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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Using TLS in Applications D. Margolis 3 Internet-Draft Google, Inc 4 Intended status: Standards Track A. Brotman 5 Expires: October 5, 2017 Comcast, Inc 6 B. Ramakrishnan 7 Yahoo!, Inc 8 J. Jones 9 Microsoft, Inc 10 M. Risher 11 Google, Inc 12 April 3, 2017 14 SMTP TLS Reporting 15 draft-ietf-uta-smtp-tlsrpt-04 17 Abstract 19 A number of protocols exist for establishing encrypted channels 20 between SMTP Mail Transfer Agents, including STARTTLS [RFC3207], DANE 21 [RFC6698], and MTA-STS (TODO: Add ref). These protocols can fail due 22 to misconfiguration or active attack, leading to undelivered messages 23 or delivery over unencrypted or unauthenticated channels. This 24 document describes a reporting mechanism and format by which sending 25 systems can share statistics and specific information about potential 26 failures with recipient domains. Recipient domains can then use this 27 information to both detect potential attackers and diagnose 28 unintentional misconfigurations. 30 Status of This Memo 32 This Internet-Draft is submitted in full conformance with the 33 provisions of BCP 78 and BCP 79. 35 Internet-Drafts are working documents of the Internet Engineering 36 Task Force (IETF). Note that other groups may also distribute 37 working documents as Internet-Drafts. The list of current Internet- 38 Drafts is at http://datatracker.ietf.org/drafts/current/. 40 Internet-Drafts are draft documents valid for a maximum of six months 41 and may be updated, replaced, or obsoleted by other documents at any 42 time. It is inappropriate to use Internet-Drafts as reference 43 material or to cite them other than as "work in progress." 45 This Internet-Draft will expire on October 5, 2017. 47 Copyright Notice 49 Copyright (c) 2017 IETF Trust and the persons identified as the 50 document authors. All rights reserved. 52 This document is subject to BCP 78 and the IETF Trust's Legal 53 Provisions Relating to IETF Documents 54 (http://trustee.ietf.org/license-info) in effect on the date of 55 publication of this document. Please review these documents 56 carefully, as they describe your rights and restrictions with respect 57 to this document. Code Components extracted from this document must 58 include Simplified BSD License text as described in Section 4.e of 59 the Trust Legal Provisions and are provided without warranty as 60 described in the Simplified BSD License. 62 Table of Contents 64 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 65 1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3 66 2. Related Technologies . . . . . . . . . . . . . . . . . . . . 4 67 3. Reporting Policy . . . . . . . . . . . . . . . . . . . . . . 4 68 3.1. Example Reporting Policy . . . . . . . . . . . . . . . . 5 69 3.1.1. Report using MAILTO . . . . . . . . . . . . . . . . . 5 70 3.1.2. Report using HTTPS . . . . . . . . . . . . . . . . . 5 71 4. Reporting Schema . . . . . . . . . . . . . . . . . . . . . . 5 72 4.1. Report Time-frame . . . . . . . . . . . . . . . . . . . . 6 73 4.2. Delivery Summary . . . . . . . . . . . . . . . . . . . . 6 74 4.2.1. Success Count . . . . . . . . . . . . . . . . . . . . 6 75 4.2.2. Failure Count . . . . . . . . . . . . . . . . . . . . 7 76 4.3. Result Types . . . . . . . . . . . . . . . . . . . . . . 7 77 4.3.1. Negotiation Failures . . . . . . . . . . . . . . . . 7 78 4.3.2. Policy Failures . . . . . . . . . . . . . . . . . . . 7 79 4.3.3. General Failures . . . . . . . . . . . . . . . . . . 8 80 4.3.4. Transient Failures . . . . . . . . . . . . . . . . . 8 81 5. Report Delivery . . . . . . . . . . . . . . . . . . . . . . . 8 82 5.1. Report Filename . . . . . . . . . . . . . . . . . . . . . 8 83 5.2. Compression . . . . . . . . . . . . . . . . . . . . . . . 9 84 5.3. Email Transport . . . . . . . . . . . . . . . . . . . . . 9 85 5.4. HTTPS Transport . . . . . . . . . . . . . . . . . . . . . 10 86 5.5. Delivery Retry . . . . . . . . . . . . . . . . . . . . . 10 87 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11 88 7. Security Considerations . . . . . . . . . . . . . . . . . . . 