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2 IETF K. Moriarty
3 Internet-Draft Dell Technologies
4 Intended status: Standards Track 24 September 2021
5 Expires: 28 March 2022
7 ACME End User Client and Code Signing Certificates
8 draft-ietf-acme-client-03
10 Abstract
12 Automated Certificate Management Environment (ACME) core protocol
13 addresses the use case of web server certificates for TLS. This
14 document extends the ACME protocol to support end user client, device
15 client, and code signing certificates.
17 Status of This Memo
19 This Internet-Draft is submitted in full conformance with the
20 provisions of BCP 78 and BCP 79.
22 Internet-Drafts are working documents of the Internet Engineering
23 Task Force (IETF). Note that other groups may also distribute
24 working documents as Internet-Drafts. The list of current Internet-
25 Drafts is at https://datatracker.ietf.org/drafts/current/.
27 Internet-Drafts are draft documents valid for a maximum of six months
28 and may be updated, replaced, or obsoleted by other documents at any
29 time. It is inappropriate to use Internet-Drafts as reference
30 material or to cite them other than as "work in progress."
32 This Internet-Draft will expire on 28 March 2022.
34 Copyright Notice
36 Copyright (c) 2021 IETF Trust and the persons identified as the
37 document authors. All rights reserved.
39 This document is subject to BCP 78 and the IETF Trust's Legal
40 Provisions Relating to IETF Documents (https://trustee.ietf.org/
41 license-info) in effect on the date of publication of this document.
42 Please review these documents carefully, as they describe your rights
43 and restrictions with respect to this document. Code Components
44 extracted from this document must include Simplified BSD License text
45 as described in Section 4.e of the Trust Legal Provisions and are
46 provided without warranty as described in the Simplified BSD License.
48 Table of Contents
50 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
51 2. Identity Proofing for Client Certificates . . . . . . . . . . 2
52 3. End User Client Certificates . . . . . . . . . . . . . . . . 3
53 4. CodeSigning Certificates . . . . . . . . . . . . . . . . . . 5
54 5. Pre-authorization . . . . . . . . . . . . . . . . . . . . . . 8
55 6. Challenge Types . . . . . . . . . . . . . . . . . . . . . . . 8
56 6.1. One Time Password (OTP) . . . . . . . . . . . . . . . . . 8
57 6.1.1. HMAC-Based One-Time Password (HOTP) . . . . . . . . . 9
58 6.1.2. Time-Based One-Time Password (TOTP) . . . . . . . . . 9
59 6.1.3. Generic One Time Password (OTP) . . . . . . . . . . . 10
60 6.2. Public Key Cryptography . . . . . . . . . . . . . . . . . 10
61 6.3. WebAuthn or Public/Private Key Pairs . . . . . . . . . . 11
62 7. Security Considerations . . . . . . . . . . . . . . . . . . . 12
63 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12
64 9. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 12
65 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 12
66 10.1. Normative References . . . . . . . . . . . . . . . . . . 12
67 10.2. Informative References . . . . . . . . . . . . . . . . . 13
68 10.3. URL References . . . . . . . . . . . . . . . . . . . . . 13
69 Appendix A. Change Log . . . . . . . . . . . . . . . . . . . . . 13
70 Appendix B. Open Issues . . . . . . . . . . . . . . . . . . . . 13
71 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 14
73 1. Introduction
75 ACME [RFC8555] is a mechanism for automating certificate management
76 on the Internet. It enables administrative entities to prove
77 effective control over resources like domain names, and automates the
78 process of generating and issuing certificates.
80 The core ACME protocol defined challenge types specific to web server
81 certificates with the possibility to create extensions, or additional
82 challenge types for other use cases and certificate types. Client
83 certificates, such as end user and code signing may also benefit from
84 automated management to ease the deployment and maintenance of these
85 certificate types, thus the definition of this extension defining
86 challenge types specific to that usage.
88 2. Identity Proofing for Client Certificates
90 As with the TLS certificates defined in the core ACME document , identity proofing for ACME issued end user
92 client, device client, and code signing certificates is a separate
93 process outside of the automation of ACME. Identity proofing may be
94 an out-of-band process, if needed, and for this draft is likely tied
95 to the credentials used for the defined challenge types.
