Analysis of the effect of different parameters of the RC4 encryption algorithm where examined. Some experimental work was performed to illustrate the performance of this algorithm based on changing some of these parameters. The execution time as a function of the encryption key length and the file size was examined; this has been stated as complexity and security. Various data types were analyzed and the role of the data type was also emphasized. The results have been analyzed and interpreted as mathematical equations showing the relationship between the examined data and hence can be used to predict any future performance of the algorithm under different conditions. The order of the polynomial to approximate the execution time was justified. Key words: RC4 cryptography, Stream Cipher, encryption key, file size, data type.