Decrypt Profiles Overview

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 Web server. 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 performs SSL encryption and decryption between the client and the server, but neither the server nor the client can detect its presence. SSL proxy ensures that it has the keys to encrypt and decrypt the payload:

For the server, SSL proxy acts as a client—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.

The below figure shows how SSL proxy works on an encrypted payload. SSL proxy uses the following services:

SSL-T-SSL terminator on the client side.
SSL-I-SSL initiator on the server side.

Figure 1: SSL Proxy on an Encrypted Payload

Supported Ciphers in Proxy Mode

An SSL cipher comprises encryption ciphers, authentication method, and compression. The below table displays a list of supported ciphers. NULL ciphers are excluded.

The following SSL protocols are supported:

SSLv3
TLS1

Table 1: Supported Ciphers in Proxy Mode
SSL Cipher	Key Exchange Algorithm	Data Encryption	Message Integrity
RSA_WITH_RC4_128_MD5	RSA key exchange	128-bit RC4	MD5 hash
RSA_WITH_RC4_128_SHA	RSA key exchange	128-bit RC4	Secure Hash Algorithm (SHA) hash
RSA_WITH_DES_CBC_SHA	RSA key exchange	DES CBC	SHA hash
RSA_WITH_3DES_EDE_CBC_SHA	RSA key exchange	3DES EDE/CBC	SHA hash
RSA_WITH_AES_128_CBC_SHA	RSA key exchange	128-bit AES/CBC	SHA hash
RSA_WITH_AES_256_CBC_SHA	RSA key exchange	256-bit AES/CBC	SHA hash
RSA_EXPORT_WITH_RC4_40_MD5	RSA-export	40-bit RC4	MD5 hash
RSA_EXPORT_WITH_DES40_CBC_SHA	RSA-export	40-bit DES/CBC	SHA hash
RSA_EXPORT1024_WITH_DES_CBC_SHA	RSA 1024 bit export	DES/CBC	SHA hash
RSA_EXPORT1024_WITH_RC4_56_MD5	RSA 1024 bit export	56-bit RC4	MD5 hash
RSA_EXPORT1024_WITH_RC4_56_SHA	RSA 1024 bit export	56-bit RC4	SHA hash
RSA-WITH-AES-256-GCM-SHA384	RSA key exchange	256-bit AES/GCM	SHA384 hash
RSA-WITH-AES-256-CBC-SHA256	RSA key exchange	256-bit AES/CBC	SHA256 hash
RSA-WITH-AES-128-GCM-SHA256	RSA key exchange	128-bit AES/GCM	SHA256 hash
RSA-WITH-AES-128-CBC-SHA256	RSA key exchange	128-bit AES/CBC	SHA256 hash

Server Authentication

Implicit trust between the client and the device (because the client accepts the certificate generated by the device) is an important aspect of SSL proxy. It is extremely important that server authentication is not compromised; however, in reality, self-signed certificates and certificates with anomalies are in abundance. Anomalies can include expired certificates, instances of common name not matching a domain name, and so forth.

You can specify that the SSL proxy should ignore server authentication completely. In this case, SSL proxy ignores errors encountered during the server certificate verification process (such as CA signature verification failure, self-signed certificates, and certificate expiry).

You can specify whether the SSL proxy should ignore server authentication errors or not during the creation of an SSL proxy profile.

If you specify that server authentication errors should not be ignored, the following scenarios occur:
- If authentication succeeds, a new certificate is generated by replacing the keys and changing the issuer name to the issuer name that is configured in the root CA certificate in the proxy profile.
- If authentication fails, the connection is dropped.
If you specify that server authentication errors should be ignored, the following scenarios occur:

Note:
We do not recommend that you configure this option for authentication because configuring it results in websites not being authenticated at all. However, you can use this option to effectively identify the root cause for dropped SSL sessions.
- If the certificate is self-signed, a new certificate is generated by replacing the keys only. The issuer name is not changed. This ensures that the client browser displays a warning that the certificate is not valid.
- If the certificate has expired or if the common name does not match the domain name, a new certificate is generated by replacing the keys and changing the issuer name to SSL-PROXY: DUMMY_CERT:GENERATED DUE TO SRVR AUTH FAILURE. This ensures that the client browser displays a warning that the certificate is not valid.

