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A Secure Key Scheduling Operation for International Data Encryption Algorithm using Serpent Key Schedule Operation

The International Data Encryption Algorithm (IDEA) is one of an encryption algorithm that uses a cyclic process in producing sub keys from secret key using its key schedule but generates large weak keys. GISKOP is a modified IDEA that uses the concept of serpent key scheduling operation to address the weak keys found on the original IDEA. Randomness test was used to identify the dependence and correlations between generated sub-keys of a key scheduling operation. Statistical evaluation was done to analyze and compare key distribution and exchange operations of the modified key scheduling operation. The GISKOP key scheduling operation obtained an increase of 8% randomness using frequency test in the sub-key independence level. Also, it was able to maintain its 100% randomness under the sub-key level independence. Thus, proving that each generated sub keys are not correlated with each other. With this, many attacks on systems that implement IDEA can be mitigated. Furthermore, the findings will take advantage of independency or nonlinear relationship between sub-keys and prevent breaking the whole cipher.