Part 1: General - Computer Security Resource Center - National ...

March, 2007
APPENDIX B: Key Recovery
Federal agencies have a responsibility to protect the information contained in, processed by and
transmitted between their Information Technology systems. Cryptographic techniques are often
used as part of this process. These techniques are used to provide confidentiality, assurance of
integrity, non-repudiation or access control. Policies shall be established to address the
protection and continued accessibility of cryptographically protected information, and
procedures shall be in place to ensure that the information remains viable during its lifetime.
When cryptographic keying material is used to protect the information, this same keying material
may need to be available to remove (e.g., decrypt) or verify (e.g., verify the MAC) those
protections.
In many cases, the keying material used for cryptographic processes might not be readily
available. This might be the case for a number of reasons, including:
1. the cryptoperiod of the key has expired, and the keying material is no longer in
operational storage,
2. the keying material has been corrupted (e.g., the system has crashed or a virus has
modified the saved keying material in operational storage), or
3. the owner of the keying material is not available, and the owner’s organization needs to
obtain the plaintext information.
In order to have this keying material available when required, the keying material needs to be
saved somewhere or to be constructible (e.g., derivable) from other available keying material.
The process of re-acquiring the keying material is called key recovery. Key recovery is often
used as one method of information recovery when the plaintext information needs to be
recovered from encrypted information. However, keying material or other related information
may need to be recovered for other reasons, such as the corruption of keying material in normal
operational storage (see Section 8.2.1), e.g., the verification of MACS for archived documents.
Key recovery may also be appropriate for situations in which it is easier or faster to recover the
keying material than it is to generate and distribute new keying material. Key recovery is
motivated by a need to recover or ascertain the validity of cryptographically protected
information (e.g., the information that has been encrypted or authenticated) on behalf of an
organization or individual.
However, there are applications that may not need to save the keying material for an extended
time because of other procedures to recover an operational capability when the keying material
or the information protected by the keying material becomes inaccessible. Applications of this
type could include telecommunications where the transmitted information could be resent, or
applications that could quickly derive, or acquire and distribute new keying material.
It is the responsibility of an organization to determine whether or not the recovery of keying
material is required for their application. The decision as to whether key recovery is required
should be made on a case by case basis, and this decision should be reflected in the Key
Management Policy and the Key Management Practices Statement (see Part 2). If the decision is
made to provide key recovery, the appropriate method of key recovery should be selected, based
on the type of keying material to be recovered and the capabilities of the organization, and a
suitable key recovery methodology should be designed and implemented.
125