I was wondering whether it is safe to use the same DH or ECDH key pair in more than one key agreement, particularly if these public keys are in a public registry. These public keys could be used by your counterparts (who also have their public keys in the same registry) to agree on a secret used to send you a message, even when you're not online. A user's public (EC)DH key is changed each time s/he goes online.
Is that system safe? Does reusing the same public key makes it more easy to solve its DLP?
EDIT : When I meant to use a public key in more than one key exchange, I meant it will be used with different counterparts.