11 89 8. Appendix 1: Example Reporting Policy . . . . . . . . . . . . 11 90 8.1. Report using MAILTO . . . . . . . . . . . . . . . . . . . 11 91 8.2. Report using HTTPS . . . . . . . . . . . . . . . . . . . 12 92 9. Appendix 2: JSON Report Schema . . . . . . . . . . . . . . . 12 93 10. Appendix 3: Example JSON Report . . . . . . . . . . . . . . . 14 94 11. Normative References . . . . . . . . . . . . . . . . . . . . 16 95 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 17 97 1. Introduction 99 The STARTTLS extension to SMTP [RFC3207] allows SMTP clients and 100 hosts to establish secure SMTP sessions over TLS. The protocol 101 design is based on "Opportunistic Security" (OS) [RFC7435], which 102 maintains interoperability with clients that do not support STARTTLS 103 but means that any attacker who can delete parts of the SMTP session 104 (such as the "250 STARTTLS" response) or redirect the entire SMTP 105 session (perhaps by overwriting the resolved MX record of the 106 delivery domain) can perform a downgrade or interception attack. 108 Because such "downgrade attacks" are not necessarily apparent to the 109 receiving MTA, this document defines a mechanism for sending domains 110 to report on failures at multiple stages of the MTA-to-MTA 111 conversation. 113 Recipient domains may also use the mechanisms defined by MTA-STS 114 (TODO: Add ref) or DANE [RFC6698] to publish additional encryption 115 and authentication requirements; this document defines a mechanism 116 for sending domains that are compatible with MTA-STS or DANE to share 117 success and failure statistics with recipient domains. 119 Specifically, this document defines a reporting schema that covers 120 failures in routing, STARTTLS negotiation, and both DANE [RFC6698] 121 and MTA-STS (TODO: Add ref) policy validation errors, and a standard 122 TXT record that recipient domains can use to indicate where reports 123 in this format should be sent. 125 This document is intended as a companion to the specification for 126 SMTP MTA Strict Transport Security (MTA-STS, TODO: Add ref). 128 1.1. Terminology 130 The keywords MUST, MUST NOT, REQUIRED, SHALL, SHALL NOT, SHOULD, 131 SHOULD NOT, RECOMMENDED, MAY, and OPTIONAL, when they appear in this 132 document, are to be interpreted as described in [RFC2119]. 134 We also define the following terms for further use in this document: 136 o MTA-STS Policy: A definition of the expected TLS availability, 137 behavior, and desired actions for a given domain when a sending 138 MTA encounters problems in negotiating a secure channel. MTA-STS 139 is defined in [TODO] 141 o DANE Policy: A mechanism by which administrators can supply a 142 record that can be used to validate the certificate presented by 143 an MTA. DANE is defined in [RFC6698]. 145 o TLSRPT Policy: A policy specifying the endpoint to which sending 146 MTAs should deliver reports. 148 o Policy Domain: The domain against which an MTA-STS or DANE Policy 149 is defined. 151 o Sending MTA: The MTA initiating the delivery of an email message. 153 2. Related Technologies 155 o This document is intended as a companion to the specification for 156 SMTP MTA Strict Transport Security (MTA-STS, TODO: Add ref). 158 o The Public Key Pinning Extension for HTTP [RFC7469] contains a 159 JSON-based definition for reporting individual pin validation 160 failures. 162 o The Domain-based Message Authentication, Reporting, and 163 Conformance (DMARC) [RFC7489] contains an XML-based reporting 164 format for aggregate and detailed email delivery errors. 166 3. Reporting Policy 168 A domain publishes a record to its DNS indicating that it wishes to 169 receive reports. These SMTP TLSRPT policies are distributed via DNS 170 from the Policy Domain's zone, as TXT records (similar to DMARC 171 policies) under the name "_smtp-tlsrpt". For example, for the Policy 172 Domain "example.com", the recipient's TLSRPT policy can be retrieved 173 from "_smtp-tlsrpt.example.com". 175 Policies consist of the following directives: 177 o "v": This value MUST be equal to "TLSRPTv1". 