Ed25519.

What it is.

Ed25519 belongs to the family of elliptic-curve cryptography (ECC). Instead of working with very large integers (as RSA does), elliptic-curve schemes work with points on a specific mathematical curve — Curve25519 in this case, in its Edwards form. The signing scheme on top of it is EdDSA, and the specific parameter set is Ed25519.

For OpenPGP, Ed25519 was standardized in RFC 8032 (the signature scheme itself) and integrated into OpenPGP via RFC 4880bis / RFC 9580. Modern OpenPGP tools — GnuPG 2.1+, GPG Suite, OpenKeychain, PGPony — generate Ed25519 keys by default for new identities.

Why it matters.

Practical advantages over RSA:

• Smaller keys. 256 bits of Ed25519 public-key material is comparable in security to 3072+ bits of RSA. Smaller fingerprints, smaller key files, less bandwidth on every operation.
• Faster operations. Signing and verifying Ed25519 is dramatically faster than RSA of equivalent strength. Generation is near-instantaneous (sub-second) where RSA-4096 takes seconds.
• Deterministic signatures. Ed25519 signatures don't depend on a random nonce per signature (unlike DSA / ECDSA), eliminating an entire class of catastrophic-implementation bugs.
• Strong security margin. Resistant to most known classes of side-channel attacks when implemented properly.

Reasons to pick RSA instead: explicit interop with a legacy system that doesn't support ECC. For practical purposes today, every current OpenPGP tool supports Ed25519, so this constraint is rare.

Related terms

• Curve25519
• RSA in OpenPGP
• PGP subkey
• OpenPGP standard