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Versions: 00 01

ENUM                                                            B. Timms
Internet-Draft                                                   J. Reid
Intended status: Experimental                                     Telnic
Expires: January 13, 2009                                    J. Schlyter
                                                                Kirei AB
                                                           July 12, 2008


                  IANA Registration for Encrypted ENUM
                   <draft-timms-encrypt-naptr-01.txt>

Status of this Memo

   By submitting this Internet-Draft, each author represents that any
   applicable patent or other IPR claims of which he or she is aware
   have been or will be disclosed, and any of which he or she becomes
   aware will be disclosed, in accordance with Section 6 of BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
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   This Internet-Draft will expire on January 13, 2009.
















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Abstract

   This document requests IANA registration of the "X-Crypto"
   Enumservice.  This Enumservice indicates that its NAPTR holds a
   Uniform Resource Identifier that carries encrypted content from the
   fields of another (unpublished) Protected NAPTR, for use in E.164
   Number Mapping (ENUM).


Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
     1.1.  The problem  . . . . . . . . . . . . . . . . . . . . . . .  3
       1.1.1.  The requirements . . . . . . . . . . . . . . . . . . .  3
     1.2.  The solution . . . . . . . . . . . . . . . . . . . . . . .  4
       1.2.1.  Protected fields . . . . . . . . . . . . . . . . . . .  4
       1.2.2.  Protection process . . . . . . . . . . . . . . . . . .  5
   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  6
   3.  Enumservice Registration - X-Crypto  . . . . . . . . . . . . .  7
   4.  Functional Specification . . . . . . . . . . . . . . . . . . .  8
     4.1.  Order  . . . . . . . . . . . . . . . . . . . . . . . . . .  8
     4.2.  Preference . . . . . . . . . . . . . . . . . . . . . . . .  8
     4.3.  Services . . . . . . . . . . . . . . . . . . . . . . . . .  8
     4.4.  Regexp . . . . . . . . . . . . . . . . . . . . . . . . . .  8
     4.5.  Replacement  . . . . . . . . . . . . . . . . . . . . . . .  8
     4.6.  Encrypted Payload Generation . . . . . . . . . . . . . . .  9
   5.  Ciphersuite Subtypes . . . . . . . . . . . . . . . . . . . . . 10
     5.1.  Crypto Algorithms  . . . . . . . . . . . . . . . . . . . . 10
     5.2.  Padding  . . . . . . . . . . . . . . . . . . . . . . . . . 10
     5.3.  Hash . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
   6.  Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
     6.1.  Terminal NAPTR Example . . . . . . . . . . . . . . . . . . 13
     6.2.  Non-Terminal NAPTR Example . . . . . . . . . . . . . . . . 14
   7.  Security Considerations  . . . . . . . . . . . . . . . . . . . 15
   8.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 17
   9.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 18
   10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 19
     10.1. Normative References . . . . . . . . . . . . . . . . . . . 19
     10.2. Informative References . . . . . . . . . . . . . . . . . . 19
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 20
   Intellectual Property and Copyright Statements . . . . . . . . . . 21










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1.  Introduction

1.1.  The problem

   The Domain Name System or DNS ([RFC1034],[RFC1035]) is a global
   system; it does not differentiate on the data it returns.  If a
   Naming Authority Pointer (NAPTR) resource record [RFC3403] is
   published in DNS, then by definition the same Resource Record Set
   (RRset) will be returned in response to a query, regardless of the
   user placing that query.

   Where Universal Resource Indicators (URIs, defined in [RFC3986]) are
   published within DNS (inside NAPTRs), the registrant may prefer to
   make these available only to groups of individuals that he or she has
   selected.  Given the global nature of DNS, this can be a problem.

   It is not reliably possible to return different RRset content to
   different queries, depending on the user making the request.  Even if
   the authoritative server has been configured to discriminate based on
   the source of the query, if there are any intermediary recursive
   resolvers, the query may not even be passed to the authoritative
   server and the response returned to the querying DNS client may not
   be as the authoritative server would have chosen.  It can also be
   challenging to configure and maintain the authoritative server, and
   this may also involve special configuration of each client that will
   query for and use the data.

1.1.1.  The requirements

   There should be no need to use any special configuration for the
   authoritative name servers, clients, or any intermediary recursive
   resolvers when using this scheme.  Also, there should be no special
   DNS processing for the resource records used in any DNS components.
   As a secondary requirement that follows from these, the same content
   should be published in DNS and so made available to all without
   discrimination.  This will match the distributed design of the DNS
   and maintain the effectiveness of the cacheing architecture.

