TLSSSLi

TLSSSLi is a cryptographic protocol that integrates features of Transport Layer Security (TLS) and Secure Sockets Layer (SSL) to provide enhanced security and compatibility across legacy and modern systems. The protocol was first proposed in 2015 by a consortium of network security researchers to address interoperability issues between older SSLv3 endpoints and newer TLS 1.3 implementations. TLSSSLi operates by negotiating a hybrid cipher suite that supports both SSLv3 and TLS 1.3 key exchange mechanisms, allowing a single handshake to secure traffic for either protocol version depending on the connection requirements.

The protocol specifies a set of extensions to the TLS handshake that indicate SSLv3 support and allows fallback to SSLv3 when necessary. TLSSSLi also includes a compatibility layer that translates between SSLv3 and TLS message formats, ensuring that sensitive authentication data such as client certificates are preserved across the transition. Because of the known security vulnerabilities in SSLv3, TLSSSLi recommends the use of TLS 1.3 whenever possible but allows explicit SSLv3 negotiation for systems that cannot upgrade.

TLSSSLi is defined in RFC 7777, which provides detailed state machine diagrams and security analyses. The protocol is implemented in several open-source libraries such as OpenSSL and BoringSSL, and it remains an active area of research for secure interoperation on heterogeneous network environments.