SuperAsset

A Fungible-Token (FT) standard for assets and smart contracts powered by Bitcoin Script and enforced by miners via the normal UTXO consensus rules at the base layer. This specification provides the same SPV-guarantees and peer-to-peer distribution for any asset or computation, just like the native Bitcoin Satoshi tokens.

Copyright 2020. MatterPool Inc. SuperAsset Smart Contract Specification, Technical Designs and Algorithms are licensed under GPLv3.

Attila Aros - Chief Technology Officer, MatterPool Inc. attila@matterpool.io

Contributors: Dean Little, Daniel Krawisz.

Special thanks to Josh Petty for suggesting the name "SuperAsset".

Document version 1.0.4

Abstract

This paper introduces a novel Fungible-Token (FT) smart contract called "SuperAsset" that has the same properties as the native Bitcoin Satoshi token unit of account. It is backed by the same proof-of-work and consensus mechanism that are enforced by Bitcoin miners. Specifically, we emulate the Conservation of Satoshi Quantity balancing requirement in Script when spending colored outputs and we therefore inherit all the capabilities afforded such as SPV, trustless verification and double-spend protection.

This is a breakthrough design and the world's first smart contract specification for a truly scalable token asset protocol that has the same "cash-like" peer-to-peer properties that users are accustomed to when transacting in native "non-colored" or "plain" Satoshis. The transaction size and history always grows linearly just like the plain Satoshi UTXOs. SPV works exactly as expected with the identical security guarantees. There is no way to corrupt state, man-in-the-middle, or pull of a replay-attack and furthermore users cannot accidentally destroy ("burn") coins nor spend coins that do not belong to them (Same guarantees as plain Satoshi UTXOs themselves).

Building on the concept of a Bitcoin Agent, we introduce a Distributed Verification Network and also introduce a novel and completely optional "asset block committment hash" technique for being able to quickly check if the other Agent operators are claiming to be in consensus or not. The key strength of this technique is that when a problem is detected, the resolution of the corruption is always in the most recent blocks and the UTXO sets can be trivially compared to identify the problem.

This design allows anyone to build a fungible (or non-fungible) smart contract asset that are truly distributed and backed by the full power of the Bitcoin proof-of-work system. It works exactly as many have desired for years. Various colored coins implementations have been created and none have been able to achieve the pure Colored Satoshi ideal, until now.

Note: Throughout this paper "Bitcoin" refers to the original protocol "Bitcoin (BSV)".

Table of Contents

Background Theory

This builds upon the concepts described in the paper introducing Bitcoin Agent. The reader may find it helpful for understanding the operations of this smart contract design.

We want our digital asset protocol to be as efficient as possible and maximally capable like the native Bitcoin system itself - but running inside the Bitcoin scripts executed by miners. Specifically we want all of the same benefits and guarantees as the native Satoshi itself as processed by any Bitcoin node. We want Byzantine consensus at scale, Simplified Payment Verification (SPV), tamper-resistance, trustless verification, and efficient zero-indexing overhead. We will have our cake and eat it too, so to speak.

This is a system capable of scaling to millions of transactions per second, ultra-low fees and full Byzantine fault tolerance and permissionless (and permissioned) smart contracting capabilities that will put Ethereum, EOS, Chainlink out of business.

We develop a smart contract specification in this paper that allows fungible types that have an initial quantity supply that can be sent around like regular Satoshis themselves (ie: transferred, merged, split, etc). Each Satoshi represents an indivisible unit of a token. This means that a Satoshi could be worth more or less than the value of the token itself. If the token is worth less, then the owner can melt out the Satoshis from the token and thereby destroying the token itself via "un-coloring" the UTXO.

The key insight is that Bitcoin nodes themselves are pattern matching the coinbase tx coin emissions and tracks their downstream transactions only in a data-structure called UTXO Set, which is built up block by block from the chain of valid state transformations (ie: spends).

Statement 1.0 We define our own "minting events" for colored coins in a matter similar to how any Bitcoin node detects the coinbase tx pattern for coin emission. Any Bitcoin Agent interested in tracking a specific colored coin types can trivially parse outputs for each transaction in a block and pattern match against the (static) smart contract code part that comprises the logic of the colored coin.

