Cisco Unified CallManager Security Guide, Release 5.0(4)
Configuring Encrypted Phone Configuration Files (Revised 10/2/2006)
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Configuring Encrypted Phone Configuration Files

Table Of Contents

Configuring Encrypted Phone Configuration Files

Understanding Encryption of the Phone Configuration File

Manual Key Distribution

Symmetric Key Encryption with Phone Public Key

Supported Phone Models

Configuration Tips for Encrypted Configuration Files

Encryption Configuration File Configuration Checklist

Enabling Phone Configuration File Encryption

Configuring Manual Key Distribution

Manual Key Distribution Configuration Settings

Entering the Symmetric Key on the Phone

Verifying That an LSC or MIC Certificate Is Installed 

Verifying That the Phone Configuration File Is Encrypted

Disabling Encryption for the Phone Configuration Files

Excluding Digest Credentials from Phone Configuration File Download

Where to Find More Information


Configuring Encrypted Phone Configuration Files


After you configure security-related settings, the phone configuration file contains sensitive information, such as digest passwords and phone administrator passwords. To ensure privacy of the configuration file, you must configure the configuration files for encryption.

This chapter contains information on the following topics:

Understanding Encryption of the Phone Configuration File

Supported Phone Models

Configuration Tips for Encrypted Configuration Files

Encryption Configuration File Configuration Checklist

Enabling Phone Configuration File Encryption

Configuring Manual Key Distribution

Manual Key Distribution Configuration Settings

Entering the Symmetric Key on the Phone

Verifying That an LSC or MIC Certificate Is Installed

Verifying That the Phone Configuration File Is Encrypted

Disabling Encryption for the Phone Configuration Files

Where to Find More Information

Understanding Encryption of the Phone Configuration File

To secure digest credentials and secured passwords in phone downloads from Cisco Unified CallManager, you must enable the TFTP Encrypted Config option in the Phone Security Profile Configuration window and perform additional tasks in Cisco Unified CallManager Administration.

After you enable the TFTP Encrypt Config option, configure the required parameters in Cisco Unified CallManager Administration and the phone, and restart required services in Cisco Unified CallManager Serviceability, the TFTP server

1. Deletes all clear text configuration files on disk

2. Generates encrypted versions of the configuration files.

If the phone supports encrypted phone configuration files and if you performed the necessary tasks for phone configuration file encryption, the phone requests an encrypted version of the configuration file.


Warning If digest authentication is True for the SIP phone when the TFTP encrypted configuration setting is False, digest credentials may get sent in the clear. See "Disabling Encryption for the Phone Configuration Files" section for more information.


Some phone models do not support encrypted phone configuration files, as described in "Supported Phone Models" section. The phone model and protocol determines the method that the system uses to encrypt the configuration file. Supported methods rely on Cisco Unified CallManager functionality and a firmware load that supports encrypted configuration files. If you downgrade the phone firmware load to a version that does not support encrypted configuration files, the TFTP server offers an unencrypted configuration file that provides minimal configuration settings, and the phone may not perform as expected.

To ensure that you maintain the privacy of the key information, Cisco strongly recommends that you perform the tasks that are associated with encrypted phone configuration files in a secure environment.

Cisco Unified CallManager supports the following methods:

Manual Key Distribution

Symmetric Key Encryption with Phone Public Key

The information in the "Manual Key Distribution" and "Symmetric Key Encryption with Phone Public Key" sections assumes that you configured the cluster for Mixed Mode and that you enabled the TFTP Encrypted Config parameter in Cisco Unified CallManager Administration.

Manual Key Distribution


Tip For a list of phone models that support this method, see "Supported Phone Models" section.


With manual key distribution, a 128- or 256-bit symmetric key, which is stored in the Cisco Unified CallManager database, encrypts the phone configuration file after the phone resets. To determine the key size for your phone model, see "Supported Phone Models" section.

