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Table Of Contents
Advanced Encryption Standard (AES)
Supported Standards, MIBs, and RFCs
Configuring an AES Transform Set
Verifying IKE and IPSec Configurations
IPSec Transform Warning Message Example
IKE Encryption Warning Message Example
Running Configuration Warning Message Example
show crypto ipsec transform-set
Advanced Encryption Standard (AES)
Feature History
This document describes the Advanced Encryption Standard (AES) feature in Cisco IOS Release 12.2(13)T. It includes the following sections:
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Supported Standards, MIBs, and RFCs
Feature Overview
The Advanced Encryption Standard (AES) feature adds support for the new encryption standard AES, with Cipher Block Chaining (CBC) mode, to IP Security (IPSec).
The National Institute of Standards and Technology (NIST) has created AES, which is a new Federal Information Processing Standard (FIPS) publication that describes an encryption method. AES is a privacy transform for IPSec and Internet Key Exchange (IKE) and has been developed to replace the Data Encryption Standard (DES). AES is designed to be more secure than DES: AES offers a larger key size, while ensuring that the only known approach to decrypt a message is for an intruder to try every possible key. AES has a variable key length—the algorithim can specify a 128-bit key (the default), a 192-bit key, or a 256-bit key.
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Benefits
This feature, which adds support for AES encryption to IPSec, introduces a new level of security strength and speed that was not present in the virtual private network (VPN) marketplace.
AES is a cryptographic algorithim that protects sensitive, unclassified information.
Restrictions
Router Requirements
To enable AES, your router must support IPSec and long keys (the "k9" subsystem).
Hardware IPSec Encryption Incompatibility
AES cannot encrypt IPSec and IKE traffic if an acceleration card is present. This restriction will be lifted in a future release.
Related Documents
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Supported Platforms
For platforms supported in Cisco IOS Release 12.2(13)T, consult Cisco Feature Navigator.
Determining Platform Support Through Cisco Feature Navigator
Cisco IOS software is packaged in feature sets that are supported on specific platforms. To obtain updated information about platform support for this feature, access Cisco Feature Navigator. Cisco Feature Navigator dynamically updates the list of supported platforms as new platform support is added for the feature.
Cisco Feature Navigator is a web-based tool that enables you to determine which Cisco IOS software images support a specific set of features and which features are supported in a specific Cisco IOS image. You can search by feature or release. In the release section, you can compare releases side by side to display both the features unique to each software release and the features that releases in common.
Cisco Feature Navigator is updated regularly when major Cisco IOS software releases and technology releases occur. For the most current information, go to the Cisco Feature Navigator home page at the following URL:
Availability of Cisco IOS Software Images
Platform support for particular Cisco IOS software releases is dependent on the availability of the software images for those platforms. Software images for some platforms may be deferred, delayed, or changed without prior notice. For updated information about platform support and availability of software images for each Cisco IOS software release, refer to the online release notes or, if supported, Cisco Feature Navigator.
Supported Standards, MIBs, and RFCs
Standard
The AES Cipher Algorithim and Its Use with IPSec
MIBs
None
To obtain lists of supported MIBs by platform and Cisco IOS release, and to download MIB modules, go to the Cisco MIB website on Cisco.com at the following URL:
http://www.cisco.com/public/sw-center/netmgmt/cmtk/mibs.shtml
To locate and download MIBs for selected platforms, Cisco IOS releases, and feature sets, use Cisco MIB Locator found at the following URL:
http://tools.cisco.com/ITDIT/MIBS/servlet/index
If Cisco MIB Locator does not support the MIB information that you need, you can also obtain a list of supported MIBs and download MIBs from the Cisco MIBs page at the following URL:
http://www.cisco.com/public/sw-center/netmgmt/cmtk/mibs.shtml
To access Cisco MIB Locator, you must have an account on Cisco.com. If you have forgotten or lost your account information, send a blank e-mail to cco-locksmith@cisco.com. An automatic check will verify that your e-mail address is registered with Cisco.com. If the check is successful, account details with a new random password will be e-mailed to you. Qualified users can establish an account on Cisco.com by following the directions found at this URL:
RFC
None
Configuration Tasks
See the following sections for configuration tasks for the Advanced Encryption Standard (AES) feature. Each task in the list is identified as either required or optional.