Any efficient token indexer will only store transaction histories of interest pertaining only to the tokens it is indexing. Specifically each UTXO should have the entire relevant parent history so that any independent user or auditor can trustlessly validate the entire parent chain of spends back to a minting event.

In other words, we modify the Bitcoin node or Agent service to ignore regular coinbases (by not adding the outpoint into the UTXO set) and instead perform a prefix match for the static part of the token minting transaction outputs it encounters. It simply peforms a "blind" (logic-less) fast rawhex pattern match against a whitelist of contracts/tokens of interest to the agent.

https://media.bitcoinfiles.org/5e3bcd98c54dad0bdc18e4a99cccf6cae92d2a610b8e5d8237be8ff7ab9dbb58

By making this one modification, it means that when reading raw blocks from the blockchain, in sequence at some starting height, then we can effectively build a zero-overhead UTXO data store that keeps precisely the relevant transactions from the minting transaction and their downstream children only. This forms a coherent UTXO shard. This shard is a subset of the total transactions, topologically related amongst themselves in inside and between blocks. There is "zero-overhead" (ie: no extra indexes are required) when compared to a regular Bitcoin 'global' node since the upper bound is identical - in the limit (ie: tracking your colored tokens and coinbase tx emission events) then it simply recovers the full blockchain UTXO set.

Statement 1.1 A Bitcoin node enforces the proof-of-work and validity of transactions. In particular it conserves the Satoshi quantity between the inputs and outputs (and any deficiency is taken as fees by the miner who included that transaction a block they mined).

https://media.bitcoinfiles.org/c5bd2fa39293542bec784546428d0aa4d359b9de1877480c1d6bc5ea80c916c3

We will show that we can build a Bitcoin script that is executed and enforced by Bitcoin nodes in the Bitcoin Virtual Machine (BVM) such that we can conserve quantities of arbitrarily "colored" Satoshis in a manner similiar to how the Bitcoin node itself enforces the balancing of the quantity of inputs and outputs. Our strategy for building a smart contract requires the power bestowed to plain uncolored Satoshis, but for any colored versions as well.

https://media.bitcoinfiles.org/0f8f81ebaa4dc3a0e22da94df66a01a3e45dd793912d0010d0c334ac915261f4

Statement 1.2: The entire chain of parent-child spend raw transaction history is required by some user or service to be able to verify authenticity with zero trust. Any wallet, user, or service can either proactively pre-index these spends (just like a Bitcoin node pre-indexes Satoshi UTXO spends, built up block by block) OR they can retro-actively ask for the entire history of the "coin title history" from the seller of the coins or a blockchain history lookup service. See: "Driving the point home..." in the Bitcoin Agent Whitepaper

This is not controversional as this is exactly what MatterCloud, ElectrumSV, Whatsonchain, Bitcoin-sv Node, Xoken Nexa, and all other mining and listening nodes perform today. That's merely what a node needs to do to build the UTXO set. They merely proactively index the entire chain of spends of coin emission events (coinbase transactions) starting from block height h=0. We generalize this concept in this paper to apply to indexing arbitrary minting "coin emission" events (ie: any smart contract or asset of interest) starting at some arbitrary block height h.

The Bitcoin Whitepaper points out that the chain of digital signatures is the coin. A single UTXO is not a coin. Neither is just the transaction id history. Nor is an SPV proof equal to a "coin", and neither is an API response from a blockchain service provider. If you do not have the chain of digital signatures, then you do not know 100% if the coins in hand are authentic. That's the trustless nature of Bitcoin in that everyone can get the complete hisory and check for themselves proactively or reactively as appropriate.

https://media.bitcoinfiles.org/774be421a944853597924127adc29ab8daced2e3305f7a02eed09c4e2d3e6a11 Source: "The Risks of Segregated Witness: Problems under Evidence Laws"

Every Bitcoin node is proactively indexing this chain of signatures and saving the raw transaction histories for later recall and re-organization. That's how the user or service knows the coins are authentic: because they verified the chain or paid someone to do it on their behalf. Such as ElectrumSV with ElectrumX and other "SPV light node" solutions or Bitcoin wallets.

