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rfc:rfc4507

Network Working Group J. Salowey Request for Comments: 4507 H. Zhou Category: Standards Track Cisco Systems

                                                             P. Eronen
                                                                 Nokia
                                                         H. Tschofenig
                                                               Siemens
                                                              May 2006
               Transport Layer Security (TLS) Session
                Resumption without Server-Side State

Status of This Memo

 This document specifies an Internet standards track protocol for the
 Internet community, and requests discussion and suggestions for
 improvements.  Please refer to the current edition of the "Internet
 Official Protocol Standards" (STD 1) for the standardization state
 and status of this protocol.  Distribution of this memo is unlimited.

Copyright Notice

 Copyright (C) The Internet Society (2006).

Abstract

 This document describes a mechanism that enables the Transport Layer
 Security (TLS) server to resume sessions and avoid keeping per-client
 session state.  The TLS server encapsulates the session state into a
 ticket and forwards it to the client.  The client can subsequently
 resume a session using the obtained ticket.

Salowey, et al. Standards Track [Page 1] RFC 4507 Stateless TLS Session Resumption May 2006

Table of Contents

 1. Introduction ....................................................3
 2. Terminology .....................................................3
 3. Protocol ........................................................3
    3.1. Overview ...................................................4
    3.2. SessionTicket TLS Extension ................................6
    3.3. NewSessionTicket Handshake Message .........................7
    3.4. Interaction with TLS Session ID ............................8
 4. Recommended Ticket Construction .................................9
 5. Security Considerations ........................................10
    5.1. Invalidating Sessions .....................................11
    5.2. Stolen Tickets ............................................11
    5.3. Forged Tickets ............................................11
    5.4. Denial of Service Attacks .................................11
    5.5. Ticket Protection Key Management ..........................12
    5.6. Ticket Lifetime ...........................................12
    5.7. Alternate Ticket Formats and Distribution Schemes .........12
    5.8. Identity Privacy, Anonymity, and Unlinkability ............12
 6. Acknowledgements ...............................................13
 7. IANA Considerations ............................................13
 8. References .....................................................14
    8.1. Normative References ......................................14
    8.2. Informative References ....................................14

Salowey, et al. Standards Track [Page 2] RFC 4507 Stateless TLS Session Resumption May 2006

1. Introduction

 This document defines a way to resume a Transport Layer Security
 (TLS) session without requiring session-specific state at the TLS
 server.  This mechanism may be used with any TLS ciphersuite.  This
 document applies to both TLS 1.0 defined in [RFC2246] and TLS 1.1
 defined in [RFC4346].  The mechanism makes use of TLS extensions
 defined in [RFC4366] and defines a new TLS message type.
 This mechanism is useful in the following situations:
 1.  servers that handle a large number of transactions from different
     users
 2.  servers that desire to cache sessions for a long time
 3.  ability to load balance requests across servers
 4.  embedded servers with little memory

2. Terminology

 Within this document, the term 'ticket' refers to a cryptographically
 protected data structure that is created by the server and consumed
 by the server to rebuild session-specific state.
 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 [RFC2119].

3. Protocol

 This specification describes a mechanism to distribute encrypted
 session-state information in the form of a ticket.  The ticket is
 created by a TLS server and sent to a TLS client.  The TLS client
 presents the ticket to the TLS server to resume a session.
 Implementations of this specification are expected to support both
 mechanisms.  Other specifications can take advantage of the session
 tickets, perhaps specifying alternative means for distribution or
 selection.  For example, a separate specification may describe an
 alternate way to distribute a ticket and use the TLS extension in
 this document to resume the session.  This behavior is beyond the
 scope of the document and would need to be described in a separate
 specification.

Salowey, et al. Standards Track [Page 3] RFC 4507 Stateless TLS Session Resumption May 2006

