Juniper SRX Services Gateway VPN Security Technical Implementation Guide

Without confidentiality protection mechanisms, unauthorized individuals may gain access to sensitive information via a remote access session. The Advance Encryption Standard (AES) encryption is critical to ensuring the privacy of the IPsec session; it is imperative that AES is used for encryption operations. Remote access is access to DoD-non-public information systems by an authorized user (or an information system) communicating through an external, non-organization-controlled network. Remote access methods include broadband and wireless connections. While there is much debate about the security and performance of AES, there is a consensus that AES is significantly more secure than other algorithms currently supported by IPsec implementations. AES is available in three key sizes: 128, 192, and 256 bits, versus the 56 bit DES. Therefore, there are approximately 1021 times more AES 128-bit keys than DES 56-bit keys. In addition, AES uses a block size of 128 bits—twice the size of DES or 3DES.

Without confidentiality protection mechanisms, unauthorized individuals may gain access to sensitive information via a remote access session. The Advance Encryption Standard (AES) algorithm is critical to ensuring the privacy of the IKE session responsible for establishing the security association and key exchange for an IPsec tunnel. AES is used for encryption operations. Remote access is access to DoD-non-public information systems by an authorized user (or an information system) communicating through an external, non-organization-controlled network. Remote access methods include broadband and wireless connections. While there is much debate about the security and performance of AES, there is a consensus that AES is significantly more secure than other algorithms currently supported by IPsec implementations. AES is available in three key sizes: 128, 192, and 256 bits, versus the 56 bit DES. Therefore, there are approximately 1021 times more AES 128-bit keys than DES 56-bit keys. In addition, AES uses a block size of 128 bits—twice the size of DES or 3DES.

Without IKE, the SPI is manually specified for each security association. IKE peers will negotiate the encryption algorithm and authentication or hashing methods as well as generate the encryption keys. An IPsec SA is established using either Internet Key Exchange (IKE) or manual configuration. When using IKE, the security associations are established when needed and expire after a period of time or volume of traffic threshold. If manually configured, they are established as soon as the configuration is complete at both end points and they do not expire. When using IKE, the Security Parameter Index (SPI) for each security association is a pseudo-randomly derived number. With manual configuration of the IPsec security association, both the cipher key and authentication key are static. Hence, if the keys are compromised, the traffic being protected by the current IPsec tunnel can be decrypted as well as traffic in any future tunnels established by this SA. Furthermore, the peers are not authenticated prior to establishing the SA, which could result in a rogue device establishing an IPsec SA with either of the VPN end points. IKE provides primary authentication to verify the identity of the remote system before negotiation begins. This feature is lost when the IPsec security associations are manually configured, which results in a non-terminating session using static pre-shared keys.

Situations may arise in which the certificate issued by a Certificate Authority (CA) may need to be revoked before the lifetime of the certificate expires. For example, the certificate is known to have been compromised. To achieve this, a list of certificates that have been revoked, known as a Certificate Revocation List (CRL), is sent periodically from the CA to the IPsec gateway. When an incoming Internet Key Exchange (IKE) session is initiated for a remote client or peer whose certificate is revoked, the CRL will be checked to see if the certificate is valid; if the certificate is revoked, IKE will fail and an IPsec security association will not be established for the remote endpoint.

To assure accountability and prevent unauthenticated access, non-privileged users must utilize multifactor authentication to prevent potential misuse and compromise of the system. Multifactor authentication uses two or more factors to achieve authentication. Use of password for user remote access for non-privileged account is not authorized. Factors include: (i) Something you know (e.g., password/PIN); (ii) Something you have (e.g., cryptographic identification device, token); or (iii) Something you are (e.g., biometric). A non-privileged account is any information system account with authorizations of a non-privileged user. Network access is any access to an application by a user (or process acting on behalf of a user) where said access is obtained through a network connection. The DoD CAC with DoD-approved PKI is an example of multifactor authentication.

Use of weak or untested encryption algorithms undermines the purposes of utilizing encryption to protect data. The network element must implement cryptographic modules adhering to the higher standards approved by the federal government since this provides assurance they have been tested and validated. RFC 6379 Suite B Cryptographic Suites for IPsec defines four cryptographic user interface suites for deploying IPsec. Each suite provides choices for Encapsulating Security Payload (ESP) and IKE. The four suites are differentiated by the choice of IKE authentication and key exchange, cryptographic algorithm strengths, and whether ESP is to provide both confidentiality and integrity or integrity only. The suite names are based on the Advanced Encryption Standard (AES) mode and AES key length specified for ESP. Two suites are defined for transporting classified information up to SECRET level—one for both confidentiality and integrity and one for integrity only. There are also two suites defined for transporting classified information up to TOP SECRET level.

Authenticity protection provides protection against man-in-the-middle attacks/session hijacking and the insertion of false information into sessions. This requirement focuses on communications protection for the application session rather than for the network packet and establishes grounds for confidence at both ends of communications sessions in ongoing identities of other parties and in the validity of information transmitted. Depending on the required degree of confidentiality and integrity, web services/SOA will require the use of mutual authentication (two-way/bidirectional). An IPsec Security Associations (SA) is established using either IKE or manual configuration.