title: Encode some plaintext twice and get the same hash
body: <p>A list of contacts will be sent periodically on my server. Then I need to encode and store the hashes in a database with no initial values (only hashes). If I received contact twice the hash must be the same for this. At the moment I want to use AES encryption. To get the same hash twice it is necessary to use the same key and the same initialization vector, and it seems very unsafe. One of the solution, maybe , is generation key and iv from contact. It's better than use one key and iv for all contacts. Is it bad idea? Could you suggest another solution?</p>