   However, the value of chosen content should be protected in such a
   way that it is understandable only by a selected set of users.

   There should be no performance impact on those clients that choose
   not to process protected data.  Thus it is important that the
   recipient of this data can detect immediately that it is protected,
   and either process it to extract the protected content using its
   private knowledge, or immediately discard the data if it is not
   interested in such protected records.




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1.2.  The solution

   A general solution for all DNS resource records that meets these
   requirements is very difficult; the performance requirements for DNS
   in general are severe.  NAPTRs stored in ENUM [RFC3761] domains may
   contain personally identifying information, so finding a solution may
   be considered more pressing for such NAPTRs, and some restrictions or
   processing costs may therefore be acceptable.  Also, in the case of
   NAPTRs a solution may be possible, as the problem is more restricted.
   NAPTRs hold a small number of well defined fields.  Not all of these
   fields in a NAPTR will be sensitive and so require protection.

   Those fields to be protected can be encrypted using a key known to
   the intended users.  Thus a "Protected" NAPTR can be processed into
   two parts; the protected fields carried in a ciphertext, and the
   public fields.  A "Container" NAPTR can itself be used to carry this
   ciphertext (inside its Regexp field content, in a URI), along with
   those fields that are considered public and are not protected.  These
   public fields can be copied from the Protected NAPTR into this
   Container NAPTR.

   The Container NAPTR can be stored and retrieved in the normal way.
   It will have an Enumservice indicating that it acts as a container
   and MUST be decoded before the original Protected NAPTR can be
   reconstructed and processed.  When an ENUM client retrieves such a
   Container NAPTR, it can immediately know that this requires
   cryptographic processing, and if that client is not interested in
   such processing, the NAPTR can be discarded.

1.2.1.  Protected fields

   There is no great benefit to encrypting all of the RDATA (Resource
   record Data) for a NAPTR.  The ORDER and PREFERENCE/PRIORITY fields
   are used to indicate the preferred order in which the records within
   a returned NAPTR RRset will be processed.  Whether a particular NAPTR
   acts as a container for a Protected NAPTR's content or not, the order
   in which it will be processed should remain the same; there is no
   change to the Dynamic Delegation Discovery System (DDDS) algorithm
   specified in [RFC3402].

   If instead the Container NAPTR had a different ORDER and PREFERENCE/
   PRIORITY field values from those held in the Protected NAPTR, it
   might be possible for a Container NAPTR to be considered first (as it
   had a low numerical order/preference value), but, once decoded, the
   Protected NAPTR content it contained was of a much lower priority,
   and so should not be processed at that point.  This would be
   inappropriate, and so the ORDER and PREFERENCE/PRIORITY fields will
   remain the same in both Protected and Container NAPTRs.



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   Thus the ORDER and PREFERENCE/PRIORITY field values should be
   considered public and be copied from the Protected NAPTR into the
   Container NAPTR.  However, all the other fields (flags, services,
   regexp, and replacement) are sensitive in nature, and so that portion
   of the binary format of the RDATA in which they are held will form
   the plaintext that will be protected before publication in DNS.

1.2.2.  Protection process

   The NAPTR to be protected can have these sensitive fields placed into
   a plaintext buffer.  The buffer content is then encrypted using an
   appropriate key to create a ciphertext.  The ciphertext can then be
   "armoured" into a form that can be presented in a data URI [RFC2397].
   That URI can then be placed in a Container NAPTR within its Regexp
   field, along with the "public" ORDER and PREFERENCE/PRIORITY fields
   copied from the Protected NAPTR, together with a dedicated
   Enumservice, terminal URI flag field ('u') and an empty Replacement
   field.

   If this Container NAPTR has an appropriate Enumservice then its
   nature will be immediately detectable by the recipient of that NAPTR.
   If the recipient has the appropriate key to decode the URI data, then
   it can decrypt the URI content to form a buffer with the plaintext
   fields.  These fields (in combination with the ORDER and PREFERENCE/
   PRIORITY fields that have been copied into the Container NAPTR and
   have not been encoded) can be reconstructed into the RDATA that would
   have existed in the original Protected NAPTR.  That Protected NAPTR
   content can then be processed by the client in the normal way.























