| 摘要 |
An encryption method and apparatus in which a cryptographic encryption key K for use to encrypt or decrypt communications is first derived from a cryptographic key Kd provided by a user. The derived encryption key is used to encrypt or decrypt communications at a selected level of encryption strength. The level of encryption strength is selected in accordance with whether or not the cryptographic key provided by the user has a particular property, such as including a particular sequence of bits, dividing exactly by a particular number, or whether a particular cryptographic check value S can be derived from it. This method prevents unauthorised users from using the apparatus at full encryption strength since the key they provide will probably not have the required properties or generate the required check value. Also described is a method and apparatus for generating a certified cryptographic key by combining the user key Kd with a check value derived from it. |