179 o "rua": A URI specifying the endpoint to which aggregate 180 information about policy failures should be sent (see the section 181 _Reporting_ _Schema_ for more information). Two URI schemes are 182 supported: "mailto" and "https". 184 * In the case of "https", reports should be submitted via POST 185 ([RFC2818]) to the specified URI. 187 * In the case of "mailto", reports should be submitted to the 188 specified email address. When sending failure reports via 189 SMTP, sending MTAs MUST deliver reports despite any TLS-related 190 failures. This may mean that the reports are delivered in the 191 clear. 193 The formal definition of the "_smtp-tlsrpt" TXT record, defined using 194 [RFC5234], is as follows: 196 tlsrpt-record = tlsrpt-version *WSP %x3B tlsrpt-rua 198 tlsrpt-version = "v" *WSP "=" *WSP %x54 %x4C %x53 199 %x52 %x50 %x54 %x76 %x31 201 tlsrpt-rua = "rua" *WSP "=" *WSP tlsrpt-uri 203 tlsrpt-uri = URI 204 ; "URI" is imported from [@!RFC3986]; commas (ASCII 205 ; 0x2C) and exclamation points (ASCII 0x21) 206 ; MUST be encoded; the numeric portion MUST fit 207 ; within an unsigned 64-bit integer 209 If multiple TXT records for "_smtp-tlsrpt" are returned by the 210 resolver, records which do not begin with "v=TLSRPTv1;" are 211 discarded. If the number of resulting records is not one, senders 212 MUST assume the recipient domain does not implement TLSRPT. 214 3.1. Example Reporting Policy 216 3.1.1. Report using MAILTO 218 _smtp-tlsrpt.example.com. IN TXT \ 219 "v=TLSRPTv1;rua=mailto:reports@example.com" 221 3.1.2. Report using HTTPS 223 _smtp-tlsrpt.example.com. IN TXT \ 224 "v=TLSRPTv1; \ 225 rua=https://reporting.example.com/v1/tlsrpt" 227 4. Reporting Schema 229 The report is composed as a plain text file encoded in the JSON 230 format ([RFC7159]). 232 Aggregate reports contain the following fields: 234 o Report metadata: 236 * The organization responsible for the report 237 * Contact information for one or more responsible parties for the 238 contents of the report 240 * A unique identifier for the report 242 * The reporting date range for the report 244 o Policy, consisting of: 246 * One of the following policy types: (1) The MTA-STS policy 247 applied (as a string) (2) The DANE TLSA record applied (as a 248 string, with each RR entry of the RRset listed and separated by 249 a semicolon) (3) The literal string "no-policy-found", if 250 neither a TLSA nor MTA-STS policy could be found. 252 * The domain for which the policy is applied 254 * The MX host 256 * An identifier for the policy (where applicable) 258 o Aggregate counts, comprising result type, sending MTA IP, 259 receiving MTA hostname, session count, and an optional additional 260 information field containing a URI for recipients to review 261 further information on a failure type. 263 Note that the failure types are non-exclusive; an aggregate report 264 may contain overlapping "counts" of failure types when a single send 265 attempt encountered multiple errors. 267 4.1. Report Time-frame 269 The report SHOULD cover a full day, from 0000-2400 UTC. This should 270 allow for easier correlation of failure events. 272 4.2. Delivery Summary 274 4.2.1. Success Count 276 o "success-count": This indicates that the sending MTA was able to 277 successfully negotiate a policy-compliant TLS connection, and 278 serves to provide a "heartbeat" to receiving domains that 279 reporting is functional and tabulating correctly. This field 280 contains an aggregate count of successful connections for the 281 reporting system. 283 4.2.2. Failure Count 285 o "failure-count": This indicates that the sending MTA was unable to 286 successfully establish a connection with the receiving platform. 287 The "Result Types" section will elaborate on the failed 288 negotiation attempts. This field contains an aggregate count of 289 failed connections. 291 4.3. Result Types 293 The list of result types will start with the minimal set below, and 294 is expected to grow over time based on real-world experience. The 295 initial set is: 297 4.3.1. Negotiation Failures 299 o "starttls-not-supported": This indicates that the recipient MX did 300 not support STARTTLS. 