Network Working Group                                         S. Farrell
Internet-Draft                                    Trinity College Dublin
Intended status: Experimental                                 P. Hoffman
Expires: January 16, 2014                                 VPN Consortium
                                                               M. Thomas
                                                           July 15, 2013

                HTTP Origin-Bound Authentication (HOBA)


   HTTP Origin-Bound Authentication (HOBA) is a design for an HTTP
   authentication method with credentials that are not vulnerable to
   phishing attacks, and that does not require a server-side password
   database.  The design can also be used in Javascript-based
   authentication embedded in HTML.  HOBA is an alternative to HTTP
   authentication schemes that require passwords with all the negative
   attributes that come with password-based systems.

Status of this Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
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   Drafts is at

   Internet-Drafts are draft documents valid for a maximum of six months
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   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on January 16, 2014.

Copyright Notice

   Copyright (c) 2013 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   ( in effect on the date of
   publication of this document.  Please review these documents

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   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
     1.1.  Interfacing to Applications (Cookies)  . . . . . . . . . .  5
     1.2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . .  6
   2.  The HOBA Authentication Scheme . . . . . . . . . . . . . . . .  6
   3.  HOBA HTTP Authentication Mechanism . . . . . . . . . . . . . .  8
   4.  Using HOBA-http  . . . . . . . . . . . . . . . . . . . . . . .  9
     4.1.  CPK Preparation Phase  . . . . . . . . . . . . . . . . . . 10
     4.2.  Signing Phase  . . . . . . . . . . . . . . . . . . . . . . 10
     4.3.  Authentication Phase . . . . . . . . . . . . . . . . . . . 10
     4.4.  Logging in on a New User Agent . . . . . . . . . . . . . . 11
   5.  Using HOBA-js  . . . . . . . . . . . . . . . . . . . . . . . . 11
     5.1.  Key Storage  . . . . . . . . . . . . . . . . . . . . . . . 12
     5.2.  User Join  . . . . . . . . . . . . . . . . . . . . . . . . 12
     5.3.  User Login . . . . . . . . . . . . . . . . . . . . . . . . 12
     5.4.  Enrolling a New User Agent . . . . . . . . . . . . . . . . 12
     5.5.  Replay Protection  . . . . . . . . . . . . . . . . . . . . 13
     5.6.  Signature Parameters . . . . . . . . . . . . . . . . . . . 13
     5.7.  Session Management . . . . . . . . . . . . . . . . . . . . 15
     5.8.  Multiple Accounts on One User Agent  . . . . . . . . . . . 15
     5.9.  Oddities . . . . . . . . . . . . . . . . . . . . . . . . . 16
   6.  Additional Services  . . . . . . . . . . . . . . . . . . . . . 16
     6.1.  Registration . . . . . . . . . . . . . . . . . . . . . . . 16
     6.2.  Associating Additional Keys to an Exiting Account  . . . . 17
     6.3.  Logging Out  . . . . . . . . . . . . . . . . . . . . . . . 18
     6.4.  Getting a Fresh Challenge  . . . . . . . . . . . . . . . . 18
   7.  Mandatory-to-Implement Algorithms  . . . . . . . . . . . . . . 18
   8.  Security Considerations  . . . . . . . . . . . . . . . . . . . 18
     8.1.  localStorage Security for Javascript . . . . . . . . . . . 19
   9.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 19
     9.1.  HOBA Authentication Scheme . . . . . . . . . . . . . . . . 20
     9.2.  .well-known URLs . . . . . . . . . . . . . . . . . . . . . 20
     9.3.  Algorithm Names  . . . . . . . . . . . . . . . . . . . . . 20
     9.4.  Key Identifier Types . . . . . . . . . . . . . . . . . . . 20
     9.5.  Device Identifier Types  . . . . . . . . . . . . . . . . . 20
   10. Implementation Status  . . . . . . . . . . . . . . . . . . . . 20
   11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 21
   12. References . . . . . . . . . . . . . . . . . . . . . . . . . . 21
     12.1. Normative References . . . . . . . . . . . . . . . . . . . 21
     12.2. Informative References . . . . . . . . . . . . . . . . . . 22
   Appendix A.  Problems with Passwords . . . . . . . . . . . . . . . 23
   Appendix B.  Examples  . . . . . . . . . . . . . . . . . . . . . . 23
   Appendix C.  Changes . . . . . . . . . . . . . . . . . . . . . . . 25
     C.1.  WG-01  . . . . . . . . . . . . . . . . . . . . . . . . . . 25
     C.2.  WG-00  . . . . . . . . . . . . . . . . . . . . . . . . . . 25
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 25

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1.  Introduction

   [[ Commentary is in double-square brackets, like this.  As you'll see
   there are a bunch of details still to be figured out.  Feedback on
   those is very welcome.  Also note that the authors fully expect that
   the description of HOBA-http and HOBA-js to be mostly merged in the
   draft; they're both here now so readers can see some alternatives and
   maybe support particular proposals. ]]

   HTTP Origin-Bound Authentication (HOBA) is an authentication design
   that can be used as an HTTP authentication scheme and for Javascript-
   based authentication embedded in HTML.  The main goal of HOBA is to
   offer an easy-to-implement authentication scheme that is not based on
   passwords, but that can easily replace HTTP or HTML forms-based
   password authentication.  If deployment of HOBA reduces the number of
   password entries in databases by any appreciable amount, then it
   would be worthwhile.  As an HTTP authentication scheme, it would work
   in the current HTTP 1.0 and HTTP 1.1 authentication framework, and
   will very likely work with whatever changes are made to the HTTP
   authentication scheme in HTTP 2.0.  As a JavaScript design, HOBA
   demonstrates a way for clients and servers to interact using the same
   credentials that are use by the HTTP authentication scheme.

