Unseenet Working Group                                     A. Lorensen
UN-RFC: 0006                                              October 2026
Category: Standards Track
Status: Draft

                  Unseenet: Proof-of-Work Postage

Abstract¶

Anonymous identities are free, so Unseenet prices posting instead: every article carries a proof of computational work ("postage"), in the spirit of Hashcash. This document defines the postage algorithm, its header, and how required difficulty is determined.

1. Header¶

Proof-Of-Work: sha256; bits=<n>; nonce=<b64>

bits is the claimed number of leading zero bits; nonce is 1 to 32 octets chosen by the poster.

2. Algorithm¶

Let C be the canonical form of the article (UN-RFC 0002 section 3).

digest = H( DS("UNSEENET-POW-1") || H(C) || nonce )

The postage is valid with difficulty n if digest begins with at least n zero bits (most significant bit of the first octet first). The claimed bits value MUST be at least n, and the digest MUST actually have at least bits leading zero bits.

Postage covers the canonical form, so it cannot be moved to another article, and it is outside the canonical form, so it does not change the signature or the Message-ID.

3. Required Difficulty¶

The difficulty an article must meet at a node is

required = max( node_min_pow, group_min_pow )

where node_min_pow is advertised as UNSEENET-MINPOW (UN-RFC 0005) and group_min_pow is the current manifest's min_pow (UN-RFC 0004), which does not apply to manifests themselves.

A node MAY raise its minimum temporarily under load. Articles already accepted are not re-checked.

Peers may have different minimums. A node SHOULD NOT forward an article to a peer whose advertised minimum the article does not meet.

4. Guidance¶

Rough cost of n bits is 2^n hash evaluations:

bits	hashes	~CPython on a laptop	~native code
16	65 k	< 0.1 s	instant
20	1 M	~1 s	~0.05 s
22	4 M	~4 s	~0.2 s
24	16 M	~15 s	~1 s

RECOMMENDED defaults: node minimum 18, open groups 20. Busy open groups under spam pressure may raise min_pow.

5. Considerations¶

SHA-256 is cheap on GPUs and ASICs, so a well-equipped spammer has an advantage of several orders of magnitude over an ordinary user. The algorithm name (sha256) exists so that a memory-hard algorithm (e.g. Argon2id) can be added by a later UN-RFC. The name argon2id is reserved for that purpose.
Postage limits volume; it does not judge content. Content filtering remains the job of moderators, node operators and readers (UN-RFC 0001 section 4).