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End User Encryption Key Protection Policy

Free Use Disclaimer: This policy was created by or for the SANS Institute for the

Internet community. All or parts of this policy can be freely used for your organization.

There is no prior approval required. If you would like to contribute a new policy or

updated version of this policy, please send email to [email protected].

Last Update Status: Updated June 2014

1. Overview Encryption Key Management, if not done properly, can lead to compromise and disclosure of

private keys use to secure sensitive data and hence, compromise of the data. While users may

understand it’s important to encryption certain documents and electronic communications, they

may not be familiar with minimum standards for protection encryption keys.

2. Purpose This policy outlines the requirements for protecting encryption keys that are under the control of

end users. These requirements are designed to prevent unauthorized disclosure and subsequent

fraudulent use. The protection methods outlined will include operational and technical controls,

such as key backup procedures, encryption under a separate key and use of tamper-resistant

hardware.

3. Scope This policy applies to any encryption keys listed below and to the person responsible for any

encryption key listed below. The encryption keys covered by this policy are:

• encryption keys issued by <Company Name>

• encryption keys used for <Company Name> business

• encryption keys used to protect data owned by <Company Name>

The public keys contained in digital certificates are specifically exempted from this policy.

4. Policy All encryption keys covered by this policy must be protected to prevent their unauthorized

disclosure and subsequent fraudulent use.

4.1 Secret Key Encryption Keys

Keys used for secret key encryption, also called symmetric cryptography, must be protected as

they are distributed to all parties that will use them. During distribution, the symmetric

encryption keys must be encrypted using a stronger algorithm with a key of the longest key

length for that algorithm authorized in <Company Name>’s Acceptable Encryption Policy. If the

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keys are for the strongest algorithm, then the key must be split, each portion of the key encrypted

with a different key that is the longest key length authorized and the each encrypted portion is

transmitted using different transmission mechanisms. The goal is to provide more stringent

protection to the key than the data that is encrypted with that encryption key.

Symmetric encryption keys, when at rest, must be protected with security measures at least as

stringent as the measures used for distribution of that key.

4.2 Public Key Encryption Keys

Public key cryptography, or asymmetric cryptography, uses public-private key pairs. The public

key is passed to the certificate authority to be included in the digital certificate issued to the end

user. The digital certificate is available to everyone once it issued. The private key should only

be available to the end user to whom the corresponding digital certificate is issued.

4.2.1 <Company Name>’s Public Key Infrastructure (PKI) Keys

The public-private key pairs used by the <Company Name>’s public key infrastructure (PKI) are

generated on the tamper-resistant smart card issued to an individual end user. The private key

associated with an end user’s identity certificate, which are only used for digital signatures, will

never leave the smart card. This prevents the Infosec Team from escrowing any private keys

associated with identity certificates. The private key associated with any encryption certificates,

which are used to encrypt email and other documents, must be escrowed in compliance with

<Company Name> policies.

Access to the private keys stored on a <Company Name>issued smart card will be protected by a

personal identification number (PIN) known only to the individual to whom the smart card is

issued. The smart card software will be configured to require entering the PIN prior to any private

key contained on the smart card being accessed.

4.2.2 Other Public Key Encryption Keys

Other types of keys may be generated in software on the end user’s computer and can be stored as

files on the hard drive or on a hardware token. If the public-private key pair is generated on

smartcard, the requirements for protecting the private keys are the same as those for private keys

associated with <Company Name’s> PKI. If the keys are generated in software, the end user is

required to create at least one backup of these keys and store any backup copies securely. The

user is also required to create an escrow copy of any private keys used for encrypting data and

deliver the escrow copy to the local Information Security representative for secure storage.

The Infosec Team shall not escrow any private keys associated with identity certificates. All

backups, including escrow copies, shall be protected with a password or passphrase that is

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compliant with <Company Name> Password Policy. Infosec representatives will store and

protect the escrowed keys as described in the <Company Name> Certificate Practice Statement

Policy.

4.2.2.1 Commercial or Outside Organization Public Key Infrastructure (PKI) Keys

In working with business partners, the relationship may require the end users to use public-

private key pairs that are generated in software on the end user’s computer. In these cases, the

public-private key pairs are stored in files on the hard drive of the end user. The private keys are

only protected by the strength of the password or passphrase chosen by the end user. For

example, when an end user requests a digital certificate from a commercial PKI, such as VeriSign

or Thawte, the end user’s web browser will generate the key pair and submit the public key as

part of the certificate request to the CA. The private key remains in the browser’s certificate store

where the only protection is the password on the browser’s certificate store. A web browser

storing private keys will be configured to require the user to enter the certificate store password

anytime a private key is accessed.

4.2.2.2 PGP Key Pairs

If the business partner requires the use of PGP, the public-private key pairs can be stored in the

user’s key ring files on the computer hard drive or on a hardware token, for example, a USB

drive or a smart card. Since the protection of the private keys is the passphrase on the secret

keying, it is preferable that the public-private keys are stored on a hardware token. PGP will be

configured to require entering the passphrase for every use of the private keys in the secret key

ring.

4.3 Hardware Token Storage

Hardware tokens storing encryption keys will be treated as sensitive company equipment, as

described in <Company Name>’s Physical Security policy, when outside company offices. In

addition, all hardware tokens, smartcards, USB tokens, etc., will not be stored or left connected to

any end user’s computer when not in use. For end users traveling with hardware tokens, they will

not be stored or carried in the same container or bag as any computer.

4.4 Personal Identification Numbers (PINs), Passwords and Passphrases

All PINs, passwords or passphrases used to protect encryption keys must meet complexity and

length requirements described in <Company Name>’s Password Policy.

4.5 Loss and Theft

The loss, theft, or potential unauthorized disclosure of any encryption key covered by this policy

must be reported immediately to The Infosec Team. Infosec personnel will direct the end user in

any actions that will be required regarding revocation of certificates or public-private key pairs.

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5. Policy Compliance 5.1 Compliance Measurement

The Infosec team will verify compliance to this policy through various methods, including but

not limited to, periodic walk-thrus, video monitoring, business tool reports, internal and external

audits, and feedback to the policy owner.

5.2 Exceptions Any exception to the policy must be approved by the Infosec Team in advance.

5.3 Non-Compliance An employee found to have violated this policy may be subject to disciplinary action, up to and

including termination of employment.

6 Related Standards, Policies and Processes • Acceptable Encryption Policy

• Certificate Practice Statement Policy

• Password Policy

• Physical Security policy

7 Definitions and Terms The following definition and terms can be found in the SANS Glossary located at:

https://www.sans.org/security-resources/glossary-of-terms/

• Certificate authority (CA)

• Digital certificate

• Digital signature

• Key escrow

• Plaintext

• Public key cryptography

• Public key pairs

• Symmetric cryptography

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8 Revision History

Date of Change Responsible Summary of Change

June 2014 SANS Policy Team Updated and converted to new format.