Curve25519.
The encryption half of your identity. Curve25519 powers X25519 — the Diffie-Hellman key agreement that lets your phone and your contact's phone arrive at a shared secret without ever transmitting one.
Curve25519 is an elliptic curve designed for the X25519 Diffie-Hellman function (RFC 7748). In CarrierPony's OpenPGP envelopes, it wraps the session key that actually encrypts each message for the recipient.
What it is
For each message, a fresh symmetric session key encrypts the content, and X25519 key agreement against your contact's Curve25519 public key wraps that session key so only their private key can unwrap it. Their app reverses the process on arrival.
Why it matters
Curve25519 was engineered for speed, small keys (32 bytes), and resistance to the subtle implementation pitfalls of older curves. It is the same primitive underneath TLS 1.3, WireGuard, and the age format used elsewhere in the Pony family.
Related terms
Common questions.
Is Curve25519 quantum-safe?
No elliptic-curve cryptography is, and neither is RSA. Post-quantum schemes are being standardized industry-wide, and OpenPGP is evolving with them; today Curve25519 represents the strong current standard.
Why two different keys?
Signing and encryption are different mathematical jobs with different failure modes. Keeping them on separate keys is standard hygiene — compromise or rotation of one doesn't automatically burn the other.
Get CarrierPony
Free private messaging and file transfer for iPhone. No accounts, no tracking, no phone numbers.