What procedure involves multiple individuals, each with access to only part of a key?

The correct answer is that the procedure involving multiple individuals, each with access to only part of a key, relates to secure multi-party computation. This technique allows a group of parties to jointly compute a function over their inputs while keeping those inputs private. In scenarios where sensitive information must remain confidential, this method enables collaboration without revealing individual data.

Secure multi-party computation ensures that no one party has complete access to the key or sensitive data and, by requiring contributions from multiple individuals, enhances security and accountability. Each individual possesses only a piece of the overall key, and only by cooperating can they reconstruct the full key or derive the desired result, thereby preventing unauthorized access.

In contrast, key sharing does not entail splitting the key among multiple parties but rather involves distributing a complete key for common use. Key recovery refers to methods designed to regain access to cryptographic keys that may be lost or forgotten, typically involving backup mechanisms rather than distributing parts of a key. Key escrow involves storing a key with a third party, which can access it under certain conditions, rather than dividing it among multiple individuals.