3.1. Overview

 The client indicates that it supports this mechanism by including a
 SessionTicket TLS extension in the ClientHello message.  The
 extension will be empty if the client does not already possess a
 ticket for the server.  The extension is described in Section 3.2.
 If the server wants to use this mechanism, it stores its session
 state (such as ciphersuite and master secret) to a ticket that is
 encrypted and integrity-protected by a key known only to the server.
 The ticket is distributed to the client using the NewSessionTicket
 TLS handshake message described in Section 3.3.  This message is sent
 during the TLS handshake before the ChangeCipherSpec message, after
 the server has successfully verified the client's Finished message.
    Client                                               Server
    ClientHello
    (empty SessionTicket extension)------->
                                                    ServerHello
                                (empty SessionTicket extension)
                                                   Certificate*
                                             ServerKeyExchange*
                                            CertificateRequest*
                                 <--------      ServerHelloDone
    Certificate*
    ClientKeyExchange
    CertificateVerify*
    [ChangeCipherSpec]
    Finished                     -------->
                                               NewSessionTicket
                                             [ChangeCipherSpec]
                                 <--------             Finished
    Application Data             <------->     Application Data
 Figure 1: Message flow for full handshake issuing new session ticket
 The client caches this ticket along with the master secret and other
 parameters associated with the current session.  When the client
 wishes to resume the session, it includes the ticket in the
 SessionTicket extension within the ClientHello message.  The server
 then decrypts the received ticket, verifies the ticket's validity,
 retrieves the session state from the contents of the ticket, and uses
 this state to resume the session.  The interaction with the TLS
 Session ID is described in Section 3.4.  If the server successfully
 verifies the client's ticket, then it may renew the ticket by
 including a NewSessionTicket handshake message after the ServerHello.

Salowey, et al. Standards Track [Page 4] RFC 4507 Stateless TLS Session Resumption May 2006

    Client                                                Server
    ClientHello
    (SessionTicket extension)      -------->
                                                     ServerHello
                                 (empty SessionTicket extension)
                                                NewSessionTicket
                                              [ChangeCipherSpec]
                                  <--------             Finished
    [ChangeCipherSpec]
    Finished                      -------->
    Application Data              <------->     Application Data
      Figure 2: Message flow for abbreviated handshake using new
                            session ticket
 A recommended ticket format is given in Section 4.
 If the server cannot or does not want to honor the ticket, then it
 can initiate a full handshake with the client.
 In the case that the server does not wish to issue a new ticket at
 this time, it just completes the handshake without including a
 SessionTicket extension or NewSessionTicket handshake message.  This
 is shown below (this flow is identical to Figure 1 in RFC 2246,
 except for the session ticket extension in the first message):
    Client                                               Server
    ClientHello
    (SessionTicket extension)    -------->
                                                    ServerHello
                                                   Certificate*
                                             ServerKeyExchange*
                                            CertificateRequest*
                                 <--------      ServerHelloDone
    Certificate*
    ClientKeyExchange
    CertificateVerify*
    [ChangeCipherSpec]
    Finished                     -------->
                                             [ChangeCipherSpec]
                                 <--------             Finished
    Application Data             <------->     Application Data
     Figure 3: Message flow for server completing full handshake
                  without issuing new session ticket

Salowey, et al. Standards Track [Page 5] RFC 4507 Stateless TLS Session Resumption May 2006

 If the server rejects the ticket, it may still wish to issue a new
 ticket after performing the full handshake as shown below (this flow
 is identical to Figure 1, except the SessionTicket extension in the
 Client Hello is not empty):
    Client                                               Server
    ClientHello
    (SessionTicket extension) -------->
                                                    ServerHello
                                (empty SessionTicket extension)
                                                   Certificate*
                                             ServerKeyExchange*
                                            CertificateRequest*
                             <--------          ServerHelloDone
    Certificate*
    ClientKeyExchange
    CertificateVerify*
    [ChangeCipherSpec]
    Finished                 -------->
                                               NewSessionTicket
                                             [ChangeCipherSpec]
                             <--------                 Finished
    Application Data         <------->         Application Data
 Figure 4: Message flow for server rejecting ticket, performing full
               handshake and issuing new session ticket

3.2. SessionTicket TLS Extension

 The SessionTicket TLS extension is based on [RFC4366].  The format of
 the ticket is an opaque structure used to carry session-specific
 state information.  This extension may be sent in the ClientHello and
 ServerHello.
 If the client possesses a ticket that it wants to use to resume a
 session, then it includes the ticket in the SessionTicket extension
 in the ClientHello.  If the client does not have a ticket and is
 prepared to receive one in the NewSessionTicket handshake message,
 then it MUST include a zero-length ticket in the SessionTicket
 extension.  If the client is not prepared to receive a ticket in the
 NewSessionTicket handshake message then it MUST NOT include a
 SessionTicket extension unless it is sending a non-empty ticket it
 received through some other means from the server.
 The server uses an zero length SessionTicket extension to indicate to
 the client that it will send a new session ticket using the
 NewSessionTicket handshake message described in Section 3.3.  The

