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Checking references for intended status: Informational ---------------------------------------------------------------------------- == Outdated reference: A later version (-43) exists of draft-ietf-tls-dtls13-32 ** Obsolete normative reference: RFC 5077 (Obsoleted by RFC 8446) == Outdated reference: A later version (-18) exists of draft-ietf-taps-impl-04 Summary: 1 error (**), 0 flaws (~~), 3 warnings (==), 1 comment (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group T. Pauly 3 Internet-Draft Apple Inc. 4 Intended status: Informational D. Schinazi 5 Expires: March 30, 2020 Google LLC 6 C. Wood 7 Apple Inc. 8 September 27, 2019 10 TLS Ticket Requests 11 draft-ietf-tls-ticketrequests-02 13 Abstract 15 TLS session tickets enable stateless connection resumption for 16 clients without server-side, per-client state. Servers vend an 17 arbitrary number of session tickets to clients, at their discretion, 18 upon connection establishment. Clients store and use tickets when 19 resuming future connections. This document describes a mechanism by 20 which clients may specify the desired number of tickets needed for 21 future connections. This extension aims to provide a means for 22 servers to determine the number of tickets to generate in order to 23 reduce ticket waste, while simultaneously priming clients for future 24 connection attempts. 26 Status of This Memo 28 This Internet-Draft is submitted in full conformance with the 29 provisions of BCP 78 and BCP 79. 31 Internet-Drafts are working documents of the Internet Engineering 32 Task Force (IETF). Note that other groups may also distribute 33 working documents as Internet-Drafts. The list of current Internet- 34 Drafts is at https://datatracker.ietf.org/drafts/current/. 36 Internet-Drafts are draft documents valid for a maximum of six months 37 and may be updated, replaced, or obsoleted by other documents at any 38 time. It is inappropriate to use Internet-Drafts as reference 39 material or to cite them other than as "work in progress." 41 This Internet-Draft will expire on March 30, 2020. 43 Copyright Notice 45 Copyright (c) 2019 IETF Trust and the persons identified as the 46 document authors. All rights reserved. 48 This document is subject to BCP 78 and the IETF Trust's Legal 49 Provisions Relating to IETF Documents 50 (https://trustee.ietf.org/license-info) in effect on the date of 51 publication of this document. Please review these documents 52 carefully, as they describe your rights and restrictions with respect 53 to this document. Code Components extracted from this document must 54 include Simplified BSD License text as described in Section 4.e of 55 the Trust Legal Provisions and are provided without warranty as 56 described in the Simplified BSD License. 58 Table of Contents 60 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 61 1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3 62 2. Use Cases . . . . . . . . . . . . . . . . . . . . . . . . . . 3 63 3. Ticket Requests . . . . . . . . . . . . . . . . . . . . . . . 4 64 4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4 65 5. Security Considerations . . . . . . . . . . . . . . . . . . . 5 66 6. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 5 67 7. References . . . . . . . . . . . . . . . . . . . . . . . . . 5 68 7.1. Normative References . . . . . . . . . . . . . . . . . . 5 69 7.2. Informative References . . . . . . . . . . . . . . . . . 6 70 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 6 72 1. Introduction 74 As per [RFC5077], and as described in [RFC8446], TLS servers send 75 clients an arbitrary number of session tickets at their own 76 discretion in NewSessionTicket messages. There are two limitations 77 with this design. First, servers choose some (often hard-coded) 78 number of tickets vended per connection. Second, clients do not have 79 a way of expressing their desired number of tickets, which may impact 80 future connection establishment. For example, clients may open 81 multiple TLS connections to the same server for HTTP, or may race TLS 82 connections across different network interfaces. The latter is 83 especially useful in transport systems that implement Happy Eyeballs 84 [RFC8305]. Since clients control connection concurrency and 85 resumption, a standard mechanism for requesting more than one ticket 86 is desirable. 88 This document specifies a new TLS extension - "ticket_request" - that 89 may be used by clients to express their desired number of session 90 tickets. Servers may use this extension as a hint of the number of 91 NewSessionTicket messages to vend. This extension is only applicable 92 to TLS 1.3 [RFC8446], DTLS 1.3 [I-D.ietf-tls-dtls13], and future 93 versions thereof. 95 1.1. Requirements Language 97 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 98 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 99 "OPTIONAL" in this document are to be interpreted as described in 100 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, 101 as shown here. 103 2. Use Cases 105 The ability to request one or more tickets is useful for a variety of 106 purposes: 108 o Parallel HTTP connections: To minimize ticket reuse while still 109 improving performance, it may be useful to use multiple, distinct 110 tickets when opening parallel connections. Clients must therefore 111 bound the number of parallel connections they initiate by the 112 number of tickets in their possession, or risk ticket re-use. 114 o Connection racing: Happy Eyeballs V2 [RFC8305] describes 115 techniques for performing connection racing. The Transport 116 Services Architecture implementation from [TAPS] also describes 117 how connections may race across interfaces and address families. 