# Off-chain verification

Proofs can be submitted to a verification service for checking.  In order to use a verification service, an endpoint must be obtained from Nebra.  (TODO: link)

Proofs can be submitted using the `upa` command line tool, or programmatically with the Typescript SDK.

## Verification using the `upa`tool

### Install the tool

The standalone `upa`tool can be installed with:

```sh
$ npm install --global @nebrazkp/upa
```

It should then be available in the shell:

```sh
$ upa version
2.0.3
```

### Specify a verification service endpoint

The `--verify-endpoint`flag, or the `VERIFY_ENDPOINT`env var can be used to specify the URL of the verification service to be queried.  It is often convenient to use a `.env`file:

```
VERIFY_ENDPOINT=<endpoint>
```

### Verifying proofs in snarkjs format

Use the `upa off-chain verify-snarkjs`command:

```
$ upa off-chain verify-snarkjs vk.json proof.json
```

(Use `--help`for the full list of arguments)

### Verify proofs in gnark format

Export the VK, proof and inputs to JSON as described [here](https://docs.nebra.one/submission-and-verification#gnark).&#x20;

Use the `upa off-chain verify-gnark`command:

```
$ upa off-chain verify-gnark vk.json proof.json inputs.json
```

### Verifying proofs in UPA format

If proofs have already been converted to the UPA format (in particular the `AppVkProofInputs` format - see the [section about proof formats](https://docs.nebra.one/submission-and-verification#step-1-export-proof-data)) they can be submitted individually or in batches using the `upa off-chain verify` command.

## Verification using the SDK

In your Typescript project, add the SDK:

```
$ yarn add @nebrazkp/upa
```

The `VerifierClient`class can then be used to submit proofs for verification:

```typescript
import VerifierClient from "@nebrazkp/sdk/offChainVerify";

const client = new VerifierClient("<ENDPOINT>");
const valid = await client.verify([vkProofInputs]);
```

Note that `vkProofInputs`must be of type \`AppVkProofInputs\`.  See [here](https://docs.nebra.one/submission-and-verification#step-1-export-proof-data) for information about converting vk and proof formats into instances of this type.