Cryptography is the art of achieving security by encoding messages to keep the information non-readable. Cryptography actually is a mathematical scrambling and unscrambling of data to achieve, Confidentiality (Readable only to sender and receiver); Integrity (not modified by any one to integrity of message); Non repudiation (sender can't refuse the claim of not sending); and Entity authentication. While sending or receiving the data, special keys are used to encrypt/decrypt data to verify the original contents. This key makes the process of cryptography secure. Public key systems use two keys such that one key, the public key, can be used to encrypt some text that can then only be decrypted using the securely-held private key. There are two approaches for the generation of encryption/decryption keys i.e. software and hardware. The purpose of this paper is to generate encryption key using hardware technique. To design electronics circuit basic concept is derived from the Knapsack problem. Then R-2R ladder network is used for the implementation of Knapsack algorithm. The electronics circuit design is evaluated using (ORCAD-Pcpise) software and analyzed practically on electronics bread board as well. The circuit implementation aim is achieved through many intermediate steps which are followed as firstly terminology and transformation are defined foe public key cryptography, then the knapsack problem is discussed and after that knapsack algorithm (greedy algorithm) is achieved using the electronics circuits. Some modification also has been discussed to make circuit more practical and more secure.