However, encrypted information is very difficult to decrypt without the algorithm and the key. The effectiveness of security measures should be evaluated by addressing both theoretical and practical security. Theoretical security deals with the question of how secure a system is against decryption when someone has unlimited time and manpower available for the analysis of intercepted encrypted information. Practical security deals with the question of whether a system is secure against a person who has a certain limited amount of time and computational power available for the analysis of intercepted encrypted information. Practical encryption methods must depend on the realistic difficulty in breaking the encryption technique, not the theoretical impossibility of such breaking.
Practical security is all that is necessary to protect most information.
What is needed is an encryption method that is relatively inexpensive to implement and use yet creates ciphers that are extremely difficult to break. If a successful attack would require more time and money than the encrypted information is worth, practical security is achieved. Current encryption procedures can provide such security. Encryption can be used to protect trade secrets, which require only that the efforts to maintain secrecy be reasonable. Second, the costs and benefits of each appropriate effort must be weighed.