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Configuring an IKE Policy
To configure an AES IKE policy, use the following commands beginning in global configuration mode:
Configuring an AES Transform Set
To define an AES transform set, use the following commands beginning in global configuration mode:
Step 1
Router(config)# crypto ipsec transform-set transform-set-name transform1 [transform2 [transform3]]
Defines a transform set and enters crypto transform configuration mode.
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Step 2
Router(cfg-crypto-tran)# mode [tunnel | transport]
(Optional) Changes the mode associated with the transform set. The mode setting is only applicable to traffic whose source and destination addresses are the IPSec peer addresses; it is ignored for all other traffic. (All other traffic is in tunnel mode only.)
Verifying IKE and IPSec Configurations
To view information about your IPSec configurations, use show crypto ipsec transform-set EXEC command.
Note
The following sample output from the show crypto ipsec transform-set command displays a warning message after a user tries to configure an IPSec transform that the hardware does not support:
Router# show crypto ipsec transform-setTransform set transform-1:{esp-256-aes esp-md5-hmac}will negotiate = {Tunnel, },WARNING:encryption hardware does not support transformesp-aes 256 within IPSec transform transform-1
To view information about your IKE configurations, use show crypto isakmp policy EXEC command.
Note
The following sample output from the show crypto isakmp policy command displays a warning message after a user tries to configure an IKE encryption method that the hardware does not support:
Router# show crypto isakmp policyProtection suite of priority 1encryption algorithm: AES - Advanced Encryption Standard (256 bit keys).WARNING:encryption hardware does not support the configuredencryption method for ISAKMP policy 1hash algorithm: Secure Hash Standardauthentication method: Pre-Shared KeyDiffie-Hellman group: #1 (768 bit)lifetime: 3600 seconds, no volume limit
Troubleshooting Tips
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Using the clear crypto sa command without parameters will clear out the full SA database, which will clear out active security sessions. You may also specify the peer, map, or entry keywords to clear out only a subset of the SA database. For more information, refer to the clear crypto sa command in the chapter "IPSec Network Security Commands" of the Cisco IOS Security Command Reference, Release 12.2.
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If a user enters an IPSec transform or an IKE encryption method that the hardware does not support, a warning message will be generated. These warning messages are also generated at boot time. When an encrypted card is inserted, the current configuration is scanned. If any IPSec transforms or IKE encryption methods are found that are not supported by the hardware, a warning message will be generated. For examples of these warning messages, see the section "Configuration Examples" immediately following this section.
Configuration Examples
This section provides the following configuration examples:
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AES Configuration Example
The following example is sample output from the show running-config command. In this example, the AES 256-bit key is enabled.
Current configuration : 1665 bytes!version 12.2service timestamps debug datetime msecservice timestamps log datetime msecno service password-encryption!hostname "Router1"!!ip subnet-zero!!no ip domain lookup!ip audit notify logip audit po max-events 100!crypto isakmp policy 10encryption aes 256authentication pre-sharelifetime 180crypto isakmp key cisco123 address 10.0.110.1!!crypto ipsec transform-set aesset esp-aes 256 esp-sha-hmacmode transport!crypto map aesmap 10 ipsec-isakmpset peer 10.0.110.1set transform-set aessetmatch address 120!!!voice call carrier capacity active!!!!!!!!!mta receive maximum-recipients 0!!!!interface FastEthernet0/0ip address 10.0.110.2 255.255.255.0ip nat outsideno ip route-cacheno ip mroute-cacheduplex autospeed autocrypto map aesmap!interface Serial0/0no ip addressshutdown!interface FastEthernet0/1ip address 11.0.110.1 255.255.255.0ip nat insideno ip route-cacheno ip mroute-cacheduplex autospeed auto!ip nat inside source list 110 interface FastEthernet0/0 overloadip classlessip route 0.0.0.0 0.0.0.0 10.5.1.1ip route 12.0.110.0 255.255.255.0 FastEthernet0/0ip route 172.18.124.0 255.255.255.0 10.5.1.1ip route 172.18.125.3 255.255.255.255 10.5.1.1ip http server!!access-list 110 deny ip 11.0.110.0 0.0.0.255 12.0.110.0 0.0.0.255access-list 110 permit ip 11.0.110.0 0.0.0.255 anyaccess-list 120 permit ip 11.0.110.0 0.0.0.255 12.0.110.0 0.0.0.255!route-map nonat permit 10match ip address 110!call rsvp-sync!!mgcp profile default!dial-peer cor custom!!!!!line con 0exec-timeout 0 0line aux 0line vty 0 4login!!endIPSec Transform Warning Message Example
The following example is a sample warning message that is displayed when a user enters an IPSec transform that the hardware does not support:
crypto ipsec transform transform-1 esp-aes 256 esp-md5WARNING:encryption hardware does not support transformesp-aes 256 within IPSec transform transform-1IKE Encryption Warning Message Example
The following example is a sample warning message that is displayed when a user enters an IKE encryption method that the hardware does not support:
encryption aes 256WARNING:encryption hardware does not support the configuredencryption method for ISAKMP policy 1Running Configuration Warning Message Example
The following example is a sample warning message that is displayed in the running configuration whenever a user tries to configure an IPSec transform or IKE encryption method that the hardware does not support:
crypto isakmp policy 1encryption aes 256! Policy disabled because algorithm not supported by encryption hardware!crypto ipsec transform-set transform-1 esp-aes 256 esp-md5-hmac! Disabled because transform not supported by encryption hardwareCommand Reference
This section documents modified commands. All other commands used with this feature are documented in the Cisco IOS Release 12.2 command reference publications.
