桃花源主, one question about 量子纠缠

I am sorry to miss your discusion with huntridge, 鲁美丽, and chezclement. 

Here is a sentence by chezclement:

纠缠中的两个粒子不管距离多远，观察一个会瞬间改变另一个的状态，速度无穷大，所以称为EPR paradox.

Please let me start with the above sentence. Assume that we have 纠缠中的两个粒子. Since they are 纠缠 together, the phase of one particle should tell the phase of the other. Then, we don't need anything else to be an encryption key.  

This is like a story as follows: you are one person and I am the other. We are 纠缠 together and so you know what I am doing and I know what you are doing, but other people don't know our secrets. If this is true, it would be the ideal for people who need to keep an secret. 

Then, why we need encryption key? If we do need it, then it is not 量子纠缠.

I actually know Schrodinger's equation, Feymann-Kac formula and other theoretical things. But I am sure if I am totally wrong in this very applied aspect.