I am working on a Golang code similar to Signal protocol. I need to modify it. I am confused on tripartite Diffie-Hellman handshake part of code, i.e. why public key has two separate parts as compared to private key which has only one part in bytes as shown below. I can more info if needed. Thanks.
The answer to this question is simple. In simple words, in elliptic curve cryptography, the public key is calculated by multiplying the private key value $s$ with the base point $G$, which results a point on the elliptic curve point: $W = s \cdot G$. This point consists of has two values on the x-axis and one on y-axis if the curve is considered to be within a 2D coordinate system.
Here is a link which gives a good idea of it: ECC with Diffie-Hellman.