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2.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [RFC2119].














































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3.  Enumservice Registration - X-Crypto

   The following template contains information required for the IANA
   registrations of the 'X-Crypto' Enumservice, according to Section 3
   of RFC 3761:

   Enumservice Name: "X-Crypto"

   Enumservice Type: "x-crypto"

   Enumservice Subtype: "data"

   Enumservice Sub-subtype: see Section 5

   URI Schemes: "data"

   Functional Specification: see Section 4

   Security Specification: see Section 7

   Intended Usage: COMMON

   Author(s): Ben Timms, Jim Reid, Jakob Schlyter. (for authors contact
   details see Authors' Addresses section).

   Any other information that the author deems interesting: None

























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4.  Functional Specification

   The basic concept is covered in Section 1.2 and the process is
   covered in Section 1.2.2.  This section describes in detail how each
   of the fields are handled.

   Publication and use of a NAPTR with this Enumservice is based on two
   concepts:

      A Protected NAPTR that contains sensitive field values, and is not
      stored and published in DNS.

      A Container NAPTR with this Enumservice that holds the protected
      fields in encrypted form within its Regexp field.  This NAPTR
      carries the "x-crypto" Enumservice

   The Container NAPTR resource record fields are as follows:

4.1.  Order

   The value of the order field is copied in clear from the RDATA of the
   Protected NAPTR into the Container NAPTR.  It is not encoded.

4.2.  Preference

   The value of the preference field is copied in clear from the RDATA
   of the Protected NAPTR to the Container NAPTR.  It is not encoded.

4.3.  Services

   The value of the services field for the Container NAPTR is set to
   "E2U+x-crypto:data:" combined with the ciphersuite sub-subtype
   (Section 5).

4.4.  Regexp

   The encrypted payload (Section 4.6) is encoded in Base64 [RFC4648],
   and transported as the value of a data URI [RFC2397] inside the
   Container NAPTR.

   Container NAPTR Regexp Example:
   !^.*$!data:;base64,bWVrbWl0YXNkaWdvYXQK!

4.5.  Replacement

   The value of the Container NAPTR's replacement field MUST be set to
   ".".




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4.6.  Encrypted Payload Generation

   The Encrypted Payload consists of a base64 "armoured" string holding
   an encrypted, optionally padded ciphertext reflecting a portion of
   the Protected NAPTR's RDATA.

   The portion of the Protected NAPTR RDATA holding its Flags, Services,
   Regexp and Replacement fields is treated as the plaintext to be
   processed.  This plaintext is (optionally) padded and the resulting
   block is then encrypted, to form the ciphertext.  Potentially, an
   optional hash may be generated from this.  Once this cipehertext has
   been generated, it is further encoded in Base64 to form the encrypted
   payload that is then used as the value of the Container NAPTR's URI.






































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5.  Ciphersuite Subtypes

   The enumservice sub-subtype carries the ciphersuite used for the
   encrypted payload.

   Ciphersuite sub-subtype example: RSA 1024-bit with PKCS#1.5 padding
   and no hash would be encoded as 0x8210 and presented as enumservice
   "E2U+x-crypto:data:8210".

5.1.  Crypto Algorithms

   A 1-byte field indicating the encryption algorithm is used for the
   encrypted payload (Section 4.6).

                     +-------+----------------------+
                     | Value | Encryption Algorithm |
                     +-------+----------------------+
                     | 0x00  | NULL                 |
                     |       |                      |
                     | 0x81  | RSA-512              |
                     |       |                      |
                     | 0x82  | RSA-1024             |
                     |       |                      |
                     | 0x83  | RSA-1536             |
                     |       |                      |
                     | 0x84  | RSA-2048             |
                     |       |                      |
                     | 0x85  | RSA-3072             |
                     |       |                      |
                     | 0x86  | RSA-4096             |
                     +-------+----------------------+

5.2.  Padding

   A 4-bit field indicating what padding algorithm is used for the
   encrypted payload (Section 4.6).

                       +-------+-------------------+
                       | Value | Padding Algorithm |
                       +-------+-------------------+
                       | 0x0   | NULL              |
                       |       |                   |
                       | 0x1   | PKCS #1.5         |
                       |       |                   |
                       | 0x2   | OAEP              |
                       +-------+-------------------+





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5.3.  Hash

   A 4-bit field indicating what hash algorithm is used for the
   encrypted payload (Section 4.6).

