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2 Web Security C. Evans
3 Internet-Draft C. Palmer
4 Intended status: Standards Track R. Sleevi
5 Expires: October 31, 2014 Google, Inc.
6 April 29, 2014
8 Public Key Pinning Extension for HTTP
9 draft-ietf-websec-key-pinning-12
11 Abstract
13 This memo describes an extension to the HTTP protocol allowing web
14 host operators to instruct user agents (UAs) to remember ("pin") the
15 hosts' cryptographic identities for a given period of time. During
16 that time, UAs will require that the host present a certificate chain
17 including at least one Subject Public Key Info structure whose
18 fingerprint matches one of the pinned fingerprints for that host. By
19 effectively reducing the number of authorities who can authenticate
20 the domain during the lifetime of the pin, pinning may reduce the
21 incidence of man-in-the-middle attacks due to compromised
22 Certification Authorities.
24 Status of This Memo
26 This Internet-Draft is submitted in full conformance with the
27 provisions of BCP 78 and BCP 79.
29 Internet-Drafts are working documents of the Internet Engineering
30 Task Force (IETF). Note that other groups may also distribute
31 working documents as Internet-Drafts. The list of current Internet-
32 Drafts is at http://datatracker.ietf.org/drafts/current/.
34 Internet-Drafts are draft documents valid for a maximum of six months
35 and may be updated, replaced, or obsoleted by other documents at any
36 time. It is inappropriate to use Internet-Drafts as reference
37 material or to cite them other than as "work in progress."
39 This Internet-Draft will expire on October 31, 2014.
41 Copyright Notice
43 Copyright (c) 2014 IETF Trust and the persons identified as the
44 document authors. All rights reserved.
46 This document is subject to BCP 78 and the IETF Trust's Legal
47 Provisions Relating to IETF Documents
48 (http://trustee.ietf.org/license-info) in effect on the date of
49 publication of this document. Please review these documents
50 carefully, as they describe your rights and restrictions with respect
51 to this document. Code Components extracted from this document must
52 include Simplified BSD License text as described in Section 4.e of
53 the Trust Legal Provisions and are provided without warranty as
54 described in the Simplified BSD License.
56 Table of Contents
58 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
59 1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3
60 2. Server and Client Behavior . . . . . . . . . . . . . . . . . 3
61 2.1. Response Header Field Syntax . . . . . . . . . . . . . . 3
62 2.1.1. The max-age Directive . . . . . . . . . . . . . . . . 5
63 2.1.2. The includeSubDomains Directive . . . . . . . . . . . 5
64 2.1.3. The report-uri Directive . . . . . . . . . . . . . . 6
65 2.1.4. Examples . . . . . . . . . . . . . . . . . . . . . . 6
66 2.2. Server Processing Model . . . . . . . . . . . . . . . . . 7
67 2.2.1. HTTP-over-Secure-Transport Request Type . . . . . . . 7
68 2.2.2. HTTP Request Type . . . . . . . . . . . . . . . . . . 8
69 2.3. User Agent Processing Model . . . . . . . . . . . . . . . 8
70 2.3.1. Public-Key-Pins Response Header Field Processing . . 8
71 2.3.2. Interaction of Public-Key-Pins and Public-Key-Pins-
72 Report-Only . . . . . . . . . . . . . . . . . . . . . 9
73 2.3.3. Noting a Pinned Host - Storage Model . . . . . . . . 10
74 2.3.4. HTTP-Equiv Element Attribute . . . . . . . . . 11
75 2.4. Semantics of Pins . . . . . . . . . . . . . . . . . . . . 11
76 2.5. Noting Pins . . . . . . . . . . . . . . . . . . . . . . . 12
77 2.6. Validating Pinned Connections . . . . . . . . . . . . . . 12
78 2.7. Interactions With Preloaded Pin Lists . . . . . . . . . . 13
79 2.8. Pinning Self-Signed End Entities . . . . . . . . . . . . 14
80 3. Reporting Pin Validation Failure . . . . . . . . . . . . . . 14
81 4. Security Considerations . . . . . . . . . . . . . . . . . . . 17
82 4.1. Maximum max-age . . . . . . . . . . . . . . . . . . . . . 18
83 4.2. Using includeSubDomains Safely . . . . . . . . . . . . . 18
84 4.3. Backup Pins . . . . . . . . . . . . . . . . . . . . . . . 19
85 5. Privacy Considerations . . . . . . . . . . . . . . . . . . . 20
86 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 21
87 7. Usability Considerations . . . . . . . . . . . . . . . . . . 21
88 8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 21
89 9. What's Changed . . . . . . . . . . . . . . . . . . . . . . . 22
90 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 22
91 10.1. Normative References . . . . . . . . . . . . . . . . . . 23
92 10.2. Informative References . . . . . . . . . . . . . . . . . 24
93 Appendix A. Fingerprint Generation . . . . . . . . . . . . . . . 24
94 Appendix B. Deployment Guidance . . . . . . . . . . . . . . . . 24
95 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 25
97 1. Introduction
99 We propose a new HTTP header to enable a web host to express to user
100 agents (UAs) which Subject Public Key Info (SPKI) structure(s) UAs
101 SHOULD expect to be present in the host's certificate chain in future
102 connections using TLS (see [RFC5246]). We call this "public key
103 pinning". At least one UA (Google Chrome) has experimented with the
104 idea by shipping with a user-extensible embedded set of Pins.
105 Although effective, this does not scale. This proposal addresses the
106 scale problem.
108 Deploying public key pinning safely will require operational and
109 organizational maturity due to the risk that hosts may make
110 themselves unavailable by pinning to a SPKI that becomes invalid.
111 (See Section 4.) We believe that, with care, host operators can
112 greatly reduce the risk of MITM attacks and other false-
113 authentication problems for their users without incurring undue risk.
115 We intend for hosts to use public key pinning together with HSTS
116 ([RFC6797]), but is possible to pin keys without requiring HSTS.
118 This draft is being discussed on the WebSec Working Group mailing
119 list, websec@ietf.org.
121 1.1. Requirements Language
123 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
124 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
125 document are to be interpreted as described in RFC 2119 [RFC2119].
127 2. Server and Client Behavior
129 2.1. Response Header Field Syntax
131 The Public-Key-Pins HTTP response header field (PKP header field)
132 indicates to a UA that it should perform Pin Validation (Section 2.6)
133 in regards to the host emitting the response message containing this
134 header field, and provides the necessary information for the UA to do
135 so.
