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

# Signature Algorithm

> Generate Ed25519 signatures for request validation.

## Basic Rules

1. The signature is generated using the **Ed25519** cryptographic signature scheme on a formatted string.
2. All fields are separated by underscore `_`, even if the field is empty.
3. All sign message characters are **lowercase**.

## Sign Message Format

### Onramp (Buy)

```
{amount}_{callback}_{chain_id}_{currency}_{recipient}_{reference_no}_{token_address}
```

### Offramp (Sell)

```
{amount}_{callback}_{chain_id}_{currency}_{bank_bin_code}_{bank_account_number}_{token_address}
```

## Example

<CodeGroup>
  ```go Go theme={null}
  package main

  import (
      "crypto/ed25519"
      "encoding/base64"
      "strings"
  )

  var sampleSignKey = "Qd2XliU6/I6YD3OELdeBQ57z6Q9/OHGBTjCNVLB8s/1KpvoU6aiuuBTgQ72IW/yA0aYYnfbCX31zhJKsPnRE5Q=="

  func sign(msg string) string {
      signKey, _ := base64.StdEncoding.DecodeString(sampleSignKey)
      signature := ed25519.Sign(ed25519.PrivateKey(signKey), []byte(msg))
      return base64.StdEncoding.EncodeToString(signature)
  }

  func main() {
      params := []string{
          "1000000",  // amount
          "",         // callback
          "56",       // chain_id
          "",         // currency
          "0x0000000000000000000000000000000000000000", // recipient
          "rmtbPVEKwLzz27Qs51Jio",                      // reference_no
          "0x55d398326f99059ff775485246999027b3197955", // token_address
      }
      signMessage := strings.Join(params, "_")
      signMessage = strings.ToLower(signMessage)
      signature := sign(signMessage)
      println("Message:", signMessage)
      println("Signature:", signature)
  }
  ```
</CodeGroup>

### Output

```
Message: 1000000__56__0x0000000000000000000000000000000000000000_rmtbpvekwlzz27qs51jio_0x55d398326f99059ff775485246999027b3197955
Signature: +EEox+pWc3dC854Av3eIzLbGthud0p2/xrosE9tcOHvLEji8uajyJzDwV95IFClhmCnCqPXtjQsZmYS0jrtgBw==
```

<Warning>
  Remember to convert the entire sign message to **lowercase** before signing.
</Warning>