A user computer generates a secret cryptographic key through communication with a server. A secret user value is provided at the user computer. A secret server value is provided at the server with a check value which encodes the secret user value and a user password. In response to input of an input password, the user computer encodes the secret user value and the input password to produce a first value corresponding to said check value, and communicates the first value to the server. The server compares the first value and check value to check whether the input password equals the user password. If so, the server encodes the first value and secret server value to produce a second value and communicates the second value to the user computer. The user computer generates the secret cryptographic key by encoding the second value, the input password and the secret user value.