302 o "certificate-host-mismatch": This indicates that the certificate 303 presented did not adhere to the constraints specified in the MTA- 304 STS or DANE policy, e.g. if the MX does not match any identities 305 listed in the Subject Alternate Name (SAN) [RFC5280]. 307 o "certificate-expired": This indicates that the certificate has 308 expired. 310 o "certificate-not-trusted": This a label that covers multiple 311 certificate related failures that include, but not limited to 312 errors such as untrusted/unknown CAs, certificate name 313 constraints, certificate chain errors etc. When using this 314 declaration, the reporting MTA SHOULD utilize the "failure-reason" 315 to provide more information to the receiving entity. 317 o "validation-failure": This indicates a general failure for a 318 reason not matching a category above. When using this 319 declaration, the reporting MTA SHOULD utilize the "failure-reason" 320 to provide more information to the receiving entity. 322 4.3.2. Policy Failures 324 4.3.2.1. DANE-specific Policy Failures 326 o "tlsa-invalid": This indicates a validation error in the TLSA 327 record associated with a DANE policy. None of the records in the 328 RRset were found to be valid. 330 o "dnssec-invalid": This would indicate that no valid records were 331 returned from the recursive resolver. The request returned with 332 SERVFAIL for the requested TLSA record. 334 4.3.2.2. MTA-STS-specific Policy Failures 336 o "sts-invalid": This indicates a validation error for the overall 337 MTA-STS policy. 339 o "webpki-invalid": This indicates that the MTA-STS policy could not 340 be authenticated using PKIX validation. 342 4.3.3. General Failures 344 When a negotiation failure can not be categorized into one of the 345 "Negotiation Failures" stated above, the reporter SHOULD use the 346 "validation-failure" category. As TLS grows and becomes more 347 complex, new mechanisms may not be easily categorized. This allows 348 for a generic feedback category. When this category is used, the 349 reporter SHOULD also use the "failure-reason-code" to give some 350 feedback to the receiving entity. This is intended to be a short 351 text field, and the contents of the field should be an error code or 352 error text, such as "X509_V_ERR_UNHANDLED_CRITICAL_CRL_EXTENSION". 354 4.3.4. Transient Failures 356 Transient errors due to too-busy network, TCP timeouts, etc. are not 357 required to be reported. 359 5. Report Delivery 361 Reports can be delivered either as an email message via SMTP or via 362 HTTP POST. 364 5.1. Report Filename 366 The filename is typically constructed using the following ABNF: 368 filename = sender "!" policy-domain "!" begin-timestamp 369 "!" end-timestamp [ "!" unique-id ] "." extension 371 unique-id = 1*(ALPHA / DIGIT) 373 sender = domain ; imported from [@!RFC5322] 375 policy-domain = domain 377 begin-timestamp = 1*DIGIT 378 ; seconds since 00:00:00 UTC January 1, 1970 379 ; indicating start of the time range contained 380 ; in the report 382 end-timestamp = 1*DIGIT 383 ; seconds since 00:00:00 UTC January 1, 1970 384 ; indicating end of the time range contained 385 ; in the report 387 extension = "json" / "json.gz" 389 The extension MUST be "json" for a plain JSON file, or "json.gz" for 390 a JSON file compressed using GZIP. 392 "unique-id" allows an optional unique ID generated by the Sending MTA 393 to distinguish among multiple reports generated simultaneously by 394 different sources within the same Policy Domain. For example, this 395 is a possible filename for the gzip file of a report to the Policy 396 Domain "example.net" from the Sending MTA "mail.sender.example.com": 398 `mail.sender.example.com!example.net!1470013207!1470186007!001.json.gz` 400 5.2. Compression 402 The report SHOULD be subjected to GZIP compression for both email and 403 HTTPS transport. Declining to apply compression can cause the report 404 to be too large for a receiver to process (a commonly observed 405 receiver limit is ten megabytes); compressing the file increases the 406 chances of acceptance of the report at some compute cost. 408 5.3. Email Transport 410 The report MAY be delivered by email. No specific MIME message 411 structure is required. It is presumed that the aggregate reporting 412 address will be equipped to extract MIME parts with the prescribed 413 media type and filename and ignore the rest. 415 If compressed, the report should use the media type "application/ 416 gzip" if compressed (see [RFC6713]), and "text/json" otherwise. 