97 Identity proofing for these certificate types present some challenges
98 for process automation. NIST SP 800-63 r3 [NIST800-63r3] serves as
99 guidance for identity proofing further detailed in NIST SP 800-63A
100 [NIST800-63A] that may occur prior to the ability to automate
101 certificate management via ACME or may obviate the need for it
102 weighing end user privacy as a higher concern and allowing for
103 credential issuance to be decoupled from identity proofing (IAL1).
104 Using this guidance, a CA might select from the identity proofing
105 levels to assert claims on the issued certificates as described in
106 NIST SP 800-63 r3 [NIST800-63r3].
108 The certificate issuing CA may make this choice by certificate type
109 issued. Once identity proofing has been performed, in cases where
110 this is part of the process, and certificates have been issued, NIST
111 SP 800-63 r3 [NIST800-63r3] includes recommendations for
112 authentication or in the context of ACME, management of issuance for
113 subsequent client, device, or code-signing certificates:
115 If federations and assertions are used for authorizing certificate
116 issuance, NIST SP 800-63 C [NIST800-63C] may be referenced for
117 guidance on levels of assurance.
119 Existing PKI certification authorities (CAs) tend to use a set of ad
120 hoc protocols for certificate issuance and identity verification.
121 For each certificate usage type, a basic process will be described to
122 obtain an initial certificate and for the certificate renewal
123 process. If higher assurance levels are desired, the guidance from
124 NIST SP 800-63 r3 [NIST800-63r3] may be useful and out-of-band
125 identity proofing options are possible options for pre-authorization
126 challenges or notifications.
128 3. End User Client Certificates
130 A client certificate used to authenticate an end user may be used for
131 mutual authentication in TLS, EAP-TLS, or messaging. The client
132 certificate in this case may be stored in a browser, PKCS-#11
133 container, KMIP (possible, but just code signing and device client
134 certificates in practice), or another key container. To obtain an
135 end user client certificate, there are several possibilities to
136 automate authentication of an identity credential intended to be tied
137 to an end user.
139 [We need to determine if it is important in ACME to define an
140 automated method that tests the identity or the user or to just have
141 consistent credentials for the authentication challenges. The
142 credentials may be distributed through an out-of-band method that
143 involves identity proofing.]
145 [Several authentication options with identity proofing are
146 intentionally provided for review and discussion by the ACME working
147 group.]
149 A trusted federated service that ties the user to an email address
150 with a reputation of the user attached to the email may be possible.
151 One such example might be the use of a JWT signed OAuth token.
153 Risk based authentication used for identity proofing with red herring
154 questions is a third option that could utilize public information on
155 individuals to authenticate. This would be similar to the signup
156 process used in some financial applications.
158 Existing credentials - for instance, FIDO. FIDO uses a public key
159 pair and does not perform identity proofing. FIDO authentication
160 provides a different key pair to each service using FIDO for
161 authentication, which are generated at the client and registered by
162 the server. This may require using the FIDO credentials from a
163 specific service for authentication to gain ACME issued crededentials
164 (not advised based on how FIDO credentials are supposed to be used).
165 Are there instances where the same provider would issue both sets of
166 credentials? You wouldn't want to expose your FIDO credentials to a
167 different party, that's why each service has their own. Would you
168 set up a mechanism to get FIDO credentials to then obtain a
169 certificate? (What use cases would this be necessary? When do you
170 need a certificate where you already have a specific public/private
171 key pair?) This can be defined as an auth type, but should it be?
173 One-time password (OTP) authentication is a secure option. In cases
174 where a higher assurance level is needed, OTP may be a good choice
175 and many options exist today for OTP that could use an app on a phone
176 for instance tied to an existing (or newly established) password.
177 The OTP may be tied to an out-of-band process and may be associated
178 with a username/password and other accounts.
180 One consideration is to understand if the use case could just use
181 FIDO and not create anything new (ACME client certificates). FIDO
182 provides a mechanism to have unique public key pair based access for
183 client authentication to web sites and they are working on non-web.
184 Identity proofing is intentionally decoupled from authentication in
185 this model as that is in line with NIST 800-63r3 recommendations for
186 privacy protections of the user. The credential in this case is
187 authenticated and would be consistent for it's use, but the identity
188 proofing for that credential is not performed. Obviously, identity
189 proofing is more important for some services, like financial
190 applications where tying the user to the identity for access to
191 financial information is important. However, is automated identity
192 proofing important for any user certificate or should it remain
193 decoupled where it could be automated by a service offering or is
194 there a need for a standardized mechanism to support it for user
195 certificates?
