The ease of sending data with the development of internet technology technology is now a concern, especially the problem of data confidentiality, integrity and information security. Cryptography is one of the techniques used to maintain data confidentiality and information security, the application of cryptographic techniques for information security and data integrity is highly dependent on the formation of keys. In this study proposed a frequency analysis approach to measure the level of information security of blowfish encryption results to determine the distribution form of each character used in the text and find out the exact frequency of each character used in the test text data. The encryption algorithm and description of blowfish method against plaintext are proven to be accurate, but the longer the key character used will greatly affect the level of information security that came  from encryption process, this is based on the results of the frequency analysis conducted.

Sistem pendukung keputusan merupakan sistem informasi interaktif yang menyediakan informasi, pemodelan dan pemanipulasian data. Sistem ini digunakan untuk membantu pengabilan keputusan dalam situasi yang semi terstruktur dan situasi tidak terstruktur. Sistem pendukung keputusan dibangun untuk mendukung solusi atas suatu masalah atau untuk mengevaluasi suatu peluang. Begitu pun untuk menentukan bidang keahlian pada SMK Swasta Mulia Pratama. Untuk menentukan bidang keahlian setiap siswa, maka dibutuhkan suatu metode promethee agar dapat memudahkan sekolah dalam menentukan bidang keahlian siswa/I tanpa harus mewawancarai secara langsung. Metode promethee ini sering disebut dengan metode penjumlahan terbobot. Konsep dasar metode promethe adalah mencari penjumlahan terbobot dari rating kinerja pada setiap alternatif pada semua atribut.

The Certainty Factor method is used as a method of resolving the problem of certainty by calculating every possible value. The Certainty Factor method calculates the probable value of all the factors involved in a problem. The result of a certainty factor calculation is the result of a combination of the calculation of each factor. The combination stage of the certainty method is standard so that the calculation results will be greatly affected by the calculation of the first-factor value calculated. The certainty factor method is also known as the expert system solution method that has been used in many studies in diagnosing a problem. The influence of probability value of the first factor greatly influence the diagnosis result, therefore needed a research which discusses modifies at combination stage of method certainty factor.