418 The [RFC5322].Subject field for individual report submissions SHOULD 419 conform to the following ABNF: 421 tlsrpt-subject = %x52.65.70.6f.72.74 1*FWS ; "Report" 422 %x44.6f.6d.61.69.6e.3a 1*FWS ; "Domain:" 423 domain-name 1*FWS ; from RFC 6376 424 %x53.75.62.6d.69.74.74.65.72.3a ; "Submitter:" 425 1*FWS domain-name 1*FWS 426 %x52.65.70.6f.72.74.2d.49.44.3a ; "Report-ID:" 427 msg-id ; from RFC 5322 429 The first domain-name indicates the DNS domain name about which the 430 report was generated. The second domain-name indicates the DNS 431 domain name representing the Sending MTA generating the report. The 432 purpose of the Report-ID: portion of the field is to enable the 433 Policy Domain to identify and ignore duplicate reports that might be 434 sent by a Sending MTA. 436 For instance, this is a possible Subject field for a report to the 437 Policy Domain "example.net" from the Sending MTA 438 "mail.sender.example.com". It is line-wrapped as allowed by 439 [RFC5322]: 441 Subject: Report Domain: example.net 442 Submitter: mail.sender.example.com 443 Report-ID: <735ff.e317+bf22029@mailexample.net> 445 Note that, when sending failure reports via SMTP, sending MTAs MUST 446 NOT honor MTA-STS or DANE TLSA failures. 448 5.4. HTTPS Transport 450 The report MAY be delivered by POST to HTTPS. If compressed, the 451 report should use the media type "application/gzip" (see [RFC6713]), 452 and "text/json" otherwise. 454 5.5. Delivery Retry 456 In the event of a delivery failure, regardless of the delivery 457 method, a sender SHOULD attempt redelivery for up to 24hrs after the 458 initial attempt. As previously stated the reports are optional, so 459 while it is ideal to attempt redelivery, it is not required. If 460 multiple retries are attempted, they should be on a logarithmic 461 scale. 463 6. IANA Considerations 465 There are no IANA considerations at this time. 467 7. Security Considerations 469 SMTP TLS Reporting provides transparency into misconfigurations or 470 attempts to intercept or tamper with mail between hosts who support 471 STARTTLS. There are several security risks presented by the 472 existence of this reporting channel: 474 o Flooding of the Aggregate report URI (rua) endpoint: An attacker 475 could flood the endpoint and prevent the receiving domain from 476 accepting additional reports. This type of Denial-of-Service 477 attack would limit visibility into STARTTLS failures, leaving the 478 receiving domain blind to an ongoing attack. 480 o Untrusted content: An attacker could inject malicious code into 481 the report, opening a vulnerability in the receiving domain. 482 Implementers are advised to take precautions against evaluating 483 the contents of the report. 485 o Report snooping: An attacker could create a bogus TLSRPT record to 486 receive statistics about a domain the attacker does not own. 487 Since an attacker able to poison DNS is already able to receive 488 counts of SMTP connections (and, absent DANE or MTA-STS policies, 489 actual SMTP message payloads), this does not present a significant 490 new vulnerability. 492 o Reports as DDoS: TLSRPT allows specifying destinations for the 493 reports that are outside the authority of the Policy Domain, which 494 allows domains to delegate processing of reports to a partner 495 organization. However, an attacker who controls the Policy Domain 496 DNS could also use this mechanism to direct the reports to an 497 unwitting victim, flooding that victim with excessive reports. 498 DMARC [RFC7489] defines an elegant solution for verifying 499 delegation; however, since the attacker had less ability to 500 generate large reports than with DMARC failures, and since the 501 reports are generated by the sending MTA, such a delegation 502 mechanism is left for a future version of this specification. 