                        +-------+----------------+
                        | Value | Hash Algorithm |
                        +-------+----------------+
                        | 0x0   | NULL           |
                        |       |                |
                        | 0x1   | MD2            |
                        |       |                |
                        | 0x2   | MD5            |
                        |       |                |
                        | 0x3   | SHA-1          |
                        |       |                |
                        | 0x4   | SHA-224        |
                        |       |                |
                        | 0x5   | SHA-256        |
                        |       |                |
                        | 0x6   | SHA-384        |
                        |       |                |
                        | 0x7   | SHA-512        |
                        +-------+----------------+



























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6.  Examples

   In these examples, a 1024-bit RSA key pair is used for encryption and
   decryption.  The plaintext has cryptographic padding applied prior to
   encryption, using the PKCS 1.5 algorithm.  There is a null hash
   applied to this.  The ciphersuite value (i.e. the Enumservice sub-
   sub-type string held in the container NAPTR) will be '8210'.  The
   resultant ciphertext is further "armoured" using Base 64 encoding,
   and is placed into a data URI in that container NAPTR.  A "default"
   or "greedy" Extended Regular Expression, or ERE (i.e. '!^.*$!') is
   used in the container NAPTR Regexp field.  Note that (in keeping with
   [RFC4648], section 3.1), the "aromouring" process MUST NOT add line
   feeds to the base-encoded data.

   For ease of presentation the examples are shown in textual form, but
   the encryption process works on the binary form of the RDATA fields.

   Note that, using this encryption, encoding and ERE mechanism, the
   limit to the length of the "plaintext" (i.e. the fields of the RDATA
   to be protected) is 117 bytes.  This is because RSA is a block
   cipher, with in this case 1024 bits (128 bytes) as the block size,
   and the PKCS #1.5 padding to be added to the plaintext consumes 11
   bytes, leaving a maximum plaintext size of 117 bytes.

   Once encrypted, the ciphertext is also 128 bytes, but this is in
   binary form, and has to be further "armoured" for carriage inside the
   data: URI.  The Base 64 encoding process expands the ciphertext to
   4/3 (rounded up to the nearest 4 bytes) of its size in binary form,
   giving a text block of 172 bytes.  To this has to be added the rest
   of the container NAPTR's Regexp content, giving a Regexp field length
   of 193 bytes.  Note that this field length is constant, as the
   ciphertext is always the same length when using the same encryption
   and padding scheme (regardless of the length of the plaintext fields
   to be protected and whether these fields reflect a terminal or non-
   terminal NAPTR).

   In the following examples, it is assumed that the private key (in
   PKCS 8 format, protected with the pass phrase "pkcs8passphrase", and
   expressed in PEM format), is:

   -----BEGIN ENCRYPTED PRIVATE KEY-----
   MIICoTAbBgkqhkiG9w0BBQMwDgQIpwb76GrK0AgCAggABIICgEsRtkQ2isuKq3Cl
   8wpAfDxzzFbumj0HdGu7WLEElVYaLt4CvRlz5kL3SK2G8ydpsdU104s0RnzgPGFv
   63zsJZ5bC6d4lCcWMjbhv+U91YUhlrc6R6UHhIN4BSBWTeA/Ia/U7bwZm/TV7ke1
   eeLOdsyzEnPr9lj3v1wdHFYU6CMY1lRP/lbqexVQMYEev5/w+tu9LyGdP3MPnnUC
   N/OVk67OkwBqrBnQpHtHLC7i0bq6srLaJWB7nFVa/iXlQ8lCwFRGwV7RDq6JvgI2
   LjgJArLG8i7QBx+WE/+LwLAessmU4RUzzvQhnlWdf3UkXR/hRDPRhJFFrr5zjfUr
   cF5CfZms4WhMh+epqnlaoaX7uEj1gQ9gLvNef3b68akpRVIFuLBnqcdbahr0rzQA



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   /LT5e62jfo2saSG9vVAY7f1fOmrh9K9+S69rlbQ4JLzx+sttPTty9CscIZf3/cDM
   1GNdumwG1HewzkVuzvIlyJfLbM1ftWhv0tWTe8pPFqccTFYvwpjVnOxN6yr8EMUy
   8VTyDCZT/us8E6vtei2fbvLHnmRzIqCgHUAYBVKM+cwrGELCuSBbx6pmOp21EyGH
   5+Lobg0XYjArVxgynNvAU/mmQWbdVqhkfrIGhywCvi1+Jpigvn+2zBayCfPitdxh
   BjvYhEp6qSE0/QWog4Qn6t5TaDK7ddV39Tw2pyuE1Gh+tAfZWrwO0aF9NKI9G5mJ
   Db3Jqm9UzAoulH8cnMdCAa7oDVCl/8ky1VKTIz8fe3bVsMCm8Cgv3/vz8vupaGV5
   exzJUEeEJweenReOaI8Eocl2qSKmcrtlhAQI+l77KnvM3J0QSPSxeH203OnLovG3
   lQkJjd4=
   -----END ENCRYPTED PRIVATE KEY-----

