Sui supports k out of n Multi-Signature (MultiSig) transactions where k is the threshold and n is the total weights of all participating parties. The maximum number of parties is required to be <= 10.

Pure Ed25519, ECDSA Secp256k1 and ECDSA Secp256r1 are supported as valid participating keys for MultiSig. A (u8) weight is set for each participating keys and the threshold can be set as u16. If the serialized MultiSig contains enough valid signatures of which the sum of weights passes the threshold, the MultiSig is considered valid and the transaction can be executed.

This topic covers:

1. The applications of Multi-Signature;
2. The workflow to create a Multi-Signature transaction in Sui.

Applications of Multi-Signature

Interestingly, cryptographic agility allows users to mix and match key schemes in a single multisig account. For example, one can pick a single Ed25519 mnemonic-based key and two ECDSA secp256r1 key to create a multisig account that always requires the Ed25519 key, but also one of the ECDSA secp256r1 keys to sign. A potential application of the above structure is using mobile secure enclave stored keys as 2FA; note that currently iPhone and high-end Android devices support ECDSA secp256r1 enclave-stored keys only.

Compared to threshold signatures, a Multi-Signature account is generally more flexible and easier to implement and use, without requiring complex multi-party computation (MPC) account setup ceremonies and related software, and any dependency in threshold crypto providers. Additionally, apart from the ability to mix and match key schemes and setting different weights for each key (which is complex in threshold cryptography), Multi-Signature accounts are by design "accountable" and "transparent" due to the fact that both participating parties and observers can see who signed each transaction. On the other hand, threshold signatures provide the benefits of hiding the threshold policy, but also resulting in a single signature payload, making it indistinguishable from a single-key account.

This table shows the MultiSig structures supported in Sui.

Example Workflow

Here we demonstrate the steps to create a MultiSig transaction in Sui using CLI and then submit it using the Sui CLI against a local network. A transaction can be a transfer of an object, publish or upgrade a package, pay Sui, etc. To learn how to set up a local network, see Sui Local Network

Step 1: Add keys to Sui keystore

Use the following command to generate a Sui address and key for each supported key scheme and add it to the sui.keystore, then list the keys.

$SUI_BINARY client new-address ed25519
$SUI_BINARY client new-address secp256k1
$SUI_BINARY client new-address secp256r1

$SUI_BINARY keytool list

The response resembles the following, but displays actual addresses and keys:

Sui Address | Public Key (Base64) | Scheme
--------------------------------------------------------------------------
$ADDR_1     | $PK_1               | secp256r1
$ADDR_2     | $PK_2               | secp256k1
$ADDR_3     | $PK_3               | ed25519

Step 2: Create a MultiSig address

To create a MultiSig address, input a list of public keys to use for the MultiSig address and a list their corresponding weights and the threshold.

$SUI_BINARY keytool multi-sig-address --pks $PK_1 $PK_2 $PK_3 --weights 1 2 3 --threshold 3
MultiSig address: $MULTISIG_ADDR

The response resembles the following:

Participating parties:
Sui Address | Public Key (Base64)| Weight
------------------------------------------
$ADDR_1    | $PK_1              |   1
$ADDR_2    | $PK_2              |   2
$ADDR_3    | $PK_3              |   3

Step 3: Send objects to a MultiSig address

This example requests gas from a local network using the default URL following the guidance in Sui Local Network.

curl --location --request POST 'http://127.0.0.1:9123/gas' --header 'Content-Type: application/json' --data-raw "{ \"FixedAmountRequest\": { \"recipient\": \"$MULTISIG_ADDR\" } }"

The response resembles the following:

{"transferred_gas_objects":[{"amount":200000,"id":"$OBJECT_ID", ...}]}

Step 3: Serialize ANY transaction

This section demonstrates how to use an object that belongs to a MultiSig address and serialize a transfer to be signed. Note that the tx_bytes can be ANY serialized transaction data where the sender is the MultiSig address, simply use the --serialize-unsigned-transaction flag for supported commands in sui client -h (e.g. publish, upgrade, call, transfer, transfer-sui, pay, pay-all-sui, pay-sui, split, merge-coin) to output the Base64 encoded transaction bytes.

$SUI_BINARY client transfer --to $SOME_ADDR --object-id $OBJECT_ID --gas-budget 100000 --serialize-unsigned-transaction

Raw tx_bytes to execute: $TX_BYTES

Step 4: Sign the transaction with two keys

Use the following code sample to sign the transaction with two keys in sui.keystore. You can do this with other tools as long as you serialize it to flag || sig || pk.

$SUI_BINARY keytool sign --address $ADDR_1 --data $TX_BYTES

Raw tx_bytes to execute: $TX_BYTES
Serialized signature (`flag || sig || pk` in Base64): $SIG_1

$SUI_BINARY keytool sign --address $ADDR_2 --data $TX_BYTES

Raw tx_bytes to execute: $TX_BYTES
Serialized signature (`flag || sig || pk` in Base64): $SIG_2

Step 5: Combine individual signatures into a MultiSig

This sample demonstrates how to combine the two signatures:

$SUI_BINARY keytool multi-sig-combine-partial-sig --pks $PK_1 $PK_2 $PK_3 --weights 1 2 3 --threshold 3 --sigs $SIG_1 $SIG_2

MultiSig address: $MULTISIG_ADDRESS # Informational
MultiSig parsed: $HUMAN_READABLE_STRUCT # Informational
MultiSig serialized: $SERIALIZED_MULTISIG

Note that only the signatures of the participating signers whose sum of weights >=k are needed. All public keys and their weights and the threshold that defined the MultiSig address are required to be provided.

Step 6: Execute a transaction with MultiSig

This sample demonstrates how to execute a transaction using MultiSig:

$SUI_BINARY client execute-signed-tx --tx-bytes $TX_BYTES --signatures $SERIALIZED_MULTISIG