   The HTTP specification defines basic and digest authentication
   methods for HTTP that have been in use for many years, but which,
   being based on passwords, are susceptible to theft of server-side
   databases.  (See [RFC2617] for the original specification, and
   [I-D.ietf-httpbis-p7-auth] for clarifications and updates to the
   authentication mechanism.)  Even though few large web sites use basic
   and digest authentication, they still use username/password
   authentication and thus have large susceptible server-side databases
   of passwords.

   Instead of passwords, HOBA uses digital signatures as an
   authentication mechanism.  HOBA also adds useful features such as
   credential management and session logout.  In HOBA, the client
   creates a new public-private key pair for each host ("web-origin") to
   which it authenticates; web-origins are defined in [RFC6454].  These
   keys are used in HOBA for HTTP clients to authenticate themselves to
   servers in the HTTP protocol or in a Javascript authentication

   HOBA keys need not be stored in public key certificates.  Because
   these are generally "bare keys", there is none of the semantic
   overhead of PKIX certificates, particularly with respect to naming
   and trust anchors.  Thus, client public keys ("CPKs") do not have any
   publicly-visible identifier for the user who possesses the
   corresponding private key, nor the web-origin with which the client

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   is using the CPK.  HOBA keys are stored in subjectPublicKeyInfo
   structures from PKIX [RFC5280]

   HOBA also defines some services that are required for modern HTTP

   o  Servers can bind a CPK with an identifier, such as an account
      name.  HOBA allows servers to define their own policies for
      binding CPKs with accounts during account registration.

   o  Users are likely to use more than one device or user agent (UA)
      for the same HTTP based service, so HOBA gives a way to associate
      more than one CPK to the same account, but without having to
      register for each separately.

   o  Users are also likely to lose a private key, or the client's
      memory of which key pair is associated with which origin.  For
      example if a user loses the computer or mobile device in which
      state is stored.  HOBA allows for clients to tell servers to
      delete the association between an existing CPK and an account.

   o  Logout features can be useful for UAs, so HOBA defines a way to
      close a current HTTP "session", and also a way to close all
      current sessions, even if more than one session is currently
      active from different UAs for the same account.

   o  Since there are always devices and applications in which state of
      the art digital signature mechanism runtimes are significant, and
      since HTTP authentication in theory requires that every HTTP
      request to a given realm have a signature in an "Authorization"
      header field, and since HOBA is a challenge response scheme, we
      also define a way in which HTTP servers can indicate the duration
      for which they will consider a given challenge value to be valid.
      As a consequence we also define a way for UAs to fetch a fresh

1.1.  Interfacing to Applications (Cookies)

   HOBA can be used as a drop-in replacement for password-based user
   authentication schemes used in common web applications.  The simplest
   way in which this can be done is to (re-)direct the UA to a HOBA
   "Login" URL and for the response to a successful HTTP request
   containing a HOBA signature to set a session cookie [RFC6265].
   Further interactions with the web application will then be secured
   via the session cookie, as is commonly done today.

   While cookies are bearer tokens, and thus weaker than HOBA
   signatures, they are currently ubiquitously used.  If non-bearer

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   token session continuation schemes are developed in future in the
   IETF or elsewhere, then those can interface to HOBA as easily as with
   any password based authentication scheme.

1.2.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in RFC 2119 [RFC2119].

   A client public key ("CPK") is the public key and associated
   cryptographic parameters needed for a server to validate a signature.

   The term "account" is (loosely) used to refer to whatever data
   structure(s) the server maintains that are associated with an
   identity.  That will contain of at least one CPK and a web-origin; it
   will also optionally include an HTTP "realm" as defined in the HTTP
   authentication specification.  It might also involve many other non-
   standard pieces of data that the server accumulates as part of
   account creation processes.  An account may have many CPKs that are
   considered equivalent in terms of being usable for authentication,
   but the meaning of "equivalent" is really up to the server and is not
   defined here.

   When describing something that is specific to HOBA as an HTTP
   authentication mechanism or HOBA as a JavaScript implementation, this
   document uses the terms "HOBA-http" and "HOBA-js", respectively.

   Web client: the content and javascript code that run within the
   context of a single UA instance (such as a tab in a web browser).

   User agent (UA): typically, but not always, a web browser.

   User: a person who is running a UA.  In this document, "user" does
   not mean "user name" or "account name".

   This specification uses the Augmented Backus-Naur Form (ABNF)
   notation of [RFC5234]

2.  The HOBA Authentication Scheme

   A UA that implements HOBA maintains a list of web-origins and realms.
   The UA also maintains one or more client credentials for each web-
   origin/realm combination for which it has created a CPK.

   On receipt of a challenge (and optional realm) from a server, the
   client marshals an HOBA to-be-signed (TBS) blob that includes a

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   client generated nonce, the web-origin, the realm, an identifier for
   the CPK and the challenge string; and signs that hashed blob with the
   private key corresponding to the CPK for that web-origin.  The
   formatting chosen for this TBS blob is chosen so as to make server-
   side signature verification as simple as possible for a wide-range of
   current server tooling.

