TLSin

TLSin is a portable, modular TLS library designed to provide Transport Layer Security in a wide range of software environments. It implements the TLS protocol for secure communications and includes components for the handshake, record layer processing, and certificate verification, with an emphasis on small footprint and ease of integration into applications.

Origin and development: The project emerged in the early 2020s from collaboration among security researchers and embedded platform developers. The goal was to offer a standards-compliant alternative to monolithic TLS stacks with a focus on modularity and cross-platform portability. Since its initial release, TLSin has continued under an open community and has introduced TLS 1.2 and 1.3 support along with performance and configurability improvements.

Architecture and features: TLSin uses a modular design with a core protocol engine, a pluggable cryptographic backend, a certificate validation subsystem, and an I/O abstraction layer. It supports TLS 1.2 and TLS 1.3, including ALPN for application protocol negotiation and session resumption via tickets and 0-RTT where applicable. It can use system trust stores or custom trust configuration and provides APIs for integrating with various event loops or non-blocking I/O models.

Security and adoption: TLSin emphasizes constant-time implementations and mitigations for common side-channel risks. It has undergone third-party audits and is used in a range of embedded and server-side projects seeking a compact TLS option. Critics note that TLSin's ecosystem remains smaller than that of larger stacks, which can affect tooling and community support, though it is commonly compared with OpenSSL and mbedTLS.

See also: Transport Layer Security, TLS 1.3, TLS 1.2, OpenSSL, BoringSSL, mbedTLS.