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Update chain signatures API #2191

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Jul 30, 2024
Merged

Update chain signatures API #2191

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04c8cde
updated chain signatures
gagdiez Jul 30, 2024
9b51fd5
fix: used main instead of branch
gagdiez Jul 30, 2024
fb7b1c0
Merge branch 'master' into chain-signatures
gagdiez Jul 30, 2024
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12 changes: 2 additions & 10 deletions docs/1.concepts/abstraction/chain-signatures.md
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Expand Up @@ -59,18 +59,10 @@ This contract has a `sign` method that takes two parameters:

For example, a user could request a signature to `send 0.1 ETH to 0x060f1...` **(transaction)** using the `ethereum-1` account **(path)**.

After a request is made, the `sign` method starts recursively calling itself to wait while the [MPC signing service](#multi-party-computation-service-mpc) signs the transaction.

Once the signature is ready, the contract gains access to it and returns it to the user. This signature is a valid signed transaction that can be readily sent to the target blockchain to be executed.
After a request is made, the `sign` method will [yield execution](/blog/yield-resume) waiting while the [MPC signing service](#multi-party-computation-service-mpc) signs the transaction.

<details>
<summary> A Contract Recursively Calling Itself? </summary>

NEAR smart contracts are currently unable to halt execution and await the completion of a process. To solve this while we await the ability to [yield & resume](https://docs.near.org/blog/yield-resume), one can make the contract call itself again and again checking on each iteration to see if the result is ready.

**Note:** Each call will take one block which equates to ~1 second of waiting. After some time the contract will either return a result that an external party provided or return an error running out of GAS waiting.

</details>
Once the signature is ready, the contract resumes computation and returns it to the user. This signature is a valid signed transaction that can be readily sent to the target blockchain to be executed.

<hr class="subsection" />

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29 changes: 7 additions & 22 deletions docs/2.build/1.chain-abstraction/chain-signatures.md
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Expand Up @@ -42,7 +42,7 @@ _Diagram of a chain signature in NEAR_

If you want to try things out, these are the smart contracts available on `testnet`:

- `v2.multichain-mpc.testnet`: [MPC signer](https://github.com/near/mpc/tree/v0.2.0/contract) contract, latest release, made up of 8 MPC nodes
- `v1.signer-prod.testnet`: [MPC signer](https://github.com/near/mpc/tree/v0.2.0/contract) contract, latest release, made up of 8 MPC nodes
- `canhazgas.testnet`: [Multichain Gas Station](multichain-gas-relayer/gas-station.md) contract
- `nft.kagi.testnet`: [NFT Chain Key](nft-keys.md) contract

Expand Down Expand Up @@ -89,7 +89,7 @@ The same NEAR account and path will always produce the same address on the targe

We recommend hardcoding the derivation paths in your application to ensure the signature request is made to the correct account

#### v2.multichain-mpc.testnet
#### v1.signer-prod.testnet
`secp256k1:4NfTiv3UsGahebgTaHyD9vF8KYKMBnfd6kh94mK6xv8fGBiJB8TBtFMP5WWXz6B89Ac1fbpzPwAvoyQebemHFwx3`

:::
Expand All @@ -104,7 +104,7 @@ Constructing the transaction to be signed (transaction, message, data, etc.) var
<TabItem value="Ξ Ethereum">
<Github language="js"
url="https://github.com/near-examples/near-multichain/blob/main/src/services/ethereum.js"
start="46" end="69" />
start="46" end="73" />

In Ethereum, constructing the transaction is simple since you only need to specify the address of the receiver and how much you want to send.

Expand Down Expand Up @@ -136,7 +136,7 @@ The method requires two parameters:
<TabItem value="Ξ Ethereum">
<Github language="js"
url="https://github.com/near-examples/near-multichain/blob/main/src/services/ethereum.js"
start="72" end="74" />
start="75" end="82" />

</TabItem>

Expand All @@ -151,22 +151,9 @@ For bitcoin, all UTXOs are signed independently and then combined into a single

</Tabs>

:::tip
Notice that the `payload` is being reversed before requesting the signature, to match the little-endian format expected by the contract
:::

:::info

The contract will take some time to respond, as the `sign` method starts recursively calling itself waiting for the **MPC service** to sign the transaction.

<details>
<summary> A Contract Recursively Calling Itself? </summary>

NEAR smart contracts are currently unable to halt execution and await the completion of a process. To solve this while we await the ability to [yield & resume](https://docs.near.org/blog/yield-resume), one can make the contract call itself again and again checking on each iteration to see if the result is ready.

**Note:** Each call will take one block which equates to ~1 second of waiting. After some time the contract will either return a result that an external party provided or return an error running out of GAS waiting.

</details>
The contract will take some time to respond, as the `sign` method [yields execution](/blog/yield-resume), waiting for the MPC service to sign the transaction.

:::

Expand All @@ -182,12 +169,10 @@ This allows the contract to generalize the signing process for multiple blockcha
<TabItem value="Ξ Ethereum">
<Github language="js"
url="https://github.com/near-examples/near-multichain/blob/main/src/services/ethereum.js"
start="76" end="90" />
start="84" end="95" />

In Ethereum, the signature is reconstructed by concatenating the `r`, `s`, and `v` values returned by the contract.

The `v` parameter is a parity bit that depends on the `sender` address. We reconstruct the signature using both possible values (`v=0` and `v=1`) and check which one corresponds to our `sender` address.

</TabItem>

<TabItem value="₿ Bitcoin">
Expand All @@ -211,7 +196,7 @@ Once we have reconstructed the signature, we can relay it to the corresponding n
<TabItem value="Ξ Ethereum">
<Github language="js"
url="https://github.com/near-examples/near-multichain/blob/main/src/services/ethereum.js"
start="94" end="98" />
start="105" end="109" />

</TabItem>

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