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Vigenère cipher is a classical cryptography algorithm and similar to other classical algorithms, it produces smaller but less secure ciphertexts than a public key cryptography algorithm. Meanwhile, Rabin-p is a public key cryptography algorithm with a stronger encryption than Vigenère cipher. Nevertheless, as a public key algorithm, Rabin-p is inefficient to encrypt vast amounts of messages such as BMP image files, since the size of the cipherimages will increase manyfold and this would lead to a problem in storing and sending the cipherimages. To overcome these problems, in this study, we combined the Vigenère cipher and the Rabin-p algorithm in a hybrid cryptosystem scheme. In the experiment, the Vigenère cipher was used to encrypt the BMP files and the Rabin-p algorithm was used to encrypt the Vigenère keys. The result showed that the size of the cipherimages did not increase and the decryption procedure could recover the original BMP files while maintaining their integrity.

The security of the RSA cryptosystem is directly proportional to the size of its modulus, n. The modulus n is a multiplication of two very large prime numbers, notated as p and q. Since modulus n is public, a cryptanalyst can use factorization algorithms such as Euler’s and Pollard’s algorithms to derive the private keys, p and q. Brute force is an algorithm that searches a solution to a problem by generating all the possible candidate solutions and testing those candidates one by one in order to get the most relevant solution. Random search is a numerical optimization algorithm that starts its search by generating one candidate solution randomly and iteratively compares it with other random candidate solution in order to get the most suitable solution. This work aims to compare the performance of brute force algorithm and random search in factoring the RSA modulus into its two prime factors by experimental means in Python programming language. The primality test is done by Fermat algorithm and the sieve of Eratosthenes.

Pathfinding is the method for determining the shortest path. Pathfinding is widely used in various fields of Computer Science. One of them is game development. This research will design and analyze the pathfinding using the A-Star algorithm and implement it on a tree planting game. The Artificial Intelligence in the game will find its own shortest path from the start node to the goal node. The heuristic of A-Star is the Manhattan Distance that allows movement in four different directions. The result shows that the number of visited nodes will increase if the grid has many obstacle nodes, and the average time of the A-Star pathfinding process is 0.0732 seconds.

Cryptography used to send digital images to keep them safe from unauthorized parties who want to see or change the digital image. In cryptography, there is Hybrid Cryptosystem method, which is a method by combining the advantages in 2 types of cryptographic algorithms, symmetrical and asymmetrical. Hill Cipher 4x4, with a 4x4 square matrix, is used as a symmetrical algorithm, which has a relatively fast processing time. ElGamal Elliptic Curve is used as an asymmetric algorithm, where the key used for the encryption and decryption process is a different key, so no key distribution is needed. The Algorithms implemented in an Android-based system using the Java programming language. The conclusion obtained from system testing is that the elliptic curve parameter generation time process is directly proportional to the magnitude of the prime number, the time process of image encryption-decryption is directly proportional to the image pixel size, and the time process of key matrix encryption-decryption is directly proportional to the value of the private key.

The Shamir three-pass protocol, which is also called Shamir no key protocol, is a cryptographic protocol that allows two parties to exchange information securely without exchanging any secret keys. In order to operate, a proper algorithm should be implemented in the three-pass protocol. The proper algorithm has to follow commutative-encryption system and has to allow fast computation since there are two encryption and two decryption processes in the three-pass protocol itself that logically take a longer time than a usual one-pass protocol. Meanwhile, there are just a few cryptographic algorithms nowadays that can be implemented in the three-pass protocol to ensure fast encryption, fast decryption, and cryptanalysis-proof. In this research, we study the eligibility of the H-Rabin algorithm, which belongs to the class of public key cryptosystems, as a candidate algorithm for the three-pass protocol. Unlike the well-known RSA and Rabin public key cryptosystems, the H-Rabin's security depends on the hardness of factoring three large prime numbers rather than two. Our study shows that the H-Rabin algorithm is an acceptable algorithm to be implemented the three-pass protocol.

