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Modifications to Vigenere cipher are possible to make in order to be effective and efficient of this algorithm. In this study, we tried to modify Vigenere by exploiting RC6 key expansion to generate new keys used for encryption process, RC6 is a well-known as a modern cryptographic algorithm. If the RC6 Key expansion process will generate the S key as much as 2r+4, in this research will produce S Key as long as the plaintext length. Then for the encryption process done twice. The results show that the method proposed producing completely different key sequences (not repetitions like Vigenere cipher) can also produce an average avalanche effect of 17 bitsof the total 64 bits or about 26,56 %, better than the standard Vigenere which only reached 7.81%, but unfortunately no better than Vigenere with the RC6 key expansion without twice encryption process that reaches31.25% and of RC6-8/5/b with 35.94%.

This paper illustrates an application of Analytical Hierarchy Process (AHP) as a potential decision-making method in water resource management related to drainage rehabilitation. The prioritization problem of urban drainage rehabilitation in Medan City due to limited budget is used as a study case. A hierarchical structure is formed for the prioritization criteria and the alternative drainages to be rehabilitated. Based on the AHP, the prioritization criteria are ranked and a descending-order list of drainage is made in order to select the most favorable drainages to have rehabilitation. A sensitivity analysis is then conducted to check the consistency of the final decisions in case of minor changes in judgements. The results of AHP computed manually are compared with that using the software Expert Choice. It is observed that the top three ranked drainages are consistent, and both results of the AHP methods, calculated manually and performed using Expert Choice, are in agreement. It is hoped that the application of the AHP will help the decision-making process by the city government in the problem of urban drainage rehabilitation.