> *Last I tried, even let's encrypt won't grant an ed25519 cert despite it being...

> Last I tried, even let's encrypt won't grant an ed25519 cert despite it being in tls 1.3 (2018?).

Talk to the CA/Browser Forum. §6.1.5 Keys Sizes:

> For RSA key pairs the CA SHALL:

> * Ensure that the modulus size, when encoded, is at least 2048 bits, and;

> * Ensure that the modulus size, in bits, is evenly divisible by 8.

> For ECDSA key pairs, the CA SHALL:

> * Ensure that the key represents a valid point on the NIST P-256, NIST P-384 or NIST P-521 elliptic curve.

> No other algorithms or key sizes are permitted.

Ed25519 (and Ed448) was only 'recently' approved by NIST FIPS 186-5 in February 2023.