118 In cases where clients have early data to send and want to 119 minimize or avoid ticket re-use, unique tickets for each unique 120 connection attempt are useful. Moreover, as some servers may 121 implement single-use tickets (and even session ticket encryption 122 keys), distinct tickets will be needed to prevent premature ticket 123 invalidation by racing. 125 o Connection priming: In some systems, connections may be primed or 126 bootstrapped by a centralized service or daemon for faster 127 connection establishment. Requesting tickets on demand allows 128 such services to vend tickets to clients to use for accelerated 129 handshakes with early data. (Note that if early data is not 130 needed by these connections, this method SHOULD NOT be used. 131 Fresh handshakes SHOULD be performed instead.) 133 o Less ticket waste: Currently, TLS servers use application- 134 specific, and often implementation-specific, logic to determine 135 how many tickets to issue. By moving the burden of ticket count 136 to clients, servers do not generate wasteful tickets for clients. 137 Moreover, as ticket generation may involve expensive computation, 138 e.g., public key cryptographic operations, avoiding waste is 139 desirable. 141 o Decline resumption: Clients may indicate they have no intention of 142 resuming connections by sending a ticket request with count of 143 zero. 145 3. Ticket Requests 147 Clients may indicate to servers their desired number of tickets for a 148 single connection via the following "ticket_request" extension: 150 enum { 151 ticket_request(TBD), (65535) 152 } ExtensionType; 154 Clients may send this extension in ClientHello. It contains the 155 following structure: 157 struct { 158 uint8 count; 159 } TicketRequestContents; 161 count The number of tickets desired by the client. 163 A supporting server MAY vend TicketRequestContents.count 164 NewSessionTicket messages to a requesting client, and SHOULD NOT send 165 more than TicketRequestContents.count NewSessionTicket messages to a 166 requesting client. Servers SHOULD place a limit on the number of 167 tickets they are willing to vend to clients. Thus, the number of 168 NewSessionTicket messages sent should be the minimum of the server's 169 self-imposed limit and TicketRequestContents.count. Servers MUST NOT 170 send more than 255 tickets to clients. 172 Servers that support ticket requests MUST NOT echo "ticket_request" 173 in the EncryptedExtensions message. A client MUST abort the 174 connection with an "illegal_parameter" alert if the "ticket_request" 175 extension is present in the EncryptedExtensions message. 177 Clients MUST NOT change the value of TicketRequestContents.count in 178 second ClientHello messages sent in response to a HelloRetryRequest. 180 4. IANA Considerations 182 IANA is requested to Create an entry, ticket_request(TBD), in the 183 existing registry for ExtensionType (defined in [RFC8446]), with "TLS 184 1.3" column values being set to "CH", and "Recommended" column being 185 set to "Yes". 187 5. Security Considerations 189 Ticket re-use is a security and privacy concern. Moreover, clients 190 must take care when pooling tickets as a means of avoiding or 191 amortizing handshake costs. If servers do not rotate session ticket 192 encryption keys frequently, clients may be encouraged to obtain and 193 use tickets beyond common lifetime windows of, e.g., 24 hours. 194 Despite ticket lifetime hints provided by servers, clients SHOULD 195 dispose of pooled tickets after some reasonable amount of time that 196 mimics the ticket rotation period. 198 6. Acknowledgments 200 The authors would like to thank David Benjamin, Eric Rescorla, Nick 201 Sullivan, Martin Thomson, and other members of the TLS Working Group 202 for discussions on earlier versions of this draft. 204 7. References 206 7.1. Normative References 208 [I-D.ietf-tls-dtls13] 209 Rescorla, E., Tschofenig, H., and N. Modadugu, "The 210 Datagram Transport Layer Security (DTLS) Protocol Version 211 1.3", draft-ietf-tls-dtls13-32 (work in progress), July 212 2019. 214 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 215 Requirement Levels", BCP 14, RFC 2119, 216 DOI 10.17487/RFC2119, March 1997, 217 . 219 [RFC5077] Salowey, J., Zhou, H., Eronen, P., and H. Tschofenig, 220 "Transport Layer Security (TLS) Session Resumption without 221 Server-Side State", RFC 5077, DOI 10.17487/RFC5077, 222 January 2008, . 224 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 225 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 226 May 2017, . 228 [RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol 229 Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018, 230 . 232 7.2. Informative References 234 [RFC8305] Schinazi, D. and T. Pauly, "Happy Eyeballs Version 2: 235 Better Connectivity Using Concurrency", RFC 8305, 236 DOI 10.17487/RFC8305, December 2017, 237 . 239 [TAPS] Brunstrom, A., Pauly, T., Enghardt, T., Grinnemo, K., 240 Jones, T., Tiesel, P., Perkins, C., and M. Welzl, 241 "Implementing Interfaces to Transport Services", draft- 242 ietf-taps-impl-04 (work in progress), July 2019. 244 Authors' Addresses 246 Tommy Pauly 247 Apple Inc. 248 One Apple Park Way 249 Cupertino, California 95014 250 United States of America 252 Email: tpauly@apple.com 254 David Schinazi 255 Google LLC 256 1600 Amphitheatre Parkway 257 Mountain View, California 94043 258 United States of America 260 Email: dschinazi.ietf@gmail.com 262 Christopher A. Wood 263 Apple Inc. 264 One Apple Park Way 265 Cupertino, California 95014 266 United States of America 268 Email: cawood@apple.com