   Figure 1 specifies the ABNF for the signature input.

              HOBA-TBS = nonce alg origin realm kid challenge
              nonce = unreserved
              alg = 1*2DIGIT
              origin = scheme authority port
              realm = unreserved
              kid = unreserved
              challenge = unreserved

                   Figure 1: To-be-signed data for HOBA

   The fields above contain the following:

   o  nonce: is a random value chosen by the UA and MUST be base64url
      encoded before being included in the HOBA-TBS value.  UAs MUST be
      able to use at least 32 bits of randomness in generating a nonce.
      UAs SHOULD be able to use up to 64 bits of randomness for nonces.

   o  alg: specifies the signature algorithm being used encoded as an
      ASCII character as defined in Section 9.3.  RSA-SHA256 MUST be
      supported, RSA-SHA1 MAY be supported.  The IANA registered
      algorithm values are encoded as ASCII numbers; for example, the
      encoding of RSA-SHA256 is 0x30.

   o  origin: is the web origin expressed as the concatenation of the
      scheme, authority and port are from [RFC3986].  These are not
      base64 encoded as they will be most readily available to the
      server in plain text.  For example, if accessing the URL
      "" then the bytes input to the
      signature process will be "httpswww.example.com8080"

   o  realm: is similarly just a string with the syntactic restrictions
      defined in [I-D.ietf-httpbis-p7-auth].  If no realm is specified
      for this authentication then this is absent.  (A missing field
      here is no problem since both sides know when it needs to be

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   o  kid: is a key identifier - this MUST be a base64url encoded value
      that is presented to the server in the HOBA client result (see

   o  challenge: MUST be a base64url encoded challenge value that the
      server chose to send to the client

   The HOBA-TBS string is the input to the client's signing process, but
   is not itself sent over the network since some fields are already
   inherent in the HTTP exchange.  The challenge however is sent over
   the network so as to make it simpler for a server to be stateless.
   (One form of stateless challenge might be a ciphertext that the
   server decrypts and checks, but that is an implementation detail.)
   The value that is sent over the network is the HOBA "client result"
   which we now define.

   The HOBA "client result" is a dot-separated string that includes the
   signature and is sent in the HTTP Authorized header field value using
   the value syntax defined in Figure 2.  The "sig" value is the
   base64url encoded version of the binary output of the signing
   process.  The kid, challenge and nonce are as defined above and are
   also base64url encoded.  [[Expect more changes here.  This is very
   like JOSE's compact form and maybe ought be an instance of that.]]

               HOBA-RES = kid "." challenge "." nonce "." sig
               sig = unreserved

                    Figure 2: HOBA Client Result value

   The HOBA scheme is far from new, for example, the basic idea is
   pretty much identical to the first two messages from "Mechanism R" on
   page 6 of [MI93] which predates HOBA by 20 years.

3.  HOBA HTTP Authentication Mechanism

   An HTTP server that supports HOBA authentication includes the "HOBA"
   auth-scheme value in a WWW-Authenticate header field when it wants
   the client to authenticate with HOBA.

   o  If the "HOBA" scheme is listed, it MUST be followed by two or more
      auth-param values.  The auth-param attributes defined by this
      specification are below.  Other auth-param attributes MAY be used
      as well.  Unknown auth-param attributes MUST be ignored by
      clients, if present.

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   o  The "challenge" attribute MUST be included.  The challenge is the
      string made up of the base64url encoded octets that the server
      wants the client to sign in its response.  The challenge SHOULD be
      unique for every HTTP 401 response in order to prevent replay
      attacks from passive observers.

   o  An "expires" attribute MUST be included that specifies the number
      of seconds from the time the HTTP response is emitted for which
      responses to this challenge can be accepted.

   o  A "realm" attribute MAY be included to indicate the scope of
      protection in the manner described in HTTP/1.1, Part 7
      [I-D.ietf-httpbis-p7-auth].  The "realm" attribute MUST NOT appear
      more than once.

   When the "client response" is created, the UA encodes the HOBA
   client-result (a string matching the HOBA-RES production in Figure 2
   as an auth-param with the name "result" and returns that in the
   Authorization header.

   Note that a HOBA signature is good for however long the expires
   attribute allows.  This means that replay is potentially possible
   within the time window specified by the "expires" value chosen by the
   server.  Servers SHOULD attempt to detect any such replay and MAY
   react to such replays by responding with a second (or subsequent)
   401-status HTTP response containing a new challenge.

   UAs MAY optimise their use of challenges by pre-fetching a challenge
   value, for example after "expires"/2 seconds have elapsed using the
   ".well-known/hoba/getChal" scheme described below.  This also allows
   for pre-calculation of HOBA signatures, if that is required in order
   to produce a responsive user interface.

4.  Using HOBA-http

   [[A lot of this is similar to the HOBA-js discussion below.  At some
   point some nuclear fusion might be nice, but for now it might be best
   to keep them separate until we understand better what can be merged,
   and what is different.]]