Salowey, et al. Standards Track [Page 6] RFC 4507 Stateless TLS Session Resumption May 2006

 server MUST send this extension in the ServerHello if it wishes to
 issue a new ticket to the client using the NewSessionTicket handshake
 message.  The server MUST NOT send this extension if it does not
 receive one in the ClientHello.
 If the server fails to verify the ticket, then it falls back to
 performing a full handshake.  If the ticket is accepted by the server
 but the handshake fails, the client SHOULD delete the ticket.
 The SessionTicket extension has been assigned the number 35.  The
 format of the SessionTicket extension is given at the end of this
 section.
    struct {
        opaque ticket<0..2^16-1>;
    } SessionTicket;

3.3. NewSessionTicket Handshake Message

 This message is sent by the server during the TLS handshake before
 the ChangeCipherSpec message.  This message MUST be sent if the
 server included a SessionTicket extension in the ServerHello.  This
 message MUST NOT be sent if the server did not include a
 SessionTicket extension in the ServerHello.  In the case of a full
 handshake, the server MUST verify the client's Finished message
 before sending the ticket.  The client MUST NOT treat the ticket as
 valid until it has verified the server's Finished message.  If the
 server determines that it does not want to include a ticket after it
 has included the SessionTicket extension in the ServerHello, then it
 sends a zero-length ticket in the NewSessionTicket handshake message.
 If the server successfully verifies the client's ticket, then it MAY
 renew the ticket by including a NewSessionTicket handshake message
 after the ServerHello in the abbreviated handshake.  The client
 should start using the new ticket as soon as possible after it
 verifies the server's Finished message for new connections.  Note
 that since the updated ticket is issued before the handshake
 completes, it is possible that the client may not put the new ticket
 into use before it initiates new connections.  The server MUST NOT
 assume that the client actually received the updated ticket until it
 successfully verifies the client's Finished message.
 The NewSessionTicket handshake message has been assigned the number 4
 and its definition is given at the end of this section.  The
 ticket_lifetime_hint field contains a hint from the server about how
 long the ticket should be stored.  The value indicates the lifetime
 in seconds as a 32-bit unsigned integer in network byte order.  A
 value of zero is reserved to indicate that the lifetime of the ticket

Salowey, et al. Standards Track [Page 7] RFC 4507 Stateless TLS Session Resumption May 2006

 is unspecified.  A client SHOULD delete the ticket and associated
 state when the time expires.  It MAY delete the ticket earlier based
 on local policy.  A server MAY treat a ticket as valid for a shorter
 or longer period of time than what is stated in the
 ticket_lifetime_hint.
    struct {
        HandshakeType msg_type;
        uint24 length;
        select (HandshakeType) {
            case hello_request:       HelloRequest;
            case client_hello:        ClientHello;
            case server_hello:        ServerHello;
            case certificate:         Certificate;
            case server_key_exchange: ServerKeyExchange;
            case certificate_request: CertificateRequest;
            case server_hello_done:   ServerHelloDone;
            case certificate_verify:  CertificateVerify;
            case client_key_exchange: ClientKeyExchange;
            case finished:            Finished;
            case session_ticket:      NewSessionTicket; /* NEW */
        } body;
    } Handshake;
    struct {
        uint32 ticket_lifetime_hint;
        opaque ticket<0..2^16-1>;
    } NewSessionTicket;

3.4. Interaction with TLS Session ID

 If a server is planning on issuing a SessionTicket to a client that
 does not present one, it SHOULD include an empty Session ID in the
 ServerHello.  If the server includes a non-empty session ID, then it
 is indicating intent to use stateful session resume.  If the client
 receives a SessionTicket from the server, then it discards any
 Session ID that was sent in the ServerHello.
 When presenting a ticket, the client MAY generate and include a
 Session ID in the TLS ClientHello.  If the server accepts the ticket
 and the Session ID is not empty, then it MUST respond with the same
 Session ID present in the ClientHello.  This allows the client to
 easily differentiate when the server is resuming a session from when
 it is falling back to a full handshake.  Since the client generates a
 Session ID, the server MUST NOT rely upon the Session ID having a
 particular value when validating the ticket.  If a ticket is
 presented by the client, the server MUST NOT attempt to use the

Salowey, et al. Standards Track [Page 8] RFC 4507 Stateless TLS Session Resumption May 2006

 Session ID in the ClientHello for stateful session resume.
 Alternatively, the client MAY include an empty Session ID in the
 ClientHello.  In this case, the client ignores the Session ID sent in
 the ServerHello and determines if the server is resuming a session by
 the subsequent handshake messages.

