DEfO developed an implementation of the encrypted Client hello (ECH) mechanism for OpenSSL. DEfO-2 is a continuation of this effort, with a focus on upstreaming the relevant ECH code to the involved projects.
The DEfO project developed an implementation of the encrypted ClientHello (ECH) mechanism for OpenSSL, which is a widely used library that provides an implementation of the Transport Layer Security (TLS) protocol.
In addition to the implementation of ECH for OpenSSL, the project also developed proof-of-concept implementations of various clients and servers that use OpenSSL as a demonstration and for interoperability testing.
DEfO-2 is a continuation of this effort; the focus is upstreaming the relevant ECH code to the various projects involved. Tolerant Networks Ltd. and people from the Guardian Project are doing the work in DEfO.