   The interaction between an HTTP client and HTTP server using HOBA
   happens in three phases: the CPK preparation phase, the signing
   phase, and the authentication phase.  The first and second phase are
   done in a standard fashion; the third is done using site-specific
   methods.  In addition, we provide a mechanism for pre-fetching

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4.1.  CPK Preparation Phase

   In the CPK preparation phase, the client determines if it already has
   a CPK for the web-origin it is going to.  If the has a CPK, the
   client will use it; if the client does not have a CPK, it generates
   one in anticipation of the server asking for one.

4.2.  Signing Phase

   In the signing phase, the client connects to the server, the server
   asks for HOBA-based authentication, and the client authenticates by
   signing a blob of information as described in the previous sections.

   The UA tries to access a protected resource on the server.  The
   server sends the HOBA WWW-Authenticate challenge.  The UA receives
   the challenge and signs the challenge using the CPK it either already
   had or just generated.  The server validates the signature.  If
   validation fails, or if the server chooses to do so for other
   reasons, then server aborts the transaction via a 403 Unauthorized
   HTTP response.

4.3.  Authentication Phase

   In the authentication phase, the server extracts the CPK from the
   signing phase and decides if it recognizes the CPK.  If the server
   recognizes the CPK, the server may finish the client authentication
   process.  If this stage of the process involves additional
   information for authentication, such as asking the user which account
   she wants to use (in the case where a UA is used for multiple
   accounts on a site), the server can prompt the user for account
   identifying information or the user could choose based on HTML
   offered by the server before the 401 is triggered.  None of this is
   standardized: it all follows the server's security policy and session
   flow.  At the end of this, the server probably assigns or updates a
   session cookie for the client.

   If the server does not recognize the CPK the server might send the
   client through a either a join or login-new-UA (see below) process.
   This process is completely up to the server, and probably entails
   using HTML and JavaScript to ask the user some questions in order to
   assess whether or not the server wants to give the client an account.
   Completion of the joining process might require confirmation by
   email, SMS, Captcha, and so on.

   Note that there is no necessity for the server to initiate a joining
   or login process upon completion of the signing phase.  Indeed, the
   server may desire to challenge the UA even for unprotected resources
   and set a session cookie for later use in a join or login process as

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   it becomes necessary.  For example, a server might only want to offer
   an account to someone who had been to a few pages on the web site; in
   such a case, the server could use the CPK from an associated session
   cookie as a way of building reputation for the user until the server
   wants the user to join.

   After the UA is authenticated (if the user had to join, this could be
   the last step of joining), the server gives the UA access to the
   protected resource that was originally requested at the beginning of
   the signing phase.  It is quite likely that the server would also
   update the UA's session cookie for the web site.

4.4.  Logging in on a New User Agent

   When a user wants to use a new UA for an existing account, the flows
   are similar to logging in with an already-joined UA or joining for
   the first time.  In fact, the CPK preparation phase (with the UA
   knowing that it needs to create a new CPK) and the signing phase are

   During the authentication phase, the server could use HTML and
   JavaScript to ask the user if they are really a new user or want to
   associate this new CPK with an already-joined CPK.  The server can
   then use some out-of-band method (such as a confirmation email round
   trip, SMS, or an UA that is already enrolled) to verify that the
   "new" user is the same as the already-enrolled one.

5.  Using HOBA-js

   [[ A description of how to use the same HOBA semantics, but doing
   everything in Javascript in a web page.  This is more of a
   demonstration that you could get the similar semantics via JS rather
   than a normative section.]]

   Web sites using javascript can also perform origin-bound
   authentication without needing to involve the http layer, and by
   inference not needing HOBA-specific support in browsers.  One element
   is required: localStorage (see, and
   one when it is available will be highly desirable: WebCrypto (see  In lieu of WebCrypto, javascript
   crypto libraries can be employed with the known deficiencies of PRNG,
   and the general immaturity of those libraries.  The following section
   outlines a mechanism for Javascript HOBA clients to initially enroll,
   subsequent enrollment on new clients, login, and how HOBA-js relates
   to web based session management.  As with HOBA-http, a pure
   Javascript implementation retains the property that only CPKs are
   stored on the server, so that server compromise doesn't suffer the

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   multiplier affect that the various recent password exposure debacles
   have vividly demonstrated.

5.1.  Key Storage

   We use HTML 5's localStorage feature for key storage.  Conceptually
   an implementation stores the dictionary account identifier, public
   key, private key tuples in the origin's localStorage for subsequent
   authentication requests.  How this is actually stored in localStorage
   is an implementation detail.  We rely on the security properties of
   the same-origin policy that localStorage enforces.  See the security
   considerations for discussion about attacks on localStorage.

5.2.  User Join

   To join a web site, the HOBA-js client generates a public/private key
   pair and takes as input the account identifier to which the key pair
   should be bound.  The key pair and account identifier are stored in
   localStorage for later use.  The UA then signs the join information
   (see below) using the private key, and forms a message with the
   public key (CPK) and the signed data.  The server receives the
   message and verifies the signed data using the supplied key.  The
   server creates the account and adds the public key to a list of
   public keys associated with this account.

5.3.  User Login

   Each time the user needs to log in to the server, it creates a login
   message (see below) and signs the message using the relevant private
   key stored in localStorage.  The signed login message along with the
   associated CPK identifier is sent to the server.  The server receives
   the message and verifies the signed data.  If the supplied public key
   is amongst the set of valid public keys for the supplied account,
   then the login proceeds.  See below for a discussion about replay.

