# Why does E91 protocol use the CHSH inequality instead of QBER?

I am now studying about E91 protocol. In the process, I saw that E91 protocol utilizes the CHSH inequality instead of QBER. Other protocol like BB84 protocol uses QBER for the rate of the existence of eve. Then, why does only E91 protocol use CHSH inequality instead of QBER? Which means, what is the advantage of using CHSH inequality?

• What is QBER? . – Norbert Schuch Nov 8 '18 at 7:11
• QBER means Quantum Bit Error Rate. It is used to evaluate the presence of Eve. – Joonm Seok Nov 13 '18 at 4:15