Statement 1.3: At some point, a user or service must necessarily process through the entire history from minting event to subsequent latest spends at least once. Bitcoin nodes enforce consensus rules, however it is up to users and businesses to decide what minting events (and therefore their downstream transactions) are interesting amongst themselves. The Bitcoin mining nodes have no concept of "colored" UTXO's, they are just blindly executing the script transition rules.

https://media.bitcoinfiles.org/02174710feda2b95d04367e8d1630fa95f55f354de269e63c32e1356bc490ec4

Statement 1.4: It is desirable to maintain all the guarantees that the native Bitcoin Satoshi value itself is afforded. In particular, consensus at scale and speed of UTXOs, SPV, distributed fault-tolerance, tamper-resistance, trustless verification, efficient zero-indexing overhead, and immediate spend state corruption detection.

We need two fundamental basic ingredients to make a colored coin smart contract that itself is enforced on the same UTXO layer, and we outline what those are next.

Essential Requirements of the Ideal "Colored Coins" Solution

  1. (Easy) Mint (and trivially recognize) arbitrary colored smart contract outputs containing satoshis as the 'supply' itself.

Example: a supply of a hypothetical "DOGEBSV" in-game rewards points is decided to be capped at total supply of 100,000,000 units. Therefore exactly 1 BSV (100 million satoshis) needs to be deposited into the smart contract. The individual Satoshis themselves represent units of the token. A "DOGEBSV" token could be worth more or less than 1 Satoshi. At the time of writing 1 Satoshi is equal to about $0.0000018 USD. Even if the Bitcoin SV value increases by 1,000x fold, then it will still only be worth about $0.0018 USD per Satoshi token.

The Bitcoin Node or Agent merely indexes these unspent outpoints as any other transaction output, but merely tags it with the color DOGEBSV along with the assetId for disambiguation.

  1. (Hard) We need some kind of clever rules in the Bitcoin script spending constraints to preserve the colored input and output balancing quantity. Effectively maintaining identity and Conservation of Satoshi value, while avoiding all possible forgery, man-in-the-middle, replay and inflation attacks.

This requirement to maintain the correct balance of colored input value to output value has never been solved until now. This is the most important requirement for the case of any fungible token because merge function needs to prevent a coin from accidentally or maliciously spent in such a way as to inflate supply (awarding the attacker with new "colored" coins that they did not have) and it also prevents accidental burning of the coins. A wallet that doesn't understand the rules will be unable to spend the coins no matter what, even accidentally.

In other words the solution to this "conservation of value" or "balancing" of colored satoshis enforced at the Bitcoin native scripting is the key to unlocking enormous potential. The bulk of the specification deals with handling the merge function as the split and transfer functions are relatively simple.

  1. (Easy, trivial) If a corrupt Agent or indexer serves up false state, then we want the full guarantees of the Bitcoin system automatically: a) User cannot accidentally destroy or "burn" their coins. b) User cannot be tricked into spending coins that do not belong to them. c) Service provider or website cannot steal funds from the user. d) User can self-evidently verify the authenticity when provided with the raw history from any service that provides the history (or from the peer user). e) The corrupt Agent can be detected trivially and data replayed quickly to pinpoint exact outpoint that is mismatched in the block update. f) In the case of corrupt state being served, we wish to know immediately of the problem (ie: within the current/last block) so that re-org and corruption damage is bounded (to at most the last 1 block in ~10 minutes). e) Users can operate "peer-to-peer" and transaction amongst themselves without a central party (ie: passing around the chain of coins to each other as described in the Bitcoin Whitepaper)

Requirement 1. is easy to satisfy because the token contract code will be constant (static) and can be easily pattern matched and indentified by a Bitcoin Node or Agent via a white list.

"Hello, which smart assets and tokens can I index and show you today? Check the following options...." - Your friendly Hypothetical Smart Contract Explorer Site.

