Is there any technique so that if I encrypt data, the ciphertext would be genuine and if someone else tries to encrypt the same data the ciphertext could be determined as fake or just invalid?
I want to create a network in which the user has to register to get a ciphertext (like a token) and only after getting a genuine ciphertext would they be allowed to communicate with other users in the network. The ciphertext would contain their identity.
However, if I simply use any simple encryption method, the user would be able to fake their identity by encrypting the data in the same format and method. I do not want to use a server/database to verify the identity. That is why I was thinking of ways to disallow fake ciphertexts.
If this is possible can you suggest a solution to achieve this? If not can you suggest an alternative?