197 Three methods for ACME client authentication, not identity proofing,
198 are proposed in the Challenge Type Section.
200 4. CodeSigning Certificates
202 The process to retrieve a code signing certificate is similar to that
203 of a web server certificate, with differences primarily in the CSR
204 request and the resulting certificate properties. [The storage and
205 access of a code signing certificate must be protected and is
206 typically done through hardware, a hardware security module (HSM),
207 which likely has a PKCS#11 interface. A code signing certificate may
208 either be a standard one or an extended validation (EV) certificate.]
210 For automation purposes, the process described in this document will
211 follow the standard process and any out-of-band preprocessing can
212 increase the level of the issued certificate if the CA offers such
213 options and has additional identity proofing mechanisms (in band or
214 out-of-band).
216 Strict vetting processes are necessary for many code signing
217 certificates to provide a high assurance on the signer. In some
218 cases, issuance of a standard CodeSigning certificate will be
219 appropriate and no additional "challenges" [RFC8555 Section 8] will
220 be necessary. In this case, the standard option could be automated
221 very similar to Web server certificates with the only changes being
222 in the CSR properties. However, this may not apply to all scenarios,
223 such as those requiring EV certificates with the possibility for
224 required out-of-band initial authentication and identity proofing.
226 EV code signing certificates have a distinct set of requirements from
227 EV web certificates. In particular, they don't have associated
228 domain names, nor is CAA checking done. The code signing certificate
229 links a public key to an organization, not a domain. CAs may chose
230 different methods to enable the use of ACME for EV code signing
231 certificates. The intent of this work is to provide additional
232 authentication challenge types that may enable their automation
233 process.
235 Organization validation is required for standard code signing
236 certificates from most issuers. The CSR is used to identify the
237 organization from the included domain name in the request. The
238 resulting certificate, however, instead contains the organization's
239 name and for EV certificates, other identifying information for the
240 organization. For EV certificates, this could require that the
241 domain is registered with the Certificate Authority provider, listed
242 in CAA [RFC6844], and administrators for the account are named with
243 provided portal access for certificate issuance and management
244 options.
246 While ACME allows for the client to directly establish an account
247 with a CA, an initial out-of-band process for this step may assist
248 with the additional requirements for EV certificates and assurance
249 levels typically required for code signing certificates. For
250 standard certificates, with a recommendation for additional vetting
251 through extended challenge options to enable ACME to establish the
252 account directly. In cases where code signing certificates are used
253 heavily for an organization, having the portal access replaced with
254 ACME authenticated client access with extra challenges for
255 authentication may be an option to automate the functionality.
257 [For standard certificates, is it worth defining SMS and email for
258 the challenge? Obviously, EV needs more, so a few choices are
259 suggested in this revision.]
261 To improve the vetting process, ACME's optional use of CAA [RFC6844]
262 with the Directory "meta" data "caaIdentities" ([RFC8555]
263 Section 9.7.6) assists with the validation that a CA may have issue
264 certificates for any particular domain and is RECOMMENDED for use
265 with code signing certificates for this additional level of
266 validation checking on issued certificates.
268 As noted in RFC8555, "the external account binding feature (see
269 Section 7.3.4) can allow an ACME account to use authorizations that
270 have been granted to an external, non-ACME account. This allows ACME
271 to address issuance scenarios that cannot yet be fully automated,
272 such as the issuance of "Extended Validation" certificates."
274 The ACME challenge object, [RFC8555] Section 7.1.5 is RECOMMENDED for
275 use for Pre-authorization ([RFC8555] Section 7.4.1). Additional
276 challenge types are added to provide higher levels of security for
277 this issuance verification step. The use of OTP, FIDO credentials
278 (public/private key pairs), or validation from a certificate issued
279 at account setup time are defined in Section 8. Pre-Authoriziation.
281 Questions for reviewers:
283 [Is there interest to set a specific or default challenge object for
284 CodeSigning Certificates? Or should this be left to individual CAs
285 to decide and differentiate? The current challenge types defined in
286 RFC8555 include HTTPS (provisioning HTTP resources) and DNS
287 (provisioning a TXT resource record). Use of DNS may be possible,
288 but the HTTP resource doesn't necessarily make sense. Since the
289 process to retrieve an EV CodeSigning certificate usually requires
290 proof of the organization and validation from one of 2 named
291 administrators, some other challenge type like public/private key
292 pairs or OTP may be needed as defined challenge types. An
293 organization may want to tie this contact to a role rather than a
294 person and that consideration should be made in the design as well as
295 implementation by organizations.]
