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SSL Proxy

 

SSL proxy acts as an intermediary, performing SSL encryption and decryption between the client and the server. Better visibility into application usage can be made available when SSL forward proxy is enabled.

SSL Proxy Overview

SSL proxy is supported on SRX Series devices only.

Secure Sockets Layer (SSL) is an application-level protocol that provides encryption technology for the Internet. SSL, also called Transport Layer Security (TLS), ensures the secure transmission of data between a client and a server through a combination of privacy, authentication, confidentiality, and data integrity. SSL relies on certificates and private-public key exchange pairs for this level of security.

Server authentication guards against fraudulent transmissions by enabling a Web browser to validate the identity of a webserver. Confidentiality mechanisms ensure that communications are private. SSL enforces confidentiality by encrypting data to prevent unauthorized users from eavesdropping on electronic communications. Finally, message integrity ensures that the contents of a communication have not been tampered with.

SSL proxy is transparent; that is, it performs SSL encryption and decryption between the client and the server.

Sharing server keys is sometimes not feasible or might not be available in certain circumstances, in which case the SSL traffic cannot be decrypted. SSL proxy addresses this problem by ensuring that it has the keys to encrypt and decrypt the payload:

  • For the server, SSL proxy acts as a client—Because SSL proxy generates the shared pre-master key, it determines the keys to encrypt and decrypt.

  • For the client, SSL proxy acts as a server—SSL proxy first authenticates the original server and replaces the public key in the original server certificate with a key that is known to it. It then generates a new certificate by replacing the original issuer of the certificate with its own identity and signs this new certificate with its own public key (provided as a part of the proxy profile configuration). When the client accepts such a certificate, it sends a shared pre-master key encrypted with the public key on the certificate. Because SSL proxy replaced the original key with its own key, it is able to receive the shared pre-master key. Decryption and encryption take place in each direction (client and server), and the keys are different for both encryption and decryption.

Figure 1 shows how SSL proxy works on an encrypted payload.

Figure 1: SSL Proxy on an Encrypted Payload
SSL Proxy on an Encrypted Payload

When Advanced Security services such as application firewall (AppFW), Intrusion Detection and Prevention (IDP),application tracking (AppTrack), UTM, and SkyATP is configured, the SSL proxy acts as an SSL server by terminating the SSL session from the client and establishing a new SSL session to the server. The SRX Series device decrypts and then reencrypts all SSL proxy traffic. SSL proxy uses the following:

  • SSL-T-SSL terminator on the client side.

  • SSL-I-SSL initiator on the server side.

IDP, AppFW, AppTracking, advanced policy-based routing (APBR), UTM, SkyATP, and ICAP service redirect can use the decrypted content from SSL proxy. If none of these services are configured, then SSL proxy services are bypassed even if an SSL proxy profile is attached to a firewall policy.

Benefits of SSL Proxy

  • Decrypts SSL traffic to obtain granular application information and enable you to apply advanced security services protection and detect threats.

  • Enforces the use of strong protocols and ciphers by the client and the server.

  • Provides visibility and protection against threats embedded in SSL encrypted traffic.

  • Controls what needs to be decrypted by using Selective SSL Proxy.

Logical Systems Support

It is possible to enable SSL proxy on firewall policies that are configured using logical systems; however, note the following limitations:

  • The “services” category is currently not supported in logical systems configuration. Because SSL proxy is under “services,” you cannot configure SSL proxy profiles on a per-logical-system basis.

  • Because proxy profiles configured at a global level (within “services ssl proxy”) are visible across logical system configurations, it is possible to configure proxy profiles at a global level and then attach them to the firewall policies of one or more logical systems.

Limitations

Note

On SRX Series devices, for a particular session, the SSL proxy is only enabled if a relevant feature related to SSL traffic is also enabled. Features that are related to SSL traffic are IDP, application identification, application firewall, application tracking, advanced policy-based routing, UTM, SkyATP, and ICAP redirect service. If none of these features are active on a session, the SSL proxy bypasses the session and logs are not generated in this scenario.

Note

On all SRX Series devices, the current SSL proxy implementation has the following connectivity limitations:

  • The SSLv3.0 protocol support is deprecated.

  • The SSLv2 protocol is not supported. SSL sessions using SSLv2 are dropped.

  • Only X.509v3 certificate is supported.

  • Client authentication of SSL handshake is not supported.

  • SSL sessions where client certificate authentication is mandatory are dropped.

  • SSL sessions where renegotiation is requested are dropped.