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Is your feature request related to a problem? Please describe.
I'm unable to implement ED448 signature algorithm support in Rustls despite ED448 being available in the RustCrypto ecosystem. The blocking issue is that the necessary algorithm identifier (alg_id) is missing from the PKI types, which prevents proper integration with the Rustls crypto provider interface.

Describe the solution you'd like
Add ED448 support to Rustls by:

• Including ED448 algorithm identifier in the PKI types crate
• Extending the AlgorithmIdentifier const to include ED448
• Adding the necessary OID mappings for ED448 certificates (OID: 1.3.101.113)
• Ensuring compatibility with existing RustCrypto's ed448 or similar implementations

Describe alternatives you've considered

• Forking and patching locally: Maintaining a fork with ED448 support, but this creates maintenance burden and divergence from upstream
• Using ED25519 only: While ED25519 is supported, some applications specifically require ED448 for its higher security margin (224-bit vs 128-bit security level)
• External wrapper: Creating a wrapper that translates ED448 operations to supported algorithms, but this adds unnecessary complexity and potential security risks

Additional context

• ED448 is part of RFC 8032 and is increasingly adopted in security-critical applications
• The RustCrypto project already provides ED448 implementation through crates like ed448
• This would align Rustls with other TLS libraries (OpenSSL, BoringSSL) that support ED448
• The missing alg_id in PKI types is the primary blocker preventing community implementation
• This feature would benefit users requiring CNSA 2.0 compliance or higher security margins

Related specifications:

• RFC 8032: Edwards-Curve Digital Signature Algorithm (EdDSA)
• RFC 8446: TLS 1.3 includes ED448 as a supported signature algorithm

Past Issues:
rustls/rustls#52
rustls/rustls#1120