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crypto ipsec transform-set
To define a transform set—an acceptable combination of security protocols and algorithms—use the crypto ipsec transform-set command in global configuration mode. To delete a transform set, use the no form of this command.
crypto ipsec transform-set transform-set-name transform1 [transform2 [transform3] [transform4]]
no crypto ipsec transform-set transform-set-name
Syntax Description
transform-set-name
Specifies the name of the transform set to create (or modify).
transform1
transform2
transform3
transform4Specifies up to four "transforms": one Authentication Header (AH), one Encapsulating Security Payload (ESP) encryption, one ESP authentication, and one compression. These transforms define the IP Security (IPSec) security protocols and algorithms. Accepted transform values are described in Table 1.
Defaults
No default behavior or values.
Command Modes
Global configuration.
This command invokes the crypto transform configuration mode.
Command History
11.3 T
This command was introduced.
12.2(13)T
The following transform options were added: esp-aes, esp-aes 192, and esp-aes 256.
Usage Guidelines
A transform set is an acceptable combination of security protocols, algorithms, and other settings to apply to IPSec protected traffic. During the IPSec security association (SA) negotiation, the peers agree to use a particular transform set when protecting a particular data flow.
You can configure multiple transform sets, and then specify one or more of these transform sets in a crypto map entry. The transform set defined in the crypto map entry is used in the IPSec SA negotiation to protect the data flows specified by that crypto map entry's access list. During the negotiation, the peers search for a transform set that is the same at both peers. When such a transform set is found, it is selected and will be applied to the protected traffic as part of both peer's IPSec SAs.
When IKE is not used to establish SAs, a single transform set must be used. The transform set is not negotiated.
Before a transform set can be included in a crypto map entry it must be defined using this command.
A transform set specifies one or two IPSec security protocols (either AH, ESP, or both) and specifies which algorithms to use with the selected security protocol. The AH and ESP IPSec security protocols are described in the section "IPSec Protocols: AH and ESP."
To define a transform set, you specify one to four "transforms"—each transform represents an IPSec security protocol (AH or ESP) plus the algorithm you want to use. When the particular transform set is used during negotiations for IPSec SAs, the entire transform set (the combination of protocols, algorithms, and other settings) must match a transform set at the remote peer.
In a transform set you could specify the AH protocol, the ESP protocol, or both. If you specify an ESP protocol in a transform set, you can specify just an ESP encryption transform or both an ESP encryption transform and an ESP authentication transform.
Table 1 lists the acceptable transform combination selections for the AH and ESP protocols.
Examples of acceptable transform combinations are as follows:
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The parser will prevent you from entering invalid combinations; for example, once you specify an AH transform it will not allow you to specify another AH transform for the current transform set.
IPSec Protocols: AH and ESP
Both the AH and ESP protocols implement security services for IPSec.
AH provides data authentication and antireplay services.
ESP provides packet encryption and optional data authentication and antireplay services.