4. Recommended Ticket Construction

 This section describes a recommended format and protection for the
 ticket.  Note that the ticket is opaque to the client, so the
 structure is not subject to interoperability concerns, and
 implementations may diverge from this format.  If implementations do
 diverge from this format, they must take security concerns seriously.
 Clients MUST NOT examine the ticket under the assumption that it
 complies with this document.
 The server uses two different keys: one 128-bit key for AES [AES] in
 CBC mode [CBC] encryption and one 128-bit key for HMAC-SHA1 [RFC2104]
 [SHA1].
 The ticket is structured as follows:
    struct {
        opaque key_name[16];
        opaque iv[16];
        opaque encrypted_state<0..2^16-1>;
        opaque mac[20];
    } ticket;
 Here, key_name serves to identify a particular set of keys used to
 protect the ticket.  It enables the server to easily recognize
 tickets it has issued.  The key_name should be randomly generated to
 avoid collisions between servers.  One possibility is to generate new
 random keys and key_name every time the server is started.
 The actual state information in encrypted_state is encrypted using
 128-bit AES in CBC mode with the given IV.  The MAC is calculated
 using HMAC-SHA1 over key_name (16 octets)and IV (16 octets), followed
 by the length of the encrypted_state field (2 octets) and its
 contents (variable length).

Salowey, et al. Standards Track [Page 9] RFC 4507 Stateless TLS Session Resumption May 2006

    struct {
        ProtocolVersion protocol_version;
        CipherSuite cipher_suite;
        CompressionMethod compression_method;
        opaque master_secret[48];
        ClientIdentity client_identity;
        uint32 timestamp;
    } StatePlaintext;
    enum {
       anonymous(0),
       certificate_based(1),
       psk(2)
   } ClientAuthenticationType;
    struct {
        ClientAuthenticationType client_authentication_type;
        select (ClientAuthenticationType) {
            case anonymous: struct {};
            case certificate_based:
                ASN.1Cert certificate_list<0..2^24-1>;
            case psk:
                opaque psk_identity<0..2^16-1>; /* from [RFC4279] */
        }
     } ClientIdentity;
 The structure StatePlaintext stores the TLS session state including
 the master_secret.  The timestamp within this structure allows the
 TLS server to expire tickets.  To cover the authentication and key
 exchange protocols provided by TLS, the ClientIdentity structure
 contains the authentication type of the client used in the initial
 exchange (see ClientAuthenticationType).  To offer the TLS server
 with the same capabilities for authentication and authorization, a
 certificate list is included in case of public-key-based
 authentication.  The TLS server is therefore able to inspect a number
 of different attributes within these certificates.  A specific
 implementation might choose to store a subset of this information or
 additional information.  Other authentication mechanisms, such as
 Kerberos [RFC2712], would require different client identity data.

5. Security Considerations

 This section addresses security issues related to the usage of a
 ticket.  Tickets must be authenticated and encrypted to prevent
 modification or eavesdropping by an attacker.  Several attacks
 described below will be possible if this is not carefully done.

Salowey, et al. Standards Track [Page 10] RFC 4507 Stateless TLS Session Resumption May 2006

 Implementations should take care to ensure that the processing of
 tickets does not increase the chance of denial of service as
 described below.

5.1. Invalidating Sessions

 The TLS specification requires that TLS sessions be invalidated when
 errors occur.  [CSSC] discusses the security implications of this in
 detail.  In the analysis in this paper, failure to invalidate
 sessions does not pose a security risk.  This is because the TLS
 handshake uses a non-reversible function to derive keys for a session
 so information about one session does not provide an advantage to
 attack the master secret or a different session.  If a session
 invalidation scheme is used, the implementation should verify the
 integrity of the ticket before using the contents to invalidate a
 session to ensure that an attacker cannot invalidate a chosen
 session.

5.2. Stolen Tickets

 An eavesdropper or man-in-the-middle may obtain the ticket and
 attempt to use the ticket to establish a session with the server;
 however, since the ticket is encrypted and the attacker does not know
 the secret key, a stolen ticket does not help an attacker resume a
 session.  A TLS server MUST use strong encryption and integrity
 protection for the ticket to prevent an attacker from using a brute
 force mechanism to obtain the ticket's contents.

