- In this paper a session based symmetric key encryption system has been proposed and is termed as Permutated Cipher Technique (PCT). This technique is more fast, suitable and secure for larger files. In this technique the input file is broken down into blocks of various sizes (of 2 power n order) and encrypted by shifting the position of each bit by a certain value for a certain number of times. A key is generated randomly wherein the length of each block is determined. Each block length generates a unique value of number of bits to be skipped. This value determines the new position of the bits within the block that are to be shifted. After the shifting and inverting each block is XORed with SHA 512 digest of the key. The resultant blocks from the cipher text. The key is generated according to the binary value of the input file size. Decryption is done following the same process as the technique is symmetric.