   The public key, expressed in PEM format, is:

   -----BEGIN PUBLIC KEY-----
   MIGfMA0GCSqGSIb3DQEBAQUAA4GNADCBiQKBgQDoOyVQpfJlai3i7RlF5iGGlYUb
   /HXOuyV1IVKoQ1iQQvm91gU5L10GwVWN1WY4yfqYtPXnJMoMbAIK72wNnaB6Jo4/
   ELbi40yOQSIe4TKXVcfMkFbpJlN7FfktHtpLai60zsT8Ywt4OF8rUFmb5CdE3gtV
   yqQfmfczYheXqPW7iwIDAQAB
   -----END PUBLIC KEY-----

6.1.  Terminal NAPTR Example

   This example shows a NAPTR holding a SIP Enumservice as the protected
   NAPTR.  Given that a terminal E2U (ENUM) NAPTR is to be protected,
   the combined maximum length of the Enumservice string, the ERE
   pattern and the original URI is (117 - 12) bytes, or 105 bytes.  If a
   "greedy" ERE field is used in that protected NAPTR, the space
   available for the Enumservice string and the URI is 105 - 4 bytes, or
   101 bytes.  In the example shown here, the NAPTR to be protected has
   a SIP Enumservice (and corresponding sip: URI scheme).  This means
   that the SIP address value can be a maximum of 94 bytes long.  In
   this case, it occuplies 24 bytes.

   The protected NAPTR RDATA:

      100 50 'u' 'E2U+sip' '!^.*$!sip:alice@wonderland.example!' .

   Is replaced by the container NAPTR RDATA:

      100 50 'u' 'E2U+X-crypto:data:8210'
      '!^.*$!data:;base64,OQZl3x9TEaZtQamA5t3IJqXaKUT6QuV+yLtW34/hszd
      D2jtSwavlxiax8CDMWekikXkgbPQqEo7X6g8aX3REiXVJ/PqrbxFASIIktnIIVE
      rZU3RVl8WAvxQvWGs+wEY3YAi4UnOoqAOdbv3tsV0i4h15I+wePz9Rw9VBpU95h
      Wc=!' .








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6.2.  Non-Terminal NAPTR Example

   In this example, a non-terminal NAPTR is protected.  As the
   replacement field in a NAPTR is not permitted (as specified in RFC
   3403) to use DNS domain compression, the fully qualified domain name
   of the target domain is held in the replacement field.  This fully
   qualified domain name is, of course, stored in binary form within the
   RDATA.

   Note that, using the same protection scheme (1024-bit RSA, with PKCS
   1.5 padding, null hash), the maximum length of the fully qualified
   domain name will be 117 - 3, or 114 bytes.  In this example, the
   fully qualified domain name is 1+5+1+10+1+7+1 = 26 bytes long.

   The protected non-terminal NAPTR RDATA:

      100 51 '' '' '' alice.wonderland.example.

   Is replaced by the container NAPTR RDATA:

      100 51 'u' 'e2u+x-crypto:data:8210'
      '!^.*$!data:;base64,j+WNPPwriy5pu4SfabMavRtE+c/f3Sk62Ab5TNYOomo
      RcGrKk5q23i6BB4fp71+z3ezK1U91jTdpzmpF0M7WVs9M9AnhDxyrbQwo1mP/uU
      YpflaZuG5aEnY14aTntAldh7UacPvfaiWc1QPg/6C9Wb7MBedmZAYajc2YZHgKQ
      1o=!' .


























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7.  Security Considerations

   This is an Enumservice for a NAPTR intended to carry protected NAPTR
   content in encrypted form.  It does not discuss the means by which
   the keys needed to decrypt the protected content are exchanged.  For
   this Enumservice registration, this is considered "out of scope".
   However, the technique used for key exchange is important, and must
   be considered thoroughly; there is little point in applying a complex
   encryption scheme if the keys are available to eavesdroppers.  Of
   course, although technically permitted, confidentiality will not be
   achieved unless a non-null encryption is applied.

