[Cryptography] "Digital" Love Locks?

Natanael natanael.l at gmail.com
Mon Oct 26 13:52:14 EDT 2015


Den 26 okt 2015 16:11 skrev "Henry Baker" <hbaker1 at pipeline.com>:
>
> FYI -- Can't we come up with a digital version of "Love Lock"
> to avoid all the damage that physical love locks do?
>
> Perhaps a Love Lock embedded in the Bitcoin blockchain?
>
> Shakespeare's "let me count the ways" should be 2^128, minimum;
> 2^64 if you both have the same birthday.  ;-)
>
> Love Locks Prevail in Cities Other than Paris
>
> http://www.nytimes.com/2015/11/01/travel/love-locks-paris-vancouver.html

What should be accomplished? My assumptions;

* The creation of some symbolic message
* The message is created together by both participants
* It is somehow made non-malleable
* It is public
* Something is thrown away to symbolically seal it

Actually this mechanism I described here could be reused almost unmodified:

http://www.metzdowd.com/pipermail/cryptography/2015-October/026774.html

We use threshold cryptography to allow two people to do it together.
We modify libforwardsec with their forward secure public key encryption +
hierarchical IBE with puncturable encryption into a signing algorithm with
otherwise the same properties.

The two participants then sign the message together with a group threshold
keypair linked to (derived from?) both their personal keypairs, to then
revoke (puncture) their ability to sign another message with the same IBE
"identity" (in standard use of libforwardsec assigned to timeslots, but can
also be assigned to different "types" of messages). If either one of the
two punctures their keypair, then the threshold cryptography makes it
impossible to sign another message to replace the first.

If the IBE identity is chosen to be the "type" called "love commitment" and
they sign the most recent blockchain hash for timestamping and then publish
the signed message on the blockchain, I think that accomplishes the goal
effectively. A key is then thrown away when leaving a public message both
parties commit to. And you can easily confirm both parties' keypairs were
used when creating the message.
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