Problem 2-1

which technique (cryptography or steganography) is used in each of the following cases for confidentiality?

a. A student writes the answers to a test on a small piece of paper, rolls up the paper and inserts it in a ball-point pen and passes the pen to another student.

b. To send a message, a spy replaces each character in the message with a symbol that was agreed upon in advance as the character's replacement.

c. a company uses special ink on its checks to prevent forgeries.

d. a graduate student uses watermarks to protect her thesis, which is posted on her website.