Standards and Protocols

Public Key Infrastructure (PKI) is composed of several standards and protocols. These standards and protocols are necessary to allow for interoperability among security products offered by different vendors . Keep in mind that digital certificates, for example, may be issued by different Certificate Authorities (CAs); therefore, a common language or protocol must exist.

X.509-Based Public Key Infrastructure

PKI based on X.509 certificates (PKIX) is the Internet Engineering Task Force (IETF) working group established for the development of Internet standards for X.509-based PKI. The group 's focus includes the following:

• Profiles of X.509 version 3 Public Key Certificates and X.509 version 2 Certificate Revocation Lists (CRLs)

• PKI management protocols

• Operational protocols

• Certificate policies and Certificate Practice Statements (CPS)

• Timestamping and data-certification services as well as validation services

Public Key Cryptography Standards (PKCS)

Whereas PKIX describes the development of Internet standards for X.509-based PKI, the Public Key Cryptography Standards (PKCS) are the de facto cryptographic message standards developed and maintained by RSA Laboratories, a division of the RSA Security Corporation. PKCS provides a basic and widely accepted framework for the development of PKI solutions. There were recently 15 documents in the PKCS specification library; however, two of the documents have been incorporated into another. These documents include the following:

• PKCS #1: RSA Cryptography Standard Provides recommendations for the implementation of public key cryptography based on the RSA algorithm.

• PKCS #2 No longer exists and has been integrated into PKCS #1.

• PKCS #3: Diffie-Hellman Key Agreement Standard Describes a method for using the Diffie-Hellman key agreement.

• PKCS #4 No longer exists and has been integrated into PKCS #1.

• PKCS #5: Password-Based Cryptography Standard Provides recommendations for encrypting a data string, such as a private key, with a secret key that has been derived from a password.

• PKCS #6: Extended-Certificate Syntax Standard Provides a method for certifying additional information about a given entity beyond just the public key by describing the syntax of a certificate's attributes.

• PKCS #7: Cryptographic Message Syntax Standard Describes the syntax for data streams, such as digital signatures, that may have cryptography applied to them.

• PKCS #8: Private Key Information Syntax Standard Describes a syntax for private key information, including the private key of a public key cryptographic algorithm.

• PKCS #9: Selected Attribute Types Defines certain attribute types of use in PKCS #6, PKCS #7, PKCS #9, and PKCS #10.

• PKCS #10: Certification Request Syntax Standard Describes the syntax for a certification request to include a distinguished name , a public key, and an optional set of attributes.

• PKCS #11: Cryptographic Token Interface Standard Defines an application programming interface (API) named Cryptoki for devices holding cryptographic information.

• PKCS #12: Personal Information Exchange Syntax Standard Specifies a format for storing and/or transporting a user 's private key, digital certificate, and attribute information.

• PKCS #13: Elliptic Curve Cryptography Standard Addresses Elliptic Curve Cryptography (ECC) as related to PKI. As of this writing, PKCS #13 is still under development.

• PKCS #14: Pseudo Random Number Generation Addresses pseudo random number generation (PRNG), which produces a sequence of bits that has a random-looking distribution. As of this writing, PKCS #14 is still under development.

• PKCS #15: Cryptographic Token Information Format Standard Establishes a standard for the format of cryptographic information on cryptographic tokens.

Each of the preceding standards documents may be revised and amended as changes in cryptography occur, and they are always accessible from RSA Security's Web site (www.rsasecurity.com) or anonymous FTP server.

X.509 Standards

It was stated earlier that PKIX is an IETF working group established to create standards for X.509 PKI. X.509 has been an International Telecommunications Union (ITU) recommendation since implemented as a de facto standard. X.509 defines a framework for authentication services by a directory.

X.509 was first published as part of the ITU's X.500 directory service standard. X.500 is similar to a telephone book in that it is a database of names . This directory may include people, computers, and printers, for example. Although X.500 has not become an accepted standard like its slimmer cousin, Lightweight Directory Access Protocol (LDAP), X.509 has become the Internet's PKI standard for digital certificates.

The X.509 standard additionally defines the format of required data for digital certificates. In the previous chapter, you were briefly introduced to the contents of a digital certificate; however, it is worth reiterating some of these fields in more detail, which include those required to be compliant with the X.509 standard:

• Version Identifies the version of the X.509 standard for which the certificate is compliant.

• Serial Number The Certificate Authority (CA) that creates the certificate is responsible for assigning a unique serial number.

• Signature Algorithm Identifier Identifies the cryptographic algorithm used by the CA to sign the certificate.

