes through your I/O routines, through SSL Plus, and then finally
        to your application. SSL Plus only manages the data flowing through
        the connection; it does not handle setting up and tearing down the
        underlying network connection; your application should open the
        network connection, then hand it off to SSL Plus for SSL handshaking
        and data transfer. (This step is not shown in the diagram).


            | Application |
                 | I/O Calls
            | WinSock |
                 | TCP Calls
            | Internet |

        SSL Plus:

            | Application |
                 | SSL I/O Calls
             ------------- I/O Callbacks --------------------
            | SSL Plus | <---------------->| Your Callback Code |
             ------------- --------------------
                                                        | I/O Calls
                                                  | WinSock |
                                                        | TCP Calls
                                                  | Internet |

    7.2.6) With the WinSock 2.0 architecture, the application need only chose
    an appropriate SSL-enabled service provider. Does SSL Plus support this?

        With WinSock 2.0 there is some discussion of functionality that
        allows you to create a module that you could add to WinSock 2.0.

        At this time we do not believe that this functionality is actually
        shipping (as Microsoft was supporting PCT but is now supporting
        SSL 3), but we do know that it is part of their plans. See the
        MS-ISF (Microsoft Internet Security Framework) description at

        We can't speak to when or if Microsoft will add it to their system
        software, or if another third-party offers such a module.

        Meanwhile, there has been some discussion on what changes might be
        required under WinSock 2.0 to do SSL. See:

    7.2.7) Does SSL Plus support yielding?

        SSL Plus includes support for processor yielding during
        cryptographic operations. Because developers provide their own I/O
        routines, they can do yielding during I/O. Our sample code include
        examples of I/O yielding.

    7.2.8) I don't understand the nomenclatures of constants such as
    "SSL_RSA_EXPORT_WITH_RC4_40_MD5" -- where are they defined?

        They are actually defined by the SSL 3.0 specification, but also see
        section 7.2.1 for an overview.

    7.2.9) In what order are the cipher suites called?

        The default order of the cipher suites is:

    7.2.10) Can I change the order of the cipher suites?

        Yes. This is easily done with the SSLSetCipherSuites function.

    7.2.11) Does SSL Plus support compression?

        Not as of 2.0. If there is a specific customer requirement, or if a
        compression cipher suite is defined we expect to support it in the
        future, but otherwise we have no plans here.

    7.2.12) In the function SSLWriteRecord(), the data buffer is
    copied, encrypted, then enqueued on the SSL write queue. The function
    then returns. What thread services the write queue? How is the
    thread created?

        The write queue is serviced by the public function called
        SSLServiceWriteQueue(). It is called in a number of places in
        ssltrspt.c, including with every call to SSLWrite(). Data to be
        written is sent to the I/O layer as you exit out of the write
        function (for example, right near the bottom of SSLWrite).

        If SSLWrite() returns SSLWouldBlockError, then make a call to
        SSLServiceWriteQueue() to service the write queue. (You could
        instead make a call to SSLWrite() with more data to be written, but
        this is unlikely.)

        The write queue is not serviced by a separate execution thread. The
        write queue mechanism was designed to support non-blocking I/O
        without undue overhead.

    7.2.13) When I call SSLRead(), on returning, the length argument should
    be replaced with the number of bytes actually read. In practice, this
    doesn't seem to be happening. What am I doing wrong?

        The difficulty is that it's hard for SSL to precisely emulate the
        behavior of Unix-style socket calls.

        The problem is that you are using SSL Plus in its blocking mode; if
        you return SSLWouldBlock from your I/O Read callback, the library
        will return the data it has along with the SSLWouldBlock error.

        The best way to solve this is always to know how much data you're
        waiting for and to request exactly that much. I know this doesn't
        work with a lot of free-form Internet protocols.

        Alternatively, you would like the call to block until it gets some
        data, then return it to you, even if it's less than 512 bytes.
        Ideally, you'd like to do this without busy-looping the CPU waiting
        for data. The best way to do this using SSL Plus is to write a
        wrapper for SSLRead() which does the following:

            * Make a blocking select() call until there is some data
              available on the TCP/IP connection over which you're speaking
              SSL. This will cause you to block in a friendly way until data

            * Call SSLRead(). If zero bytes are returned from the read,
              loop and do the select() again. Otherwise, return whatever
              came back.

            * Make your Read() callback non-blocking. The easiest thing to
              do is to check how much data is available on the incoming
              connection and return SSLWouldBlockErr if you can't completely
              fulfill the request. (You can optionally read what data there
              is and return it first; this won't affect functionality).

        This will result in the following behavior:

        1. Your program will block gracefully in the select() call until
           something arrives on the connection.

        2. You will then ask SSL Plus to read some data.

        3. SSL Plus will ask the Read() callback to read the header of the
           next record (3 or 5 bytes).

        4. The Read() callback will fulfill that, if possible

        5. SSL Plus will ask to read the body of the record (whose length
           will be equal to how much data was sent by the other side, plus
           MAC and encryption padding).

        6. The Read() callback will fulfill that, if possible.

        7. If the amount of data received is greater than or equal to how
           much was requested in 2., the data will be returned

        8. Otherwise, go back to 3.

        What will happen in practice looks something like this: because the
        SSL peer on the other end of the connection generates record layer
        records monolithically, and they're relatively small, the header and
        content of a record will arrive at your machine all together. Thus,
        when your select() call returns, you will be able to successfully
        read a header and body without blocking. When SSL Plus goes to read
        another one, your Read() callback will see that there's no data
        available on the connection (assuming another record hasn't arrived)
        and return SSLWouldBlockErr. SSL Plus will then return the data it
        has received and the error SSLWouldBlockErr; you can return that
        data as a partial completion of the desired read.

        If a partial record arrives, your select() will wake up, but SSL
        Plus won't be able to decrypt and check a complete record before the
        Read() callback returns SSLWouldBlockErr; thus, your read will
        return with zero bytes returned. Since this isn't the behavior your
        client expects, you should select() again until more data arrives,
        hopefully completing the record.

    7.2.14) If session cache is stored in a database, can multiple Unix
    processes share the same session data?

        There is no information stored in the session database which can't
        be passed between processes. Specifically, there is no pointer
        indirection. Of course, you'll have to figure out how to pass
        session database records (and their changes or deletions) between
        processes; that is not part of SSL Plus.



    This sub-section contains information specific to the SSLeay
    toolkit developed by Eric Young <eay@mincom.com>

    7.3.1) Where is the SSLeay FAQ?

        There is a very complete SSLeay FAQ at:
    .. Shannon Appel Consensus Development Corporation ..
    .. Research Assistant a subsidiary of Certicom Corporation ..
    .. <SAppel@consensus.com> 2930 Shattuck Ave. #206 ..
    .. <http://www.consensus.com> Berkeley, CA 94705-1883 ..
    .. <http://www.certicom.com> o510/649-3300 f510/649-3301 ..

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