NAC Gateway

NAC (Cross-Runtime Atomic Calls) is the Tezos X mechanism for routing execution between the Tezos L1 Michelson runtime and the Tezlink EVM runtime within a single atomic operation.

The two directions

NAC is bidirectional. Each direction uses a different surface:

Direction	Surface	Used by
EVM → Michelson	NAC precompile at 0xff00...0007, called via the EVM selector callMichelson(string,string,bytes)	dApps running on Tezlink that want to invoke a Michelson contract
Michelson → EVM	NAC gateway contract (KT1...) on Tezos L1, entrypoint call_evm	The relayer — wraps every user EVM transaction as a Tezos L1 op

What the relayer does

The relayer uses the Michelson → EVM direction. Temple can only sign Tezos L1 operations, so instead of submitting an EVM transaction directly, the relayer wraps the user's intent into a Tezos L1 op targeting the NAC gateway's call_evm entrypoint. The Tezos X kernel receives the op, synthesizes the corresponding EVM transaction, and executes it with msg.sender set to the user's EVM alias.

call_evm entrypoint signature

pair string (pair string bytes)

Field	Type	Content
destination	string	The target EVM contract address (0x...)
method_sig	string	The full text signature of the EVM function, e.g. "transfer(address,uint256)". The kernel recomputes the 4-byte selector from this string.
calldata	bytes	ABI-encoded parameters (no selector prefix — the kernel prepends it)

Micheline built by the relayer

For a non-empty calldata EVM transaction, GatewayBuilder.fromEthTransaction produces:

{
  "prim": "Pair",
  "args": [
    { "string": "0xTargetEvmAddress" },
    { "prim": "Pair", "args": [
        { "string": "transfer(address,uint256)" },
        { "bytes": "abi-encoded-params-hex" }
      ]
    }
  ]
}

For a bare XTZ transfer (no calldata), the relayer uses the default entrypoint instead:

{ "string": "0xRecipient" }

Flow

Sender identity

When the kernel executes the synthesized EVM transaction:

• On the EVM side: msg.sender is the user's EVM alias (0x...), derived deterministically from their tz1 address via tez_getTezosEthereumAddress.
• On the Michelson side (if the EVM call then invokes callMichelson): Tezos.get_sender returns the user's tz1 address, not the NAC gateway's address.

info

The NAC gateway is a pass-through for identity. Both the EVM alias and the tz1 address refer to the same user, and the kernel preserves this mapping across the runtime boundary.