Cryptography: Cipher Strength

•Perfect or Unconditional security

–no matter how much computer power or time is available, the cipher cannot be broken since the ciphertext provides insufficient information to uniquely determine the corresponding plaintext

•Computational or Conditional security

–given limited computing resources (e.g. time needed for calculations is greater than age of universe), the cipher cannot be broken 

In other words, security system is said to be conditionally secured if the cost of breaking the system is way higher than the hack value we get from breaking that system.