To maintain the confidential data, a scheme or algorithm is needed to protect the data from many attacks. Recently, many cryptography schemes and algorithms have been introduced. One of them is the cryptography algorithm based on chaotic maps. The nature of the chaotic maps gives many advantages to the algorithm. In this paper, an algorithm to encrypt the text is purposed. The algorithm utilizes the nature of the chaotic map by using the MS map as a keystream generator. The ciphertext found by the purposed algorithm is very difficult to be cracked by the bruce-force attack and known-plaintext attack. The decryption process has been tested using 3 different secret keys (that is very similar with the secret key on the encrypted process), and resulting the decrypted text is the same with plaintext only if the input is exactly the same secret key as in encrypted process.