This article uses Elliptic Curve Cryptography, but when it comes to signing and verifying messages it is not using the ECDSA signature algorithm. In the article, they mentioned that the communication cost for a single message is 104 bytes. According to what I've read about ECDSA signatures is that their sizes are 2 times longer than the private key (For the secp192k1 curve, the private key is 192-bit integer (24 bytes) so the signature will be equal to 384-bit (48 bytes)). So, I was wondering:
First how to calculate the communication cost because I didn't understand exactly how did they find in the article the result 104 bytes?
Second which is more secure and has less communication cost (lightweight), is it the ECSDA or the article's method for calculating the signatures?