Which criterion is vital for effective key management in a cryptosystem?

Confidentiality is a fundamental criterion for effective key management in a cryptosystem because it ensures that encryption keys are protected from unauthorized access or disclosure. If keys are not kept confidential, an attacker could gain access to sensitive data by decrypting it, which would compromise the security of the entire cryptosystem. Maintaining the confidentiality of keys involves using secure storage solutions, access controls, and strong encryption practices to prevent unauthorized users from obtaining them.

Others aspects, such as accessibility, are important as well, but they must not come at the cost of confidentiality. The assurance that keys remain confidential is paramount, as it directly impacts the overall security and trustworthiness of the cryptographic operations within the system.