297 ACME provides an option for notification of the operator via email or
298 SMS upon issuance/renewal of a certificate after the domain has been
299 validated as owned by the requestor. This option is RECOMMENDED due
300 to the security considerations of code signing certificates as a way
301 to limit or reduce the possibility of a third party gaining access to
302 a code signing certificate inappropriately. Development of
303 additional challenge types is included in this document to support
304 this for pre-authorization, which would better match the security
305 considerations for this certificate type. Additional types may be
306 added if agreed upon by the working group.
308 Since DNS is used to identify the organization in the request, the
309 identifier "type" ([RFC8555]Section 7.4) is set to dns, not requiring
310 any additions to the ACME protocol for this type of certificate. The
311 distinction lies in the CSR, where the values are set to request a
312 CodeSigning certificate for a client certificate. [Question: Is it
313 helpful to define an identifier for the administrator or for the
314 developer to distinguish the certificate type in ACME and not just
315 the CSR?]
317 KeyUsage (DigitalSignature) and ExtendedKeyUsage (CodeSigning) in the
318 CSR MUST be set to the correct values for the CA to see the request
319 is for a Code Signing certificate. The Enhanced Key Usage SHOULD be
320 set to show this is a client certificate., using OID
321 "1.3.6.1.5.5.7.3.2". The CN MUST be set to the expected registered
322 domain with the CA account.
324 An advantage of ACME is the ability to automate rollover to allow for
325 easy management of short expiry times on certificates. The lifetime
326 of CodeSigning certificates is typically a year or two, but
327 automation could allow for shorter expiry times becoming feasible.
328 However, lifetimes are less of an issue for code signing certificates
329 than other certificate types. however there is a legitmate case for
330 "one signature per certificate." Automation might be helpful in this
331 case if patches or software updates were frequent or to minimize the
332 knowledge needed for the organization using this method.
334 Automation of storage to an HSM, which typically requires
335 authentication is intentionally left out-of-scope.
337 5. Pre-authorization
339 Additional challenge types are defined here for the verification of
340 administrators at an organization requesting CodeSigning
341 certificates. SMS and email are listed as possible in RFC8555 and
342 may be used singularly or in combination as the ACME protocol allows
343 for multiple pre-authorization challenges to be issued. Additional
344 pre-authorization types are defined that provide a higher level of
345 assurance to authorize a request.
347 6. Challenge Types
349 The challenge types defined in the following subsections are to
350 authenticate individuals or holders of specific pre-issued
351 credentials (users acting in roles for an organization). The
352 challenge types can be used to obtain end user certificate types or
353 as a pre-authorization challenges with certificate types such as the
354 Code Signing Certificate. Please note that the pre-authorization
355 challenge is also coupled with the account certificate in ACME for
356 verification. The process for obtaining EV Code Signing Certificates
357 typically requires authorization from one or more individuals in a
358 role for the organization. The use of pre-issued secure credentials,
359 at an assurance level appropriate for the certificate type being
360 issued, provides a way to automate the issuance and renewal process.
362 6.1. One Time Password (OTP)
364 There are numerous one time password technologies with slight
365 variations between implementations. The response to the challenge is
366 entered in the provided URL, offering flexibility to those using this
367 challenge type to acomodate the specific requirements of their
368 solution. Looking at 2 OTP solutions, the challenge response is
369 provided via a tool or app without any user interaction of
370 information required from the server to generate the challenge. The
371 2 solutions that operate in this manner include SecureID and Duo
372 Security. If a challenge is required to generate the response to be
373 provided in the URL, the token can supply the challenge.
375 type (required, string): The string "otp-01".
377 token (required, string): A random value that uniquely identifies
378 the challenge. OTP types and input vary between technologies.
379 The token value will match the type expected for the pre-issued
380 OTP credential. The user will be able to supply a response in the
381 provided URL from this challenge. It MUST NOT contain any
382 characters outside the base64url alphabet and MUST NOT include
383 base64 padding characters ("=").
