Department of Mathematics
National University of Singapore
There are many situations in life where you
want to encode messages, so that even if
they are seen, they will not be understood
by other people than then intended recipient.
The study of such encodings and decodings
is called cryptography.
The message you want to hide is called the
plaintext, and the act of encoding it is called
encryption or enciphering. The encoded plain-
text is called the crypttext or the ciphertext,
and the act of decoding it is called decryption
or deciphering. The encryption system, also