L3 Important terms part3

8-Security of Algorithms.
Different algorithms offer different degrees of security; it depends on how hard they are to break. If the cost required to break an algorithm is greater than the value of the encrypted data, then you’re probably safe. If the time required to break an algorithm is longer than the time the encrypted data must remain secret, then you’re probably safe. If the amount of data encrypted with a single key is less than the amount of data necessary to break the algorithm, then you’re probably safe. I say “probably” because there is always a chance of new breakthroughs in cryptanalysis. On the other hand, the value of most data decreases over time. It is important that the value of the data always remain less than the cost to break the security protecting it. Lars Knudsen classified these different categories of breaking an algorithm. In decreasing order of severity:
1. Total break. A cryptanalyst finds the key, K, such that DK(C) = P.
2. Global deduction. A cryptanalyst finds an alternate algorithm, A, equivalent to DK(C), without knowing K.
3. Instance (or local) deduction. A cryptanalyst finds the plaintext of an intercepted ciphertext.
4. Information deduction. A cryptanalyst gains some information about the key or plaintext. This information could be a few bits of the key, some information about the form of the plaintext, and so forth.