137 Figure 1 describes the ABNF (Augmented Backus-Naur Form) syntax of
138 the header field. It is based on the Generic Grammar defined in
139 Section 2 of [RFC2616] (which includes a notion of "implied linear
140 whitespace", also known as "implied *LWS").
142 Public-Key-Pins =
143 "Public-Key-Pins" ":" [ directive ] *( ";" [ directive ] )
144 Public-Key-Pins-Report-Only =
145 "Public-Key-Pins-Report-Only" ":" [ directive ] *( ";" [ directive ] )
147 directive = simple-directive
148 / pin-directive
150 simple-directive = directive-name [ "=" directive-value ]
151 directive-name = token
152 directive-value = token
153 / quoted-string
155 pin-directive = "pin-" token "=" quoted-string
157 Figure 1: HPKP Header Syntax
159 token and quoted-string are used as defined in [RFC2616],
160 Section 2.2.
162 The directives defined in this specification are described below.
163 The overall requirements for directives are:
165 1. The order of appearance of directives is not significant.
167 2. All simple-directives MUST appear only once in a PKP header
168 field. Directives are either optional or required, as stipulated
169 in their definitions.
171 3. Directive names are case-insensitive.
173 4. UAs MUST ignore any PKP header fields containing directives, or
174 other header field value data, that do not conform to the syntax
175 defined in this specification.
177 5. If a PKP header field contains any directive(s) the UA does not
178 recognize, the UA MUST ignore those directives.
180 6. If the PKP header field otherwise satisfies the above
181 requirements (1 through 5), the UA MUST process the directives it
182 recognizes.
184 Additional directives extending the semantic functionality of the PKP
185 header field can be defined in other specifications, with a registry
186 (having an IANA policy definition of IETF Review [RFC2616]) defined
187 for them at such time. Such future directives will be ignored by UAs
188 implementing only this specification, as well as by generally non-
189 conforming UAs.
191 In the pin-directive, the token is the name of a cryptographic hash
192 algorithm, and MUST be "sha256". (In the future, additional hash
193 algorithms MAY be registered and used.) The quoted-string is a
194 sequence of base 64 digits: the base 64-encoded SPKI Fingerprint
195 ([RFC4648]). See Section 2.4.
197 The UA MUST ignore pin-directives with tokens naming hash algorithms
198 it does not recognize. If the set of remaining effective pin-
199 directives is empty, and if the connection passed Pin Validation with
200 the UA's existing noted pins for the Host (i.e. the Host is a Known
201 Pinned Host), the UA MUST cease to consider the Host as a Known
202 Pinned Host. (I.e. the UA should fail open.) The UA SHOULD indicate
203 to users that the Host is no longer a Known Pinned Host.
205 2.1.1. The max-age Directive
207 The REQUIRED "max-age" directive specifies the number of seconds,
208 after the reception of the PKP header field, during which the UA
209 SHOULD regard the host (from whom the message was received) as a
210 Known Pinned Host. The delta-seconds production is specified in
211 [RFC2616].
213 The syntax of the max-age directive's REQUIRED value (after quoted-
214 string unescaping, if necessary) is defined as:
216 max-age-value = delta-seconds
217 delta-seconds = 1*DIGIT
219 Figure 2: max-age Value Syntax
221 delta-seconds is used as defined in [RFC2616], Section 3.3.2.
223 NOTE: A max-age value of zero (i.e., "max-age=0") signals the UA to
224 cease regarding the host as a Known Pinned Host, including the
225 includeSubDomains directive (if asserted for that Known Pinned Host).
226 See Section 2.3.1.
228 2.1.2. The includeSubDomains Directive
230 The OPTIONAL "includeSubDomains" directive is a valueless directive
231 which, if present (i.e., it is "asserted"), signals to the UA that
232 the Pinning Policy applies to this Pinned Host as well as any
233 subdomains of the host's domain name.
235 2.1.3. The report-uri Directive
237 The OPTIONAL "report-uri" directive indicates the URI to which the UA
238 SHOULD report Pin Validation failures (Section 2.6). The UA POSTs
239 the reports to the given URI as described in Section 3.
241 When used in the Public-Key-Pins or Public-Key-Pins-Report-Only
242 header, the presence of a report-uri directive indicates to the UA
243 that in the event of Pin Validation failure it SHOULD POST a report
244 to the report-uri. If the header is Public-Key-Pins, the UA should
245 do this in addition to terminating the connection (as described in
246 Section 2.6).
248 Hosts may set report-uris that use HTTP, HTTPS, or other schemes. If
249 the scheme in the report-uri is HTTPS, UAs MUST perform Pinning
250 Validation when the host in the report-uri is a Known Pinned Host;
251 similarly, UAs MUST apply HSTS if the host in the report-uri is a
252 Known HSTS Host.
254 Note that the report-uri need not necessarily be in the same Internet
255 domain or web origin as the Known Pinned Host.
257 UAs SHOULD make their best effort to report Pin Validation failures
258 to the report-uri, but may fail to report in exceptional conditions.
259 For example, if connecting the report-uri itself incurs a Pinning
260 Validation failure or other certificate validation failure, the UA
261 MUST cancel the connection (and MAY attempt to re-send the report
262 later). Similarly, if Known Pinned Host A sets a report-uri
263 referring to Known Pinned Host B, and if B sets a report-uri
264 referring to A, and if both hosts fail Pin Validation, the UA SHOULD
265 detect and break the loop by failing to send reports to and about
266 those hosts.
268 UAs SHOULD limit the rate at which they send reports. For example,
269 it is unnecessary to send the same report to the same report-uri more
270 than once.
272 UAs MUST NOT send a report if the Host is not already a Known Pinned
273 Host. (I.e., the UA's first connection to a Host fails Pin
274 Validation.) The reason for this is so that a potential active
275 network attacker cannot learn about a UA's certificate validation and
276 Pin Validation procedures and state.
278 2.1.4. Examples
280 Figure 3 shows some example response header fields using the Pins
281 extension (folded for clarity).
