AES and 3-DES Encryption Support for SNMP Version 3

The AES and 3-DES Encryption Support for SNMP Version 3 feature enhances the encryption capabilities of Simple Network Management Protocol (SNMP) Version 3.

The AES and 3-DES Encryption Support for SNMP Version 3 feature adds Advanced Encryption Standard (AES) 128-bit encryption in compliance with RFC 3826.

Prerequisites for AES and 3-DES Encryption Support for SNMP Version 3

  • The network management station (NMS) must support Simple Network Management Protocol (SNMP) Version 3 to be able to use this feature.

  • This feature is available only in Cisco software images that support encryption algorithms.

  • It is important to understand the SNMP architecture and the terminology of the architecture to understand the security model used and how the security model interacts with the other subsystems in the architecture.

Information About AES and 3-DES Encryption Support for SNMP Version 3

Cipher Block Chaining/Data Encryption Standard (CBC-DES) is the privacy protocol for the AES and 3-DES Encryption Support for SNMP Version 3 feature. Prior to the introduction of this feature, only DES was supported (as per RFC 3414). This feature adds support for AES-128 (as per RFC 3826) and AES-192, and AES-256 and 3-DES (as per CISCO-SNMP-USM-OIDS-MIB). RFC 3826 extensions have been included in the SNMP-USM-AES-MIB. In addition, Cisco-specific extensions to support Triple-Data Encryption Algorithm (3-DES) and AES 192-bit and 256-bit encryption have been added to the CISCO-SNMP-USM-MIB. Additional information can be found in the Internet-Draft titled Extension to the User-Based Security Model (USM) to Support Triple-DES EDE in "Outside" CBC Mode .

The encryption key sizes are:

  • AES encryption uses the Cipher Feedback (CFB) mode with encryption key sizes of 128, 192, or 256 bits.

  • 3-DES encryption uses the 168-bit key size for encryption.

The AES Cipher Algorithm in the Simple Network Management Protocol (SNMP) User-based Security Model (USM) draft describes the use of AES with 128-bit key size. However, the other options are also implemented with the extension to use the USM. There is no standard for generating localized keys for 192- or 256-bit size keys for AES or for 168-bit size key for 3-DES. There is no authentication protocol available for longer keys.

Support for SNMP Version 3 USM is compliant with RFC 3414, which defines DES as the only required method of message encryption for SNMP Version 3 authPriv mode.

The AES and 3-DES Encryption Support for SNMP Version 3 feature supports the selection of privacy protocols through the CLI and the MIB. A new standard MIB, SNMP-USM-AES-MIB, provides support for the 128-bit key in the Advanced Encryption Standard (AES). The extended options of AES with 192- or 256-bit keys and 3-DES are supported as extensions to the SNMP-USM-MIB in the Cisco-specific MIB—CISCO-SNMP-USM-EXT-MIB.

AES and 3-DES Encryption Support Overview

Each Simple Network Management Protocol (SNMP) entity includes a single SNMP engine. An SNMP engine implements functions for sending and receiving messages, authenticating and encrypting/decrypting messages, and controlling access to managed objects. These functions are provided as services to one or more applications that are configured with the SNMP engine to form an SNMP entity. The RFC 3411 describes the SNMP engine as composed of the following components:

  • Dispatcher

  • Message Processing Subsystem

  • Security Subsystem

  • Access Control Subsystem

Cipher Block Chaining/Data Encryption Standard (CBC-DES) is the privacy protocol for the AES and 3-DES Encryption Support for SNMP Version 3 feature. Prior to the introduction of this feature, only DES was supported (as per RFC 3414). This feature adds support for AES-128 (as per RFC 3826) and AES-192, AES-256 and 3-DES (as per CISCO-SNMP-USM-OIDS-MIB). RFC 3826 extensions have been included in the SNMP-USM-AES-MIB. In addition, Cisco-specific extensions to support Triple-Data Encryption Algorithm (3-DES) and AES 192-bit and 256-bit encryption have been added to the CISCO-SNMP-USM-MIB. Additional information can be found in the Internet-Draft titled Extension to the User-Based Security Model (USM) to Support Triple-DES EDE in "Outside" CBC Mode .