• Issuer Identifies the directory name of the entity signing the certificate, which is typically a CA.

• Validity Period Identifies the time frame for which the private key is valid, if the private key has not been compromised. This period is indicated with both a start and an end time and may be of any duration, but it is often set to one year.

• Subject Name The name of the entity that is identified in the public key associated with the certificate. This name uses the X.500 standard for globally unique naming and is often called the Distinguished Name ( DN ) for example, CN=Michael Dalton, OU=Security Architecture Division, O=Castadream Inc, and C=US.

• Subject Public Key Information Includes the public key of the entity named in the certificate as well as a cryptographic algorithm identifier and optional key parameters associated with the key.

There are currently three versions of X.509:

• Version 1 This version has been around since 1988, and although it is the most generic, it is also the most ubiquitous.

• Version 2 This version is not widely used. It introduced the idea of unique identifiers for the issuing entity and the subject.

• Version 3 This version was introduced in 1996. It supports an optional extension field to provide for more informational fields. Therefore, an extension can be defined by an entity and included in the certificate.

Other Standards and Protocols

So far we have provided a good foundation of knowledge covering the standards for the deployment of cryptography and a Public Key Infrastructure. However, many other standards and protocols still need to be considered . The following list touches on many of the additional acronyms you should understand:

• Secure Sockets Layer ( SSL ) SSL is the most widely used protocol for managing secure communication between a client and server over the Web. It provides for client- and server-side authentication as well as an encrypted connection between the two. SSL operates at the Session layer of the OSI model.

• Transport Layer Security ( TLS ) TLS is the successor to SSL and similar to SSL in that it ensures secure communication between two parties on the Internet. TLS consists of two additional protocols: TLS Record Protocol and TLS Handshake Protocol. The TLS Handshake Protocol allows the client and server to authenticate to one another, and the TLS Record Protocol provides connection security.

• Internet Security Association and Key Management Protocol ( ISAKMP ) This protocol defines a common framework for the creation, negotiation, modification, and deletion of security associations in Virtual Private Networks (VPNs). ISAKMP is quite flexible in that it may be implemented over any transport protocol.

• Certificate Management Protocol ( CMP ) This protocol provides a mechanism for advanced management functions associated with the use of digital certificates, such as certificate issuance, exchange, invalidation , revocation, and key commission. CMP is also capable of operating over any transport protocol.

• XML Key Management Specification ( XKMS ) This specification defines protocols for distributing and registering public key information for use with XML signatures and is composed of the XML Key Information Service Specification (X-KISS) and the XML Key Registration Service Specification (X-KRSS). X-KISS is designed to minimize the complexity of applications using XML signatures, and X-KRSS allows key owners to register their key information for use in X-KISS.

• Secure Multipurpose Internet Mail Extensions (S/ MIME ) This specification provides email privacy using encryption and authentication via digital signatures. It is a new and secure version of the popular Multi-Purpose Internet Mail Extensions (MIME). S/MIME supports the DES, 3DES, and RC2 encryption algorithms and is integrated in many email products, thus allowing for easy interoperability among different clients .

• Pretty Good Privacy ( PGP ) Like S/MIME, PGP is based on public key encryption and is used for encrypting email messages. Not only is PGP a specification, but it is also an application available from the PGP Corporation, which has integrated it into popular email packages.

• Hypertext Transfer Protocol over Secure Sockets Layer ( HTTPS ) As opposed to SSL, HTTPS is used specifically for HTTP data communication. HTTPS is essentially the transmission of data using HTTP over SSL. Web addresses using HTTP over SSL start with https:// instead of http:// .

• Internet Protocol Security (IPSec) IPSec is a set of protocols widely implemented to support VPNs. It provides for the secure exchange of packets at the IP layer; therefore, organizations can leverage IPSec to exchange private information over public networks such as the Internet. IPSec achieves this higher level of assurance for data transport through the use of multiple protocols, including Authentication Header (AH), Encapsulated Secure Payload (ESP), and Internet Key Exchange (IKE). The AH protocol provides data integrity, authentication, and, optionally , anti-replay capabilities for packets. ESP provides for confidentiality of the data being transmitted and also includes authentication capabilities. Although IPSec can be implemented with IKE, IKE provides for additional features and ease of configuration. IKE specifically provides authentication for IPSec peers and negotiates IPSec keys and security associations.

• Certificate Enrollment Protocol ( CEP ) A proprietary protocol developed by Cisco, CEP allows Cisco devices to acquire and utilize digital certificates from CAs. CEP is primarily used for the deployment of IPSec VPNs when using Cisco devices and digital certificate authentication.