283 Public-Key-Pins: max-age=3000;
284 pin-sha256="d6qzRu9zOECb90Uez27xWltNsj0e1Md7GkYYkVoZWmM=";
285 pin-sha256="E9CZ9INDbd+2eRQozYqqbQ2yXLVKB9+xcprMF+44U1g=";
287 Public-Key-Pins: max-age=2592000;
288 pin-sha256="E9CZ9INDbd+2eRQozYqqbQ2yXLVKB9+xcprMF+44U1g=";
289 pin-sha256="LPJNul+wow4m6DsqxbninhsWHlwfp0JecwQzYpOLmCQ="
291 Public-Key-Pins: max-age=2592000;
292 pin-sha256="E9CZ9INDbd+2eRQozYqqbQ2yXLVKB9+xcprMF+44U1g=";
293 pin-sha256="LPJNul+wow4m6DsqxbninhsWHlwfp0JecwQzYpOLmCQ=";
294 report-uri="http://example.com/pkp-report"
296 Public-Key-Pins-Report-Only: max-age=2592000;
297 pin-sha256="E9CZ9INDbd+2eRQozYqqbQ2yXLVKB9+xcprMF+44U1g=";
298 pin-sha256="LPJNul+wow4m6DsqxbninhsWHlwfp0JecwQzYpOLmCQ=";
299 report-uri="http://example.com/pkp-report"
301 Public-Key-Pins:
302 pin-sha256="d6qzRu9zOECb90Uez27xWltNsj0e1Md7GkYYkVoZWmM=";
303 pin-sha256="LPJNul+wow4m6DsqxbninhsWHlwfp0JecwQzYpOLmCQ=";
304 max-age=259200
306 Public-Key-Pins:
307 pin-sha256="d6qzRu9zOECb90Uez27xWltNsj0e1Md7GkYYkVoZWmM=";
308 pin-sha256="E9CZ9INDbd+2eRQozYqqbQ2yXLVKB9+xcprMF+44U1g=";
309 pin-sha256="LPJNul+wow4m6DsqxbninhsWHlwfp0JecwQzYpOLmCQ=";
310 max-age=10000; includeSubDomains
312 Figure 3: HPKP Header Examples
314 2.2. Server Processing Model
316 This section describes the processing model that Pinned Hosts
317 implement. The model comprises two facets: the processing rules for
318 HTTP request messages received over a secure transport (e.g. TLS
319 [RFC5246]); and the processing rules for HTTP request messages
320 received over non-secure transports, such as TCP.
322 2.2.1. HTTP-over-Secure-Transport Request Type
324 When replying to an HTTP request that was conveyed over a secure
325 transport, a Pinned Host SHOULD include in its response exactly one
326 PKP header field that MUST satisfy the grammar specified above in
327 Section 2.1.
329 Establishing a given host as a Known Pinned Host, in the context of a
330 given UA, MAY be accomplished over the HTTP protocol, which is in
331 turn running over secure transport, by correctly returning (per this
332 specification) at least one valid PKP header field to the UA. Other
333 mechanisms, such as a client-side pre-loaded Known Pinned Host list
334 MAY also be used.
336 2.2.2. HTTP Request Type
338 Pinned Hosts SHOULD NOT include the PKP header field in HTTP
339 responses conveyed over non-secure transport. UAs MUST ignore any
340 PKP header received in an HTTP response conveyed over non-secure
341 transport.
343 2.3. User Agent Processing Model
345 This section describes the HTTP Public Key Pinning processing model
346 for UAs.
348 The UA processing model relies on parsing domain names. Note that
349 internationalized domain names SHALL be canonicalized according to
350 the scheme in Section 10 of [RFC6797].
352 2.3.1. Public-Key-Pins Response Header Field Processing
354 If the UA receives, over a secure transport, an HTTP response that
355 includes a PKP header field conforming to the grammar specified in
356 Section 2.1, and there are no underlying secure transport errors or
357 warnings (see Section 2.5), the UA MUST either:
359 o Note the host as a Known Pinned Host if it is not already so noted
360 (see Section 2.3.3),
362 or,
364 o Update the UA's cached information for the Known Pinned Host if
365 any of of the max-age, includeSubDomains, or report-uri header
366 field value directives convey information different than that
367 already maintained by the UA.
369 o The max-age value is essentially a "time to live" value relative
370 to the time of the most recent observation of the PKP header
371 field.
373 o If the max-age header field value token has a value of 0, the UA
374 MUST remove its cached Pinning Policy information (including the
375 includeSubDomains directive, if asserted) if the Pinned Host is
376 Known, or, MUST NOT note this Pinned Host if it is not yet Known.
378 o If a UA receives more than one PKP header field in an HTTP
379 response message over secure transport, then the UA MUST process
380 only the first such header field.
382 Otherwise:
384 o If the UA receives the HTTP response over insecure transport, or
385 if the PKP header is not a Valid Pinning Header (see Section 2.5),
386 the UA MUST ignore any present PKP header field(s).
388 o The UA MUST ignore any PKP header fields not conforming to the
389 grammar specified in Section 2.1.
391 2.3.2. Interaction of Public-Key-Pins and Public-Key-Pins-Report-Only
393 A server MAY set both the Public-Key-Pins and Public-Key-Pins-Report-
394 Only headers simultaneously. The headers do not interact with one
395 another but the UA MUST process the Public-Key-Pins header and SHOULD
396 process both.
398 The Public-Key-Pins header is processed as according to
399 Section 2.3.1.
401 When the Public-Key-Pins-Report-Only header is used with a report-
402 uri, the UA SHOULD POST reports for Pin Validation failures to the
403 indicated report-uri, although the UA MUST NOT enforce Pin
404 Validation. That is, in the event of Pin Validation failure when the
405 host has set the Public-Key-Pins-Report-Only header, the UA performs
406 Pin Validation only to check whether or not it should POST a report,
407 but not for causing connection failure.
409 Note: There is no purpose to using the Public-Key-Pins-Report-Only
410 header without the report-uri directive. User Agents MAY discard
411 such headers without interpretting them further.
413 If a Host sets the Public-Key-Pins-Report-Only header, the UA SHOULD
414 note the Pins and directives given in the Public-Key-Pins-Report-Only
415 header as specified by the max-age directive. If the UA does note
416 the Pins and directives in the Public-Key-Pins-Report-Only header it
417 SHOULD evaluate the specified policy and SHOULD report any would-be
418 Pin Validation failures that would occur if the report-only policy
419 were enforced.
