This is the source code repository of the epoint transaction service.

Source
------

web:
	http://repo.or.cz/w/epoint-server.git
git:
	git clone git://repo.or.cz/epoint-server.git


Build
-----

epoint-server depends on a patched version of the latest go source
to get it (see http://golang.org/doc/install.html for details) run
	hg clone https://go.googlecode.com/hg/ go
	cd go/src
	hg patch path/to/epoint-server/patches/*.diff
	./all.bash

to build and install (into $GOROOT/bin) run
	make


Contact
-------

discuss@epointsystem.org
TODO: mailing list


About
-----

The goal of the epoint service is to provide secure and efficient
bookkeeping of transferrable debt denominated in currencies that
are issued by the anonymous clients of the system themselvs.

The central bookkeeping is designed to be auditable by any client
and proofs can be constructed in case of errors.

To convert between the various currencies a currency market can
be used that is outside of the scope of the epoint service.

The agreements and authentication methods between the issuers and
holders of debt is outside the epoint system as well.

This project originates from the ePoint Transfer Protocol.
Description about that design is at the epointsystem.org website:
	https://www.epointsystem.org/trac/epoint_issuer
	https://www.epointsystem.org/trac/website


Design
------

An epoint server is a large billboard, where clients can publish
draft documents (acknowledging debt, "i owe you")

Draft documents are digitally signed by the clients and the
clients are identified by their public key.

Any client can issue debt (issuer), and a client holding the
debt (holder) can transfer parts of it to any other client using
draft documents. A draft specifies the drawer (the client who
transfers the debt), the beneficiary (the new holder of the
debt), the issuer (the client who owes) and an integer amount
that is transferred. The draft is signed by the drawer.

Drafts with different issuers are independent, the debt of
different issuers are denominated in different currencies and
cannot be mixed.

The balance of a client with respect to an issuer is the
agregate value of all the drafts that transfer debt of the given
issuer to or from the given client.

The main constraint is that a holder cannot transfer more debt
than its balance. Such drafts are invalid and must be rejected.
If the issuer is the drawer of a draft then there is no such
constraint. The balance of the issuer is <=0 and the balance of
a holder of the issuer's debt is >=0 at any given time. All the
balances together give 0.

The main purpose of the server is to make it easy to check the
current balance of a client with respect to an issuer at any
given time.

To achieve this the server needs to store all the drafts and the
public keys of the clients so the drafts are verifiable. The
ordering of the drafts matters when the constraints are checked
so the server must keep track of the balances in such a way that
there is no ambiguity. It must be easy to audit the server and
prove if it does not calculate the balances properly. This is
done using server signed certificates declaring the balance of
a client after each change and referencing related documents
(draft, previous certificates) with cryptographic hash.