Elliptic Curve Point compression/decompression for mbedTLS
This is all about two helper methods called
They perform X25519 / Curve25519 point compression and decompression.
mbedTLS will likely never support decompression, as it is not mandated in the TLS specification.
EC crypto keys for TLS consist of concatenated x and y coordinates (hence a point), which makes them rather long to print out. But since the function is known, only x really needs to be transmitted. This can help to keep QR-Codes smaller, as less data needs to be transmitted.
3 mod 4 are supported:
See this post.