In this paper, the authors propose a session based bit level symmetric key cryptographic technique and it is termed as Spiral Matrix Based Bit Orientation Technique (SMBBOT). SMBBOT consider the input plain text as binary bit stream. During encryption this stream is chopped into manageable sized blocks with variable lengths. Bits of these blocks are taken from MSB to LSB to fit into a square matrix of suitable order following the concept of Spiral matrix. This square matrix splits into 2x2 sub-matrices. Bits are taken column-wise from all 2x2 sub-matrices to form the encrypted binary string. Cipher text is generated from this encrypted binary string.