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(Cryptography Advanced Encryption Standard (AES) for File Document Encryption). Advanced Encryption Standard (AES) is a cryptographic algorithms as a standard symmetric key encryption algorithm that used in current time. AES 128 has 1 blok plaintext with 128 bit sized, where in the process of cryptographic algorithms, first the plaintext is converted into hexadecimal-sized 4 x 4 matrices called the state, where each element of state has 1 byte size. The process of encryption on AES is the transformation towards the state repeatedly in the 10th round. Each round of AES requires one key result of the key generation using 2 basic transformation, i.e. substitution and transformation. AES encryption using 4 transformation by the following sequence: subbytes, shiftrows, mixcolumns, and addroundkey. On the other hand, the process of decryption is using the inverse of all the basic transformation of AES algorithm, except addroundkey. Therefore, the sequence of transformation on the decription is invshiftrows, invsubbytes, invmixcolumns, and addroundkey. In the data text, the encryption process is initiated with convertion the data text into ASCII code in hexadecimal numbers that are molded into the matrix 4 x 4 bytes. Next, do some basic transformation such as subbytes, shiftrows, mixcolumns, and addroundkey. However, when performing the transformation, the processed data on every trasformation is in the form of binary data obtained from the hexadecimal matrix. AES 128 bit cryptography have room 2128 keys which is a tremendous value and is considered secure to use to avoid the brute force attack.

In the daily use of technology, humans cannot be separated from the internet as a need to exchange information. People at this time spend more time in front of computer screens, laptops, even smartphones to find out information, send data to some of their friends. One of the information that is often sought or sent is a file. Apart from that, image files are files that are much searched for and sent, and many also contain important information in them. Image file security is of course very important so that unauthorized parties do not hack or manipulate information from the image. There is a way to secure information so that it does not leak to unauthorized parties, namely by using cryptography and steganography. By combining these two methods, you can maintain the confidentiality and security of a file, especially image files. In this study the algorithm and method used is the AES cryptographic algorithm (Advanced Encryption Standard) 256 and the LSB (Least Significant Bit) steganography method. Data integrity needs to be tested to ensure that the encryption and decryption processes are running properly. Data integrity testing uses the SHA-1 method. Likewise, the image quality after insertion will experience a decrease in quality. To evaluate this, it is necessary to test using the PSNR method. From the results of data integrity testing by comparing the hash value of the decrypted image file with the original image file, there is no difference. So this shows that the encryption and decryption process was successful. While in testing using the PSNR method, the average PSNR value is 44.14086 dB and with an average error value of 2.830403 dB, which means there is a small decrease in quality. From the implementation and testing results, it can be concluded that the AES 256 cryptographic algorithm and the steganography method LSB can be implemented in maintaining the confidentiality and security of secret messages.    

In order to send data or information  processed by using cryptography people can use XML(eXtensible Markup Language). XML data are general texts file which consist of several different tagswhich are defined by the XML document maker. In this research, the XML data were processed by usingPassword Based Encryption cryptography. This method consists of encryption and decryption meant toalter plaintext into chipertext which in turn creates chipertext from plaintext by using password key.²The implementation of the program in this research is a prototype of Hospital’s web facilitated withencyption menus and decryption data which are meant to protect the saved data which are in turn accessedand processed by authorized people. The implementation of the program is built as a web application withJava Server Page (JSP) in NetBeans 6.0 with Password Based Encryption cryptography provided by JavaCryptography Extension (JCE).

Cryptography is a science which studying about safety of messages, so it makes themessages cannot be read by unauthorized persons. Cryptography have two kinds of algorithmfirst is encryption algorithm, that is algorithm altering plaintext become the ciphertext, and thesecond is decryption algorithm that is algorithm altering ciphertext become the plaintext,  thatconducive of message can only be made and read by authorized persons. Plaintext represent themessage able to be read,  while ciphertext is message which have pass by the encryption process,so that order the ciphertext difficult to be translated or read. And method of substitution andtranspotition method are some of conventional technique able to be used to protect the picturesfiles, so that produce the pictures files which do not easy to to be read. The conventionaltechnique basically use a same key to do the encryption  and decryption process.

Kriptografi (cryptography) merupakan ilmu dan seni untuk menjaga pesan agar aman. (Cryptography is the art and science of keeping messages secure) “Crypto” berarti “secret” (rahasia) dan “graphy” berarti “writing” (tulisan). Para pelaku atau praktisi kriptografi disebut cryptographers. Sebuah algoritma kriptografik (cryptographic algorithm), disebut cipher, merupakan persamaan matematik yangdigunakan untuk proses enkripsi dan dekripsi. Biasanya kedua persamaan matematik (untuk enkripsi dan dekripsi) tersebut memiliki hubungan matematis yang cukup erat. Enkripsi digunakan untuk menyandikan data-data atau informasi sehingga tidak dapat dibaca oleh orang yang tidak berhak. Dengan enkripsi data disandikan (encrypted) dengan menggunakan sebuah kunci (key). Untuk membuka (decrypt) data tersebut digunakan juga sebuah kunci yang sama dengan kunci untuk mengenkripsi (untuk kasus private key cryptography) atau dengan kunci yang berbeda (untuk kasus public key cryptography).