To encrypt the configuration file, the administrator can either manually enter the key into Cisco Unified CallManager Administration or prompt Cisco Unified CallManager Administration to generate the key in the Phone Configuration window. After the key exists in the database, the administrator or user must enter the key into the phone by accessing the user interface on the phone; the phone stores the key in flash as soon as you press the Accept softkey. After the key is entered, the phone requests an encrypted configuration file after it is reset. After the required tasks occur, the symmetric key uses RC4 or AES 128 encryption algorithms to encrypt the configuration file. To determine which phones use the RC4 or AES 128 encryption algorithms, see "Supported Phone Models" section.

When the phone contains the symmetric key, the phone always requests the encrypted configuration file. Cisco Unified CallManager downloads the encrypted configuration file to the phone, which the TFTP server signs. Not all phone types validate the signer of the configuration file; see "Supported Phone Models" section for more information.

The phone decrypts the file contents by using the symmetric key that is stored in flash. If decryption fails, the configuration file does not get applied to the phone.


Tip If the TFTP Encrypted Config setting gets disabled, administrators must remove the symmetric key from the phone GUI so that the phone requests an unencrypted configuration file the next time that it is reset.


Symmetric Key Encryption with Phone Public Key


Tip For a list of phone models that support this method, see "Supported Phone Models" section.

For more information about The Certificate Authority Proxy Function (CAPF), see "Certificate Authority Proxy Function Overview" section on page 6-2. The Certificate Authority Proxy Function (CAPF) authenticates Cisco Unified IP Phones to Cisco Unified Call Manager and issues phone certificates (LSCs)


If the phone contains a manufacturing-installed certificate (MIC) or a locally significant certificate (LSC), the phone contains a public and private key pair, which are used for PKI encryption.

If you are using this method for the first time, the phone compares the MD5 hash of the phone certificate in the configuration file to the MD5 hash of the LSC or MIC. If the phone does not identify a problem, the phone requests an encrypted configuration file from the TFTP server after the phone resets. If the phone identifies a problem, for example, the hash does not match, the phone does not contain a certificate, or the MD5 value is blank, the phone attempts to initiate a session with CAPF unless the CAPF authentication mode equals By Authentication String (in which case, you must manually enter the string). CAPF extracts the phone public key from the LSC or MIC, generates a MD5 hash, and stores the values for the public key and certificate hash in the Cisco Unified CallManager database. After the public key gets stored in the database, the phone resets and requests a new configuration file.

After the public key exists in the database and the phone resets, the symmetric key encryption process begins after the database notifies TFTP that the public key exists for the phone. The TFTP server generates a 128-bit symmetric key, which encrypts the configuration file with the Advanced Encryption Standard (AES) 128 encryption algorithm. Then, the phone public key encrypts the symmetric key, which it includes in the signed envelope header of the configuration file. The phone validates the file signing, and, if the signature is valid, the phone uses the private key from the LSC or MIC to decrypt the encrypted symmetric key. The symmetric key then decrypts the file contents.

Every time that you update the configuration file, the TFTP server automatically generates a new key to encrypt the file.


Tip For phones that support this encryption method, the phone uses the encryption configuration flag in the configuration file to determine whether to request an encrypted or unencrypted file. If the TFTP Encrypted Config setting is disabled, and Cisco Unified IP Phone models 7911, 7941, 7961, 7970, and 7971 request an encrypted file (.enc.sgn file), Cisco Unified CallManager sends a `file not found error' to the phone. The phone then requests an unencrypted, signed file (.sgn file).

If the TFTP Encrypted Config setting is enabled but the phone requests an unencrypted configuration file for some reason, the TFTP server offers an unencrypted file that contains minimal configuration settings. After the phone receives the minimum configuration, the phone can detect error conditions, such as key mismatch, and may start a session with CAPF to synchronize the phone public key with the Cisco Unified CallManager database. If the error condition is resolved, the phone requests an encrypted configuration file the next time that it resets.


