rustls
Modern, memory-safe TLS implementation in pure Rust. Supports TLS 1.2 and TLS 1.3. Does not use OpenSSL — eliminates OpenSSL's C code vulnerabilities. Used by major projects including the Rust toolchain, wasmtime, and the Let's Encrypt certbot replacement. Integrates with tokio-rustls for async TLS and reqwest for HTTPS clients.
Score Breakdown
⚙ Agent Friendliness
🔒 Security
Pure Rust implementation — no C library vulnerabilities. TLS 1.2/1.3 only (modern security). Memory-safe by construction. Audited codebase.
⚡ Reliability
Best When
Building Rust network applications that need TLS without OpenSSL's C dependency or security baggage.
Avoid When
You need OpenSSL-specific features, TLS 1.0/1.1, or PKCS11 integration.
Use Cases
- • Add TLS to Rust servers and clients without OpenSSL dependency or C library security vulnerabilities
- • Build HTTPS clients with reqwest that uses rustls instead of openssl: reqwest = { features = ['rustls-tls'] }
- • Implement mTLS (mutual TLS) client certificate authentication in Rust microservices
- • Create custom TLS servers with certificate management in pure Rust without C library deps
- • Deploy Rust applications in environments where OpenSSL is unavailable or prohibited (WASM, embedded)
Not For
- • Applications requiring OpenSSL-specific features (custom engines, PKCS11) — use native-tls for OpenSSL compatibility
- • TLS 1.0/1.1 support — rustls only supports TLS 1.2+ by design (security best practice)
- • Legacy certificate formats — rustls enforces modern cryptographic standards; very old certs may not be supported
Interface
Authentication
TLS library — authentication is implemented via certificates and keys, not library auth.
Pricing
Open source TLS implementation. ISRG (Let's Encrypt parent) provides stewardship.
Agent Metadata
Known Gotchas
- ⚠ rustls does not support TLS 1.0 or 1.1 — connecting to servers that only support older TLS versions will fail; use native-tls for legacy compatibility
- ⚠ Certificate loading requires explicit format handling — rustls uses its own certificate parsing, not OpenSSL PEM parsing; use rustls-pemfile crate for PEM files
- ⚠ tokio-rustls is required for async usage — rustls alone is synchronous; import tokio-rustls for integration with tokio async runtime
- ⚠ rustls v0.22+ changed the crypto provider API — code from older tutorials may use deprecated APIs; check version-specific documentation
- ⚠ SNI (Server Name Indication) is required for most HTTPS connections — rustls enforces SNI by default; disable only for specific IP-only scenarios
- ⚠ Custom certificate authorities require explicit trust anchor configuration — rustls doesn't use the system certificate store by default; add rustls-native-certs crate
Alternatives
Full Evaluation Report
Detailed scoring breakdown, competitive positioning, security analysis, and improvement recommendations for rustls.
Scores are editorial opinions as of 2026-03-06.