421 If a Host sets both the Public-Key-Pins header and the Public-Key-
422 Pins-Report-Only header, the UA MUST note and enforce Pin Validation
423 as specified by the Public-Key-Pins header, and SHOULD note the Pins
424 and directives given in the Public-Key-Pins-Report-Only header. If
425 the UA does note the Pins and directives in the Public-Key-Pins-
426 Report-Only header it SHOULD evaluate the specified policy and SHOULD
427 report any would-be Pin Validation failures that would occur if the
428 report-only policy were enforced.
430 2.3.3. Noting a Pinned Host - Storage Model
432 The Effective Pin Date of a Known Pinned Host is the time that the UA
433 observed a Valid Pinning Header for the host. The Effective
434 Expiration Date of a Known Pinned Host is the Effective Pin Date plus
435 the max-age. A Known Pinned Host is "expired" if the Effective
436 Expiration Date refers to a date in the past. The UA MUST ignore all
437 expired Known Pinned Hosts from its cache if, at any time, an expired
438 Known Pinned Host exists in the cache.
440 If the substring matching the host production from the Request-URI
441 (of the message to which the host responded) syntactically matches
442 the IP-literal or IPv4address productions from Section 3.2.2 of
443 [RFC3986], then the UA MUST NOT note this host as a Known Pinned
444 Host.
446 Otherwise, if the substring does not congruently match a Known Pinned
447 Host's domain name, per the matching procedure specified in
448 Section 8.2 of [RFC6797], then the UA MUST note this host as a Known
449 Pinned Host, caching the Pinned Host's domain name and noting along
450 with it the Effective Expiration Date (or enough information to
451 calculate it, i.e. the Effective Pin Date and the value of the max-
452 age directive), whether or not the includeSubDomains directive is
453 asserted, the value of the report-uri directive (if present). If any
454 other metadata from optional or future PKP header directives is
455 present in the Valid Pinning Header, the UA MAY note them if it
456 understands them, and need not note them if it does not understand
457 them.
459 UAs MAY set an upper limit on the value of max-age, so that UAs that
460 have noted erroneous Pins (whether by accident or due to attack) have
461 some chance of recovering over time. If the server sets a max-age
462 greater than the UA's upper limit, the UA MAY behave as if the server
463 set the max-age to the UA's upper limit. For example, if the UA caps
464 max-age at 5184000 seconds (60 days), and a Pinned Host sets a max-
465 age directive of 90 days in its Valid Pinning Header, the UA MAY
466 behave as if the max-age were effectively 60 days. (One way to
467 achieve this behavior is for the UA to simply store a value of 60
468 days instead of the 90 day value provided by the Pinned Host.) For
469 UA implementation guidance on how to select a maximum max-age, see
470 Section 4.1.
472 The UA MUST NOT modify any pinning metadata of any superdomain
473 matched Known Pinned Host.
475 2.3.4. HTTP-Equiv Element Attribute
477 UAs MUST NOT heed http-equiv="Public-Key-Pins" or http-equiv="Public-
478 Key-Pins-Report-Only" attribute settings on elements
479 [W3C.REC-html401-19991224] in received content.
481 2.4. Semantics of Pins
483 An SPKI Fingerprint is defined as the output of a known cryptographic
484 hash algorithm whose input is the DER-encoded ASN.1 representation of
485 the SubjectPublicKeyInfo (SPKI) field of an X.509 certificate. A Pin
486 is defined as the combination of the known algorithm identifier and
487 the SPKI Fingerprint computed using that algorithm.
489 The SPKI Fingerprint is encoded in base 64 for use in an HTTP header.
490 (See [RFC4648].)
492 In this version of the specification, the known cryptographic hash
493 algorithm is SHA-256, identified as "sha256" ([RFC4634]). (Future
494 versions of this specification may add new algorithms and deprecate
495 old ones.) UAs MUST ignore Pins for which they do not recognize the
496 algorithm identifier. UAs MUST continue to process the rest of a PKP
497 response header field and note Pins for algorithms they do recognize;
498 UAs MUST recognize "sha256".
500 Figure 4 reproduces the definition of the SubjectPublicKeyInfo
501 structure in [RFC5280].
503 SubjectPublicKeyInfo ::= SEQUENCE {
504 algorithm AlgorithmIdentifier,
505 subjectPublicKey BIT STRING }
507 AlgorithmIdentifier ::= SEQUENCE {
508 algorithm OBJECT IDENTIFIER,
509 parameters ANY DEFINED BY algorithm OPTIONAL }
511 Figure 4: SPKI Definition
513 If the SubjectPublicKeyInfo of a certificate is incomplete when taken
514 in isolation, such as when holding a DSA key without domain
515 parameters, a public key pin cannot be formed.
517 We pin public keys, rather than entire certificates, to enable
518 operators to generate new certificates containing old public keys
519 (see [why-pin-key]).
521 See Appendix A for an example non-normative program that generates
522 SPKI Fingerprints from SubjectPublicKeyInfo fields in certificates.
524 2.5. Noting Pins
526 Upon receipt of the Public-Key-Pins response header field, the UA
527 notes the host as a Pinned Host, storing the Pins and their
528 associated directives in non-volatile storage (for example, along
529 with the HSTS metadata). The Pins and their associated directives
530 are collectively known as Pinning Metadata.
532 The UA MUST observe these conditions when noting a Host:
534 o The UA MUST note the Pins if and only if it received the Public-
535 Key-Pins response header field over an error-free TLS connection.
536 If the host is a Pinned Host, this includes the validation added
537 in Section 2.6.
539 o The UA MUST note the Pins if and only if the TLS connection was
540 authenticated with a certificate chain containing at least one of
541 the SPKI structures indicated by at least one of the given SPKI
542 Fingerprints. (See Section 2.6.)
544 o The UA MUST note the Pins if and only if the given set of Pins
545 contains at least one Pin that does NOT refer to an SPKI in the
546 certificate chain. (That is, the host must set a Backup Pin; see
547 Section 4.3.)
549 If the Public-Key-Pins response header field does not meet all three
550 of these criteria, the UA MUST NOT note the host as a Pinned Host. A
551 Public-Key-Pins response header field that meets all these critera is
552 known as a Valid Pinning Header.