5.4.  Enrolling a New User Agent

   When a user wants to start using a different UA, the website has two
   choices: use a currently enrolled UA to permit the enrollment or use
   a trusted out of band mechanism (eg email, sms, etc).  To enroll a
   new UA using an existing UA, the web site can display a one-time
   password on the currently enrolled UA.  This password is a one-time
   password and expires in a fixed amount of time (say, 30 minutes).  It
   doesn't need to be an overly fussy password since it's one-time and
   times out quickly.  The user then inputs the one-time password and
   the new UA generates a new asymmetric key pair and includes the one-
   time password in the login message to the server (see below).

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   Alternatively if an enrolled UA is not available, and the site has an
   out of band communication mechanism (eg, sms, email, etc) a user can
   request that a one-time password be sent to the user.  The server
   generates and stores the one-time password as above.  The user
   receives the one-time password, inputs as above on the new UA, and
   the HOBA-js client forms the login message as above.

   In both cases, when the server receives a login message with a one-
   time password, it checks to see if the password supplied is in a list
   of unexpired one-time passwords associated with that account.  If the
   password matches, the server verifies the signature, expires or
   deletes the one-time password and adds the supplied public key to the
   list of public keys associated with the user assuming the signature
   verified correctly.  Subsequent logins proceed as above in User

5.5.  Replay Protection

   To guard against replay of a legitimate login/join message, we use
   Kerberos-like timestamps in the expectation of synchronization
   between the browser's and server's clocks is sufficiently reliable.
   This saves an HTTP round trip which is desirable, though a challenge-
   response mechanism as in HOBA-http could also be used.  The client
   puts the current system time into the URL, and the server side vets
   it against its system time.  Like Kerberos, a replay cache covering a
   signature timeout window is required on the server.  This can be done
   using a database table that is keyed (in the database sense of the
   term) using the signature bits.  If the signature is in the replay
   table, it ought be rejected.  If the timestamp in the signature is
   outside the current replay cache window then it also gets rejected.

   [[ An addition of the ability for the server to reject a client with
   potential time skew and give it a nonce (as with HOBA-http) would
   allow the size of the replay cache to be set to just a few minutes
   rather than a much longer period.  Or the HOBA server could always
   use a nonce method.  This is worthy of more discussion. ]].

5.6.  Signature Parameters

   Since we only require agreement between the server and the client
   where the client is under the control of the server, the actual url
   parameter names here are only advisory.  For each signed url, the
   client forms a url with the necessary login/join information.  For
   example, suppose has login and join scripts with various


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   The client then appends a signature parameter block to the url:

   o  curtime: the time in milliseconds since unix epoch (ie, new Date
      ().getTime ()).

   o  pubkey: the url encoded public key.  See DKIM for the format of
      the base64 encoded PEM formated key.

   o  temppass: an optional url encoded one-time password for subsequent

   o  keyalg: currently RSA. 2048 bit keys should be use if WebCrypto is

   o  digestalg: currently SHA1.  SHA256 should be used if WebCrypto is

   o  signature: empty for signing canonicalization purposes

   [[ Signing the full url is problematic with PHP; we should take a
   clue from what OAUTH does here; we almost certainly need to add some
   host identifying information...]]  To create the signature, the
   canonical text includes the path portion, the site-specific url
   parameters and appends a signature block onto the end of the url.
   The signature block consists of the parameters listed above with an
   empty signature parameter (ie, signature=), eg:

   o  Login: /site/

   o  Join: /site/

   o  Login New User Agent: /site/

   The canonical signature text is then signed with the private key
   associated with the account.  The signature is then base64 encoded
   and appended to the full url, and sent to the server using
   XMLHttpRequest as usual.  On receipt of the login request, the server
   first extracts the timestamp (curtime) and determines whether the

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   timestamp is fresh (see above) rejecting the request if stale.  The
   server then removes the scheme and domain:port portion of the
   incoming url, and removes the signature value only to create the
   canonical signature text.  The server then extracts the public key
   along with the account and verifies the signature.  If the signature
   verifies, the server then determines whether this is an enrolled
   public key for the user.  If it is, login/join succeeds.  If the key
   is not enrolled, the server then checks to see if a one-time password
   was supplied.  If not, login/join fails.  If a one-time password was
   supplied, the server checks to see if a one-time password is valid
   and fails if not.  If valid, the server disables the one-time
   password (eg, deletes it from its database) and adds the new public
   key to the list of enrolled public keys for this user.

   Once verified, the server may start up normal cookie-based session
   management (see below).  The server should send back status to the
   HOBA-js client to determine whether the login/join was successful.
   The details are left as an implementation detail.

   Note: the client SHOULD use an HTTP POST for the XMLHttpRequest as
   both the public key and signature blocks may exhaust the maximum size
   for a GET request (typically around 2KB).

5.7.  Session Management

   Session Management is identical to username/password session
   management.  That is, the session management tool (such as PHP,
   Python CGI, and so on) inserts a session cookie into the output to
   the browser, and logging out simply removes the session cookie.
   HOBA-js does nothing to help or hurt session cookie hijacking -- TLS
   is still our friend.