Requirement 2. Is much more difficult because we need a way to create constraints on the total colored input quantity compared to the total colored output quantity. The main problem we run into is that each inputs' unlocking script does not have access to each other sibling input's data directly nor it's value directly when under the BVM execution context. We will show in the rest of the paper how we can achieve this knowledge and create such a completely tight constraint.

Observe that Requirement 3.'s properties are actually just a mere consequence of Requirements 1. and 2. because they make the colored coins operation isomorphic to the UTXO Satoshi transfers themselves (they piggyback "on top, fused" to the Satoshi itself). We therefore inherent all the properties and benefits that the Bitcoin system affords these native Satoshis.

A note about the last point of Requirement 3f), it would be extremely undesirable to detect corruption that happened 100+ blocks ago. The recovery effort will be challenging and many systems would have ingested the corrupt data, leading to a small mutiny on your hands from your information technology teams and loss of trust with your customers and partners. This problem is fully solved in this specification below and introduces a novel and completely unrequired and optional Distributed Verification Nework that can be used to quickly detect corrupt service providers or mistakes almost immediately.

In the sections below we invent and describe the world's first fully permission-less fungible asset protocol for Bitcoin with identical security guarantees as the Bitcoin system itself. It is trivial to extend it to the permissioned cases with regulated issuers. It operates at the speed and efficiency of the UTXO model, it's inherent parallelizability, and extreme low-cost fees with the same (and better) capabilities than Ethereum, EOS, Chainlink, or anything that other blockchain systems attempt to provide.

The potenial of this technique and algorithm has applications far beyond simple fungible "colored coins" and will form a powerful substrate to carry any incentivized (valued) workload or computation across autonomous agents. The applications of this technology will completely transform the fields of commerce and finance, distributed systems, crowd-sourced intelligence, gaming, reputation systems, automated arbitration and insurance, logistics, amongst many others.

We use the following sections to detail the smart contract layout and algorithm for making this a reality.

Smart Contract Technical Specification

The smart contract's output is laid out in the following manner. The fields [ mergeCounter prevOuts input1PrevTx input2PrevTx ...] are present only in the case of the merge function and can be omitted for transfer, issue, and split. We should also opt to keep mergeCounter and prevOuts in all other functions as it gives extra confidence and fully binds every input to every output scenario.

Transaction Output Layout:

==========================================================================================
|      |
| CODE | OP_RETURN assetID ownerPubKey [ mergeCounter prevOuts input1PrevTx input2PrevTx ...]
|      |
==========================================================================================

The hardest case is merge, so we explore it first. Specifically we are going to briefly discuss an n-way input merge that results in combining up to n colored input satoshis into a single colored output. The details and diagrams of the function is provided below.

The bulk of the complexity for merge is dealing with Requirement 2. above for conserving the Satoshi quantity. This smart contract invention is the world's first solution to solve the n-way colored input merge with a O(N) growth rate in the number of inputs.

The challenging part is that each input does not know the other inputs' outpoint or satoshi value. The novel technique we introduce is to place the prevOut bytes and the respective parent input raw transaction bytes into the one and only colored output (in case of "merge"). In this way all colored inputs must necessarily validate that their view of hash(prevOuts) obtained from their preimage matches the prevOuts hash in the output. We must also include each and every rawtx for each colored input, to the end of the output script because that's how we can know the correct satoshi value being spent after we parse the transaction. The prevouts are checked in the input parent raw tx's and then also in the inputs themselves, creating a tight severally and jointly bound constraint amongst all colored inputs and outputs.

Here is the information available from the pre-image:

https://media.bitcoinfiles.org/a17176cb5bce91f89d76f74bef41243ccb6ea6149e1c127b8602efcf1f28444f

We can see that if we provide the prevOuts in the single output and then we enforce each unlocked input to also have the same hash(prevOuts) (via checkcing it's own Preimage using a technique like OP_PUSH_TX and then we can effectively bind the balance to be conserved and validating all inputs and outputs are known in each execution context. Forgeries, attacks, man-in-the-middle, are all not possible. The colored coins can only be spent if they conform to the rules exactly.

