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Marques 3 Internet-Draft pEp Foundation 4 Intended status: Informational B. Hoeneisen 5 Expires: January 3, 2019 Ucom.ch 6 July 02, 2018 8 pretty Easy privacy (pEp): Mapping of Privacy Rating 9 draft-marques-pep-rating-00 11 Abstract 13 In many Opportunistic Security scenarios end-to-end encryption is 14 automatized for Internet users. In addition, it is often required to 15 provide the users with easy means to carry out authentication. 17 Depending on several factors, each communication channel to different 18 peers may have a different Privacy Status, e.g., unencrypted, 19 encrypted and encrypted as well as authenticated. Even each message 20 from/to a single peer may have a different Privacy Status. 22 To display the actual Privacy Status to the user, this document 23 defines a Privacy Rating scheme and its mapping to a traffic-light 24 semantics. A Privacy Status is defined on a per-message basis as 25 well as on a per-identity basis. The traffic-light semantics (as 26 color rating) allows for a clear and easily understandable 27 presentation to the user in order to optimize the User Experience 28 (UX). 30 This rating system is most beneficial to Opportunistic Security 31 scenarios and is already implemented in several applications of 32 pretty Easy privacy (pEp). 34 Status of This Memo 36 This Internet-Draft is submitted in full conformance with the 37 provisions of BCP 78 and BCP 79. 39 Internet-Drafts are working documents of the Internet Engineering 40 Task Force (IETF). Note that other groups may also distribute 41 working documents as Internet-Drafts. The list of current Internet- 42 Drafts is at https://datatracker.ietf.org/drafts/current/. 44 Internet-Drafts are draft documents valid for a maximum of six months 45 and may be updated, replaced, or obsoleted by other documents at any 46 time. It is inappropriate to use Internet-Drafts as reference 47 material or to cite them other than as "work in progress." 48 This Internet-Draft will expire on January 3, 2019. 50 Copyright Notice 52 Copyright (c) 2018 IETF Trust and the persons identified as the 53 document authors. All rights reserved. 55 This document is subject to BCP 78 and the IETF Trust's Legal 56 Provisions Relating to IETF Documents 57 (https://trustee.ietf.org/license-info) in effect on the date of 58 publication of this document. Please review these documents 59 carefully, as they describe your rights and restrictions with respect 60 to this document. Code Components extracted from this document must 61 include Simplified BSD License text as described in Section 4.e of 62 the Trust Legal Provisions and are provided without warranty as 63 described in the Simplified BSD License. 65 Table of Contents 67 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 68 2. Terms . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 69 3. Per-Message Privacy Rating . . . . . . . . . . . . . . . . . 4 70 3.1. Rating Codes . . . . . . . . . . . . . . . . . . . . . . 4 71 3.2. Color Codes . . . . . . . . . . . . . . . . . . . . . . . 5 72 3.3. Surjective Mapping of Rating Codes into Color Codes . . . 6 73 3.4. Semantics of Color and Rating Codes . . . . . . . . . . . 6 74 3.4.1. Red . . . . . . . . . . . . . . . . . . . . . . . . . 6 75 3.4.2. No Color . . . . . . . . . . . . . . . . . . . . . . 6 76 3.4.3. Yellow . . . . . . . . . . . . . . . . . . . . . . . 7 77 3.4.4. Green . . . . . . . . . . . . . . . . . . . . . . . . 7 78 4. Per-Identity Privacy Rating . . . . . . . . . . . . . . . . . 7 79 5. Security Considerations . . . . . . . . . . . . . . . . . . . 8 80 6. Implementation Status . . . . . . . . . . . . . . . . . . . . 8 81 6.1. Introduction . . . . . . . . . . . . . . . . . . . . . . 8 82 6.2. Running Code . . . . . . . . . . . . . . . . . . . . . . 9 83 7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 9 84 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 9 85 8.1. Normative References . . . . . . . . . . . . . . . . . . 9 86 8.2. Informative References . . . . . . . . . . . . . . . . . 10 87 Appendix A. Excerpts from the pEp Reference Implementation . . . 11 88 A.1. pEp rating . . . . . . . . . . . . . . . . . . . . . . . 11 89 Appendix B. Document Changelog . . . . . . . . . . . . . . . . . 11 90 Appendix C. Open Issues . . . . . . . . . . . . . . . . . . . . 11 91 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 12 93 1. Introduction 95 In many Opportunistic Security [RFC7435] scenarios end-to-end 96 encryption is automatized for Internet users. In addition, it is 97 often required to provide the users with easy means to carry out 98 authentication. 