Please define one word answer for following: 1-According to Shannon's Theorem the Scheme will provide computational security if encryption is applied separately and independently on each letter (or one letter at a time),is that true or false?

2-[(a mod n).(b mod n)]mod n = ___________________

Note: (.) means multiplication

3-______________________ Service provides protection against denial by one of the communicating parties after sending a message.

4-In ____________ mode the pattern of plaintext may be reflected in ciphertext.

5-Digital Signatures are used for achieving Authentication and Confidentiality in message communication.