Traditionally, secure encrypted communication between two parties required them to first exchange keys with safe physical means. B for example lists of paper keys, which are carried by a trusted delivery driver. The Diffie Hellman key exchange method allows two parties who don`t have prior knowledge to set up a common secret key together via an unsecured channel. This key can then be used to encrypt the next communication with a symmetrical key siffre. These last two steps are of course symmetrical: Bob and Alice can both encrypt and decipher data with the secret key. You can also send and receive data. Note: It should be difficult for Alice to solve Bob`s private keys or solve for Bob for Alice`s private key. If it`s not difficult for Alice to solve Bob`s private keys (or vice versa), Eve can simply replace her own pair of private/public keys, put Bob`s public keys in her private key, create a common secret key and solve Bob`s private key (and use this to solve the shared secret key). Eve can try to choose a pair of public/private keys that allows her to easily solve Bob`s private key. Hybrid systems use cryptography with a public key to exchange secret keys that are then used in a cryptography system with symmetrical keys.

Most practical applications of cryptography use a combination of cryptographic functions to deploy a global system that provides the four desirable functions of secure communication (confidentiality, integrity, authentication and non-contestable). If a third party listened to the exchange, they would know only the usual color (yellow) and the first mixed colors (orange-tan and light blue), but it would be difficult for that party to determine the final secret color (yellow-brown). To reintegrate the analogy with large numbers rather than colors in a real exchange, this provision is mathematically expensive. Even for modern supercomputers, it is impossible to calculate in practical time. Alice uses her private key and Bob`s public key to create a secret key. In the KeyAgreement class, this requires two phases: one that uses its private key and the other that uses its public key. The following graph shows who knows what, again with non-secret values in blue and secret values in red. Here`s Eva an earpiece — she observes what`s being broadcast between Alice and Bob, but she doesn`t change the content of her communications.

Note that secrets leaked in this way may not be evenly distributed in the key area. For this reason, a common secret key is usually transmitted by another function as an information word like SHA2 (perhaps first combine common secrecy with other well-defined data). Direct use of a common secret key as an encryption key can lead to distortions in encryption implementation, which can lead to security vulnerabilities. You can find an example in section 2.1.2 of RFC 2631 in practice. If the sharedSecret buffer is too small to keep the result, a reception at the bottom is triggered.