100 Depending on several factors, each communication channel to different 101 identities may have a different Privacy Status, e.g. 103 o unreliable 105 o encrypted 107 o encrypted and authenticated 109 o mistrusted 111 Even each message from or to a single peer may have a different 112 Privacy Status. 114 To display the actual Privacy Status to the user, this document 115 defines a Privacy Rating scheme and its mapping to a traffic-light 116 semantics, i.e., a mapping to different color codes as used in a 117 traffic-light: 119 o red 121 o yellow 123 o green 125 o no color (or gray) 127 Note: While "yellow" color is used in the context of traffic-lights 128 (e.g., in North America), in other parts of the world (e.g., the UK) 129 this is generally referred to as "orange" or "amber" lights. For the 130 scope of this document, "yellow", "amber", and "orange" refer to the 131 same semantics. 133 A Privacy Status is defined on a per-message basis as well as on a 134 per-identity basis. The traffic-light semantics (as color rating) 135 allows for a clear and easily understandable presentation to the user 136 in order to optimize the User Experience (UX). To serve also 137 (color-)blind Internet users or those using monochrome displays, the 138 traffic light color semantics may also be presented by simple texts 139 and symbols for signaling the corresponding Privacy Status. 141 The proposed definitions are already implemented and used in 142 applications of pretty Easy privacy (pEp) [I-D.birk-pep]. This 143 document is targeted to applications based on the pEp framework and 144 Opportunistic Security [RFC7435]. However, it may be also used in 145 other applications as suitable. 147 Note: The pEp [I-D.birk-pep] framework proposes to automatize the use 148 of end-to-end encryption for Internet users of email and other 149 messaging applications and introduces methods to easily allow 150 authentication. 152 2. Terms 154 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 155 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 156 document are to be interpreted as described in [RFC2119]. 158 o Handshake: The process when Alice - e.g., in-person or via phone - 159 contacts Bob to verify Trustwords (or by fallback: fingerprints) 160 is called handshake. [I-D.marques-pep-handshake] 162 o Trustwords: A scalar-to-word representation of 16-bit numbers (0 163 to 65535) to natural language words. When doing a handshake, 164 peers are shown combined Trustwords of both public keys involved 165 to ease the comparison. [I-D.birk-pep-trustwords] 167 o Trust on First Use (TOFU): cf. [RFC7435] 169 o Man-in-the-middle attack (MITM): cf. [RFC4949] 171 3. Per-Message Privacy Rating 173 3.1. Rating Codes 175 To rate messages (cf. also Appendix A.1), the following 13 Rating 176 codes are defined as scalar values (decimal): 178 +-------------+------------------------+ 179 | Rating code | Rating label | 180 +-------------+------------------------+ 181 | -3 | under attack | 182 | | | 183 | -2 | broken | 184 | | | 185 | -1 | mistrust | 186 | | | 187 | 0 | undefined | 188 | | | 189 | 1 | cannot decrypt | 190 | | | 191 | 2 | have no key | 192 | | | 193 | 3 | unencrypted | 194 | | | 195 | 4 | unencrypted for some | 196 | | | 197 | 5 | unreliable | 198 | | | 199 | 6 | reliable | 200 | | | 201 | 7 | trusted | 202 | | | 203 | 8 | trusted and anonymized | 204 | | | 205 | 9 | fully anonymous | 206 +-------------+------------------------+ 208 3.2. Color Codes 210 For an Internet user to understand what the available Privacy Status 211 is, the following colors (traffic-light semantics) are defined: 213 +------------+-------------+ 214 | Color code | Color label | 215 +------------+-------------+ 216 | -1 | red | 217 | | | 218 | 0 | no color | 219 | | | 220 | 1 | yellow | 221 | | | 222 | 2 | green | 223 +------------+-------------+ 225 3.3. Surjective Mapping of Rating Codes into Color Codes 227 Corresponding User Experience (UX) implementations use a surjective 228 mapping of the Rating Codes into the Color Codes (in traffic light 229 semantics) as follows: 231 +--------------+------------+---------------+ 232 | Rating codes | Color code | (Color label) | 233 +--------------+------------+---------------+ 234 | -3 to -1 | -1 | (red) | 235 | | | | 236 | 0 to 5 | 0 | (no color) | 237 | | | | 238 | 6 | 1 | (yellow) | 239 | | | | 240 | 7 to 9 | 2 | (green) | 241 +--------------+------------+---------------+ 243 This mapping is used in current pEp implementations to signal the 244 Privacy Status (cf. Section 6.2). 246 3.4. Semantics of Color and Rating Codes 248 3.4.1. Red 250 The red color MUST only be used in three cases: 252 o Rating code -3: A man-in-the-middle (MITM) attack could be 253 detected. 