Data security is not a top priority of most people at the moment. So the common misuse of the data and other security disturbances. To address the security disorder, can be used in the science of encryption data such as Cryptography and Steganography. The science of Cryptography use randomize or disguise the data, whereas the science of Steganography to hide data in a way. In this research the cryptographic algorithms used are Affine cipher Algorithm. Affine cipher algorithm requires a key that contains two integers, i.e. a and k. plaintext encryption process is transformed into ciphertext. Next do the embedding (concealment of data) on image Steganography techniques with the Least Significant Bit (LSB) and insert a message at the last bits of the image. It was needed extraction process to get the previous ciphertext. Then through the decryption stage to get the original plaintext. With a combination of Affine and LSB, data security will increase because after the message is scrambled into a ciphertext, the ciphertext will be inserted into the image file.

Transferring an image is one of the common processes. The image transferring, the sender wants to send a picture by maintaining the security and integrity and even the confidentiality of an image. One of the techniques to manage that aspect is cryptography – hybrid cryptosystem and Rivest-Shamir-Adleman algorithm. Hybrid cryptosystem uses RSA-OTP algorithm for its combination. Hybrid cryptosystem has the strength to secure an image because of its combination of the algorithm. A hybrid use symmetric algorithm to encrypt the image and asymmetric algorithm to encrypt the key from a symmetric algorithm. Rivest-Shamir-Adleman algorithm is an asymmetric algorithm which is hard to guess because of its different key. Rivest-Shamir Adleman Algorithm has a public key to encrypt and private key to decrypt; also prime test was implemented using the Agrawal-Kayal-Saxena algorithm. One-Time-Pad algorithm is a symmetric algorithm that is too hard to guess because this algorithm must have a key which length must be similar to plain’s length, the more length of the plain, the harder key to guess.

This study aims to combine the trithemus algorithm and double transposition cipher in file security that will be implemented to be an Android-based application. The parameters being examined are the real running time, and the complexity value. The type of file to be used is a file in PDF format. The overall result shows that the complexity of the two algorithms with duper encryption method is reported as Θ (n 2). However, the processing time required in the encryption process uses the Trithemius algorithm much faster than using the Double Transposition Cipher. With the length of plaintext and password linearly proportional to the processing time.

Confidentiality, integrity, and efficiency are the crucial aspects of data security. Among the other digital data, image data is too prone to abuse of operation like duplication, modification, etc. There are some data security techniques, one of them is cryptography. The security of Vernam Cipher cryptography algorithm is very dependent on the key exchange process. If the key is leaked, security of this algorithm will collapse. Therefore, a method that minimizes key leakage during the exchange of messages is required. The method which is used, is known as Three-Pass Protocol. This protocol enables message delivery process without the key exchange. Therefore, the sending messages process can reach the receiver safely without fear of key leakage. The system is built by using Java programming language. The materials which are used for system testing are image in size 200×200 pixel, 300×300 pixel, 500×500 pixel, 800×800 pixel and 1000×1000 pixel. The result of experiments showed that Vernam Cipher algorithm in Three-Pass Protocol scheme could restore the original image.

Security becomes a very important issue in data transmission and there are so many methods to make files more secure. One of that method is cryptography. Cryptography is a method to secure file by writing the hidden code to cover the original file. Therefore, if the people do not involve in cryptography, they cannot decrypt the hidden code to read the original file. There are many methods are used in cryptography, one of that method is hybrid cryptosystem. A hybrid cryptosystem is a method that uses a symmetric algorithm to secure the file and use an asymmetric algorithm to secure the symmetric algorithm key. In this research, TEA algorithm is used as symmetric algorithm and LUC algorithm is used as an asymmetric algorithm. The system is tested by encrypting and decrypting the file by using TEA algorithm and using LUC algorithm to encrypt and decrypt the TEA key. The result of this research is by using TEA Algorithm to encrypt the file, the cipher text form is the character from ASCII (American Standard for Information Interchange) table in the form of hexadecimal numbers and the cipher text size increase by sixteen bytes as the plaintext length is increased by eight characters.