5.3. Forged Tickets

 A malicious user could forge or alter a ticket in order to resume a
 session, to extend its lifetime, to impersonate as another user, or
 to gain additional privileges.  This attack is not possible if the
 ticket is protected using a strong integrity protection algorithm
 such as a keyed HMAC-SHA1.

5.4. Denial of Service Attacks

 The key_name field defined in the recommended ticket format helps the
 server efficiently reject tickets that it did not issue.  However, an
 adversary could store or generate a large number of tickets to send
 to the TLS server for verification.  To minimize the possibility of a
 denial of service, the verification of the ticket should be
 lightweight (e.g., using efficient symmetric key cryptographic
 algorithms).

Salowey, et al. Standards Track [Page 11] RFC 4507 Stateless TLS Session Resumption May 2006

5.5. Ticket Protection Key Management

 A full description of the management of the keys used to protect the
 ticket is beyond the scope of this document.  A list of RECOMMENDED
 practices is given below.
 o  The keys should be generated securely following the randomness
    recommendations in [RFC4086].
 o  The keys and cryptographic protection algorithms should be at
    least 128 bits in strength.
 o  The keys should not be used for any other purpose than generating
    and verifying tickets.
 o  The keys should be changed regularly.
 o  The keys should be changed if the ticket format or cryptographic
    protection algorithms change.

5.6. Ticket Lifetime

 The TLS server controls the lifetime of the ticket.  Servers
 determine the acceptable lifetime based on the operational and
 security requirements of the environments in which they are deployed.
 The ticket lifetime may be longer than the 24-hour lifetime
 recommended in [RFC2246].  TLS clients may be given a hint of the
 lifetime of the ticket.  Since the lifetime of a ticket may be
 unspecified, a client has its own local policy that determines when
 it discards tickets.

5.7. Alternate Ticket Formats and Distribution Schemes

 If the ticket format or distribution scheme defined in this document
 is not used, then great care must be taken in analyzing the security
 of the solution.  In particular, if confidential information, such as
 a secret key, is transferred to the client, it MUST be done using
 secure communication so as to prevent attackers from obtaining or
 modifying the key.  Also, the ticket MUST have its integrity and
 confidentiality protected with strong cryptographic techniques to
 prevent a breach in the security of the system.

5.8. Identity Privacy, Anonymity, and Unlinkability

 This document mandates that the content of the ticket is
 confidentiality protected in order to avoid leakage of its content,
 such as user-relevant information.  As such, it prevents disclosure
 of potentially sensitive information carried within the ticket.
 The initial handshake exchange, which was used to obtain the ticket,
 might not provide identity confidentiality of the client based on the
 properties of TLS.  Another relevant security threat is the ability

Salowey, et al. Standards Track [Page 12] RFC 4507 Stateless TLS Session Resumption May 2006

 for an on-path adversary to observe multiple TLS handshakes where the
 same ticket is used and therefore to conclude that they belong to the
 same communication endpoints.  Application designers that use the
 ticket mechanism described in this document should consider that
 unlinkability [ANON] is not necessarily provided.
 While a full discussion of these topics is beyond the scope of this
 document, it should be noted that it is possible to issue a ticket
 using a TLS renegotiation handshake that occurs after a secure tunnel
 has been established by a previous handshake.  This may help address
 some privacy and unlinkability issues in some environments.

6. Acknowledgements

 The authors would like to thank the following people for their help
 with preparing and reviewing this document: Eric Rescorla, Mohamad
 Badra, Tim Dierks, Nelson Bolyard, Nancy Cam-Winget, David McGrew,
 Rob Dugal, Russ Housley, Amir Herzberg, Bernard Aboba, and members of
 the TLS working group.
 [CSSC] describes a solution that is very similar to the one described
 in this document and gives a detailed analysis of the security
 considerations involved.  [RFC2712] describes a mechanism for using
 Kerberos [RFC4120] in TLS ciphersuites, which helped inspire the use
 of tickets to avoid server state.  [EAP-FAST] makes use of a similar
 mechanism to avoid maintaining server state for the cryptographic
 tunnel.  [SC97] also investigates the concept of stateless sessions.

7. IANA Considerations

 IANA has assigned a TLS extension number of 35 to the SessionTicket
 TLS extension from the TLS registry of ExtensionType values defined
 in [RFC4366].
 IANA has assigned a TLS HandshakeType number 4 to the
 NewSessionTicket handshake type from the TLS registry of
 HandshakeType values defined in [RFC4346].