385 {
386 "type": "otp-01",
387 "url": "https://example.com/acme/chall/WrV_H87EyD3",
388 "status": "pending",
389 "token": "challenge"
390 }
392 6.1.1. HMAC-Based One-Time Password (HOTP)
394 HOTP([RFC4226]) describes an algorithm for the generation of time-
395 based password values.
397 type (required, string): The string "hotp-01".
399 token (required, string): The HOTP value. This SHOULD be the 6
400 digit representation.
402 {
403 "type": "hotp-01",
404 "url": "https://example.com/acme/chall/WrV_H87EyD3",
405 "status": "pending",
406 "token": "123456"
407 }
409 6.1.2. Time-Based One-Time Password (TOTP)
411 TOTP([RFC6238]) describes an algorithm for the generation of time-
412 based password values, an extension from HOTP.
414 type (required, string): The string "totp-01".
416 token (required, string): The TOTP value. This SHOULD be the 6
417 digit representation.
419 {
420 "type": "totp-01",
421 "url": "https://example.com/acme/chall/WrV_H87EyD3",
422 "status": "pending",
423 "token": "123456"
424 }
426 6.1.3. Generic One Time Password (OTP)
428 There are numerous other one time password technologies with slight
429 variations between implementations. The response to the challenge is
430 entered in the provided URL, offering flexibility to those using this
431 challenge type to acomodate the specific requirements of their
432 solution. Looking at 2 OTP solutions, the challenge response is
433 provided via a tool or app without any user interaction of
434 information required from the server to generate the challenge. The
435 2 solutions that operate in this manner include SecureID and Duo
436 Security. If a challenge is required to generate the response to be
437 provided in the URL, the token can supply the challenge.
439 type (required, string): The string "otp-01".
441 token (required, string): A random value that uniquely identifies
442 the challenge. OTP types and input vary between technologies.
443 The token value will match the type expected for the pre-issued
444 OTP credential. The user will be able to supply a response in the
445 provided URL from this challenge. It MUST NOT contain any
446 characters outside the base64url alphabet and MUST NOT include
447 base64 padding characters ("=").
449 {
450 "type": "otp-01",
451 "url": "https://example.com/acme/chall/WrV_H87EyD3",
452 "status": "pending",
453 "token": "challenge"
454 }
456 6.2. Public Key Cryptography
458 Certificates may be pre-issued and stored according to assurance
459 level requirements for the purpose of identifying a user's identity.
460 If a higher assurance level is needed for a user serving in a
461 specific role or for that individual, it is possible for identity
462 proofing to occur in person using identifiers acceptable for the
463 specified process and the private key stored appropriately for the
464 required assurance level. PKCS#11 software or hardware tokens are
465 both possible options. This model assumes that there may be multiple
466 authorized users with different certificates that can be used for the
467 authorization or pre-authentication challenge. As such, the user
468 first provides the digital signature, so the account management can
469 determine if one of the acceptable certificates was used to digitally
470 sign the token.
472 type (required, string): The string "cert-01".
474 token (required, string): A random value that uniquely identifies
475 the challenge. The token for a certificate authentication
476 challenge includes a value for the recipeint to digitally sign
477 using their private key and post to the provided URL. The ACME
478 server then uses the digitally signed content to verify that the
479 challenge was signed using authorized credentials (certificate
480 issued and authorized for this challenge type). It MUST NOT
481 contain any characters outside the base64url alphabet and MUST NOT
482 include base64 padding characters ("=").
484 {
485 "type": "cert-01",
486 "url": "https://example.com/acme/chall/WrV_H87EyD3",
487 "status": "pending",
488 "token": "Some challenge to digitally sign"
489 }
491 6.3. WebAuthn or Public/Private Key Pairs
493 W3C's WebAuthn uses raw public/private key pairs that are issued
494 specific to a service. If WebAuthn or public/private key pairs
495 (PPKP) are selected as the challenge type, the account and credential
496 issuance will have to occur prior to use of this challenge type. The
497 WebAuthn or public/private key pair credentials would be specific to
498 the certificate management account and would be created by the
499 client, then registered with the service as occurs with normal
500 WebAuthn regisration of credentials. As with normal WebAuthn and
501 public/private key pairs, the token or challenge is digitally signed
502 to prove possession of the private key.
504 type (required, string): The string "ppkp-01".
