# Significance of y-coordinates in ECDH public key exchange

In the research paper Breaking the Bluetooth Pairing – The Fixed Coordinate Invalid Curve Attack? by Biham and Neumann, 2019, they talk about attacks in Bluetooth pairing, they state that in the pairing process which involves ECDH key exchange- "sending both the x-coordinate and the y-coordinate during the public key exchange is a design flaw as it is unnecessary and highly inadvisable, and it greatly increases the attack surface"

I'm aware that in other implementations only $$x$$-coordinate is sent in compressed form. I'm curious to know how sending both coordinates increases the attack surface, how important it is to know the information about the $$y$$-coordinate and what are the possible attacks related to this.

• p.s - if interested, this is the paper I'm referring to - eprint.iacr.org/2019/1043.pdf (section 5.1) Aug 12 '20 at 20:11

• During our research we discovered multiple design flaws in the Bluetooth specification. We then tested different Bluetooth implementations and found that a large majority of the Bluetooth devices are vulnerable. So, some has better team despite of the protocol flaw, or they just lucky. Aug 12 '20 at 21:45