# 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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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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