Byte size of Diffie-Hellman public values
$A$ and $B$ have values between 1 and $P-1$, and can in fact take on half the values in that range.  As $P$ is 256 bytes long, so will $A$ and $B$.  As there are approximately $2^{2047} &gt; 256^{255}$ potential values that they can take on, we can't express them in 255 bytes.