Root CA

In a public key infrastructure (PKI) hierarchy, the root CA is at the top of the trust path. The root CA identifies the server certificate as a trusted certificate.

Trusted CA List

SSL proxy ensures secure transmission of data between a client and a server. Before establishing a secure connection, SSL proxy checks certificate authority (CA) certificates to verify signatures on server certificates. For this reason, a reasonable list of trusted CA certificates is required to effectively authenticate servers.

Session Resumption

An SSL session refers to the set of parameters and encryption keys that are created when a full handshake is performed. A connection is the conversation or active data transfer that occurs within the session. The computational overhead of a complete SSL handshake and generation of primary keys is considerable. In short-lived sessions, the time taken for the SSL handshake can be more than the time for data transfer. To improve throughput and still maintain an appropriate level of security, SSL session resumption provides a mechanism for caching sessions. This way, session information, such as the pre-master secret key and agreed-upon ciphers, can be cached for both the client and the server. A session ID identifies the cached information. In subsequent connections, both parties agree to use the session ID to retrieve the information rather than create pre-master secret key. Session resumption shortens the handshake process and accelerates SSL transactions.

SSL Proxy Logs

When logging is enabled in an decrypt profile, the SSL proxy can generate the messages shown in the below table.

Table 2: SSL Proxy Logs
Log Type	Description
All	All logs are generated.
Warning	Logs used for reporting warnings.
Info	Logs used for reporting general information.
Error	Logs used for reporting errors.
Session Whitelisted	Logs generated when a session is allowed.
Session Allowed	Logs generated when a session is processed by SSL proxy even after encountering some minor errors.
Session Dropped	Logs generated when a session is dropped by SSL proxy.

All logs contain similar information; the message field contains the reason for the log generation. One of three prefixes shown below identifies the source of the message. Other fields are descriptively labeled.

Table 3: SSL Proxy Log Prefixes
Prefix	Description
system	Logs generated because of errors related to the device or an action taken as part of the decrypt profile. Most logs fall into this category.
openssl error	Logs generated during the handshake process if an error is detected by the openssl library.
certificate error	Logs generated during the handshake process if an error is detected in the certificate (X.509 related errors).

Use the Decrypt Profiles page to view and to manage decrypt profiles. To access this page, click Security Subscriptions > Decrypt > Decrypt Profiles.

Field Descriptions

Table 4: Fields on the Decrypt Profiles Page
Field	Description
Name	Name of the decrypt profile.
Preferred Cipher	Preferred cipher associated with the profile.
Custom Ciphers	The set of ciphers, if the preferred cipher is Custom, which the SSH server uses to perform the encryption and the decryption functions.
Exempted Address	Addresses that are exempted from decrypt processing.
Description	Description of the decrypt profile.
Root Certificate	Root certificate associated with the decrypt profile.

Table 5: View Decrypt Profile Details Page Fields
Field	Description
General Information
Name	Name of the decrypt profile.
Description	Description of the decrypt profile.
Preferred Cipher	Preferred cipher associated with the proxy profile.
Custom Ciphers	The set of ciphers, if the preferred cipher is Custom, which the SSH server uses to perform the encryption and the decryption functions.
Flow Trace Enabled	Indicates whether flow tracing is enabled or disabled.
Certificates	Displays the root certificate and the trusted certificate authorities associated with the root certificate.
Exempted Address	Addresses that are exempted from decrypt processing.
Exempted URL Categories	URL categories that are exempted from decrypt processing.
Actions
Ignore	Indicates whether server authentication failure is ignored (Enabled) or not (Disabled).
Session Resumption	Indicates whether session information is cached to enable session resumption (Enabled) or not (Disabled).
Logging	If logging is enabled, indicates the type of events that are logged.
Renegotiation	Indicates the type of renegotiation required for a change in SSL parameters after creating a session and establishing the SSL tunnel transport.

ON THIS PAGE