[1] The Internet Security Research Group (ISRG), a nonprofit organization based in the United States, has sponsored the project since 2021 as part of its Prossimo initiative.

[4][5] ISRG aims to make Rustls a viable alternative to OpenSSL, which is widely used by internet servers but difficult to use correctly and has had security bugs, such as Heartbleed, caused by memory-unsafe code.

[4][6] ISRG has paid several programmers to work on Rustls, including Birr-Pixton, Daniel McCarney, and Dirkjan Ochtman, using money contributed by Google and other companies and organizations.

[4][7] In 2023, the Open Source Security Foundation's Alpha-Omega initiative gave ISRG $530,000 for development of the option to use different cryptographic backends and for the separate project Rust for Linux.

[11] The Sovereign Tech Fund, supported by the German government, gave $1.5 million to ISRG in 2023 for work on Rustls and other projects that provide memory-safe versions of open source tools critical to internet security.

[16] The United States Office of the National Cyber Director has encouraged work on memory-safe security software[17] and complimented the Rustls team.

[19] By default Rustls uses cryptographic primitives from Amazon Web Services Libcrypto for Rust (aws-lc-rs), which supports Federal Information Processing Standards (FIPS).

[1] In 2020, the Cloud Native Computing Foundation funded a security audit of Rustls and two Rust libraries it used, ring and webpki, with positive results.

[45][46] In 2024, ISRG announced plans to start replacing OpenSSL with Rustls in Let's Encrypt, their free certificate authority used by hundreds of millions of websites.