Practical Evaluation
Block ciphers may be evaluated according to multiple criteria in practice. Common factors include:
- Key parameters, such as its key size and block size, both which provide an upper bound on the security of the cipher.
- The estimated security level, which is based on the confidence gained in the block cipher design after it has largely withstood major efforts in cryptanalysis over time, the design's mathematical soundness, and the existence of practical or certificational attacks.
- The cipher's complexity and its suitability for implementation in hardware or software. Hardware implementations may measure the complexity in terms of gate count or energy consumption, which are important parameters for resource-constrained devices.
- The cipher's performance in terms of processing throughput on various platforms, including its memory requirements.
- The cost of the cipher, which refers to licensing requirements that may apply due to intellectual property rights.
- The flexibility of the cipher, which includes its ability to support multiple key sizes and block lengths.
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