Page 448 - (ISC)² CISSP Certified Information Systems Security Professional Official Study Guide

Asymmetric Key Management

When working within the public key infrastructure, it’s important that
you comply with several best practice requirements to maintain the
security of your communications.

First, choose your encryption system wisely. As you learned earlier,
“security through obscurity” is not an appropriate approach. Choose
an encryption system with an algorithm in the public domain that has
been thoroughly vetted by industry experts. Be wary of systems that
use a “black-box” approach and maintain that the secrecy of their
algorithm is critical to the integrity of the cryptosystem.

You must also select your keys in an appropriate manner. Use a key
length that balances your security requirements with performance
considerations. Also, ensure that your key is truly random. Any
patterns within the key increase the likelihood that an attacker will be
able to break your encryption and degrade the security of your
cryptosystem.

When using public key encryption, keep your private key secret! Do

not, under any circumstances, allow anyone else to gain access to your
private key. Remember, allowing someone access even once
permanently compromises all communications that take place (past,
present, or future) using that key and allows the third party to
successfully impersonate you.

Retire keys when they’ve served a useful life. Many organizations have
mandatory key rotation requirements to protect against undetected

key compromise. If you don’t have a formal policy that you must
follow, select an appropriate interval based on the frequency with
which you use your key. You might want to change your key pair every
few months, if practical.

Back up your key! If you lose the file containing your private key
because of data corruption, disaster, or other circumstances, you’ll
certainly want to have a backup available. You may want to either

create your own backup or use a key escrow service that maintains the
backup for you. In either case, ensure that the backup is handled in a