rsa crate is vulnerable to timing attack (RUSTSEC-2023-0071)

[hardcodes]

See https://rustsec.org/advisories/RUSTSEC-2023-0071.html and RustCrypto/RSA#19.

Once a fix is available, this crate should update the minimum required version of rsa in Cargo.toml.

The security risk should be low and have no real impact on this project.