255 o Rating code -2: The message was tempered with. 257 o Rating code -1: The user explicitly states he mistrusts a peer, 258 e.g., because a Handshake [I-D.marques-pep-handshake] mismatched 259 or when the user learns the communication partner was attacked and 260 might have gotten the corresponding secret key leaked. 262 3.4.2. No Color 264 No specific (or a gray color) MUST be shown in the following cases: 266 o Rating code 0: A message can be rendered, but the encryption 267 status is not clear, i.e., undefined 269 o Rating code 1: A message cannot be decrypted (because of an error 270 not covered by rating code 2 below). 272 o Rating code 2: No key is available to decrypt a message (because 273 it was encrypted with a public key for which no secret key could 274 be found). 276 o Rating code 3: A message is received or sent out unencrypted 277 (because it was received unencrypted or there's no public key to 278 encrypt a message to a recipient). 280 o Rating code 4: A message is sent out unencrypted for some of the 281 recipients of a group (because there's at least one recipient in 282 the group whose public key is not available to the sender). 284 o Rating code 5: A message is encrypted, but cryptographic 285 parameters (e.g., the cryptographic method employed or key length) 286 are insufficient. 288 3.4.3. Yellow 290 o Rating code 6: Whenever a message can be encrypted or decrypted 291 with sufficient cryptographic parameters, it's considered 292 reliable. It is mapped into the yellow color code. 294 3.4.4. Green 296 o Rating code 7: A message is mapped into the green color code only 297 if a pEp handshake [I-D.marques-pep-handshake] was successfully 298 carried out. 300 By consequence that means, that the pEp propositions don't strictly 301 follow the TOFU (cf. [RFC7435]) approach, in order to avoid 302 signaling trust without peers verifying their channel first. 304 In current pEp implementations (cf. Section 6) only rating code 7 is 305 achieved. 307 The rating codes 8 and 9 are reserved for future use in pEp 308 implementations which also secure meta-data (rating code 8), by using 309 a peer-to-peer framework like GNUnet [GNUnet], and/or allow for fully 310 anonymous communications (rating code 9), where sender and receiver 311 don't know each other, but trust between the endpoints could be 312 established nevertheless. 314 4. Per-Identity Privacy Rating 316 The same Color Codes (red, no color, yellow and green) as for 317 messages (cf. Section 3.2) MUST be applied for identities (peers), 318 so that a user can easily understand, which identities private 319 communication is possible with. 321 The green color code MUST be applied to an identity whom the pEp 322 handshake [I-D.marques-pep-handshake] was successfully carried out 323 with. 325 The yellow color code MUST be set whenever a public key could be 326 obtained to securely encrypt messages to an identity, although a MITM 327 attack cannot be excluded. 329 The no color code MUST be used for the case that no public key is 330 available to engage in private communications with an identity. 332 The red color code MUST only be used when an identity is marked as 333 mistrusted. 335 [[ It's not yet clear if there are proper cases where it makes sense 336 to set an identity automatically to the red color code, as it appears 337 to be difficult to detect attacks (e.g., secret key leakage) at the 338 other endpoint with certainty. ]] 340 5. Security Considerations 342 [[ TODO ]] 344 6. Implementation Status 346 6.1. Introduction 348 This section records the status of known implementations of the 349 protocol defined by this specification at the time of posting of this 350 Internet-Draft, and is based on a proposal described in [RFC7942]. 351 The description of implementations in this section is intended to 352 assist the IETF in its decision processes in progressing drafts to 353 RFCs. Please note that the listing of any individual implementation 354 here does not imply endorsement by the IETF. Furthermore, no effort 355 has been spent to verify the information presented here that was 356 supplied by IETF contributors. This is not intended as, and must not 357 be construed to be, a catalog of available implementations or their 358 features. Readers are advised to note that other implementations may 359 exist. 