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[liberationtech] Private Information Sharing Protocol [P.I.S.P.] Requesting input, thoughts, comments.

Yosem Companys companys at stanford.edu
Wed Jan 25 19:55:09 PST 2017


From: CANNON *CIOTA *<cannon at cannon-ciota.info>

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Hash: SHA512

Title: Private Information Sharing Protocol [P.I.S.P.]
 Draft Version 1.1
  Author: Cannon Ciota <cannon at cannon-ciota.info> Created: 2017-01-21

 Abstract
        Opt in method of using publicly accessible directories,
        particularly namecoin, to list updatable information which
        can only be viewed by authorized entities.

 Motivation
        Primarily intended as a usecase for (but not limited to)
        namecoin as a proposal for a standard allowing entries such
        as contact information i.e. phone numbers, addresses, etc. to
        be listed in a way that allows only authorized entities of the
        entry owner's choice to be able to interpret such information.
        Namecoin, a secure decentralized universal directory, is
        great for binding a multitude of information to a single human
        readable identity in such a way that is not only censorship
        resistant, resilient, and verifiable, but also immune from
        tampering. However, due to the public nature of blockchain,
        what namecoin currently lacks in is a standard way to list
        specific portions of an identity's datastore in a way which
        allows sharing of such information to authorized entities only,
        at the control and discretion of the identity owner.

  Specification
        Each namecoin identity would have listed a public key, or
        pointer to a public key of which the owner's namecoin client
        software has a corresponding private key. This public/private
        keypair would be used for this Private Information Sharing
        Protocol, or P.I.S.P for short.  The public key would be
        denoted in the standard namecoin JSON format using one of two
        forms, embedded or as a pointer. A pointer would be useful
        in scenarios in which a large key is used or if space within
        the namecoin identity's limited size for data is scarce.

Examples

Embedded:
- ---------
 {
   "pisp-pub":"026D3CA82768BC8D8E512EC97DFFAA7CACD52FF913A66911CFF074172F3C
B0934E"
}

Pointer:
- --------
{
  "pisp-point":
   {
    "url":"http://cannon-ciota.bit/cannon-ciota_publickey.pisp",
    "fingerprint":"2BB515CD66E74E2845DC6494A5A22879"
   }
}

or optionally we can use a hashsum of the pointed file in case the
file contains more fields than just the public key, to allow for
future extensions to PISP proposed standard.

{
  "pisp-point":
   {
    "url":"http://cannon-ciota.bit/cannon-ciota_publickey.pisp",
    "sha256":"5580aaa1a28145a1ec6c4136af58bdafb23fc13dbdb820ef1da7753e9f74
4f7d"
   }
}

Contents of cannon-ciota_publickey.pisp:
- ----------------------------------------
 {
   "pisp-pub":"026D3CA82768BC8D8E512EC97DFFAA7CACD52FF913A66911CFF074172F3C
B0934E"
}

        Whenever looking up someone’s PISP public key from their
        namecoin identity, the client would first search for the
        pisp-pub (PISP public key) field, and if not found will proceed
        to search for the pointer field denoted as pisp-point (PISP
        pointer). The PISP pointer field would have the location of the
        public key used for PISP along with the fingerprint, or hashsum
        of the pointed file. The contents of the file mentioned in the
        pointer field would have the public key in the same JSON format
        as would be if directly in the namecoin datastore. Reason why
        is to allow the enabling of any future extensions to the PISP
        proposed standard.  PISP would be opt in. To opt in one would
        simply include a field in their namecoin identity to advertise
        their PISP public key, using either pisp-pub or pisp-point.
        For purpose of demonstration we will assume Alice and Bob both
        have a PISP public key included in their namecoin ID. Bob
        wants his phone number listed in his namecoin identity so
        his contacts can reach him, even if his phone number changes
        frequently. However Bob only wants specific contacts to know
        his current personal phone number, and Bob may want a seperate
        group of contacts to know his business phone number. Bob may
        also have another phone number that is public. And so Bob's
        phone entry in his namecoin ID might look like the following

{
   "phone":
   {
    "pisp":"http://EXAMPLE.URL/bobs-phone.pisp"
   }
}

or for multiple phones

{
   "phone":
   {
    "public":"+99 1234567890",
    "business":
      {
                "pisp":"http://EXAMPLE.URL/bobs-business-phone.pisp"
      },
    "personal":
      {
                "pisp":"http://EXAMPLE.URL/bobs-phone.pisp"
      }
   }
}

        The .pisp file would have the relevant information but
        encrypted to the pisp public key of each of the contacts Bob
        authorizes to have access to such information. To prevent Bob's
        connections from being revealed each encrypted data snippet
        (one per contact) would not list public keys, only encrypted
        data. And so any contact would have to attempt to decrypt
        each snippet within the .pisp file until it finds a snippet
        it is able to decrypt. As a result outsiders cannot determine
        whom Bob's connections are, only the number of authorized
        connections. One mitigation to advertising number of authorized
        contacts would be to pad the .pisp file with decoy snippets. As
        a precaution against bruteforcing data to matching cypher text
        each snippet would also include a random salt unique for each
        snippet before encrypting.  And so if Bob wanted his number
        visible to Alice, he would include his current phone number
        (with a random salt) encrypted to Alice's listed PISP key and
        include the encrypted snippet into his .pisp file referenced
        in his namecoin identity. Alice's addressbook app on her phone
        would automatically lookup Bob's number from his namecoin ID,
        after seeing it as not publicly viewable but protected by
        PISP it would then use Alice's private PISP key to attempt to
        decrypt each snippet in Bob's .pisp file until successfully
        decrypting a snippet which then reveals Bob's number to Alice.
        If Bob's PISP protected phone number is not visible to Alice,
        after finding no decipherable snippet the app can tell Alice
        "not authorized to view this information". Alice then can
        hit a button on her app such as "request contact info for
        Bob's phone" which would send a request to Bob through a
        communications channel (such as publically listed email
        address or bitmessage address in Bob's namecoin ID) which
        would request Bob to include Alice as an authorized contact
        for that specified piece of information (in this case, Bob's
        personal number). The request would be signed by Alice's
        PISP key before being encrypted to Bob's PISP key to protect
        from spoofing and to maintain confidentiality of both the
        contents and identity of requester, to anyone who is not Bob.
        Upon receiving such request, Bob can choose to either allow
        Alice access or ignore such request. Because denying access
        is passive rather than active unlike granting access, this
        provides plausible deniability for Bob. If Bob chooses to
        not allow Alice as an authorized contact to view his number,
        he simply does nothing which provides plausible deniability
        of Bob's decision as Alice would not know if Bob explicitly
        chose to not to acknowledge request, or if Bob simply just
        forgot, or did not read the request.

//EOF
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--
Cannon
PGP Fingerprint: 2BB5 15CD 66E7 4E28 45DC 6494 A5A2 2879 3F06 E832
Email: cannon at cannon-ciota.info

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