   There are limitations on field size within DNS, so that, for example,
   the Regexp field has a maximum length of 255 bytes.  Several of these
   bytes will be taken up in the container NAPTR's Regexp field with the
   sub-field delimiters, with the ERE sub-field content, and with the
   URI scheme itself.  There is limited space to carry the armoured
   ciphertext as the data URI value, given the armouring choice proposed
   here and the simple use of the existing Regexp field to carry the
   protected data.  This will in turn limit the choices for encryption
   method, hash algorithm, and any padding.  See also the examples
   above.

   Even if an eavesdropper cannot decode the content carried in a
   container NAPTR, the fact that ORDER and PREFERENCE/PRIORITY fields
   are copied from the protected NAPTR opens the possibility of opaque
   traffic analysis.  If the ORDER and PREFERENCE/PRIORITY field values
   for a NAPTR within a RRSet change (for example, to reflect the domain
   owner going from office to home) then this change will be reflected
   in the NAPTR even if it is protected.  Simply due to changes in RRSet
   relative ORDER and PREFERENCE/PRIORITY values, an attacker might
   surmise that the protected data was associated with the domain
   owner's office or home number.  This information might in itself be
   useful to the attacker (for example, by indicating when the domain
   owner was or was not present at a particular location).

   Finally, if the value of a contact (such as a SIP URI or telephone
   number) were to be available to an attacker using other means, then
   there may be potential for differential cryptographic analysis based
   on an assumed "known plaintext".  The amount of data available to an
   attacker with realistic numbers of NAPTRs is small, but it is
   important to use appropriate cryptographic padding to limit the
   potential for such an attack.

   These issues mean that the environment in which NAPTRs with this
   Enumservice can be used may be restricted, and further security
   analysis will depend on deployment experience.




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   An analysis of threats specific to the dependence of ENUM on the DNS,
   and the applicability of DNSSEC ("Domain Name Security") [RFC4035] to
   these, is provided in [RFC3833].
















































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8.  IANA Considerations

   This document requests registration of the "X-Crypto" Enumservice
   with the "x-crypto:data:<ciphersuite>" type according to the
   guidelines and specifications in RFC 3761 [RFC3761] and the
   definitions in this document.  This Enumservice is intended for use
   with the "data:" URI scheme.












































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9.  Acknowledgements

   The authors gratefully acknowledge the contributions of Romek
   Szczesniak.  He helped greatly to clarify some of the issues with
   deployed security schemes and current implementations.  We also
   acknowledge the support of Khashayar Mahdavi whose original idea this
   draft embodies, and Henri Asseily for driving the development of the
   environment in which this is being used.











































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10.  References

10.1.  Normative References

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

   [RFC2397]  Masinter, L., "The "data" URL scheme", RFC 2397,
              August 1998.

   [RFC3402]  Mealling, M., "Dynamic Delegation Discovery System (DDDS)
              Part Two: The Algorithm", RFC 3402, October 2002.

   [RFC3403]  Mealling, M., "Dynamic Delegation Discovery System (DDDS)
              Part Three: The Domain Name System (DNS) Database",
              RFC 3403, October 2002.

   [RFC3761]  Faltstrom, P. and M. Mealling, "The E.164 to Uniform
              Resource Identifiers (URI) Dynamic Delegation Discovery
              System (DDDS) Application (ENUM)", RFC 3761, April 2004.

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

10.2.  Informative References

   [RFC1034]  Mockapetris, P., "Domain names - concepts and facilities",
              STD 13, RFC 1034, November 1987.

   [RFC1035]  Mockapetris, P., "Domain names - implementation and
              specification", STD 13, RFC 1035, November 1987.

   [RFC3833]  Atkins, D. and R. Austein, "Threat Analysis of the Domain
              Name System (DNS)", RFC 3833, August 2004.

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

   [RFC4035]  Arends, R., Austein, R., Larson, M., Massey, D., and S.
              Rose, "Protocol Modifications for the DNS Security
              Extensions", RFC 4035, March 2005.









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Authors' Addresses

   Ben Timms
   Telnic
   37 Percy Street
   London  W1T 2DJ
   United Kingdom

   Email: btimms@telnic.org


   Jim Reid
   Telnic
   37 Percy Street
   London  W1T 2DJ
   United Kingdom

   Email: jim@telnic.org


   Jakob Schlyter
   Kirei AB
   P.O. Box 53204
   Goteborg  SE-400 16
   Sweden

   Email: jakob@kirei.se
























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