5.8.  Multiple Accounts on One User Agent

   A shared UA with multiple accounts is possible if the account
   identifier is stored along with the asymmetric key pair binding them
   to one another.  Multiple entries can be kept, one for each account,
   and selected by the current user.  This, of course, is fraught with
   the possibility for abuse, since you're enrolling the device
   potentially long-term.  A couple of things can possibly be done to
   combat that.  First, the user can request that the credential be
   erased from keystore.  Similarly, in the enrollment phase, a user
   could request that the key pair only be kept for a certain amount of
   time, or that it not be stored at all.  Last, it's probably best to
   just not use shared devices at all since that's never especially

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5.9.  Oddities

   With the same-origin policy, subdomains do not have access to the
   same localStorage as parent domains do.  For larger/more complex
   sites this could be an issue that requires enrollment into subdomains
   with the requisite hassle for users.  One way to get around this is
   to use session cookies as they can be used across subdomains.  That
   is, login using a single well-known domain, and then use session
   cookies to navigate around a site.

6.  Additional Services

   HOBA uses a well-known URL [RFC5785] "hoba" as a base URI for
   performing many tasks: "".
   These URLs are based on the name of the host that the HTTP client is
   accessing.  There are many use cases for these URLs to redirect to
   other URLs: a site that does registration through a federated site, a
   site that only does registration under HTTPS, and so on.  Like any
   HTTP client, HOBA clients MUST be able to handle redirection of these
   URLs.  [[There are a bunch of security issues to consider related to
   cases where a re-direct brings you off-origin.]]

   All additional services MUST be done in TLS-protected sessions

6.1.  Registration

   Normally, a registration is expected to happen after a UA receives a
   WWW-Authenticate for a web-origin and realm for which it has no
   associated CPK.  The (protocol part of the) process of registration
   for a HOBA account on a server is relatively light-weight.  The UA
   generates a new key pair, and associates it with the web-origin/realm
   in question.  The UA sets up a TLS-protected session, goes to the
   registration URL ".well-known/hoba/register", and submits the CPK
   using a POST message as described below.  It is up to the server to
   decide what kind of user interaction is required before the account
   is finally set up.

   If the UA has a CPK associated with the web-origin, but not for the
   realm concerned, then a new registration is REQUIRED.  If the server
   did not wish for that outcome, then it ought not use a different

   The POST message sent to the registration URL contains an HTML form
   (x-www-form-encoded) with one mandatory field (pub) and some optional
   fields that allow the UA to specify the type and value of key and
   device identifiers that the UA wishes to use.  [[The device stuff is

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   just a thought.]]

   o  pub: is a mandatory field containing the PEM formatted public key
      of the client.  See Appendix C of [RFC6376] for an example of how
      to generate this key format.

   o  kidtype: contains the type of key identifier, this is a numeric
      value intended to contain one of the values from Section 9.4.  If
      this is not present then the mandatory to implement "DANE-hash"
      option MUST be used.

   o  kid: contains the key identifier as a base64url encoded string
      that is of the type indicated in the kidtype.  If the kid is a
      hash of a public key then the correct (base64url encoded) hash
      value MUST be provided and the server SHOULD check that and refuse
      the registration if an incorrect value was supplied.

   o  didtype: specifies a kind of device identifier intended to contain
      one of the values from Section 9.5, if absent then the "string"
      form of device identifier MUST be used.

   o  did: A UTF8 string that specifies the device identifier.  This can
      be used to help a user be confident that authentication has
      worked, e.g., following authentication some web content might say
      "You last logged in from device 'did' at time T."

6.2.  Associating Additional Keys to an Exiting Account

   It is common for a user to have multiple UAs, and to want all those
   UAs to be able to authenticate to a single account.  One method to
   allow a user who has an existing account to be able to authenticate
   on a second device is to securely transport the private and public
   keys and the origin information from the first device to the second.
   Previous history with such key transport has been spotty at best.  As
   an alternative, HOBA allows associating a CPK from the second device
   to the account created on the first device.

   Instead of registering on the new device, the UA generates a new key
   pair, associates it with the web-origin/realm in question, goes to
   the URL for starting an association, ".well-known/hoba/
   associate-start" in a TLS-protected session, and submits the new CPK
   using a POST message. [[ More description is clearly needed here. ]]
   The server's response to this request is a nonce with at least 128
   bits of entropy.  That nonce SHOULD be easy for the user to copy and
   type, such as using Base32 encoding (see [RFC4648]).  The user then
   uses the first UA to log into the origin, goes to the URL for
   finishing an association, ".well-known/hoba/associate-finish", and
   submits the nonce using a POST message. [[ More description is

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   clearly needed here. ]].  The server then knows that the
   authenticated user is associated with the second CPK.  The server can
   choose to associate the two CPKs with one account.  Whether to do so
   is entirely at the server's discretion however, but the server SHOULD
   make the outcome clear to the user.

6.3.  Logging Out

   When the user wishes to logout, the UA simply goes to ".well-known/
   hoba/logout".  The UA MAY also delete session cookies associated with
   the session.  [[Is that right?, maybe a SHOULD- or MUST-delete would
   be better]]

   The server-side MUST NOT allow TLS session resumption for any logged
   out session and SHOULD also revoke or delete any cookies associated
   with the session.

6.4.  Getting a Fresh Challenge

   If the UA would like a "fresh" challenge then it can send a POST or
   GET message to ".well-known/hoba/getchal".  A successful (200 status)
   response MUST include a fresh (base64url encoded) HOBA challenge for
   this origin in the body of the response.

