# Can two different CA's/End Entities in different PKI's have the same asymmetric key pair?

Example: $X$ and $Y$ have the same asymmetric key pair. $X$ communicates with $A$ and gives it's PubKey to $A$.

So, $A$ has the PubKey of $X$ which also happens to be the PubKey/PrivKey of $Y$. Now intentionally or by chance, can $A$ intercept and read the signed messages of $Y$?

If this can happen, does this not make the PKI vulnerable?

• It is not really clear what you are asking. Can you edit to add more detail? – mikeazo Sep 18 '17 at 13:07
• "Can" is ambiguous: is that from the standpoint of having the PKI work (and then is that from a mathematical or security/legal standpoint?). Or are you asking if this can happen by chance/or accident? – fgrieu Sep 18 '17 at 13:16
• Sure, but what is the chance? – Dr_Bunsen Sep 18 '17 at 13:55
• Are the keypair in question used for encryption or signing? – DannyNiu Sep 19 '17 at 6:15
• what will be the case for each of these transactions i.e. signing and encryption? – Yash Sep 19 '17 at 6:33