GnuTLS is a secure communications library that implements SSL, TLS and DTLS protocols with C language API, supporting TLS 1.3, 1.2, 1.1, 1.0 protocols and (optionally) SSL 3.0, as well as DTLS 1.2 and 1.0 protocols. The library includes support for certificate path validation, DANE, trust on first use, and the Online Certificate Status Protocol (OCSP). It uses public key methods such as RSA and Elliptic curves, as well as password and key authentication methods such as SRP and PSK protocols. It also supports strong encryption algorithms like AES and CPU-assisted cryptography with VIA padlock and AES-NI instruction sets. GnuTLS runs on most Unix platforms and Windows and supports cryptographic accelerator drivers via /dev/crypto.

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