554 Whenever a UA receives a Valid Pinning Header, it MUST set its
555 Pinning Metadata to the exact Pins, max-age, and (if any) report-uri
556 given in the most recently received Valid Pinning Header.
558 For forward compatibility, the UA MUST ignore any unrecognized
559 Public-Key-Pins header directives, while still processing those
560 directives it does recognize. Section 2.1 specifies the directives
561 max-age, Pins, includeSubDomains, and report-uri but future
562 specifications and implementations might use additional directives.
564 2.6. Validating Pinned Connections
566 When a UA connects to a Pinned Host, if the TLS connection has
567 errors, the UA MUST terminate the connection without allowing the
568 user to proceed anyway. (This behavior is the same as that required
569 by [RFC6797].)
570 If the connection has no errors, then the UA will determine whether
571 to apply a new, additional correctness check: Pin Validation. A UA
572 SHOULD perform Pin Validation whenever connecting to a Known Pinned
573 Host, but MAY allow Pin Validation to be disabled for Hosts according
574 to local policy. For example, a UA may disable Pin Validation for
575 Pinned Hosts whose validated certificate chain terminates at a user-
576 defined trust anchor, rather than a trust anchor built-in to the UA.
578 To perform Pin Validation, the UA will compute the SPKI Fingerprints
579 for each certificate in the Pinned Host's validated certificate
580 chain, using each supported hash algorithm for each certificate.
581 (For the purposes of Pin Validation, the UA MUST ignore certificates
582 whose SPKI cannot be taken in isolation, and MUST ignore superfluous
583 certificates in the chain that do not form part of the validating
584 chain.) The UA will then check that the set of these SPKI
585 Fingerprints intersects the set of SPKI Fingerprints in that Pinned
586 Host's Pinning Metadata. If there is set intersection, the UA
587 continues with the connection as normal. Otherwise, the UA MUST
588 treat this Pin Failure as a non-recoverable error. Any procedure
589 that matches the results of this Pin Validation procedure is
590 considered equivalent.
592 Note that, although the UA has previously received Pins at the HTTP
593 layer, it can and MUST perform Pin Validation at the TLS layer,
594 before beginning an HTTP conversation over the TLS channel. The TLS
595 layer thus evaluates TLS connections with pinning information the UA
596 received previously, regardless of mechanism: statically preloaded,
597 via HTTP header, or some other means (possibly in the TLS layer
598 itself).
600 2.7. Interactions With Preloaded Pin Lists
602 UAs MAY choose to implement additional sources of pinning
603 information, such as through built-in lists of pinning information.
604 Such UAs SHOULD allow users to override such additional sources,
605 including disabling them from consideration.
607 UAs that support additional sources of pinning information MUST use
608 the most recently observed pinning information when performing Pin
609 Validation for a host. The most recently observed pinning
610 information is determined based upon the most recent Effective Pin
611 Date, as described in Section 2.3.3. The Effective Pin Date of
612 built-in pin lists is UA implementation-defined.
614 If the result of noting a Valid Pinning Header is to disable pinning
615 for the host, such as through supplying a max-age directive with a
616 value of 0, UAs MUST allow this new information to override any other
617 pinning data. That is, a host must be able to un-pin itself, even in
618 the presence of built-in Pins.
620 Example: A UA may ship with a pre-configured list of Pins that are
621 collected from past observations of Valid Pinning Headers supplied by
622 hosts. In such a solution, the pre-configured list should track when
623 the Valid Pinning Header was last observed, in order to permit site
624 operators to later update the value by supplying a new Valid Pinning
625 Header. Updates to such a pre-configured list should not update the
626 Effective Pin Dates for each host unless the list vendor has actually
627 observed a more recent header. This is to prevent situations where
628 updating the Effective Pin Date on a pre-configured list of Pins may
629 effectively extend the max-age beyond the site operator's stated
630 policy.
632 Example: A UA may ship with a pre-configured list of Pins that are
633 collected through out-of-band means, such as direct contact with the
634 site operator. In such a solution, the site operator accepts
635 responsibility for keeping the configured Valid Pinning Header in
636 sync with the vendor's list, allowing the UA vendor to have each
637 update to the list be treated as as an update of the Effective Pin
638 Date.
640 2.8. Pinning Self-Signed End Entities
642 If UAs accept hosts that authenticate themselves with self-signed end
643 entity certificates, they MAY also allow hosts to pin the public keys
644 in such certificates. The usability and security implications of
645 this practice are outside the scope of this specification.
647 3. Reporting Pin Validation Failure
649 When a Known Pinned Host has set the report-uri directive, the UA
650 SHOULD report Pin Validation failures to the indicated URI. The UA
651 does this by POSTing a JSON ([RFC4627]) message to the URI; the JSON
652 message takes this form:
654 {
655 "date-time": date-time,
656 "hostname": hostname,
657 "port": port,
658 "effective-expiration-date": expiration-date,
659 "include-subdomains": include-subdomains,
660 "served-certificate-chain": [
661 pem1, ... pemN
662 ],
663 "validated-certificate-chain": [
664 pem1, ... pemN
665 ],
666 "known-pins": [
667 known-pin1, ... known-pinN
668 ]
669 }
671 Figure 5: JSON Report Format
673 Whitespace outside of quoted strings is not significant. The key/
674 value pairs may appear in any order, but each SHOULD appear only
675 once.
677 The date-time indicates the time the UA observed the Pin Validation
678 failure. It is provided as a string formatted according to
679 Section 5.6, "Internet Date/Time Format", of [RFC3339].
681 The hostname is the hostname to which the UA made the original
682 request that failed Pin Validation. It is provided as a string.
684 The port is the port to which the UA made the original request that
685 failed Pin Validation. It is provided either as a string or as an
686 integer.
688 The effective-expiration-date is the Effective Expiration Date for
689 the noted Pins. It is provided as a string formatted according to
690 Section 5.6, "Internet Date/Time Format", of [RFC3339].
692 include-subdomains indicates whether or not the UA has noted the
693 includeSubDomains directive for the Known Pinned Host. It is
694 provided as one of the JSON identifiers true or false.
696 The served-certificate-chain is the certificate chain, as served by
697 the Known Pinned Host during TLS session setup. It is provided as an
698 array of strings; each string pem1, ... pemN is the PEM
699 representation of each X.509 certificate as described in
700 [I-D.josefsson-pkix-textual].
