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    Inspection of SSL Traffic Overview

    Secure Sockets Layer (SSL) is a cryptographic protocol that adds security to TCP/IP communication. Several versions of the SSL and Transport Layer Security (TLS) protocols are in widespread use in applications like Web browsing, electronic mail, Internet faxing, instant messaging, and voice over IP (VoIP). SSL and TLS encrypt the Transport Layer protocol datagrams that carry the payload of these communications. While encryption is an excellent way to keep private data from prying eyes, without inspection by the IDP Series device, it also unwittingly opens a network to dangerous viruses, trojans, or network attacks.

    To inspect the HTTP payload of HTTPS traffic, the IDP Series device must decrypt the HTTPS session. Your security policy can examine both the SSL session and the decrypted HTTP payload.

    The following sections describe alternative methods you can use to enable SSL inspection:

    Using the SSL Server Private Keys

    Beginning with IDP OS Release 3.2r1, we support inspection of client-to-server traffic to internal SSL servers. As shown in Figure 1, this method depends on administrative access to the SSL server private keys.

    Figure 1: SSL Inspection Using SSL Server Private Keys

    Image g036644.gif

    You must be able to copy the SSL server private key to the IDP SSL keystore. The IDP Series device uses the key to decrypt the inbound traffic so that it can inspect the payload. The private key must be in Privacy-Enhanced Mail (PEM) format. We have verified support for the following RSA private key lengths: 1024 bits, 2048 bits, 3072 bits, and 4096 bits.

    Using a Root Certificate Authority in SSL Forward Proxy Operations

    Beginning with IDP OS Release 5.0r2, we support inspection of traffic to HTTPS servers where you do not have access to the SSL private key, such as outbound traffic to the WWW. As shown in Figure 2, this method uses a root certificate authority (CA) to proxy the SSL key negotiation. The IDP Series device inserts itself into the SSL key negotiation phase so that it can decrypt the HTTPS session and inspect the session and payload according to your security policy.

    Figure 2: SSL Inspection Using a Root CA

    Image g036645.gif

    When the special root CA is present, the IDP Series device intercepts the HTTPS connection and makes a request to the server as if it were the client; it presents to the client a CA (derived from the special root CA) as if it were the server. The IDP Series device then negotiates the key exchange, decrypts the session, inspects the payload, and re-encrypts the session as necessary before forwarding.

    To ensure employee or customer privacy, you can configure a whitelist to exclude matching sessions from being processed by the SSL forward proxy feature. Traffic to destination servers on your whitelist is not intercepted and is passed through uninspected.

    Note: When both the CA and server private keys are present, the IDP Series device uses the SSL forward proxy method to inspect HTTPS traffic.

    Supported SSL Specifications

    The IDP Series device supports decryption of HTTPS traffic that uses SSLv3 and TLSv1. The IDP Series device can inspect an SSLv2 header for anomalies, but it cannot decrypt and examine the HTTP payload in such sessions. In addition, the IDP Series device does not support inspection of compressed TLS traffic.

    Table 1 lists the SSL cipher suites supported by the two IDP SSL inspection methods.

    Table 1: Supported SSL Cipher Suites

    Cipher Suite

    Decryption Using Private Keys

    Decryption Using Forward Proxy

    Name: TLS_RSA_WITH_NULL_MD5

    Authorization: RSA

    Key Exchange: RSA

    Encryption: NULL

    Digest: MD5

    Yes

    Yes

    Name: TLS_RSA_WITH_NULL_SHA

    Authorization: RSA

    Key Exchange: RSA

    Encryption: NULL

    Digest: SHA

    Yes

    Yes

    Name: TLS_RSA_WITH_RC4_128_MD5

    Authorization: RSA

    Key Exchange: RSA

    Encryption: RC4_128

    Digest: MD5

    Yes

    Yes

    Name: TLS_RSA_WITH_RC4_128_SHA

    Authorization: RSA

    Key Exchange: RSA

    Encryption: RC4_128

    Digest: SHA

    Yes

    Yes

    Name: TLS_RSA_WITH_DES_CBC_SHA

    Authorization: RSA

    Key Exchange: RSA

    Encryption: DES_CBC

    Digest: SHA

    Yes

    Yes

    Name: TLS_RSA_WITH_3DES_EDE_CBC_SHA

    Authorization: RSA

    Key Exchange: RSA

    Encryption: 3DES_EDE_CBC

    Digest: SHA

    Yes

    Yes

    Name: TLS_RSA_WITH_AES_128_CBC_SHA

    Authorization: RSA

    Key Exchange: RSA

    Encryption: AES_128_CBC

    Digest: SHA

    Yes

    Yes

    Name: TLS_RSA_WITH_AES_256_CBC_SHA

    Authorization: RSA

    Key Exchange: RSA

    Encryption: AES_256_CBC

    Digest: SHA

    Yes

    Yes


    Published: 2011-02-08