Cryptosystems are systems that encrypt data using encryption methods. In addition to encrypting data, a cryptosystem is also concerned with encrypting and securely transporting information between a sending station and a receiving station.
A cryptosystem encrypts plaintexts with cryptographic keys. The resulting ciphertexts can only be decrypted and converted back into plaintexts using the correct cryptographic key. The more extensive the crypto key, the more secure the ciphertext.
Cryptosystems can conceptually use symmetric encryption, asymmetric encryption, or hybrid encryption. In symmetric encryption, the cipher keys for ciphering and deciphering are identical or can be derived directly from each other. In contrast, asymmetric encryption uses different keys for encryption and decryption. Both keys are completely independent of each other, there is no connection. In hybrid encryption, both previously mentioned encryption methods are used: Symmetric encryption is used for fast data transfer, and asymmetric encryption is used to exchange the session key.