<b>Symmetric Key Generation Algorithm in Linear Block Cipher Over LU Decomposition Method </b> In symmetric key algorithm in linear block cipher to encrypt and decrypt the messages using matrix and inverse matrix In this proposed technique generate lower and upper triangular matrices from the square matrix using decomposition In encryption process, the key is a lower triangular matrix and decryption process, the key is upper triangular matrix under modulation of the prime number We illustrate the proposed technique with help of examples liner block cipher, symmetric matrix key, encryption, and decryption, lower and upper triangular decomposition Issue-4 Volume-1 P.Sundarayya | M.G.Vara Prasad