7.  Mandatory-to-Implement Algorithms

   RSA-SHA256 MUST be supported.  RSA-SHA1 MAY be used.  RSA modulus
   lengths of at least 2048 bits SHOULD be used.

   [[Maybe we should add ECDSA with P256 for shorter signatures.]]

8.  Security Considerations

   If key binding was server-selected then a bad actor could bind
   different accounts belonging to the user from the network with
   possible bad consequences, especially if one of the private keys was
   compromised somehow.

   Binding my CPK with someone else's account would be fun and
   profitable so SHOULD be appropriately hard.  In particular the string
   generated by the server MUST be hard to guess, for whatever level of
   difficulty is chosen by the server.  The server SHOULD NOT allow a
   random guess to reveal whether or not an account exists.

   [[The potential impact on privacy of HOBA needs to be addressed.  If
   a site can use a 401 and a CPK to track users without permission that

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   would be not-so-nice so some guidance on how a UA could indicate to a
   user that HOBA stuff is going on might be needed.]]

   [[lots more TBD, be nice to your private keys etc. etc.]]

8.1.  localStorage Security for Javascript

   Our use of localStorage will undoubtedly be a cause for concern.
   localStorage uses the same-origin model which says that the scheme,
   domain and port define a localStorage instance.  Beyond that, any
   code executing will have access to private keying material.  Of
   particular concern are XSS attacks which could conceivably take the
   keying material and use it to create UAs under the control of an
   attacker.  But XSS attacks are in reality across the board
   devastating since they can and do steal credit card information,
   passwords, perform illicit acts, etc, etc.  It's not clear that we
   introduce unique threats from which clear text passwords don't
   already suffer.

   Another source of concern is local access to the keys.  That is, if
   an attacker has access to the UA itself, they could snoop on the key
   through a javascript console, or find the file(s) that implement
   localStorage on the host computer.  Again it's not clear that we are
   worse in this regard because the same attacker could get at browser
   password files, etc too.  One possible mitigation is to encrypt the
   keystore with a password/pin the user supplies.  This may sound
   counter intuitive, but the object here is to keep passwords off of
   servers to mitigate the multiplier effect of a large scale compromise
   ala LinkedIn because of shared passwords across sites.

   It's worth noting that HOBA uses asymmetric keys and not passwords
   when evaluating threats.  As various password database leaks have
   shown, the real threat of a password breach is not just to the site
   that was breached, it's all of the sites a user used the same
   password on too.  That is, the collateral damage is severe because
   password reuse is common.  Storing a password in localStorage would
   also have a similar multiplier effect for an attacker, though perhaps
   on a smaller scale than a server-side compromise: one successful
   crack gains the attacker potential access to hundreds if not
   thousands of sites the user visits.  HOBA does not suffer from that
   attack multiplier since each asymmetric key pair is unique per site/

9.  IANA Considerations

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9.1.  HOBA Authentication Scheme

   Authentication Scheme Name: HOBA

   Pointer to specification text: [[ this document ]]

   Notes (optional): The HOBA scheme can be used with either HTTP
   servers or proxies.  [[But we need to figure out the proxy angle;-)]]

9.2.  .well-known URLs

   We probably want a new registry for the labels beneath .well-known/
   hoba so that other folks can add additional features in a controlled
   way, e.g. for CPK/account revocation or whatever.

9.3.  Algorithm Names

   TBD, hopefully re-use and existing registry

   "0" means RSA-SHA256

   "1" means RSA-SHA1

9.4.  Key Identifier Types

   "0" means a hashed public key, as done in DANE.  [RFC6698]

   "1" means a URI, such as a mailto: or acct: URI, but anything
   conforming to [RFC3986] is ok.i

   "2" means an unformatted string, at the user's/UA's whim

9.5.  Device Identifier Types

   "0" means an unformatted nickname, at the user's/UA's whim

10.  Implementation Status

   [[Note to RFC editor - please delete this section before

   This section records the status of known implementations of the
   protocol defined by this specification at the time of posting of this
   Internet-Draft, and is based on a proposal described in
   [I-D.sheffer-running-code].  The description of implementations in
   this section is intended to assist the IETF in its decision processes
   in progressing drafts to RFCs.  Please note that the listing of any

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   individual implementation here does not imply endorsement by the
   IETF.  Furthermore, no effort has been spent to verify the
   information presented here that was supplied by IETF contributors.
   This is not intended as, and must not be construed to be, a catalog
   of available implementations or their features.  Readers are advised
   to note that other implementations may exist.

   According to [RFC Editor: replace by a reference to this document],
   "this will allow reviewers and working groups to assign due
   consideration to documents that have the benefit of running code, by
   considering the running code as evidence of valuable experimentation
   and feedback that has made the implemented protocols more mature.  It
   is up to the individual working groups to use this information as
   they see fit".

   At the time of writing there are two known implementations.  One done
   by Stephen Farrell of HOBA-HTTP and a HOBA-JS variant and another by
   Michael Thomas of an HOBA-JS variant.  More details will be provided
   in future drafts as those implementations mature and e.g. open-source
   licensing terms and release schedules are figured out.

