What is the difference between an unconditionally secure cipher and a computationally secure cipher?

            An encryption scheme is unconditionally secure if the cipher text generated by the scheme does not contain enough information to determine uniquely the corresponding plaintext, no matter how much cipher text is available.

            An encryption scheme is said to be computationally secure if:

• The cost of breaking the cipher exceeds the value of the encrypted information.

• The time required to break the cipher exceeds the useful lifetime of the information.