> ## Documentation Index
> Fetch the complete documentation index at: https://t2z.d4mr.com/llms.txt
> Use this file to discover all available pages before exploring further.

# sign_transparent_input

> Sign a transparent input with an in-memory private key

Convenience function that combines `get_sighash` and `append_signature` for cases where the private key is available in memory.

## Signature

<Tabs>
  <Tab title="TypeScript">
    ```typescript theme={null}
    function sign_transparent_input(
      pczt: WasmPczt,
      input_index: number,
      private_key: string
    ): WasmPczt
    ```
  </Tab>

  <Tab title="Go">
    ```go theme={null}
    func SignTransparentInput(
      pczt *Pczt,
      inputIndex uint32,
      privateKey []byte,
    ) (*Pczt, error)
    ```
  </Tab>

  <Tab title="Kotlin">
    ```kotlin theme={null}
    fun signTransparentInput(
      pczt: Pczt,
      inputIndex: UInt,
      privateKey: ByteArray
    ): Pczt
    ```
  </Tab>
</Tabs>

## Parameters

<ResponseField name="pczt" type="Pczt" required>
  The PCZT to sign
</ResponseField>

<ResponseField name="input_index" type="number" required>
  Index of the transparent input (0-based)
</ResponseField>

<ResponseField name="private_key" type="string" required>
  32-byte secp256k1 private key (hex)
</ResponseField>

## Returns

Updated PCZT with the signature added.

## Example

```typescript theme={null}
// Sign input 0
pczt = t2z.sign_transparent_input(pczt, 0, privateKeyHex);

// Sign all inputs
for (let i = 0; i < inputs.length; i++) {
  pczt = t2z.sign_transparent_input(pczt, i, keys[i]);
}
```

## When to Use

Use this function when:

* Private key is available in memory
* Testing or development
* Simple single-party transactions

For hardware wallets or HSMs, use [`get_sighash`](/api-reference/get-sighash) + [`append_signature`](/api-reference/append-signature) instead.

## See Also

* [`get_sighash`](/api-reference/get-sighash)
* [`append_signature`](/api-reference/append-signature)
* [Transaction Flow: Sign](/flow/sign)