Contract Fields

CODE (required): Unchanging static smart contract code. Any Agent or node can trivially check this raw bytes and then add it to their spend or UTXO set. The reason the contract code appears at the beginning of the output bytes is to faciliate a fast prefix match. Any agents do not care about the particular assetID or state and just blindly process transaction outputs with no regard to the operation of SuperAsset style outputs.

This part remains constant in all transactions for the lifetime of the asset and cannot be changed. Everything after the OP_RETURN is the state data for the instance and must confirm to the rules in CODE at each step of the way.

assetID (required): Set to 000000000000000000000000000000000000000000000000000000000000000000000000 (36 bytes) upon initial deployment to the blockchain. After issuing/minting the asset, then the smart contract enforces setting the assetID to the prevOutpoint (36B) of the issuing transaction to prevent replay attacks.

Tokens cannot be forged without getting a different globally unique identifier making replays and forgeries trivial to detect.

ownerPubKey (required): Set to public key of initial owner (33B) on minting to initialize. Subsequent transfers can set any new owner. Only the current ownerPubKey can spend the output because the contract enforces a signature to be provided by the current owner to authorize the transaction.

mergeCounter (optional - required to be set to 02, (then 01...) for 'Merge')

To prevent the UTXO history chain from growing too fast, we enforce that a recently merged UTXO cannot be then again merged immediately. Instead the wallet must do two (2) regular transfers or split of the UTXO first before the merge operation can be performed again. This means the entire UTXO history (ancestor outputs) will grow only linearly O(n) in the size of the chain of digital signatures going back to the minting event from the particular UTXO's being merged.

In other words, the spending transaction cannot include any inputs where mergeCounter > 00 until it was split or transferred again twice (when it is then set to mergeCounter=00 (or omitted) after a regular transfer or split). This is an inconvenience that can be invisible to the user with a wallet that is aware of the mergeCounter status and can automatically spend them behind the scenes, so that all the user's tokens are always in a "mergeable" state if desired.

Without this requirement, then token histories would grow exponentially (when doing multiple merges in succession). We call this technique of "mergeability" a forward constraint on spends of the parents. Other token examples try to solve this by "looking backwards" and therefore cannot avoid the super linear factor in storage requirements that renders them useless after a few dozen or hundred transfers. (ie: 42TB in size after just a mere 32 transfers)

prevOuts (optional - required only for 'Transfer', 'Split' and 'Merge' function)

This is the raw bytes of the prevOuts of the current transaction. This gives us the information we need to know the structure of the sibling prevOuts. It makes the other inputs "knowable" (via hash(prevOuts)) to all inputs in the unlocking execution context. We write this to the single merged output, and each input is enforced to match it's own view of the hash(prevOuts) via the preimage. This means no other fake or corrupt inputs can be used to spend the transaction. The token will not be accepted for spending by Bitcoin miners in the case of a malicious or accidental forgery.

The outpoint (txid+index) array is included in the prevOuts and we therefore can look at the fields input1PrevTx, input2PrevTx, ... to get the Satoshi value of the respective unlocked outpoints. The raw transaction bytes for each of the input parent's are needed because the prevOuts do not contain the satoshi value being redeemed. We must always get that from the complete parent transaction which contains the outpoint and the satoshi value being locked. (See next field below)

Observe that the size prevouts itself grows with O(N) space and time complexity where N in this case is the number of inputs to the current transaction.

input1PrevTx, input2PrevTx, input3PrevTx, ... (optional - required only for 'Merge')

In the case of a merge operation, there must be at least n rawtx's of the respective parent previous transactions for each of the colored token inputs. This is required because we must hash the rawtx to arrive at the txid (trustlessly) and then constrain the unlocking prevOut txid+index to it's associated rawtx (then comparing to hash(prevOuts)). Effectively binding severally and jointly each input to the merged output. SIGHASH_ALL signature is required on all colored inputs except the 1 funding input UTXO and output UTXO (which is signed with SIGHASH_SINGLE)

The number of rawtx's to include is linear in the number of inputs to the current transaction, just like the prevOuts bytes field.