ESP encapsulates the protected data—either a full IP datagram (or only the payload)—with an ESP header and an ESP trailer. AH is embedded in the protected data; it inserts an AH header immediately after the outer IP header and before the inner IP datagram or payload. Traffic that originates and terminates at the IPSec peers can be sent in either tunnel or transport mode; all other traffic is sent in tunnel mode. Tunnel mode encapsulates and protects a full IP datagram, while transport mode encapsulates/protects the payload of an IP datagram. For more information about modes, refer to the mode (IPSec) command description.
Selecting Appropriate Transforms
The following tips may help you select transforms that are appropriate for your situation:
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Note
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Suggested transform combinations follow:
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The Crypto Transform Configuration Mode
After you issue the crypto ipsec transform-set command, you are put into the crypto transform configuration mode. While in this mode, you can change the mode to tunnel or transport. (These are optional changes.) After you have made these changes, type exit to return to global configuration mode. For more information about these optional changes, refer to the match address (IPSec) and mode (IPSec) command descriptions.
Changing Existing Transforms
If one or more transforms are specified in the crypto ipsec transform-set command for an existing transform set, the specified transforms will replace the existing transforms for that transform set.
If you change a transform set definition, the change is only applied to crypto map entries that reference the transform set. The change will not be applied to existing SAs, but will be used in subsequent negotiations to establish new SAs. If you want the new settings to take effect sooner, you can clear all or part of the SA database by using the clear crypto sa command.
Examples
The following example defines two transform sets. The first transform set will be used with an IPSec peer that supports the newer ESP and AH protocols. The second transform set will be used with an IPSec peer that only supports the older transforms.
crypto ipsec transform-set newer esp-3des esp-sha-hmaccrypto ipsec transform-set older ah-rfc-1828 esp-rfc1829The following example is a sample warning message that is displayed when a user enters an IPSec transform that the hardware does not support:
crypto ipsec transform transform-1 esp-aes 256 esp-md5WARNING:encryption hardware does not support transformesp-aes 256 within IPSec transform transform-1Related Commands
encryption (IKE policy)
To specify the encryption algorithm within an Internet Key Exchange (IKE) policy, use the encryption command in Internet Security Association Key Management Protocol (ISAKMP) policy configuration mode. IKE policies define a set of parameters to be used during IKE negotiation. To reset the encryption algorithm to the default value, use the no form of this command.
encryption {des | 3des | aes | aes 192 | aes 256}
no encryption
Syntax Description
Defaults
The 56-bit DES-CBC encryption algorithm.
Command Modes
ISAKMP policy configuration
Command History
11.3 T
This command was introduced.
12.0(2)T
The 3des option was added.
12.2(13)T
The following keywords were added: aes, aes 192, and aes 256.
Usage Guidelines
Use this command to specify the encryption algorithm to be used in an IKE policy.
If a user enters an IKE encryption method that the hardware does not support, a warning message will be displayed immediately after the encryption command is entered.
Examples
The following example configures an IKE policy with the 3DES encryption algorithm (all other parameters are set to the defaults):
crypto isakmp policyencryption 3desexitThe following example is a sample warning message that is displayed when a user enters an IKE encryption method that the hardware does not support:
encryption aes 256WARNING:encryption hardware does not support the configuredencryption method for ISAKMP policy 1Related Commands
show crypto isakmp policy
To view the parameters for each Internet Key Exchange (IKE) policy, use the show crypto isakmp policy command in EXEC mode.
show crypto isakmp policy
Syntax Description
This command has no arguments or keywords.
Command Modes
EXEC
Command History
Examples
The following is sample output from the show crypto isakmp policy command, after two IKE policies have been configured (with priorities 15 and 20 respectively):
Router# show crypto isakmp policyProtection suite priority 15encryption algorithm: DES - Data Encryption Standard (56 bit keys)hash algorithm: Message Digest 5authentication method: Rivest-Shamir-Adleman SignatureDiffie-Hellman Group: #2 (1024 bit)lifetime: 5000 seconds, no volume limitProtection suite priority 20encryption algorithm: DES - Data Encryption Standard (56 bit keys)hash algorithm: Secure Hash Standardauthentication method: preshared KeyDiffie-Hellman Group: #1 (768 bit)lifetime: 10000 seconds, no volume limitDefault protection suiteencryption algorithm: DES - Data Encryption Standard (56 bit keys)hash algorithm: Secure Hash Standardauthentication method: Rivest-Shamir-Adleman SignatureDiffie-Hellman Group: #1 (768 bit)lifetime: 86400 seconds, no volume limit
Note
The following sample output from the show crypto isakmp policy command displays a warning message after a user tries to configure an IKE encryption method that the hardware does not support:
Router# show crypto isakmp policyProtection suite of priority 1encryption algorithm: AES - Advanced Encryption Standard (256 bit keys).WARNING:encryption hardware does not support the configuredencryption method for ISAKMP policy 1hash algorithm: Secure Hash Standardauthentication method: Pre-Shared KeyDiffie-Hellman group: #1 (768 bit)lifetime: 3600 seconds, no volume limitRelated Commands
show crypto ipsec transform-set
To view the configured transform sets, use the show crypto ipsec transform-set command in EXEC mode.
