To obtain S3 credentials, you will need to register the access grant you got in the UI or generate using satellite address + API key + encryption passphrase. The latter is the most secure way but requires an additional step. Here’s how to do this: Create Access Grant in CLI | Storj Docs. Of course, you can also use access grant you can get in the UI: Create an Access Grant | Storj Docs.
Having the access grant, you need to register it. You can follow these steps, but you can also register it using uplink CLI (see uplink help access register).
In the backup tool, I also recommend bumping S3 Multipart Threshold and Chunksize to something like 63MiB. This will help you achieve optimal performance.
One more thing I want to add is that you can retrieve your data using access grant and Access Key ID/Secret Access Key (as long as they are a result of registering that specific access grant; you can also register multiple times and get many S3 credentials pairs for one access grant) interchangeably. I recommend reading about Storj’s access model here: Secure access control in the decentralized cloud. S3 credentials you can obtain are only an extension to this access model and used to represent an access grant in the S3 world. I know it can be confusing at first, and it’s a steep learning curve, but it’s a great access model, and I hope you will benefit from using it!
You should use the same encryption phrase in the Access Grant, then register it on Gateway-MT to get a new pack of Access Key, Secret Key and Endpoint.
If the encryption phrase is the same - you will got an access to your data.