The decryption process is the inverse of encryption process, which enables the encrypted image to become the initial image before encryption. The encryption process starts with getting the RGB intensity of each pixels from the image, then the RGB values are encrypted using Vigenere algorithm, after that RSA Algorithm encrypt those values, the values of RSA Algorithm encryption are limited so the value can be within the intervals of RGB values and the after limitation the values after being limited become the RGB values in the encrypted image.
RSA algorithm are based on the difficulty of factorizing large numbers that have 2 and only 2 factors (Prime numbers). Vigenere algorithm is a symmetric key algorithm which is a variety from Caesar algorithm where the similarity is in both of them are based on shifting the index of alphabet letters. In this thesis digital image is encrypted using hybrid algorithm Vigenere and RSA. From the test results obtained ciphertext that can be read.Digital image is digital pictures on a two-dimensional plane which consists of pixels, where every pixels has Red, Green, Blue (RGB) with varying intensity depending on the image. However, there are some alphabet consonants are not replaced, this is because the frequency of the alphabet is rarely used in an Indonesian text. Caesar cipher modification is done by replacing the alphabet into two parts, the vocals were replaced with the alphabet vocal too, and the consonant alphabet was replaced with a consonantal alphabet. With the ciphertext that can be read, then cryptanalysis not suspicious of the ciphertext. In this paper, the authors modify the Caesar cipher method that produces ciphertext that can be read. While the use of steganography owner of the information is difficult to determine the method or pattern to be formed in composing the message that will be hidden. Thus, the cryptanalyst attempts to break the encrypted message. This is possible because usually a text message unreadable gives someone suspicion that the text message contains a certain meaning for the owner of the message. On the other side, it turns out the use of cryptography can often be solved / translated by another person or cryptanalyst. However, both methods have the same goal, namely the attempt to conceal the message.
In a secret message, cryptography is more directed to the encrypted message while steganography is more directed at the hidden message.
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