Contract Methods

Initial Deployment

Upon initial deployment, the user locks up a number of Satoshis. For example, if the user intends to issue 100,000,000 colored asset tokens, then they lock up that number of satoshis in the "genesis" transaction.

https://media.bitcoinfiles.org/ee14f80ff6c0f024eebc2f2945be3ebd4f9f1b9e68aee05a78675ec1d0a66a83

Issue

The issue function gives a unique identity to the asset by enforcing that assetID must be equal to the minting txid+index (prevOut) of the issue transaction. This can never be changed for the lifetime of the asset in subsequent UTXO's. Any agent can trivially check a UTXO and locate the initial deployment of the smart contract and trustlessly build up the history if necessary.

Note: that SIGHASH_SINGLE is used on a funding input (not pictured) that is used to pay the mining fee in non-colored Satoshis as normal. Therefore an non-colored change output is also needed (in output position 0)

https://media.bitcoinfiles.org/c5d3ec9230674a45e2a0640df8749fdc9c8ed376e851b7d4e2fada8cf1b0191e

Transfer

A simple transfer function that allows spending a single input to another output. This is useful for making recently merged outputs to create a "gap" so that there is never 2 consecutive merges in a row. This can also be used to transfer ownership to any other owner.

Note: that SIGHASH_SINGLE is used on a funding input (not pictured) that is used to pay the mining fee in non-colored satoshis as normal. Therefore an non-colored change output is also needed (in output position 0)

https://media.bitcoinfiles.org/edc57bc86e1841a3621f3148a8ed078996780af2aae11c3780a34d9760e3bc55

Split

A colored asset UTXO can be split to n-outputs (2 outputs are pictured), conserving the satotshi quantity so that coins cannot be created or destroyed.

Note: that SIGHASH_SINGLE is used on a funding input (not pictured) that is used to pay the mining fee in non-colored satoshis as normal. Therefore an non-colored change output is also needed (in output position 0)

https://media.bitcoinfiles.org/d71b869bcc74b14718f6e6194570cebf8240cabae39ae65c07bd754863ecf54e

Merge

https://media.bitcoinfiles.org/837a90464ba04fcef5eb166e6e2022c5ad2cabacf5947aa01c6368cc7271e58b

Any number of colored inputs can be safely merged with the transaction only growing linear O(n) in the number of inputs. After a merge is completed, then the flag mergeCounter=02 is set so that the wallet or user cannot accidentally merge an already recently merged UTXO thereby avoiding the exponential doubling in transaction size.

The wallet can trivially check the user has unspent coins with mergeCounter=02 and then automatically spend them to the same ownerPublicKey twice in a row (mergeCounter=02, then mergeCounter=01 and then it is removed). This can be invisible to the user, and imposes no cognitive overhead or manual action because it can be fully automated with ease.

The only reason n-input merging works successfully is because each unlocking input context has it's own preimage and therefore can impose a mutually binding constraint on every input by projecting forward the prevOuts and the raw transactions of the immediate prev parents. Recall that we can obtain hash(prevOuts) from the raw prevOuts and also from the outputs being spent in the respective parent prev transactions that are also embedded in the newly created output.

Note: that SIGHASH_SINGLE is used on a funding input (not pictured) that is used to pay the mining fee in non-colored satoshis as normal. Therefore an non-colored change output is also needed (in output position 0)

https://media.bitcoinfiles.org/9245a290b80bfd3e31ad651d17fe61cc7666e834a5a036fdc9290036e5b5b24d

Melt

A user can "melt" (ie: destroy) their asset tokens and redeem the underlying satotshi conttent back to non-colored "plain" native satoshis. A user may opt to do this if the underlying asset becomes worth less than the value of the satoshi.

Future versions of this SuperAsset standard could include an immutable issuerPubKey in the initial deployment to allow only the original issuer to "melt" or redeem the colored outputs.

https://media.bitcoinfiles.org/b1b9a97f514bee686d486cdcfb7e3c79b19d1c2c0145b576751de32f3396311b

Distributed Verification and Consensus

https://media.bitcoinfiles.org/c0a6ca522ed3a265b94745758f6724b35a83c76e88d458bb139d26c90be881ed

Similiar to how the blockhash is a commitment to the transactions in the block, we introduce an optional "asset block committment hashes" that gives independent agents a way to know they have arrived at the same consensus state. This also serves the purpose for informing partners, customers, and even adversaries that consensus state is achieved (or lost, so that the correction can be made quickly and efficiently).