Supported Phone Models

You can encrypt the phone configuration file for the following Cisco Unified IP Phone models:

Phone Model and Protocol
Encryption Method

Cisco Unified SIP IP Phone 7905 or 7912

Supports manual key distribution—
Encryption algorithm: RC4
Key size: 256 bits

File signing support: No

Cisco Unified SIP IP Phone 7940 or 7960

Supports manual key distribution—
Encryption algorithm: Advanced Encryption Standard (AES) 128
Key size: 128 bits

File signing support: These SIP phones receive signed, encrypted configuration files but ignore the signing information

Cisco Unified SIP IP Phone 7970 or 7971; Cisco Unified  SIP IP Phone 7941 or 7961; Cisco Unified  SIP IP Phone 7911;
Cisco Unified  SIP IP Phone 7906

Cisco Unified SCCP IP Phone 7970 or 7971; Cisco Unified  SCCP IP Phone 7941 or 7961; Cisco Unified  SCCP IP Phone 7911; Cisco Unified  SCCP IP Phone 7906

Supports symmetric key encryption with phone public key (PKI encryption)—
Encryption algorithm: AES 128
Key size: 128 bits

File signing support: Yes


Configuration Tips for Encrypted Configuration Files

Cisco recommends that you enable the TFTP Encrypted Config flag to secure confidential data in phone downloads. For phones that do not have PKI capabilities, you must also configure a symmetric key in Cisco Unified CallManager Administration and in the phone. If the symmetric key is missing from either the phone or Cisco Unified CallManager or if a mismatch occurs when the TFTP Encrypted Config flag is set, the phone cannot register.

Consider the following information when you configure encrypted configuration files in Cisco Unified CallManager Administration:

Only phones that support encrypted configuration files display the TFTP Encrypted Config flag in the phone security profile. You cannot configure encrypted configuration files for Cisco Unified IP SCCP Phone models 7905, 7912, 7940, and 7960 because these phones do not receive confidential data in the configuration file download.

Only SIP phone security profiles display the Enable Digest Authentication flag and the TFTP Exclude Digest Credentials in Configuration File flag.

The default setting for TFTP Encrypted Config specifies false (not checked). If you apply the default, non-secure profile to the phone, digest credentials and secured passwords get sent in the clear.

For Cisco Unified Phone models that use public key encryption, Cisco Unified CallManager does not require you to set the Device Security Mode to authenticated or encrypted to enable encrypted configuration files. Cisco Unified CallManager uses the CAPF process for downloading its public key during registration.

You may choose to download unencrypted configuration files to phones if you know your environment is secure or to avoid manually configuring symmetric keys for phones that are not PKI-enabled; however, Cisco does not recommend using this method.

For Cisco Unified IP SIP Phone models 7905, 7912, 7940, and 7960, Cisco Unified CallManager Administration provides a method of sending digest credentials to the phone that is easier, but less secure, than using an encrypted configuration file. This method, which is useful for initializing digest credentials because it does not require you to first configure a symmetric key and enter it on the phone, uses the TFTP Exclude Digest Credential in Configuration File setting.

With this method, you send the digest credentials to the phone in an unencrypted configuration file. After the credentials are in the phone, Cisco recommends that you keep the TFTP file encryption setting disabled and enable the TFTP Exclude Digest Credential in Configuration File flag on the corresponding security profile window, which will exclude digest credentials from future downloads.

After digest credentials exist in these phones and an incoming file does not contain digest credentials, the existing credentials remain in place. The digest credentials remain intact until the phone is factory reset or new credentials (including blanks) are received.

If you change digest credentials for a phone or end user, temporarily disable the Exclude Digest Credentials flag on the corresponding security profile window to download the new digest credentials to the phone.

Be aware that the TFTP Exclude Digest Credentials flag is valid for all Cisco Unified IP SIP Phone models. If the TFTP Exclude Digest Credentials flag is set for these phone models, Cisco Unified CallManager excludes the digest credentials, regardless whether the TFTP Encrypted Config flag is set. Be sure that the digest credentials are loaded on the phone at least once, or the phone may fail to register.

Encryption Configuration File Configuration Checklist

Use Table 7-1 to guide you through the configuration process for encrypted configuration files in Cisco  Unified CallManager Administration.

Table 7-1 Encryption Configuration File Configuration Checklist 

Configuration Steps
Related Procedures and Topics

Step 1 

Verify that the Cluster Security Mode is configured for Mixed Mode.

Configuring the Cisco CTL Client

Step 2 

In Cisco  Unified CallManager Administration, check the TFTP Encrypted Config check box in the Phone Security Profile. Be sure to apply the profile to the phone.