504 8. Appendix 1: Example Reporting Policy 506 8.1. Report using MAILTO 508 _smtp-tlsrpt.mail.example.com. IN TXT \ 509 "v=TLSRPTv1;rua=mailto:reports@example.com" 511 8.2. Report using HTTPS 513 _smtp-tlsrpt.mail.example.com. IN TXT \ 514 "v=TLSRPTv1; \ 515 rua=https://reporting.example.com/v1/tlsrpt" 517 9. Appendix 2: JSON Report Schema 519 The JSON schema is derived from the HPKP JSON schema [RFC7469] (cf. 520 Section 3) 522 { 523 "organization-name": organization-name, 524 "date-range": { 525 "start-datetime": date-time, 526 "end-datetime": date-time 527 }, 528 "contact-info": email-address, 529 "report-id": report-id, 530 "policy": { 531 "policy-type": policy-type, 532 "policy-string": policy-string, 533 "policy-domain": domain, 534 "mx-host": mx-host-pattern 535 }, 536 "summary": { 537 "success-aggregate": total-successful-session-count, 538 "failure-aggregate:" total-failure-session-count 539 } 540 "failure-details": [ 541 { 542 "result-type": result-type, 543 "sending-mta-ip": ip-address, 544 "receiving-mx-hostname": receiving-mx-hostname, 545 "receiving-mx-helo": receiving-mx-helo, 546 "session-count": failed-session-count, 547 "additional-information": additional-info-uri, 548 "failure-reason-code": "Text body" 549 } 550 ] 551 } 553 Figure: JSON Report Format 555 o "organization-name": The name of the organization responsible for 556 the report. It is provided as a string. 558 o "date-time": The date-time indicates the start- and end-times for 559 the report range. It is provided as a string formatted according 560 to Section 5.6, "Internet Date/Time Format", of [RFC3339]. The 561 report should be for a full UTC day, 0000-2400. 563 o "email-address": The contact information for a responsible party 564 of the report. It is provided as a string formatted according to 565 Section 3.4.1, "Addr-Spec", of [RFC5322]. 567 o "report-id": A unique identifier for the report. Report authors 568 may use whatever scheme they prefer to generate a unique 569 identifier. It is provided as a string. 571 o "policy-type": The type of policy that was applied by the sending 572 domain. Presently, the only three valid choices are "tlsa", 573 "sts", and the literal string "no-policy-found". It is provided 574 as a string. 576 o "policy-string": The string serialization of the policy, whether 577 TLSA record or MTA-STS policy. Any linefeeds from the original 578 policy MUST be replaced with [SP]. TODO: Help with specifics. 580 o "domain": The Policy Domain upon which the policy was applied. 581 For messages sent to "user@example.com" this field would contain 582 "example.com". It is provided as a string. 584 o "mx-host-pattern": The pattern of MX hostnames from the applied 585 policy. It is provided as a string, and is interpreted in the 586 same manner as the "Checking of Wildcard Certificates" rules in 587 Section 6.4.3 of [RFC6125]. 589 o "result-type": A value from the _Result Types_ section above. 591 o "ip-address": The IP address of the sending MTA that attempted the 592 STARTTLS connection. It is provided as a string representation of 593 an IPv4 or IPv6 address in dot-decimal or colon-hexadecimal 594 notation. 596 o "receiving-mx-hostname": The hostname of the receiving MTA MX 597 record with which the sending MTA attempted to negotiate a 598 STARTTLS connection. 600 o "receiving-mx-helo": (optional) The HELO or EHLO string from the 601 banner announced during the reported session. 603 o "success-aggregate": The aggregate number (integer) of 604 successfully negotiated SSL-enabled connections to the receiving 605 site. 607 o "failure-aggregate": The aggregate number (integer) of failures to 608 negotiate an SSL-enabled connection to the receiving site. 610 o "session-count": The number of (attempted) sessions that match the 611 relevant "result-type" for this section. 613 o "additional-info-uri": An optional URI pointing to additional 614 information around the relevant "result-type". For example, this 615 URI might host the complete certificate chain presented during an 616 attempted STARTTLS session. 618 o "failure-reason-code": A text field to include an SSL-related 619 error code or error message. 