# Request signing

The Loopring API involves two different categories of signatures.

* API Request Signature - is used to verify that the API invocations have been authenticated
* Off-chain Request Signature - is used by Loopring to verify that off-chain requests have been authenticated. We will explain each of these two categories separately.

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#### References <a href="#references" id="references"></a>

You can learn more about the Poseidon hash and EdDSA signature through the following literature and github repositories.

1. **ethsnarks**: <https://github.com/HarryR/ethsnarks.git>
2. **SHA256 Hash**: <https://en.wikipedia.org/wiki/SHA-2>
3. **EdDSA**: <https://en.wikipedia.org/wiki/EdDSA>
4. **Poseidon Hash**: <https://www.poseidon-hash.info/>

You can also refer to our [example code](https://docs-protocol.loopring.io/resources/signature/sdk-signature/mock-signature) for more details.
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### &#x20;<a href="#references" id="references"></a>


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# Agent Instructions: Querying This Documentation

If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter:

```
GET https://docs-protocol.loopring.io/resources/request-signing.md?ask=<question>
```

The question should be specific, self-contained, and written in natural language.
The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.