Which cryptography concept is based on trap-door, one-way functions?

What is wrong with the following loop?

While (sum <= 1000) { sum = sum + 30; } a) The parenthesis should be braces. b) The braces around sum = sum +30; should be removed. c) While should be while. d) There should be a semicolon after While (sum <=1000).

Briefly describe the three main types of software maintenance. Why is it sometimes difficult to distinguish between them?

What will be an ideal response?