Doesn't TLS allow a third party to verify data authenticity?

No, it does not. TLS is designed to guarantee the authenticity of data only to the participants of the TLS connection. TLS does not have a mechanism to enable the server to "sign" the data.

The TLSNotary protocol overcomes this limitation by making the third-party Verifier a participant in the TLS connection.

How exactly does a Verifier participate in the TLS connection?

The Verifier collaborates with the Prover using secure multi-party computation (MPC). There is no requirement for the Verifier to monitor or to access the Prover's TLS connection. The Prover is the one who communicates with the server.

What are the trust assumptions of the TLSNotary protocol?

The protocol does not have trust assumptions. In particular, it does not rely on secure hardware or on the untamperability of the communication channel.

The protocol does not rely on participants to act honestly. Specifically, it guarantees that, on the one hand, a malicious Prover will not be able to convince the Verifier of the authenticity of false data, and, on the other hand, that a malicious Verifier will not be able to learn the private data of the Prover.

What is the role of a Notary?

In some scenarios where the Verifier is unable to participate in a TLS connection, they may choose to delegate the verification of the online phase of the protocol to an entity called the Notary.

Just like the Verifier would (see FAQ above), the Notary collaborates with the Prover using MPC to enable the Prover to communicate with the server. At the end of the online phase, the Notary produces an attestation trusted by the Verifier. Then, in the offline phase, the Verifier is able to ascertain data authenticity based on the attestation.

Is the Notary an essential part of the TLSNotary protocol?

No, it is not essential. The Notary is an optional role which we introduced in the tlsn library as a convenience mode for Verifiers who choose not to participate in the TLS connection themselves.

For historical reasons, we continue to refer to the protocol between the Prover and the Verifier as the "TLSNotary" protocol, even though the Verifier may choose not to use a Notary.

Which TLS versions are supported?

We support TLS 1.2, which is an almost-universally deployed version of TLS on the Internet. There are no immediate plans to support TLS 1.3. Once the web starts to transition away from TLS 1.2, we will consider adding support for TLS 1.3 or newer.

What is the overhead of using the TLSNotary protocol?

Due to the nature of the underlying MPC, the protocol is bandwidth-bound. We are in the process of implementing more efficient MPC protocols designed to decrease the total data transfer.

With the upcoming protocol upgrade planned for 2025, we expect the Prover's upload data overhead to be:

~25MB (a fixed cost per one TLSNotary session) + ~10 MB per every 1KB of outgoing data + ~40KB per every 1 KB of incoming data.

In a concrete scenario of sending a 1KB HTTP request followed by a 100KB response, the Prover's overhead will be:

25 + 10 + 4 = ~39 MB of upload data.