702 The validated-certificate-chain is the certificate chain, as
703 constructed by the UA during certificate chain verification. (This
704 may differ from the served-certificate-chain.) It is provided as an
705 array of strings; each string pem1, ... pemN is the PEM
706 representation of each X.509 certificate as described in
707 [I-D.josefsson-pkix-textual]. For UAs that build certificate chains
708 in more than one way during the validation process, they SHOULD send
709 the last chain built. In this way they can avoid keeping too much
710 state during the validation process.
712 The known-pins are the Pins that the UA has noted for the Known
713 Pinned Host. They are provided as an array of strings with the
714 syntax:
716 known-pin = token "=" quoted-string
718 Figure 6: Known Pin Syntax
720 As in Section 2.4, the token refers to the algorithm name, and the
721 quoted-string refers to the base 64 encoding of the SPKI Fingerprint.
722 When formulating the JSON POST body, the UA MUST either use single-
723 quoted JSON strings, or use double-quoted JSON strings and \-escape
724 the embedded double quotes in the quoted-string part of the known-
725 pin.
727 Figure 7 shows an example of a Pin Validation failure report. (PEM
728 strings are shown on multiple lines for readability in this
729 document.)
731 {
732 "date-time": "2014-04-06T13:00:50Z",
733 "hostname": "www.example.com",
734 "port": 443,
735 "effective-expiration-date": "2014-05-01T12:40:50Z"
736 "include-subdomains": false,
737 "served-certificate-chain": [
738 "-----BEGIN CERTIFICATE-----\n
739 MIIEBDCCAuygAwIBAgIDAjppMA0GCSqGSIb3DQEBBQUAMEIxCzAJBgNVBAYTAlVT\n
740 ...
741 HFa9llF7b1cq26KqltyMdMKVvvBulRP/F/A8rLIQjcxz++iPAsbw+zOzlTvjwsto\n
742 WHPbqCRiOwY1nQ2pM714A5AuTHhdUDqB1O6gyHA43LL5Z/qHQF1hwFGPa4NrzQU6\n
743 yuGnBXj8ytqU0CwIPX4WecigUCAkVDNx\n
744 -----END CERTIFICATE-----",
745 ...
746 ],
747 "validated-certificate-chain": [
748 "-----BEGIN CERTIFICATE-----\n
749 MIIEBDCCAuygAwIBAgIDAjppMA0GCSqGSIb3DQEBBQUAMEIxCzAJBgNVBAYTAlVT\n
750 ...
751 HFa9llF7b1cq26KqltyMdMKVvvBulRP/F/A8rLIQjcxz++iPAsbw+zOzlTvjwsto\n
752 WHPbqCRiOwY1nQ2pM714A5AuTHhdUDqB1O6gyHA43LL5Z/qHQF1hwFGPa4NrzQU6\n
753 yuGnBXj8ytqU0CwIPX4WecigUCAkVDNx\n
754 -----END CERTIFICATE-----",
755 ...
756 ],
757 "known-pins": [
758 'pin-sha256="d6qzRu9zOECb90Uez27xWltNsj0e1Md7GkYYkVoZWmM="',
759 "pin-sha256=\"E9CZ9INDbd+2eRQozYqqbQ2yXLVKB9+xcprMF+44U1g=\""
760 ]
761 }
763 Figure 7: Pin Validation Failure Report Example
765 4. Security Considerations
767 Pinning public keys helps hosts strongly assert their cryptographic
768 identity even in the face of issuer error, malfeasance or compromise.
769 But there is some risk that a host operator could lose or lose
770 control of their host's private key (such as by operator error or
771 host compromise). If the operator had pinned only the key of the
772 host's end entity certificate, the operator would not be able to
773 serve their web site or application in a way that UAs would trust for
774 the duration of their pin's max-age. (Recall that UAs MUST close the
775 connection to a host upon Pin Failure.)
777 Therefore, there is a necessary trade-off between two competing
778 goods: pin specificity and maximal reduction of the scope of issuers
779 on the one hand; and flexibility and resilience of the host's
780 cryptographic identity on the other hand. One way to resolve this
781 trade-off is to compromise by pinning to the key(s) of the issuer(s)
782 of the host's end entity certificate(s). Often, a valid certificate
783 chain will have at least two certificates above the end entity
784 certificate: the intermediate issuer, and the trust anchor.
785 Operators can pin any one or more of the public keys in this chain,
786 and indeed could pin to issuers not in the chain (as, for example, a
787 Backup Pin). Pinning to an intermediate issuer, or even to a trust
788 anchor or root, still significantly reduces the number of issuers who
789 can issue end entity certificates for the Known Pinned Host, while
790 still giving that host flexibility to change keys without a
791 disruption of service.
793 4.1. Maximum max-age
795 As mentioned in Section 2.3.3, UAs MAY cap the max-age value at some
796 upper limit. There is a security trade-off in that low maximum
797 values provide a narrow window of protection for users who visit the
798 Known Pinned Host only infrequently, while high maximum values might
799 potentially result in a UA's inability to successfully perform Pin
800 Validation for a Known Pinned Host if the UA's noted Pins and the
801 Host's true Pins diverge.
803 Such divergence could occur for several reasons, including: UA error;
804 Host operator error; network attack; or a Known Pinned Host that
805 intentionally migrates all pinned keys, combined with a UA that has
806 noted true Pins with a high max-age value and has not had a chance to
807 observe the new true Pins for the Host. (This last example
808 underscores the importance for Host operators to phase in new keys
809 gradually, and to set the max-age value in accordance with their
810 planned key migration schedule.)
812 There is probably no ideal upper limit to the max-age directive that
813 would satisfy all use cases. However, a value on the order of 60
814 days (5184000 seconds) may be considered a balance between the two
815 competing security concerns.