• Federal Information Processing Standard ( FIPS ) FIPS includes standards issued by the United States government for the evaluation of cryptographic modules, such as hardware, firmware, or software using cryptography that will be used in solutions for the U.S. government. FIPS 140-2 is the specific standard typically associated with PKI, and it specifies four levels of security with specific requirements, where level one provides for the lowest level of security and level four provides for the highest.

• Common Criteria ( CC ) CC is a specification designed to set a baseline for security evaluations of security devices and solutions beyond United States standards. It is also referred to as the Common Criteria for Information Technology Security Evaluation .

• Wireless Transport Layer Security ( WTLS ) WTLS is the security layer for the Wireless Application Protocol (WAP) and is used to establish secure communication channels between WAP-enabled devices (for example, mobile phones and personal digital assistants) and WAP-enabled servers. Although it is similar in function to SSL and TLS, WTLS is optimized for use with mobile devices.

• Wired Equivalent Privacy ( WEP ) WEP is a standard used in 802.11 wireless networks and is designed to protect wireless local area network connections from eavesdropping. WEP does not provide end-to-end security because it only operates at the lower two levels of the OSI modelthe Physical and Data Link layers .

• ISO 17799 This detailed, internationally recognized security standard provides a comprehensive set of controls comprising best practices in information security. This standard is rapidly gaining popularity and is composed of 10 broad sections.

IPSec can achieve greater levels of assurance for data transport through the use of additional protocols, two of which you should remember include the Authentication Header and the Encapsulated Secure Payload . The AH protocol provides data integrity, authentication, and, optionally, anti-replay capabilities for data packets. ESP provides confidentiality of the data being transmitted and also includes authentication capabilities.

ISO 17799

It is worth discussing ISO 17799 in further detail because it deals with many of the important security topics pertinent to many security professionals. ISO 17799, also known as the Code of Practice for Information Security Management , is composed of 10 major sections, each covering an information security topic. The sections and their purposes as defined by the standard are as follows :

• Business Continuity Planning Used to counteract interruptions to business activities and to critical business processes from the effects of major failures or disasters.

• System Access Control Used to (1) control access to information; (2) prevent unauthorized access to information systems; (3) ensure the protection of networked services; (4) prevent unauthorized computer access; (5) detect unauthorized activities; and (6) ensure information security when using mobile computing and telenetworking facilities.

• System Development and Maintenance Used to (1) ensure security is built in to operational systems; (2) prevent loss, modification, or misuse of user data in application systems; (3) protect the confidentiality, authenticity, and integrity of information; (4) ensure IT projects and support activities are conducted in a secure manner; and (5) maintain the security of application system software and data.

• Physical and Environmental Security Used to (1) prevent unauthorized access, damage, and interference to business premises and information; (2) prevent loss, damage, or compromise of assets and interruption to business activities; and (3) prevent compromise or theft of information and information-processing facilities.

• Compliance Used to (1) avoid breaches of any criminal or civil law, statutory , regulatory, or contractual obligations, and of any security requirements; (2) ensure compliance of systems with organizational security policies and standards; and (3) maximize the effectiveness of and minimize interference to/from the system-audit process.

• Personnel Security Used to (1) reduce the risks of human error, theft, fraud, or misuse of facilities; (2) ensure that users are aware of information security threats and concerns and are equipped to support the corporate security policy in the course of their normal work; and (3) minimize the damage from security incidents and malfunctions and learn from such incidents.

• Security Organization Used to (1) manage information security within the company; (2) maintain the security of organizational information-processing facilities and information assets accessed by third parties; and (3) maintain the security of information when the responsibility for information processing has been outsourced to another organization.

• Computer and Operations Management Used to (1) ensure the correct and secure operation of information-processing facilities; (2) minimize the risk of systems failures; (3) protect the integrity of software and information; (4) maintain the integrity and availability of information processing and communication; (5) ensure the safeguarding of information in networks and the protection of the supporting infrastructure; (6) prevent damage to assets and interruptions to business activities; and (7) prevent loss, modification, or misuse of information exchanged between organizations.

• Asset Classification and Control Used to maintain appropriate protection of corporate assets and ensure that information assets receive an appropriate level of protection.

• Security Policy Used to provide management direction and support for information security.

In the previous chapter, we discussed the management structure for digital certificates. In this chapter, we've discussed the standards and protocols available to utilize them. In the following section, we'll discuss the management structure for the keys themselves . This includes the critical elements that must be taken into account to properly protect and account for the private key material, which is the most important element of a PKI solution.