Salowey, et al. Standards Track [Page 13] RFC 4507 Stateless TLS Session Resumption May 2006

8. References

8.1. Normative References

 [RFC2119]   Bradner, S., "Key words for use in RFCs to Indicate
             Requirement Levels", BCP 14, RFC 2119, March 1997.
 [RFC2246]   Dierks, T. and C. Allen, "The TLS Protocol Version 1.0",
             RFC 2246, January 1999.
 [RFC4346]   Dierks, T. and E. Rescorla, "The Transport Layer Security
             (TLS) Protocol Version 1.1", RFC 4346, April 2006.
 [RFC4366]   Blake-Wilson, S., Nystrom, M., Hopwood, D., Mikkelsen,
             J., and T. Wright, "Transport Layer Security (TLS)
             Extensions", RFC 4366, April 2006.

8.2. Informative References

 [AES]       National Institute of Standards and Technology, "Advanced
             Encryption Standard (AES)", Federal Information
             Processing Standards (FIPS) Publication 197,
             November 2001.
 [ANON]      Pfitzmann, A. and M. Hansen, "Anonymity, Unlinkability,
             Unobservability, Pseudonymity, and Identity Management -
             A Consolidated Proposal for Terminology",
             http://dud.inf.tu-dresden.de/literatur/
             Anon_Terminology_v0.26-1.pdf, Draft 0.26, December 2005.
 [CBC]       National Institute of Standards and Technology,
             "Recommendation for Block Cipher Modes of Operation -
             Methods and Techniques", NIST Special Publication 800-
             38A, December 2001.
 [CSSC]      Shacham, H., Boneh, D., and E. Rescorla, "Client-side
             caching for TLS", Transactions on Information and System
             Security (TISSEC) , Volume 7, Issue 4, November 2004.
 [EAP-FAST]  Cam-Winget, N., McGrew, D., Salowey, J., and H. Zhou,
             "EAP Flexible Authentication via Secure Tunneling (EAP-
             FAST)", Work in Progress, April 2005.
 [RFC2104]   Krawczyk, H., Bellare, M., and R. Canetti, "HMAC: Keyed-
             Hashing for Message Authentication", RFC 2104,
             February 1997.

Salowey, et al. Standards Track [Page 14] RFC 4507 Stateless TLS Session Resumption May 2006

 [RFC2712]   Medvinsky, A. and M. Hur, "Addition of Kerberos Cipher
             Suites to Transport Layer Security (TLS)", RFC 2712,
             October 1999.
 [RFC4086]   Eastlake, D., Schiller, J., and S. Crocker, "Randomness
             Requirements for Security", BCP 106, RFC 4086, June 2005.
 [RFC4120]   Neuman, C., Yu, T., Hartman, S., and K. Raeburn, "The
             Kerberos Network Authentication Service (V5)", RFC 4120,
             July 2005.
 [RFC4279]   Eronen, P. and H. Tschofenig, "Pre-Shared Key
             Ciphersuites for Transport Layer Security (TLS)",
             RFC 4279, December 2005.
 [SC97]      Aura, T. and P. Nikander, "Stateless Connections",
             Proceedings of the First International Conference on
             Information and Communication Security (ICICS '97), 1997.
 [SHA1]      National Institute of Standards and Technology, "Secure
             Hash Standard (SHS)", Federal Information Processing
             Standards (FIPS) Publication 180-2, August 2002.

Salowey, et al. Standards Track [Page 15] RFC 4507 Stateless TLS Session Resumption May 2006

Authors' Addresses

 Joseph Salowey
 Cisco Systems
 2901 3rd Ave
 Seattle, WA  98121
 US
 EMail: jsalowey@cisco.com
 Hao Zhou
 Cisco Systems
 4125 Highlander Parkway
 Richfield, OH  44286
 US
 EMail: hzhou@cisco.com
 Pasi Eronen
 Nokia Research Center
 P.O. Box 407
 FIN-00045 Nokia Group
 Finland
 EMail: pasi.eronen@nokia.com
 Hannes Tschofenig
 Siemens
 Otto-Hahn-Ring 6
 Munich, Bayern  81739
 Germany
 EMail: Hannes.Tschofenig@siemens.com

Salowey, et al. Standards Track [Page 16] RFC 4507 Stateless TLS Session Resumption May 2006

Full Copyright Statement

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 contained in BCP 78, and except as set forth therein, the authors
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Salowey, et al. Standards Track [Page 17]

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