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1Logical Operations
2Logical operations such as AND, OR and especially XOR are most com-
3mon components of secret-key ciphers and are clearly small and fast in any
4software or hardware system. However we cannot expect much security of
5them.
6{ Arithmetic Operations
7Arithmetic operations such as additions, subtractions and sometimes multi-
8plications are also commonly used in software-oriented ciphers because they
9can be carried out by one instruction on many processors and fairly con-
10tribute to their security. However, in hardware, their eect on data diusion
11is not necessarily high enough, considering their encryption speed, since their
12delay time due to carry-spreading is often long and expensive.
13{ Shift
14compatibility between their security level and software/hardware eciency.
15{ Logical Operations
16Logical operations such as AND, OR and especially XOR are most com-
17mon components of secret-key ciphers and are clearly small and fast in any
18software or hardware system. However we cannot expect much security of
19them.
20{ Arithmetic Operations
21Arithmetic operations such as additions, subtractions and sometimes multi-
22plications are also commonly used in software-oriented ciphers because they
23can be carried out by one instruction on many processors and fairly con-
24tribute to their security. However, in hardware, their eect on data diusion
25is not necessarily high enough, considering their encryption speed, since their
26delay time due to carry-spreading is often long and expensive.
27{ Shift Operations
28Shift operations, especially rotate-shifting, are frequently used in designing
29secret-key ciphers. They indirectly improve data diusion, and in hardware
30they are obviously cheap and fast if the number of shift counts is xed. We
31should note, however, that software performance of shift operations heavily
32depends on their target size; for instance, when a rotate shift of 32-bit data
33is executed on 8-bit or 16-bit microprocessors, its speed may be quite slow.
34{ Look-up Tables
35In software, eciency of loop-up tables strongly depends on memory access
36speed. In early microprocessors, memory access was much more expensive
37than register access, while many recent processors can read from and write to
38memory in one cycle (or often less than one cycle due to parallel processing)
39under certain conditions. On the other hand, in hardware, the use of ROM
40is slow in general, but i