Stake V8

Gridcoin PoS kernel v8

Author: Tomáš Brada. With credits to the PeerCoin and BlackCoin developers.

This document describes internals, effects and design decisions of Gridcoin PoS kernel stakev8. This V8 kernel will be used in blocks version 8 and replaces the previous kernel, V3, which was used in in blocks version 7.

Versions 4-7 were skipped and the kernel was simply named after the block version in order to reduce the amount of separate version numbers needed.

The most notable effect is that magnitude does no longer affect your stake weight. Investors and BOINCers now have the same chances to mint a block. This drastic change was needed to eliminate an exploit. On the other hand a compensation for less rich BOINCers is already being designed.

Basics

To create a next block in chain, miner must find a valid proof of something for it. Gridcoin is a PoS coin so the permission to create a next block is derived from the coins they own. There is also PoW, where the permission is derived from useless computation work the miner has to do.

First a data string (called kernel) is formed from the kernel components, then the kernel is hashed to obtain a proof hash, and then this proof hash is compared to the current difficulty target. Both proof hash and target are (big) numbers. The kernel forms a valid proof only if the proof hash is less than the difficulty target.

Change list

What changed in stake weight calculation and why:

• RSA_WEIGHT (and thus magnitude) was removed from the weight calculation.
  • multiplication issue
  • not checked when receiving

What changed in stake kernel and why:

• removed RSA_WEIGHT was removed from kernel
  • iterable nonce
• Explicitly mask timestamps with STAKE_TIMESTAMP_MASK
  • just to be sure
  • mask was enforced elsewhere in prior version
• removed por_nonce
  • iterable nonce
• added Stake Modifier

  • prevent precomputation

    ss << RSA_WEIGHT << CoinBlock.nTime << CoinTx.nTime << CoinTx.GetHash() << CoinTxN << nTimeTx << por_nonce;

New Components

Stake weight of Mature Unspent Transaction Output (MUTXO) is a linear function of only it's value.

Stake kernel is composed out of the following items:

• current Stake Modifier
  • a number composed of enthropy gathered from past blocks
  • anti-pre-computation
• Masked timestamp of the block where transaction whose output is used in this kernel is from
  • identification of the UTXO
• hash of the abovementioned transaction
  • identification of the UTXO
• output number of the kernel utxo
  • identification of the UTXO
• current masked timestamp
  • time-bound iterable
  • a value that makes the kernel change in controlled manner

Old Issues

Total defeat of PoS purpose

Multiplication issue

Unchecked newbie weight bonus

Precomputation

See also

Blackcoin wiki