> ## 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.

# append_signature

> Add a pre-computed signature to a transparent input

Adds a DER-encoded ECDSA signature to a transparent input in the PCZT.

## Signature

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

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

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

## Parameters

<ResponseField name="pczt" type="Pczt" required>
  The PCZT to add the signature to
</ResponseField>

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

<ResponseField name="pubkey" type="string" required>
  33-byte compressed public key (hex)
</ResponseField>

<ResponseField name="signature" type="string" required>
  DER-encoded ECDSA signature with sighash type byte appended (hex)
</ResponseField>

## Returns

Updated PCZT with the signature added.

## Signature Format

The signature must be DER-encoded with SIGHASH\_ALL (0x01) appended:

```
[DER signature (70-72 bytes)] + [0x01]
```

## Example

```typescript theme={null}
import { secp256k1 } from '@noble/curves/secp256k1';

// Get sighash
const sighash = t2z.get_sighash(pczt, 0);

// Sign
const sig = secp256k1.sign(hexToBytes(sighash), privateKey);
const derSig = sig.toDERRawBytes();

// Append sighash type
const sigWithType = new Uint8Array([...derSig, 0x01]);

// Add to PCZT
pczt = t2z.append_signature(pczt, 0, pubkeyHex, bytesToHex(sigWithType));
```

## See Also

* [`get_sighash`](/api-reference/get-sighash)
* [`sign_transparent_input`](/api-reference/sign-transparent-input)