The encryption key sizes are:

  • AES encryption uses the Cipher Feedback (CFB) mode with encryption key sizes of 128, 192, or 256 bits.

  • 3-DES encryption uses the 168-bit key size for encryption.

The AES Cipher Algorithm in the Simple Network Management Protocol (SNMP) User-based Security Model (USM) draft describes the use of AES with 128-bit key size. However, the other options are also implemented with the extension to use the USM. There is no standard for generating localized keys for 192- or 256-bit size keys for AES or for 168-bit size key for 3-DES. There is no authentication protocol available for longer keys.

Support for SNMP Version 3 USM is compliant with RFC 3414, which defines DES as the only required method of message encryption for SNMP Version 3 authPriv mode.

The AES and 3-DES Encryption Support for SNMP Version 3 feature supports the selection of privacy protocols through the CLI and the MIB. A new standard MIB, SNMP-USM-AES-MIB, provides support for the 128-bit key in the Advanced Encryption Standard (AES). The extended options of AES with 192- or 256-bit keys and 3-DES are supported as extensions to the SNMP-USM-MIB in the Cisco-specific MIB—CISCO-SNMP-USM-EXT-MIB.

Encryption Key Support

MIB Support

How to Configure AES and 3-DES Encryption Support for SNMP Version 3

Adding a New User to an SNMP Group

SUMMARY STEPS

  1. enable
  2. configure terminal
  3. snmp-server user username group-name [remote host [udp-port port ]] {v1 | v2c | v3 [encrypted ] [auth {md5 | sha } auth-password ]} [priv {des | 3des | aes {128 | 192 |256} } privpassword ] [access [ipv6 nacl ] {acl-number | acl-name }]
  4. exit

DETAILED STEPS

  Command or Action Purpose
Step 1

enable

Example:


Device> enable

Enters privileged EXEC mode.

  • Enter your password when prompted.
Step 2

configure terminal

Example:


Device# configure terminal

Enters global configuration mode.

Step 3

snmp-server user username group-name [remote host [udp-port port ]] {v1 | v2c | v3 [encrypted ] [auth {md5 | sha } auth-password ]} [priv {des | 3des | aes {128 | 192 |256} } privpassword ] [access [ipv6 nacl ] {acl-number | acl-name }]

Example:


Device(config)# snmp-server user new-user new-group v3 auth md5 secureone priv aes 128 privatetwo access 2

Adds an SNMP user, specifies a group to which the user belongs, specifies the authorization algorithm to be used (MD5 or SHA), specifies the privacy algorithm to be used (DES, 3-DES, AES, AES-192, or AES-256), and specifies the password to be associated with this privacy protocol.

Step 4

exit

Example:

Device(config)# exit
Exits global configuration mode and returns to privileged EXEC mode.

Verifying the SNMP User Configuration

To display information about the configured characteristics of Simple Network Management Protocol (SNMP) users, use the show snmp user command in privileged EXEC mode.


Note
The show snmp user command displays all the users configured on the device. However, unlike other SNMP configurations, the snmp-server user command will not appear on the “show running” output.

SUMMARY STEPS

  1. enable
  2. show snmp user [username ]

DETAILED STEPS

Step 1

enable

Example:


Device> enable

Enters privileged EXEC mode. Enter your password when prompted.

Step 2

show snmp user [username ]

Example:


Device# show snmp user abcd
 
User name: abcd 
Engine ID: 00000009020000000C025808 
storage-type: nonvolatile       active access-list: 10
Rowstatus: active 
Authentication Protocol: MD5
Privacy protocol: 3DES 
Group name: VacmGroupName 
Group name: VacmGroupName

The above example specifies the username as abcd, the engine ID string as 00000009020000000C025808, and the storage type as nonvolatile:

Additional References

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