[openssl-users] X25519 - why openssl shows server temp key as 253 bits?

[M K Saravanan]

Hi,

When using openssl with X25519, why it shows the server temp key as 253 bits?

Example:

---
No client certificate CA names sent
Peer signing digest: SHA256
Peer signature type: RSA
Server Temp Key: X25519, 253 bits
---

I thought Curve25519 is using 256 bit keys.

Why 253 instead of 256?

with regards,
Saravanan