The commitment hash is simply the:

  • hash(blockhash + txids_of_colored_inputs_in_current_block)

We can even distribute this "colored token block" in serialized form and merklize the transactions so we could serve mini-SPV-like committments. It is not necessary for agents to use this committment scheme and no additional guarantees are provided except for the convenience notion that a large operator with many Bitcoin Agents can trivially see when a computer or hard drive has become corrupted.

Consider the following three Agents and a token type DOGEBSV being tracked by all three.

https://media.bitcoinfiles.org/68a217b7dcd6fc7cad66dd8ef7145f20b6933b2529a90894b890db7d7bb12613

Agent 1:

DOGEBSV:
650,003: f7a8211a...
650,002: 5de1d2d...
650,001: bf3994a4...
650,000: e4bc9513...

Agent 2:

DOGEBSV:
650,003: ab1802e...   (DIFFERENT!)
650,002: 5de1d2d...
650,001: bf3994a4...
650,000: e4bc9513...

Agent 3:

DOGEBSV:
650,003: f7a8211a...
650,002: 5de1d2d...
650,001: bf3994a4...
650,000: e4bc9513...

In the example above we can see that Agent 2 arrived at a different committment hash, perhaps because their disk or RAM got corrupted and a bit was flipped. By comparing to at least one other agent, it can be quickly determined what the problem is and recover gracefully.

Economic Disincentive for Attackers

Even though a forgery is trivially detected by inspecting the history or proactively indexing assets of interest, there will still be attackers who attempt to pass off a fake asset, just like they may attempt with fake native satoshi UTXOs.

As long as the user makes a request to a blockchain provider to fetch the entire parent history (or demands that a seller of an asset provide their complete copy of the history) then the user cannot be tricked into accepting a fake asset.

Notice the disincentive for an attacker: since the supply is one and the same as the Satoshi unit of account it then means they must give away free fake colored satoshis. Upon discovering this forgery, the new owner of these fake assest (which themselves are real valuable satoshis) can be melted back for a small tiny profit.

Transaction History and Size Calculations

The size of output itself grows with O(N) space and time complexity where N in this case is the number of inputs to the current transaction. Even though we embed the entire prev raw transactions it is still linear and this will be scalable for n-inputs and not just a 2-input merge scenario.

Also let's recognize that the size of the history of the UTXO token state grows linearly for sufficiently large constant C=2 kilobytes. Because we do not allow merging immediately after a merge, then the history will grow O(C*N) = O(N) which is still linear space and time complexity. If we allowed a merge to immediately follow a merge, then the transaction size would grow double in size with each subsequent merge. That is why it is disallowed.

Example: a 4KB output smart contract will grow in size with 3 inputs like so:

  • Base Input Size: 4kb * 3 inputs = 12 kb
  • Base Output Size: 4kb * 3 inputs = 12 kb
  • Parent Input's Rawtx embedded in outputs: 4kb * 3 = 12kb
  • Sum: 12kb + 12kb + 12kb = 3*12kb = 36kb

An example with 4-way mergeable inputs:

  • Base Input Size: 4kb * 4 inputs = 16 kb
  • Base Output Size: 4kb * 4 inputs = 16 kb
  • Parent Input's Rawtx embedded in outputs: 4kb * 4 = 16kb
  • Sum: 16kb + 16kb + 16kb = 4*12kb = 48kb

Additions and Variations

Extending the base contract can be done easily, and a number of important vareties can be created.

Issuer / Redeemer

If the issuer enforces that it's issuerPubKey is minted into the deployment, and carried forward in all subsequent UTXOs, then the melt function could be changed to allow only spending to the issuerPubKey is possible (ie: issuer needs to authorize the redemption or melting)

Continuous Supply Increases

When the contract is deployed, we can create two outputs: 1 for issue and another for a supplyIncrease output. This second output represents a "supply increase output baton" that can be spent by the issuer to increase supply of the token quantity. This can be a useful technique for also 'recycling' coins to reduce the history for the users of the token asset. And of course it is inherently useful for coins which naturally get lost or decay and must be replenished.

