A small piece of data cryptographically tied to a chunk carrying the following information can act as postage payment for spam protection and syncing incentivization:
- The swarm hash of the chunk
- Amount paid on-chain to an appropriate smart contract.
- Timestamp of beginning of validity period
- Timestamp of the end of validity period (expiration time)
- Proof of the above. In the first version, a corresponding digital signature, later some ZKP not revealing anything beyond the above, but proving it.
Chunks can have multiple (valid) postage stamps attached to them. The “value density” of a postage stamp is measured in wei/second/chunk. By definition, it is zero, if the chunk has no currently valid stamps attached to it. The value densities conferred to the chunk by valid postage stamps simply add up. The value density of a stamp is calculated as the value of the payment divided by the number of chunks stamped from the same payment and further divided by the length of the validity period of the stamp.
If the same chunk is encountered with a different set of stamps, these sets are merged.