SSH Keys in 2024: Why Ed25519 Replaced RSA as the Default

If you've ever set up GitHub, configured a server, or worked with remote machines, you've encountered SSH keys. Take a look in your ~/.ssh/ directory and you'll likely find files named id_rsa or id_ed25519. These represent two generations of cryptography—and understanding the difference matters for both security and performance. What These Files Actually Are SSH keys come in pairs: a private key (kept secret on your machine) and a public key (shared with servers). The names id_rsa and id_ed25519 refer to the cryptographic algorithms used to generate them: id_rsa id_ed25519 Algorithm RSA (1977) Ed25519 (2011) Mathematical foundation Integer factorization Elliptic curve cryptography Key size 2048–4096+ bits Fixed 256 bits Standard since Early SSH days OpenSSH 6.5+ (2014) The Technical Shift RSA relies on the difficulty of factoring large prime numbers which is a problem that has served cryptography for decades but requires increasingly large keys to maintain security. Modern 2048-bit RSA