Sign the transaction

After building, the SDK automatically decodes the transaction, signs it locally with your private key and re-encodes it. Your key never leaves your device.

The Signing Process

The API returns a base64-encoded wire transaction. This is the serialized transaction format that Solana uses. To sign it:

Decode from base64 to get the transaction bytes
Sign the transaction with your keypair
Re-encode back to base64 wire format

Your private key stays on your machine during this entire process.

Code Examples

The API returns a base64-encoded wire transaction; you decode it, sign it then re-encode it back to base64 wire format.

TypeScript
Python

import bs58 from 'bs58';
import {
  getTransactionDecoder,
  signTransaction,
  getBase64EncodedWireTransaction,
  createKeyPairFromBytes,
} from '@solana/kit';

// 1) Create signer (base58-encoded 64-byte secret key)
const SECRET_KEY_BASE58 = 'SECRET_KEY_BASE58';
const signer: CryptoKeyPair = await createKeyPairFromBytes(bs58.decode(SECRET_KEY_BASE58));

// 2) Deserialize base64 → Transaction
const unsignedTx = getTransactionDecoder().decode(
  Buffer.from('BASE_64_ENCODED_UNSIGNED_TRANSACTION', 'base64'),
);

// 3) Sign
const signedTx = await signTransaction([signer], unsignedTx as any);

// 4) Serialize Transaction → base64 wire
const signedTxBase64Wire = getBase64EncodedWireTransaction(signedTx);
console.log(signedTxBase64Wire);

import base64
import base58
from solders.keypair import Keypair
from solders.transaction import VersionedTransaction

# 1) Create signer (base58-encoded 64-byte secret key)
SECRET_KEY_BASE58 = "SECRET_KEY_BASE58"
signer = Keypair.from_bytes(base58.b58decode(SECRET_KEY_BASE58))

# 2) Deserialize base64 wire → VersionedTransaction
unsigned_bytes = base64.b64decode("BASE_64_ENCODED_UNSIGNED_TRANSACTION")
unsigned_tx = VersionedTransaction.from_bytes(unsigned_bytes)

# 3) Sign (rebuild the tx with the same message + new signature)
signed_tx = VersionedTransaction(unsigned_tx.message, [signer])

# 4) Serialize VersionedTransaction → base64 wire
SIGNED_TX_BASE64_WIRE = base64.b64encode(bytes(signed_tx)).decode("utf-8")
print(SIGNED_TX_BASE64_WIRE)

Notes

Sign fast: expiresAt is short (~30s). Build and sign immediately before submitting.
Don’t mutate the transaction/message: the submit endpoint validates message bytes against what the server built.