Configuration Tips for Encrypted Configuration Files

Enabling Phone Configuration File Encryption

Applying a Phone Security Profile, page 5-9

Step 3 

Determine which phones support manual key distribution and which phones support symmetric key encryption with phone public key (PKI encryption).

Supported Phone Models

Step 4 

If your phone supports manual key distribution, perform the manual key distribution tasks in Cisco Unified CallManager Administration.

Configuration Tips for Encrypted Configuration Files

Configuring Manual Key Distribution

Manual Key Distribution Configuration Settings

Step 5 

If your phone supports manual key distribution, enter the symmetric key on the phone; reset the phone.

Entering the Symmetric Key on the Phone

Step 6 

If your phone supports the method, symmetric key encryption with phone public key (PKI encryption), verify that a manufacture-installed certificate (MIC) or locally significant certificate (LSC) exists in the phone.

Verifying That an LSC or MIC Certificate Is Installed

Using the Certificate Authority Proxy Function, page 6-1

Enabling Phone Configuration File Encryption

The TFTP server queries the database when it builds the configuration file. If the phone security profile that is applied to the phone has the TFTP encrypted configuration flag set, the TFTP server builds an encrypted configuration file.

To access the TFTP encryption flag, find the appropriate device security profile for the phone, as described in "Finding a Phone Security Profile" section on page 5-2. Check the TFTP Encrypted Config check box to enable configuration file encryption.

Additional Information

See the "Related Topics" section

Configuring Manual Key Distribution

To determine whether your phone supports manual key distribution, see "Supported Phone Models" section.

The following procedure assumes that

The phone exists in the Cisco Unified CallManager database,

A compatible firmware load exists on the TFTP server,

You enabled the TFTP Encrypted Config parameter in Cisco Unified CallManager Administration.

Procedure


Step 1 Find the phone, as described in the Cisco Unified CallManager Administration Guide.

Step 2 After the Phone Configuration window displays, configure the manual key distribution settings that are described in Table 7-2. Once configured, the key should not be changed.

Step 3 Click Save.

Step 4 Enter the symmetric key on the phone and then reset the phone. For information on how to perform these tasks, refer to the phone administration guide that supports your phone model.


Additional Information

See the "Related Topics" section.

Manual Key Distribution Configuration Settings

Table 7-2 describes the manual distribution configuration settings in the Phone Configuration window.

For configuration tips, see "Configuration Tips for Encrypted Configuration Files" section.

For related information and procedures, see the "Related Topics" section.

Table 7-2 Manual Key Distribution Configuration Settings  

Setting
Description

Symmetric Key

Enter a string of hexadecimal characters that you want to use for the symmetric key. Valid characters include numerals, 0-9, and uppercase /lowercase characters, A-F (or a-f).

Make sure that you enter the correct bits for the key size; otherwise, Cisco Unified CallManager rejects the value. Cisco Unified CallManager supports the following key sizes:

Cisco Unified IP Phone models 7905 and 7912 (SIP Protocol only)—256 bits

Cisco Unified IP Phone models 7940 and 7960 (SIP Protocol only)—128 bits

After the key is configured, you should not change it.

Generate String

If you want Cisco Unified CallManager Administration to generate a hexadecimal string for you, click the Generate String button.

After the key is configured, you should not change it.

Revert to Database Value

If you want to restore the value that exists in the database, click this button.


Entering the Symmetric Key on the Phone

For information on how to enter the symmetric key on the phone after you configure manual key distribution in Cisco Unified CallManager Administration, refer to the Cisco Unified IP Phone administration guide that supports your phone model and protocol.

Verifying That an LSC or MIC Certificate Is Installed 

This procedure applies to Cisco Unified IP Phones that use PKI encryption.To determine whether your phone supports the method, symmetric key encryption with phone public key (PKI encryption), see the "Supported Phone Models" section.

The following procedure assumes that the phone exists in the Cisco Unified CallManager database and that you enabled the TFTP Encrypted Config parameter in Cisco Unified CallManager Administration.

Procedure


Step 1 Verify that a manufacture-installed certificate (MIC) or a locally significant certificate (LSC) exists in the phone.