Non-Fungible Token Variation

We can create a Non-Fungible Token (NFT) where the satoshi value is equal to 1 (then by definition it is non-fungible). However we wish to make a modification that does not allow merge, nor split but instead allows a single quantity of Satoshis (say 100,000) to be fused into the NFT which in essence acts as a kind of "bitcoin reserve value" on the price floor of the asset.

Composability Considerations

The specification and examples above use an Address (Ripemd160) for change address output. However this need not be the case and we can allow any other valid output to receive the change. The only restriction we must enforce is that this change output does not contain the constant static part tof the CODE. We must ensure the change is not-colored and that is how we can enforce it easily.

Furthermore, by allowing any funding inputs to be added, other smart contracts can interact with this contract and be used to trigger various events. More work needs to be done to explore this area.

Applications in Various Fields

Voting: By issuing 'voting tokens', then each UTXO holder can update a payload via a potential updateState method that can express a voting preference. Resolving the current voting result status is siimply enumerating all UTXO's and then aggregating their responses, weighted by total voting token quanitty.

Distributed Computation: A recursive computation can be incentivized and a value assigned so that independent workers can process the work in parallel and receiving the 'reward' for their work by 'melting' down the token upon submission of a successful solution to unlock the native satoshis underneath.

Games: The ability to create non-divisible (in the case of a token supply of 1 satoshi) and divisible assets means users can own unique property that they control directly. Games can create an in-game currency that has inherent value because they are backed by satoshis themselves. Items can be "infused with Bitcoin" to give them value. Imagine a powerful sword item with 0.25 Bitcoins that gets passed along to the future owners (hopefully after turning a tidy profit and healthy margin on this one-of-a-kind in game item.)

Logistics and Tracking: A shipping company can track each vehicle with a unique colored UTXO. When a new stage or delivery checkpoint is met, then the truck driver can update the UTXO state with it's coordinates and status. Real-time analysis is possible and history can be analyzed for patterns.

Trade and commerce: Businesses and users can easily issue and loyalty points, coupons, and other rewards to increase business and customer options. The nature of the token makes it easy to integrate with any point-of-sale system, reporting requirements, and mobile kiosks in exactly the same way as sending regular Bitcoin cryptocurrency.

Conclusion

This paper introduced a novel Fungible-Token (FT) smart contract called "SuperAsset" that has the same properties as the native Bitcoin Satoshi token unit of account. It is backed by the same proof-of-work and consensus mechanism that are enforced by Bitcoin miners. As a result we inherit all the capabilities afforded such as SPV, trustless verification and double-spend protection.

This breakthrough design for a token smart contract specification enables a truly scalable token asset protocol that has the same "cash-like" peer-to-peer properties that users are accustomed to when transacting in native "non-colored" or "plain" Satoshis. The transaction size and history always grows linearly just like the plain Satoshi UTXOs. SPV works exactly as expected with the identical security guarantees. There is no way to corrupt state, man-in-the-middle, or pull of a replay-attack and furthermore users cannot accidentally burn coins nor spend coins that do not belong to them (Same guarantees as plain Satoshi UTXOs themselves).

We introduced a distributed verification network upon the conceptual framework of the Bitcoin Agent, w and also introduce a novel and completely optional "asset block committment hash" technique for quickly checking consensus state with other peers. The key strength of this technique is that when a problem is detected, the resolution of the corruption is always in the most recent blocks and the UTXO sets can be trivially compared to identify the problem.

This design allows anyone to build a fungible (or non-fungible) smart contract asset that are truly distributed and backed by the full power of the Bitcoin proof-of-work system.

License

GNU GENERAL PUBLIC LICENSE Version 3, 29 June 2007

Copyright (C) 2007 Free Software Foundation, Inc. https://fsf.org/ Everyone is permitted to copy and distribute verbatim copies of this license document, but changing it is not allowed.

Preamble

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Also add information on how to contact you by electronic and paper mail.

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