show crypto ipsec transform-set [tag transform-set-name]
Syntax Description
tag transform-set-name
(Optional) Displays only the transform sets with the specified transform-set-name.
Command Modes
EXEC
Command History
Examples
The following is sample output for the show crypto ipsec transform-set command:
Router# show crypto ipsec transform-setTransform set combined-des-sha: { esp-des esp-sha-hmac }will negotiate = { Tunnel, },Transform set combined-des-md5: { esp-des esp-md5-hmac }will negotiate = { Tunnel, },Transform set t1: { esp-des esp-md5-hmac }will negotiate = { Tunnel, },Transform set t100: { ah-sha-hmac }will negotiate = { Transport, },Transform set t2: { ah-sha-hmac }will negotiate = { Tunnel, },{ esp-des }will negotiate = { Tunnel, },The following configuration was in effect when the previous show crypto ipsec transform-set command was issued:
crypto ipsec transform-set combined-des-sha esp-des esp-sha-hmaccrypto ipsec transform-set combined-des-md5 esp-des esp-md5-hmaccrypto ipsec transform-set t1 esp-des esp-md5-hmaccrypto ipsec transform-set t100 ah-sha-hmacmode transportcrypto ipsec transform-set t2 ah-sha-hmac esp-desThe following sample output from the show crypto ipsec transform-set command displays a warning message after a user tries to configure an IPSec transform that the hardware does not support:
Router# show crypto ipsec transform-setTransform set transform-1:{ esp-256-aes esp-md5-hmac }will negotiate = { Tunnel, },WARNING:encryption hardware does not support transformesp-aes 256 within IPSec transform transform-1Glossary
DES—Data Encryption Standard. DES is used to encrypt packet data. Cisco IOS implements the mandatory 56-bit DES-CBC with Explicit IV. Cipher Block Chaining (CBC) requires an initialization vector (IV) to start encryption. The IV is explicitly given in the IPSec packet.
Cisco IOS also implements Triple DES (168-bit) encryption, depending on the software versions available for a specific platform. Triple DES (3DES) is a strong form of encryption that allows sensitive information to be transmitted over untrusted networks. It enables customers to utilize network layer encryption.
IKE—Internet Key Exchange. A hybrid protocol that implements Oakley key exchange and Skeme key exchange inside the ISAKMP framework. Although IKE can be used with other protocols, its initial implementation is with IPSec. IKE provides authentication of the IPSec peers, negotiates IPSec keys, and negotiates IPSec security associations.
IPSec—IP Security. A framework of open standards developed by the Internet Engineering Task Force (IETF). IPSec provides security for transmission of sensitive information over unprotected networks such as the Internet. IPSec acts at the network layer, protecting and authenticating IP packets between participating IPSec devices ("peers"), such as Cisco routers.
SA—security association. Security association is a description of how two or more entities will use security services in the context of a particular security protocol (AH or ESP) to communicate securely on behalf of a particular data flow. It includes such things as the transform and the shared secret keys to be used for protecting the traffic.
The IPSec security association is established either by IKE or by manual user configuration. Security associations are unidirectional and are unique per security protocol. So when security associations are established for IPSec, the security associations (for each protocol) for both directions are established at the same time.
When using IKE to establish the security associations for the data flow, the security associations are established when needed and expire after a period of time (or volume of traffic). If the security associations are manually established, they are established as soon as the necessary configuration is completed and do not expire.
transform—Transform is the list of operations done on a dataflow to provide data authentication, data confidentiality, and data compression. For example, one transform is the ESP protocol with the HMAC-MD5 authentication algorithm; another transform is the AH protocol with the 56-bit DES encryption algorithm and the ESP protocol with the HMAC-SHA authentication algorithm.