361 According to [RFC7942], "[...] this will allow reviewers and working 362 groups to assign due consideration to documents that have the benefit 363 of running code, which may serve as evidence of valuable 364 experimentation and feedback that have made the implemented protocols 365 more mature. It is up to the individual working groups to use this 366 information as they see fit." 368 6.2. Running Code 370 In pEp for email contexts, pEp rating codes are already implemented 371 for the following platforms: 373 o Android, in pEp for Android - release [SRC.pepforandroid] 375 o Enigmail, in the Enigmail/pEp mode - release used for new Enigmail 376 users of version 2.0 [SRC.enigmailpep] 378 o iOS, in pEp for iOS - not yet released [SRC.pepforios] 380 o Outlook, in pEp for Outlook - commercial release 381 [SRC.pepforoutlook] 383 7. Acknowledgments 385 The authors would like to thank the following people who have 386 provided feedback or significant contributions to the development of 387 this document: Leon Schumacher and Volker Birk 389 This work was initially created by pEp Foundation, and then reviewed 390 and extended with funding by the Internet Society's Beyond the Net 391 Programme on standardizing pEp. [ISOC.bnet] 393 8. References 395 8.1. Normative References 397 [I-D.birk-pep] 398 Birk, V., Marques, H., and S. Shelburn, "pretty Easy 399 privacy (pEp): Privacy by Default", draft-birk-pep-02 400 (work in progress), June 2018. 402 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 403 Requirement Levels", BCP 14, RFC 2119, 404 DOI 10.17487/RFC2119, March 1997, 405 . 407 [RFC4949] Shirey, R., "Internet Security Glossary, Version 2", 408 FYI 36, RFC 4949, DOI 10.17487/RFC4949, August 2007, 409 . 411 [RFC7435] Dukhovni, V., "Opportunistic Security: Some Protection 412 Most of the Time", RFC 7435, DOI 10.17487/RFC7435, 413 December 2014, . 415 8.2. Informative References 417 [GNUnet] Grothoff, C., "The GNUnet System", October 2017, 418 . 420 [I-D.birk-pep-trustwords] 421 Birk, V., Marques, H., and B. Hoeneisen, "IANA 422 Registration of Trustword Lists: Guide, Template and IANA 423 Considerations", draft-birk-pep-trustwords-02 (work in 424 progress), June 2018. 426 [I-D.marques-pep-handshake] 427 Marques, H. and B. Hoeneisen, "pretty Easy privacy (pEp): 428 Contact and Channel Authentication through Handshake", 429 draft-marques-pep-handshake-00 (work in progress), June 430 2018. 432 [ISOC.bnet] 433 Simao, I., "Beyond the Net. 12 Innovative Projects 434 Selected for Beyond the Net Funding. Implementing Privacy 435 via Mass Encryption: Standardizing pretty Easy privacy's 436 protocols", June 2017, . 440 [RFC7942] Sheffer, Y. and A. Farrel, "Improving Awareness of Running 441 Code: The Implementation Status Section", BCP 205, 442 RFC 7942, DOI 10.17487/RFC7942, July 2016, 443 . 445 [SRC.enigmailpep] 446 "Source code for Enigmail/pEp", July 2018, 447 . 449 [SRC.pepforandroid] 450 "Source code for pEp for Android", July 2018, 451 . 453 [SRC.pepforios] 454 "Source code for pEp for iOS", July 2018, 455 . 457 [SRC.pepforoutlook] 458 "Source code for pEp for Outlook", July 2018, 459 . 461 Appendix A. Excerpts from the pEp Reference Implementation 463 This section provides excerpts of the running code from the pEp 464 reference implementation pEp engine (C99 programming language). 466 A.1. pEp rating 468 From the reference implementation by the pEp foundation, src/ 469 message_api.h: 471 typedef enum _PEP_rating { 472 PEP_rating_undefined = 0, 473 PEP_rating_cannot_decrypt, 474 PEP_rating_have_no_key, 475 PEP_rating_unencrypted, 476 PEP_rating_unencrypted_for_some, 477 PEP_rating_unreliable, 478 PEP_rating_reliable, 479 PEP_rating_trusted, 480 PEP_rating_trusted_and_anonymized, 481 PEP_rating_fully_anonymous, 483 PEP_rating_mistrust = -1, 484 PEP_rating_b0rken = -2, 485 PEP_rating_under_attack = -3 486 } PEP_rating; 488 Appendix B. Document Changelog 490 [[ RFC Editor: This section is to be removed before publication ]] 492 o draft-birk-pep-rating-00: 494 * Initial version 496 Appendix C. Open Issues 498 [[ RFC Editor: This section should be empty and is to be removed 499 before publication ]] 501 o Better explain usage of Color Codes in Per-Identity Privacy Rating 503 o Decide whether rating code scalars 6 and 7-9 should be raised to 504 leave space for future extensions 506 o Add Security Considerations 508 o Add more source code excerpts to Appendix 509 o Add rating codes for secure cryptographic methods and parameters 510 and reference them 512 Authors' Addresses 514 Hernani Marques 515 pEp Foundation 516 Oberer Graben 4 517 CH-8400 Winterthur 518 Switzerland 520 Email: hernani.marques@pep.foundation 521 URI: https://pep.foundation/ 523 Bernie Hoeneisen 524 Ucom Standards Track Solutions GmbH 525 CH-8046 Zuerich 526 Switzerland 528 Phone: +41 44 500 52 44 529 Email: bernie@ietf.hoeneisen.ch (bernhard.hoeneisen AT ucom.ch) 530 URI: https://ucom.ch/