506 token (required, string): A random value that uniquely identifies
507 the challenge. This challenge will operate much in the same way
508 as the certificate challenge as the operations are largely the
509 same. The user will be able to supply a response in the provided
510 URL from this challenge. It MUST NOT contain any characters
511 outside the base64url alphabet and MUST NOT include base64 padding
512 characters ("=").
514 {
515 "type": "ppkp-01",
516 "url": "https://example.com/acme/chall/WrV_H87EyD3",
517 "status": "pending",
518 "token": "Some challenge to sign"
519 }
521 7. Security Considerations
523 This will likely be full of considerations and is TBD for this
524 revision until challenge types are settled.
526 8. IANA Considerations
528 This memo includes no request to IANA, yet.
530 9. Contributors
532 Thank you to reviewers and contributors who helped to improve this
533 document. Thank you to Thomas Peterson who added the one-time
534 password types, HOTP and TOTP. Thank you to Tim Hollebeek for your
535 early review and added text specific to EV certificate issuance and
536 one time use code signing certificates. Thank you to Andrei Popov
537 and Deb Cooley for your reviews and suggestions made in -04. Thank
538 you to those who reviewed the CAA text removed in version -05
539 including: Carl Mehner, Roland Shoemaker, Ben Schwartz, and Ryan
540 Sleevi. Posted WG version. -02 updates authors email address.
542 10. References
544 10.1. Normative References
546 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
547 Requirement Levels", BCP 14, RFC 2119,
548 DOI 10.17487/RFC2119, March 1997,
549 .
551 [RFC4226] M'Raihi, D., Bellare, M., Hoornaert, F., Naccache, D., and
552 O. Ranen, "HOTP: An HMAC-Based One-Time Password
553 Algorithm", RFC 4226, DOI 10.17487/RFC4226, December 2005,
554 .
556 [RFC6238] M'Raihi, D., Machani, S., Pei, M., and J. Rydell, "TOTP:
557 Time-Based One-Time Password Algorithm", RFC 6238,
558 DOI 10.17487/RFC6238, May 2011,
559 .
561 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
562 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
563 May 2017, .
565 [RFC8555] Barnes, R., Hoffman-Andrews, J., McCarney, D., and J.
566 Kasten, "Automatic Certificate Management Environment
567 (ACME)", RFC 8555, DOI 10.17487/RFC8555, March 2019,
568 .
570 [RFC7030] Pritikin, M., Ed., Yee, P., Ed., and D. Harkins, Ed.,
571 "Enrollment over Secure Transport", RFC 7030,
572 DOI 10.17487/RFC7030, October 2013,
573 .
575 10.2. Informative References
577 [I-D.ietf-acme-ip]
578 Shoemaker, R. B., "Automated Certificate Management
579 Environment (ACME) IP Identifier Validation Extension",
580 Work in Progress, Internet-Draft, draft-ietf-acme-ip-08, 1
581 October 2019, .
584 10.3. URL References
586 [NIST800-63r3]
587 US National Institute of Standards and Technology,
588 "https://nvlpubs.nist.gov/nistpubs/SpecialPublications/
589 NIST.SP.800-63-3.pdf".
591 [NIST800-63A]
592 US National Institute of Standards and Technology,
593 "https://nvlpubs.nist.gov/nistpubs/SpecialPublications/
594 NIST.SP.800-63a.pdf".
596 [NIST800-63B]
597 US National Institute of Standards and Technology,
598 "https://nvlpubs.nist.gov/nistpubs/SpecialPublications/
599 NIST.SP.800-63b.pdf".
601 [NIST800-63C]
602 US National Institute of Standards and Technology,
603 "https://nvlpubs.nist.gov/nistpubs/SpecialPublications/
604 NIST.SP.800-63c.pdf".
606 Appendix A. Change Log
608 Note to RFC Editor: if this document does not obsolete an existing
609 RFC, please remove this appendix before publication as an RFC.
611 02 draft added subsections contributed from Thomas Peterson on HOTP
612 and TOTP.
614 Appendix B. Open Issues
616 Note to RFC Editor: please remove this appendix before publication as
617 an RFC.
619 Author's Address
621 Kathleen M. Moriarty
622 Dell Technologies
623 176 South Street
624 Hopkinton,
625 United States of America
627 Email: Kathleen.Moriarty.ietf@gmail.com