Is WinSCP S3 Transfer Protocol secure?

I'm looking at ways of securely transferring data into an S3 bucket. I was able to successfully connect to my S3 bucket using WinSCP but I need to confirm if this is a secure transfer method.

I see the S3 protocol utilizes the REST interface but to my understanding, that doesn't necessarily mean it's using TLS.

So my question is data transferred via the S3 protocol in WinSCP encrypted during transfer?

Thank you

Yes, WinSCP S3 sessions are encrypted with TLS.
In the log, you should see:

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WinSCP does not even support unencrypted S3 sessions:
Issue 1995 – Support S3 servers without TLS encryption