11.  Acknowledgements

   Thanks to the following for good comments received during the
   preparation of this specification: Julian Reschke [[and many more to
   be added].  All errors and stupidities are of course the editors'

12.  References

12.1.  Normative References

              Fielding, R. and J. Reschke, "Hypertext Transfer Protocol
              (HTTP/1.1): Authentication", draft-ietf-httpbis-p7-auth-23
              (work in progress), July 2013.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC3986]  Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
              Resource Identifier (URI): Generic Syntax", STD 66,
              RFC 3986, January 2005.

   [RFC5234]  Crocker, D. and P. Overell, "Augmented BNF for Syntax
              Specifications: ABNF", STD 68, RFC 5234, January 2008.

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   [RFC5246]  Dierks, T. and E. Rescorla, "The Transport Layer Security
              (TLS) Protocol Version 1.2", RFC 5246, August 2008.

   [RFC5785]  Nottingham, M. and E. Hammer-Lahav, "Defining Well-Known
              Uniform Resource Identifiers (URIs)", RFC 5785,
              April 2010.

   [RFC6454]  Barth, A., "The Web Origin Concept", RFC 6454,
              December 2011.

   [RFC6698]  Hoffman, P. and J. Schlyter, "The DNS-Based Authentication
              of Named Entities (DANE) Transport Layer Security (TLS)
              Protocol: TLSA", RFC 6698, August 2012.

12.2.  Informative References

              Sheffer, Y. and A. Farrel, "Improving Awareness of Running
              Code: the Implementation Status Section",
              draft-sheffer-running-code-06 (work in progress),
              June 2013.

   [MI93]     Mitchell and Thomas, "Standardising Authentication
              Protocols Based on Public-Key Techniques.", Journal of
              Computer Security 2 (1993): 23-36. , 1993.

   [RFC2617]  Franks, J., Hallam-Baker, P., Hostetler, J., Lawrence, S.,
              Leach, P., Luotonen, A., and L. Stewart, "HTTP
              Authentication: Basic and Digest Access Authentication",
              RFC 2617, June 1999.

   [RFC4648]  Josefsson, S., "The Base16, Base32, and Base64 Data
              Encodings", RFC 4648, October 2006.

   [RFC5280]  Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
              Housley, R., and W. Polk, "Internet X.509 Public Key
              Infrastructure Certificate and Certificate Revocation List
              (CRL) Profile", RFC 5280, May 2008.

   [RFC6265]  Barth, A., "HTTP State Management Mechanism", RFC 6265,
              April 2011.

   [RFC6376]  Crocker, D., Hansen, T., and M. Kucherawy, "DomainKeys
              Identified Mail (DKIM) Signatures", STD 76, RFC 6376,
              July 2013.

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Appendix A.  Problems with Passwords

   By far the most common mechanism for web authentication is passwords
   that can be remembered by the user, called "memorizable passwords".
   There is plenty of good research on how users typically use
   memorizable passwords ([[ handful of citations goes here ]]), but
   some of the highlights are that users typically try hard to reuse
   passwords on as many web sites as possible, and that web sites often
   use either email addresses or users' names as the identifier that
   goes with these passwords.

   If an attacker gets access to the database of memorizable passwords,
   that attacker can impersonate any of the users.  Even if the breach
   is discovered, the attacker can still impersonate users until every
   password is changed.  Even if all the passwords are changed or at
   least made unusable, the attacker now possesses a list of likely
   username/password pairs that might exist on other sites.

   Using memorizable passwords on unencrypted channels also poses risks
   to the users.  If a web site uses either the HTTP Plain
   authentication method, or an HTML form that does no cryptographic
   protection of the password in transit, a passive attacker can see the
   password and immediately impersonate the user.  If a hash-based
   authentication scheme such as HTTP Digest authentication is used, a
   passive attacker still has a high chance of being able to determine
   the password using a dictionary of known passwords.

   [[ Say a bit about non-memorizable passwords.  Still subject to
   database attack, although that doesn't give the attacker knowledge
   for other systems.  Safe if digest authentication is used, but that's
   rare. ]]

Appendix B.  Examples

   [[Will add more later and probably use]]

   The following values show an example of HOBA-HTTP authentication to
   the origin  Carriage-returns have been added
   and need to be removed to validate the example.

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   -----BEGIN PRIVATE KEY-----
   -----END PRIVATE KEY-----

   Key Identifier: Zhh5vD5ovE0NqTDOufSUFRu5dzZMe-KOrMX2cN3vqWw

   Challenge: zzrYL7BaOQtlzOsl4fMY+EYcG4eT2h+JXi+jEGzozQ0=

   Nonce: xXSFdZ-7ahM

   Tbsorigin: httpshoba-local.ie443

   The resulting signature is:


   The final HTTP header field sent with a request is then:

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   Authorization: result="Zhh5vD5ovE0NqTDOufSUFRu5dzZMe-KOrMX2cN3vq

Appendix C.  Changes

   [[Note to RFC editor - please delete this section before

C.1.  WG-01

   o  A few clarifications/fixes.

   o  Added getchal interface and expires attribute

   o  Added Implementation Status section

   o  Added examples

C.2.  WG-00

   o  First WG draft, replacing draft-farrell-httpbis-hoba-02

   o  Fleshed out HTTP scheme some more.

   o  Fleshed out registration form more.

Authors' Addresses

   Stephen Farrell
   Trinity College Dublin
   Dublin,   2

   Phone: +353-1-896-2354

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   Paul Hoffman
   VPN Consortium


   Michael Thomas


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