While traversing, the history observed few ways of ensuring security when data is transmitted through some unsecured path. One such way is cryptography which is being used for centuries for securing the information. Symmetric key encryption algorithm uses one single key to send and receive the data, which means the sender and receiver share the unique key, known only to those two parties involved in the transaction. Stream cipher and block cipher are two ways to implement the symmetric key algorithm. Stream cipher plays with individual bits along with the key, whereas block of plaintext is given as an input for processing, and finally, a block of ciphertext is retrieved. This research paper highlights the most desirable properties like avalanche effect, completeness and statistical independence of a symmetric key block cipher. This article depicts that the block cipher algorithm should possess the features mentioned above as very basic to ensure security. The paper also sheds light on nth Prime Number (NPN) algorithm by illustrating the features above. It also shows a basic comparative analysis of existing algorithms like Data Encryption Standard, Advanced Encryption Standard by avalanche effect. This paper also proposed a framework for NPN, and where NPN can be implemented in real life.