621 10. Appendix 3: Example JSON Report 622 { 623 "organization-name": "Company-X", 624 "date-range": { 625 "start-datetime": "2016-04-01T00:00:00Z", 626 "end-datetime": "2016-04-01T23:59:59Z" 627 }, 628 "contact-info": "sts-reporting@company-x.com", 629 "report-id": "5065427c-23d3-47ca-b6e0-946ea0e8c4be", 630 "policy": { 631 "policy-type": "sts", 632 "policy-string": "{ \"version\": \"STSv1\",\"mode\": \"report\", \"mx\": [\"*.mail.company-y.com\"], \"max_age\": 86400 }", 633 "policy-domain": "company-y.com", 634 "mx-host": "*.mail.company-y.com" 635 }, 636 "summary": { 637 "success-aggregate": 5326, 638 "failure-aggregate": 303 639 } 640 "failure-details": [{ 641 "result-type": "certificate-expired", 642 "sending-mta-ip": "98.136.216.25", 643 "receiving-mx-hostname": "mx1.mail.company-y.com", 644 "session-count": 100 645 }, { 646 "result-type": "starttls-not-supported", 647 "sending-mta-ip": "98.22.33.99", 648 "receiving-mx-hostname": "mx2.mail.company-y.com", 649 "session-count": 200, 650 "additional-information": "hxxps://reports.company-x.com/ 651 report_info?id=5065427c-23d3#StarttlsNotSupported" 652 }, { 653 "result-type: "validation-failure", 654 "sending-mta-ip": "47.97.15.2", 655 "receiving-mx-hostname: "mx-backup.mail.company-y.com", 656 "session-count": 3, 657 "failure-error-code": "X509_V_ERR_PROXY_PATH_LENGTH_EXCEEDED" 658 }] 659 } 661 Figure: Example JSON report for a messages from Company-X to 662 Company-Y, where 100 sessions were attempted to Company Y servers 663 with an expired certificate and 200 sessions were attempted to 664 Company Y servers that did not successfully respond to the "STARTTLS" 665 command. Additionally 3 sessions failed due to 666 "X509_V_ERR_PROXY_PATH_LENGTH_EXCEEDED". 668 11. Normative References 670 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 671 Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/ 672 RFC2119, March 1997, 673 . 675 [RFC2818] Rescorla, E., "HTTP Over TLS", RFC 2818, DOI 10.17487/ 676 RFC2818, May 2000, 677 . 679 [RFC3207] Hoffman, P., "SMTP Service Extension for Secure SMTP over 680 Transport Layer Security", RFC 3207, DOI 10.17487/RFC3207, 681 February 2002, . 683 [RFC3339] Klyne, G. and C. Newman, "Date and Time on the Internet: 684 Timestamps", RFC 3339, DOI 10.17487/RFC3339, July 2002, 685 . 687 [RFC5234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax 688 Specifications: ABNF", STD 68, RFC 5234, DOI 10.17487/ 689 RFC5234, January 2008, 690 . 692 [RFC5322] Resnick, P., Ed., "Internet Message Format", RFC 5322, DOI 693 10.17487/RFC5322, October 2008, 694 . 696 [RFC6125] Saint-Andre, P. and J. Hodges, "Representation and 697 Verification of Domain-Based Application Service Identity 698 within Internet Public Key Infrastructure Using X.509 699 (PKIX) Certificates in the Context of Transport Layer 700 Security (TLS)", RFC 6125, DOI 10.17487/RFC6125, March 701 2011, . 703 [RFC6698] Hoffman, P. and J. Schlyter, "The DNS-Based Authentication 704 of Named Entities (DANE) Transport Layer Security (TLS) 705 Protocol: TLSA", RFC 6698, DOI 10.17487/RFC6698, August 706 2012, . 708 [RFC6713] Levine, J., "The 'application/zlib' and 'application/gzip' 709 Media Types", RFC 6713, DOI 10.17487/RFC6713, August 2012, 710 . 712 [RFC7159] Bray, T., Ed., "The JavaScript Object Notation (JSON) Data 713 Interchange Format", RFC 7159, DOI 10.17487/RFC7159, March 714 2014, . 716 [RFC7435] Dukhovni, V., "Opportunistic Security: Some Protection 717 Most of the Time", RFC 7435, DOI 10.17487/RFC7435, 718 December 2014, . 720 [RFC7469] Evans, C., Palmer, C., and R. Sleevi, "Public Key Pinning 721 Extension for HTTP", RFC 7469, DOI 10.17487/RFC7469, April 722 2015, . 724 [RFC7489] Kucherawy, M., Ed. and E. Zwicky, Ed., "Domain-based 725 Message Authentication, Reporting, and Conformance 726 (DMARC)", RFC 7489, DOI 10.17487/RFC7489, March 2015, 727 . 729 Authors' Addresses 731 Daniel Margolis 732 Google, Inc 734 Email: dmargolis (at) google.com 736 Alexander Brotman 737 Comcast, Inc 739 Email: alex_brotman (at) comcast.com 741 Binu Ramakrishnan 742 Yahoo!, Inc 744 Email: rbinu (at) yahoo-inc (dot com) 746 Janet Jones 747 Microsoft, Inc 749 Email: janet.jones (at) microsoft (dot com) 751 Mark Risher 752 Google, Inc 754 Email: risher (at) google (dot com)