Which of the following can best be defined as a key recovery technique for storing knowledge of a
cryptographic key by encrypting it with another key and ensuring that only certain third parties can perform the
decryption operation to retrieve the stored key?

A.
Key escrow

B.
Fair cryptography

C.
Key encapsulation

D.
Zero-knowledge recovery

Explanation:
According to RFC 4949, key encapsulation is a key recovery technique for storing knowledge of a cryptographic
key by encrypting it with another key and ensuring that only certain third parties called “recovery agents” can
perform the decryption operation to retrieve the stored key. Key encapsulation typically permits direct retrieval
of a secret key used to provide data confidentiality.
Incorrect Answers:
A: A key recovery technique for storing knowledge of a cryptographic key or parts thereof in the custody of one
or more third parties called “escrow agents”, so that the key can be recovered and used in specified
circumstances. This is not what is described in the question.
B: Fair cryptography is not a valid answer.
D: Zero-knowledge recovery is not a valid answer.

http://tools.ietf.org/html/rfc4949