2. Consider the following certificate mechanism. X.509 Certificate Structures Version Serial Number Algorithm identifier: Algorithm Parameters Issuer Period of Validity: Not before date Not after date Subject Subject's public key: Algorithm Parameters Public Key Signature Determines the format Given by CA Refers to signature algorithm Name of the CA Lifetime information Name of the user Refers to key's algorithm By the CA 69 a) The CA generates the signature but the message to be signed excludes the lifetime information. Describe how the security could be compromised in the real world. (3 marks) b) The CA generates the signature but the message to be signed excludes "Refer to Key's Algorithm". Describe how the security could be compromised in the real world. (3 marks)