Yesterday the genesis block of GRIN was found and the GRIN blockchain launched.
What can GRIN do
Grin is a privacy focused blockchain where almost all information is hidden. The public onchain data are just some hashes and signatures and an external party cannot gain any information about who or how much was transacted between the parties. There are some links visible as how many people paid how many, but even this can sometimes be cut out.
This protocol is called MimbleWimble and just like Bitcoin was published by an anonymous founder.
The grin blocks are essentially just a random combination of numbers and only the people involved in the transactions know what they mean.
The system can still be fully verified, which may sound surprising. This is done via rangeproofs that show that even though you do not know who paid whom for how much, you can still verify that no coins were created and all that happened was coins moving from one commit to another. And in reality this is all that needs to be verified. It is the same in cash or gold. When I give somebody else a piece of gold, nobody needs to know. The fundamental properties of gold make it such that whatever I do, the amount of gold in the world stays the same. In that sense GRIN is more like gold than bitcoin. Grin has the same fundamental property enforced by cryptography. Bitcoin does not have in in the same way. It is only not created out of thin air because everything is fully public and we constanly keep looking into each wallet.
What makes GRIN truly revolutionary is the MimbleWimble protocol that is even lighter than bitcoin, while other privacy coins typically are much more heavyweight. Monero for example uses the old concept of tracking all transactions and adding math to hide what happened on top of that. GRIN just gets rid of all the transaction history. It does not need to be saved as the only thing we care about is proving that whatever happed, no new coins were added. It has more privacy than bitcoin and at the same time can scale much better.
What GRIN cannot do
The math makes it such that GRIN has zero support for scripts or smart contracts. It has just payments. And even these are complicated as the payment protocol is interactive. Both sender and receiver must be online and exchange information to finalise a transaction. There are no addresses that are linked to persons. A wallet can handle all that automatically, but has to be online to receive payments. Maybe in the world of tomorrow that is no problem, but right now it is an annoyance.
Scripts can however be added by the special properties of linear signatures such as Schnorr signatures that can be aggregated. In this way some basic functionality such as n-of-m multisig can be realised. Not on a script level, but by distributing keys and aggregating them offchain to form valid signatures. The same idea also allows for hash-key locks. Together with onchain timelocks this is in theory just enough to build a working lightning implementation for GRIN. Even though that would less private than the fundamental onchain layer. In the same way atomic crosschain swaps can be realised.
Lets see if somebody comes up with even smarter ideas how some script functionality could be hardcoded in the cryptography.
Common criticisms
While the tech of GRIN is very different from other blockchains and probably will be the most innovative blockchain to be released in 2019, there are some common criticisms.
GRIN does not have a limited supply. Every second one GRIN is released to the miners, forever. While I am not a fan of this reward structure, people tend to overestimate the impact. Yes there can be an infinite number of GRINS, but only in the infinite future. In my lifetime there is a very real limited pool of GRIN.
Also the GRIN inflation is continuously decreasing. In ten years it will be 10% and in 100 it will be 1%. If you ask me that is too slow, but it will allow for cheap transactions and a very stable mining incentive. Bitcoin inflation is dropping much faster and after 10 years is now at 4% and in 100 years it will be at less than 0.01%.
The theoretical 21 million cap is actually not that relevant. If bitcoin would logarithmically go to infinity there would be no practical difference. What matters is the evolution of the inflation rate and there Bitcoin sees to have a better model. But GRIN can still serve as a highly private and scalable transfer of value and eventually also as store of value. And while lightning makes bitcoin much more private, as soon as a channel hits the main chain, that privacy is at least partially compromised.
Where to get GRIN
GRIN was just launched and because there was no premine, there are very few coins available right now. If anything the current prices should be too high. In a month or so this will have stabilised and there will be a solid supply of GRINS on the markets. If you need GRIN right now the best way is to start mining which requires a solid graphics card (8gb ram +) and some computer skills.