Tip By choosing the Troubleshooting option in the CAPF settings section of the Phone Configuration window, you can verify that an LSC or MIC exists in the phone.The Delete and Troubleshoot options do not display if a certificate does not exist in the phone.

Step 2 If a certificate does not exist, install an LSC by using the CAPF functionality in the Phone Configuration window. For information on how to install a LSC, see the "Using the Certificate Authority Proxy Function" section on page 6-1.

Step 3 After you configure the CAPF settings, click Save.

Step 4 In the Phone Configuration window, click Reset. The phone requests an encrypted configuration file from the TFTP server after the phone resets


Additional Information

See the "Related Topics" section.

Verifying That the Phone Configuration File Is Encrypted

When the phone configuration file is encrypted, it uses the following format:

Cisco Unified IP Phone models 7905 and 7912 (SIP protocol only)—LD <MAC>.x

Cisco Unified IP Phone models 7940 and 7960 (SIP protocol only)—SIP<MAC>.cnf.enc.sgn

Cisco Unified IP Phone models 7911, 7941, 7961, 7970, and 7971 (SIP protocol only)—SIP<MAC>.cnf.xml.enc.sgn

Cisco Unified IP Phone models 7911, 7941, 7961, 7970, and 7971 (SCCP protocol only)—SEP<MAC>.cnf.xml.enc.sgn

Disabling Encryption for the Phone Configuration Files

To disable encryption for the phone configuration files, you must uncheck the TFTP Encrypted Config check box in the phone security profile in Cisco Unified CallManager Administration and save your change.


Warning If digest authentication is True for the SIP phone when the TFTP encrypted configuration setting is False, digest credentials may get sent in the clear.


After you update the setting, the encryption keys for the phone remain in the Cisco Unified CallManager database.

If Cisco Unified IP Phone models 7911, 7941, 7961, 7970, and 7971 request an encrypted file (.enc.sgn file) when the encrypted configuration setting gets updated to false, the phone requests a unencrypted, signed file (.sgn file).

If Cisco Unified IP SIP Phone models 7940/7960/7905/7912 request an encrypted file when the encryption configuration setting gets updated to false, administrators must remove the symmetric key from the phone GUI so that the phone requests an unencrypted configuration file the next time that it is reset.


Tip For Cisco Unified IP SIP Phone models 7940 and 7960, enter a 32-byte 0 as the key value for the symmetric key at the phone GUI to disable encryption. For Cisco Unified IP SIP Phone models 7905 and 7912, delete the symmetric key at the phone GUI to disable encryption. For information on how to perform these tasks, refer to the phone administration guide that supports your phone model.


Excluding Digest Credentials from Phone Configuration File Download

To exclude digest credentials from the configuration file that is sent to phones after the initial configuration, check the TFTP Exclude Digest Credentials in Configuration File check box for the security profile that is applied to the phone. Only Cisco Unified IP SIP Phone models 7905, 7912, 7940, and 7960 support this option. For other Cisco Unified IP SIP Phone models, please check the TFTP Encrypted Config check box to protect the configuration file sent from Cisco Unified CallManager to the phones.

You may need to uncheck this check box to update the configuration file for changes to digest credentials. See "Configuration Tips for Encrypted Configuration Files" section for more information

Additional Information

See the "Related Topics" section.

Where to Find More Information

Related Topics

Understanding Encryption of the Phone Configuration File

Supported Phone Models

Configuration Tips for Encrypted Configuration Files

Encryption Configuration File Configuration Checklist

Enabling Phone Configuration File Encryption

Configuring Manual Key Distribution

Manual Key Distribution Configuration Settings

Entering the Symmetric Key on the Phone

Verifying That an LSC or MIC Certificate Is Installed

Verifying That the Phone Configuration File Is Encrypted

Disabling Encryption for the Phone Configuration Files

Excluding Digest Credentials from Phone Configuration File Download

Using the Certificate Authority Proxy Function, page 6-1

Configuration Tips for Phone Security Profiles, page 5-1

Related Cisco documentation

Cisco Unified CallManager Bulk Administration Guide

Cisco Unified IP Phone administration guide for the phone model and protocol