Shielded Writes

Send encrypted write transactions with shieldedWriteContract

Shielded writes encrypt transaction calldata before submission. This prevents calldata from being visible on-chain -- an observer can see that a transaction was sent to a particular contract address, but not what function was called or what arguments were passed.

seismic-viem provides two approaches:

• shieldedWriteContract() -- standalone function, same API shape as viem's writeContract

• contract.write.functionName() -- via a ShieldedContract from getShieldedContract

Both produce the same on-chain result: an encrypted type 0x4A Seismic transaction.

Standalone: shieldedWriteContract

import { shieldedWriteContract } from "seismic-viem";

Parameters

Parameter	Type	Required	Description
address	Hex	Yes	Contract address
abi	Abi	Yes	Contract ABI
functionName	string	Yes	Function to call
args	array	No	Function arguments
gas	bigint	No	Gas limit
gasPrice	bigint	No	Gas price
value	bigint	No	ETH value to send

Returns

Promise<Hash> -- the transaction hash.

Example

import { shieldedWriteContract } from "seismic-viem";

const hash = await shieldedWriteContract(client, {
  address: "0x1234567890abcdef1234567890abcdef12345678",
  abi: myContractAbi,
  functionName: "transfer",
  args: ["0xRecipient...", 100n],
  gas: 100_000n,
});

---

Debug: shieldedWriteContractDebug

Returns the plaintext transaction, the shielded (encrypted) transaction, and the transaction hash. Useful for inspecting what the SDK encrypts and broadcasts.

import { shieldedWriteContractDebug } from "seismic-viem";

const { plaintextTx, shieldedTx, txHash } = await shieldedWriteContractDebug(
  client,
  {
    address: "0x1234567890abcdef1234567890abcdef12345678",
    abi: myContractAbi,
    functionName: "transfer",
    args: ["0xRecipient...", 100n],
  },
);

console.log("Plaintext calldata:", plaintextTx.data);
console.log("Encrypted calldata:", shieldedTx.data);
console.log("Transaction hash:", txHash);

---

Low-level: sendShieldedTransaction

For cases where you have raw transaction data instead of ABI-encoded calls -- for example, contract deployments, pre-encoded calldata, or bypassing the contract abstraction entirely:

const hash = await client.sendShieldedTransaction({
  to: "0x1234567890abcdef1234567890abcdef12345678",
  data: "0x...", // raw calldata
  value: 0n,
  gas: 100_000n,
  gasPrice: 1_000_000_000n,
});

---

How It Works

When you call shieldedWriteContract (or contract.write.functionName), the SDK performs the following steps:

1. ABI-encode the function call into plaintext calldata

2. Build Seismic metadata -- encryption nonce, recent block hash, expiry block

3. Encrypt calldata with AES-GCM using a shared key derived via ECDH between your ephemeral keypair and the node's TEE public key

4. Construct a type 0x4A transaction with the encrypted calldata and Seismic-specific fields

5. Sign and broadcast the transaction

The encrypted calldata is bound to the transaction context (chain ID, nonce, block hash, expiry) via AES-GCM additional authenticated data, so it cannot be replayed or tampered with.

---

Security Parameters

Every shielded transaction includes a block-hash freshness check and an expiry window. The defaults are sensible for most cases, but you can override them per-call via SeismicSecurityParams:

Parameter	Type	Default	Description
blocksWindow	bigint	100n	Number of blocks before the transaction expires
encryptionNonce	Hex	Random	Override the encryption nonce
recentBlockHash	Hex	Latest	Override the recent block hash
expiresAtBlock	bigint	Calculated	Override the expiry block directly

const hash = await shieldedWriteContract(client, {
  address: "0x...",
  abi: myContractAbi,
  functionName: "transfer",
  args: ["0x...", 100n],
  securityParams: {
    blocksWindow: 50n, // expires after 50 blocks instead of 100
  },
});

The default 100-block window, random nonce, and latest block hash are appropriate for nearly all use cases. Override these only if you have a specific reason -- for example, reducing the window for time-sensitive operations or pinning the block hash in tests.

See Also

• Contract Instance -- getShieldedContract with .write and .dwrite namespaces

• Signed Reads -- Authenticated reads that also use the encryption pipeline

• Encryption -- ECDH key exchange and AES-GCM details

• Shielded Wallet Client -- Creating the client used for shielded writes