817 4.2. Using includeSubDomains Safely
819 It may happen that Pinned Hosts whose hostnames share a parent domain
820 use different Valid Pinning Headers. If a Host whose hostname is a
821 parent domain for another Host sets the includeSubDomains directive,
822 the two Hosts' Pins may conflict with each other. For example,
823 consider two Known Pinned Hosts, example.com and
824 subdomain.example.com. Assume example.com sets a Valid Pinning
825 Header such as this:
827 Public-Key-Pins: max-age=12000; pin-sha256="ABC..."; pin-sha256="DEF...";
828 includeSubDomains
830 Figure 8: example.com Valid Pinning Header
832 Assume subdomain.example.com sets a Valid Pinning Header such as
833 this:
835 Public-Key-Pins: pin-sha256="GHI..."; pin-sha256="JKL..."
837 Figure 9: subdomain.example.com Valid Pinning Header
839 Assume a UA that has not previously noted any Pins for either of
840 these Hosts. If the UA first contacts subdomain.example.com, it will
841 note the Pins in the Valid Pinning Header, and perform Pin Validation
842 as normal on subsequent conections. If the UA then contacts
843 example.com, again it will note the Pins and perform Pin Validation
844 on future connections. However, if the UA happened to first
845 example.com before subdomain.example.com, the UA would, due to
846 example.com's use of the includeSubDomains directive, attempt to
847 perform Pin Validation for subdomain.example.com using the SPKI
848 hashes ABC... and DEF..., which are not valid for the certificate
849 chains subdomain.example.com (which uses certificates with SPKIs
850 GHI... and JLK...). Thus, depending on the order in which the UA
851 observes the Valid Pinning Headers for hosts example.com and
852 subdomain.example.com, Pin Validation might or might not fail for
853 subdomain.example.com, even if the certificate chain the UA receives
854 for subdomain.example.com is perfectly valid.
856 Thus, Pinned Host operators must use the includeSubDomains directive
857 with care. For example, they may choose to use overlapping pin sets
858 for hosts under a parent domain that uses includeSubDomains, or to
859 not use the includeSubDomains directive in their effective-second-
860 level domains, or to simply use the same pin set for all hosts under
861 a given parent domain.
863 4.3. Backup Pins
865 The primary way to cope with the risk of inadvertent Pin Failure is
866 to keep a Backup Pin. A Backup Pin is a fingerprint for the public
867 key of a secondary, not-yet-deployed key pair. The operator keeps
868 the backup key pair offline, and sets a pin for it in the Public-Key-
869 Pins header. Then, in case the operator loses control of their
870 primary private key, they can deploy the backup key pair. UAs, who
871 have had the backup key pair pinned (when it was set in previous
872 Valid Pinning Headers), can connect to the host without error.
874 Because having a backup key pair is so important to recovery, UAs
875 MUST require that hosts set a Backup Pin. (See Section 2.5.)
877 5. Privacy Considerations
879 Conforming implementations (as well as implementations conforming to
880 [RFC6797]) must store state about which domains have set policies,
881 hence which domains the UA has contacted. A forensic attacker might
882 find this information useful, even if the user has cleared other
883 parts of the UA's state.
885 More importantly, Hosts can use HSTS or HPKP as a "super-cookie", by
886 setting distinct policies for a number of subdomains. For example,
887 assume example.com wishes to track distinct UAs without explicitly
888 setting a cookie, or if a previously-set cookie is deleted from the
889 UA's cookie store. Here are two attack scenarios.
891 o example.com can use report-uri and the ability to pin arbitrary
892 identifiers to distinguish UAs.
894 1. example.com sets a Valid Pinning Header in its response to
895 requests. The header asserts the includeSubDomains directive,
896 and specifies a report-uri directive as well. Pages served by
897 the host also include references to subresource https://
898 bad.example.com/foo.png.
900 2. The Valid Pinning Header includes a "pin" that is not really
901 the hash of an SPKI, but is instead an arbitrary
902 distinguishing string sent only in response to a particular
903 request. For each request, the Host creates a new, distinct
904 distinguishing string and sets it as if it were a pin.
906 3. The certificate chain served by bad.example.com does not pass
907 Pin Validation given the pin set the Host asserted in (1).
908 The HPKP-conforming UA attempts to report the Pin Validation
909 failure to the specified report-uri, including the certificate
910 chain it observed and the SPKI hashes it expected to see.
911 Among the SPKI hashes is the distinguishing string in step
912 (2).
914 o example.com can use SNI and subdomains to distinguish UAs.
916 1. example.com sets a Valid Pinning Header in its response to
917 requests. The header asserts the includeSubDomains directive.
919 2. On a subsequent page view, the Host responds with a page
920 including the subresource https://0.fingerprint.example.com/
921 foo.png, and the server responds using a certificate chain
922 that does not pass Pin Validation for the pin-set defined in
923 the Valid Pinning Header in step (1). The HPKP-conforming UA
924 will close the connection, never completing the request to
925 0.fingerprint.example.com. The Host may thus note that this
926 particular UA had noted the (good) Pins for that subdomain.
928 3. example.com can distinguish 2^N UAs by serving Valid Pinning
929 Headers from an arbitrary number N distinct subdomains, giving
930 some UAs Valid Pinning Headers for some, but not all
931 subdomains (causing subsequent requests for
932 n.fingerprint.example.com to fail), and giving some UAs no
933 Valid Pinning Header for other subdomains (causing subsequent
934 requests for m.fingerprint.example.com to succeed).
936 6. IANA Considerations
938 IANA is requested to register the header described in this document
939 in the "Message Headers" registry, with the following parameters:
941 o Header Field Names should be "Public-Key-Pins" and "Public-Key-
942 Pins-Report-Only".
944 o Protocol should be "http"
946 o Status should be "standard"
948 o Reference should be this document
950 7. Usability Considerations
952 When pinning works to detect impostor Pinned Hosts, users will
953 experience denial of service. UAs MUST explain the reason why, i.e.
954 that it was impossible to verify the confirmed cryptographic identity
955 of the host.
957 UAs MUST have a way for users to clear current Pins for Pinned Hosts.
958 UAs SHOULD have a way for users to query the current state of Pinned
959 Hosts.
961 8. Acknowledgements
963 Thanks to Tobias Gondrom, Jeff Hodges, Paul Hoffman, Ivan Krstic,
964 Adam Langley, Nicolas Lidzborski, SM, James Manger, Yoav Nir, Eric
965 Rescorla, and Tom Ritter for suggestions and edits that clarified the
966 text. Thanks to Trevor Perrin for suggesting a mechanism to
967 affirmatively break Pins ([pin-break-codes]).
969 9. What's Changed
971 [RFC EDITOR: PLEASE REMOVE THIS SECTION]
973 Removed the strict directive.
975 Removed the requirement that the server set the Valid Pinning Header
976 on every response.
