These keys are mathematically linked. Throughout the key lifecycle, secret keys must remain secret from all parties except those who are owner and are authorized to use them. The key parameters given to the vendor or which will get into the POS are those in the public part of the RSA key: $(N,e)$. •Requirements -It must be computationally easy to encipher or decipher a message given the appropriate key -It must be computationally infeasible to derive the private key from the public key -It must be computationally infeasible to determine the private key from a chosen plaintext attack It is computationally easy for a party B to generate a pair [KU b, KR b]. For n individuals to communicate, number of keys required = 2 x n = 2n keys. There are legitimate interoperability requirements for these. There are legitimate interoperability requirements for these. Requirements for Public-Key Cryptography The cryptosystem illustrated in Figures 9.2 through 9.4 depends on a cryptographic algorithm based on two related keys. Asymmetric Encryption Algorithms- Assurance of public keys. Unlike symmetric key algorithms that rely on one key to both encrypt and decrypt, each key performs a unique function. This is how asymmetric encryption or public-key cryptography works. The Public key is used by everyone else to encrypt messages for that user. It is computationally easy for a party B to generate a pair of key (public key PUb, private key PRb). It is computationally easy for a sender A, knowing the public key and the message to be encrypted M, to generate the corresponding ciphertext: C=EKU b (M). To implement public-key encryption on a large scale, such as a secure Web server might need, requires a different approach. Requirement of Public key Cryptography 1. However, they did lay out the conditions that such algorithms must fulfill [DIFF76b]. It is easy for a sender A, knowing the public key and message to be encrypt. It is easy for party B to generate a pair of keys (public key PUb, Mr. Gopal Sakarkar Private key PRb). Diffie and Hellman postulated this system without demonstrating that such algorithms exist. It is computationally easy for a sender A, knowing the public key and the message to be encrypted, M, to generate the corresponding ciphertext:  C = E (PUb, M)  3. The Private key is used to decrypt messages from other users. Public-key cryptography, or asymmetric cryptography, is an encryption scheme that uses two mathematically related, but not identical, keys - a public key and a private key. There are two specific requirements of key management for public key cryptography. This is where digital certificates come in. 2 Requirements for public key cryptography . For every user, there is 1 Private key and 1 Public key. If you have 5 users, there are 5 Private keys and 5 Public keys. 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