978 Added normative references for SHA, JSON, and base-64.
980 Added the Privacy Considerations section.
982 Changed non-normative pin generation code from Go to POSIX shell
983 script using openssl.
985 Changed max-max-age from SHOULD to MAY, and used the example of 60
986 days instead of 30.
988 Removed the section "Pin Validity Times", which was intended to be in
989 harmony with [I-D.perrin-tls-tack]. Now using max-age purely as
990 specified in [RFC6797].
992 Added new directives: includeSubDomains, report-uri and strict.
994 Added a new variant of the PKP Header: Public-Key-Pins-Report-Only.
996 Removed the section on pin break codes and verifiers, in favor the of
997 most-recently-received policy (Section 2.5).
999 Now using a new header field, Public-Key-Pins, separate from HSTS.
1000 This allows hosts to use pinning separately from Strict Transport
1001 Security.
1003 Explicitly requiring that UAs perform Pin Validation before the HTTP
1004 conversation begins.
1006 Backup Pins are now required.
1008 Separated normative from non-normative material. Removed tangential
1009 and out-of-scope non-normative discussion.
1011 10. References
1012 10.1. Normative References
1014 [I-D.josefsson-pkix-textual]
1015 Josefsson, S. and S. Leonard, "Text Encodings of PKIX and
1016 CMS Structures", draft-josefsson-pkix-textual-02 (work in
1017 progress), October 2013.
1019 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
1020 Requirement Levels", BCP 14, RFC 2119, March 1997.
1022 [RFC2616] Fielding, R., Gettys, J., Mogul, J., Frystyk, H.,
1023 Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext
1024 Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999.
1026 [RFC3339] Klyne, G., Ed. and C. Newman, "Date and Time on the
1027 Internet: Timestamps", RFC 3339, July 2002.
1029 [RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
1030 Resource Identifier (URI): Generic Syntax", STD 66, RFC
1031 3986, January 2005.
1033 [RFC4627] Crockford, D., "The application/json Media Type for
1034 JavaScript Object Notation (JSON)", RFC 4627, July 2006.
1036 [RFC4634] Eastlake, D. and T. Hansen, "US Secure Hash Algorithms
1037 (SHA and HMAC-SHA)", RFC 4634, July 2006.
1039 [RFC4648] Josefsson, S., "The Base16, Base32, and Base64 Data
1040 Encodings", RFC 4648, October 2006.
1042 [RFC4648] Josefsson, S., "The Base16, Base32, and Base64 Data
1043 Encodings", RFC 4648, October 2006.
1045 [RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
1046 IANA Considerations Section in RFCs", BCP 26, RFC 5226,
1047 May 2008.
1049 [RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security
1050 (TLS) Protocol Version 1.2", RFC 5246, August 2008.
1052 [RFC5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
1053 Housley, R., and W. Polk, "Internet X.509 Public Key
1054 Infrastructure Certificate and Certificate Revocation List
1055 (CRL) Profile", RFC 5280, May 2008.
1057 [RFC6797] Hodges, J., Jackson, C., and A. Barth, "HTTP Strict
1058 Transport Security (HSTS)", RFC 6797, November 2012.
1060 [W3C.REC-html401-19991224]
1061 Raggett, D., Hors, A., and I. Jacobs, "HTML 4.01
1062 Specification", World Wide Web Consortium Recommendation
1063 REC-html401-19991224, December 1999,
1064 .
1066 10.2. Informative References
1068 [I-D.perrin-tls-tack]
1069 Marlinspike, M., "Trust Assertions for Certificate Keys",
1070 draft-perrin-tls-tack-02 (work in progress), January 2013.
1072 [pin-break-codes]
1073 Perrin, T., "Self-Asserted Key Pinning", September 2011,
1074 .
1076 [why-pin-key]
1077 Langley, A., "Public Key Pinning", May 2011,
1078 .
1080 Appendix A. Fingerprint Generation
1082 This POSIX shell program generates SPKI Fingerprints, suitable for
1083 use in pinning, from PEM-encoded certificates. It is non-normative.
1085 openssl x509 -noout -in certificate.pem -pubkey | \
1086 openssl asn1parse -noout -inform pem -out public.key
1087 openssl dgst -sha256 -binary public.key | base64
1089 Figure 10: Example SPKI Fingerprint Generation Code
1091 Appendix B. Deployment Guidance
1093 This section is non-normative guidance which may smooth the adoption
1094 of public key pinning.
1096 o Operators SHOULD get the backup public key signed by a different
1097 (root and/or intermediary) CA than their primary certificate, and
1098 store the backup key pair safely offline. The semantics of an
1099 SPKI Fingerprint do not require the issuance of a certificate to
1100 construct a valid Pin. However, in many deployment scenarios, in
1101 order to make a Backup Pin operational the server operator will
1102 need to have a certificate to deploy TLS on the host. Failure to
1103 obtain a certificate through prior arrangement will leave clients
1104 that recognize the site as a Known Pinned Host unable to
1105 successfully perform Pin Validation until such a time as the
1106 operator can obtain a new certificate from their desired
1107 certificate issuer.
1109 o It is most economical to have the backup certificate signed by a
1110 completely different signature chain than the live certificate, to
1111 maximize recoverability in the event of either root or
1112 intermediary signer compromise.
1114 o Operators SHOULD periodically exercise their Backup Pin plan -- an
1115 untested backup is no backup at all.
1117 o Operators SHOULD start small. Operators SHOULD first deploy
1118 public key pinning by using the report-only mode together with a
1119 report-uri directive that points to a reliable report collection
1120 endpoint. When moving out of report-only mode, operators should
1121 start by setting a max-age of minutes or a few hours, and
1122 gradually increase max-age as they gain confidence in their
1123 operational capability.
1125 Authors' Addresses
1127 Chris Evans
1128 Google, Inc.
1129 1600 Amphitheatre Pkwy
1130 Mountain View, CA 94043
1131 US
1133 Email: cevans@google.com
1135 Chris Palmer
1136 Google, Inc.
1137 1600 Amphitheatre Pkwy
1138 Mountain View, CA 94043
1139 US
1141 Email: palmer@google.com
1143 Ryan Sleevi
1144 Google, Inc.
1145 1600 Amphitheatre Pkwy
1146 Mountain View, CA 94043
1147 US
1149 Email: sleevi@google.com