Quick mode failed - Cisco Community
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In aggressive mode, the DH computation is performed parallel to authentication. A peer that is not yet authenticated can force processor intensive Diffie-Hellman computations on the other peer. When dealing with remote access, IKE has additional modes: Hybrid mode provides an alternative to IKE phase I, where the Security Gateway is allowed to authenticate using certificates and the client via some other means, such as SecurID. For more information on Hybrid mode, see: Office mode is an extension to the IKE protocol.
Office Mode is used to resolve routing issues between remote access clients and the VPN domain. During config mode, the remote access client requests an IP address from the Security Gateway.
The virtual adapter uses the assigned IP address. For further information, see: For this reason, IKE phase I is performed less frequently. The period between each renegotiation is known as the lifetime.
Generally, the shorter the lifetime, the more secure the IPsec tunnel at the cost of more processor intensive IKE negotiations. With longer lifetimes, future VPN connections can be set up more quickly.
The relevant properties are under the community set: Change from false default to true. Modify to include the required rekeying value default For this reason, the use of a single DH key may weaken the strength of subsequent keys. If one key is compromised, subsequent keys can be compromised with less effort. In cryptography, Perfect Forward Secrecy PFS refers to the condition in which the compromise of a current session key or long-term private key does not cause the compromise of earlier or subsequent keys.
Security Gateways meet this requirement with a PFS mode. The DH group used during PFS mode is configurable between groups 1, 2, 5 and 14, with group 2 bits being the default. Note - PFS mode is supported only between gateways, not between Security Gateways and remote access clients. Such a reduction can cause significant improvement in performance.
When identity protection is not needed, "Aggressive Mode" can be used to reduce round trips even further. Developer hints for doing these optimizations are included below.
It should also be noted that using public key encryption to authenticate an Aggressive Mode exchange will still provide identity protection. This protocol does not define its own DOI per se.
All of these attributes are mandatory and MUST be negotiated. In addition, it is possible to optionally negotiate a psuedo-random function "prf". There are currently no negotiable pseudo-random functions defined in this document. Private use attribute values can be used for prf negotiation between consenting parties.CHIT CHAT GWRM-FAILED RELATIONSHIPS -ONLINE DATING!WORKING WITH MAJOR BRANDS+ LIFE TRANSITIONS!!!
Other non- mandatory attributes are described in Appendix A. The Diffie-Hellman group MUST be either specified using a defined group description section 6 or by defining all attributes of a group section 5. Group attributes such as group type or prime-- see Appendix A MUST NOT be offered in conjunction with a previously defined group either a reserved group description or a private use description that is established after conclusion of a New Group Mode exchange.
The key is derived according to Appendix B. Exchanges There are two basic methods used to establish an authenticated key exchange: Main Mode and Aggressive Mode. Each generates authenticated keying material from an ephemeral Diffie-Hellman exchange.
Exchanges conform to standard ISAKMP payload syntax, attribute encoding, timeouts and retransmits of messages, and informational messages-- e. Except where otherwise noted, there are no requirements for ISAKMP payloads in any message to be in any particular order.
The Diffie-Hellman public value passed in a KE payload, in either a phase 1 or phase 2 exchange, MUST be the length of the negotiated Diffie-Hellman group enforced, if necessary, by pre-pending the value with zeros. The length of nonce payload MUST be between 8 and bytes inclusive. The first two messages negotiate policy; the next two exchange Diffie-Hellman public values and ancillary data e.
The authentication method negotiated as part of the initial ISAKMP exchange influences the composition of the payloads but not their purpose. The first two messages negotiate policy, exchange Diffie-Hellman public values and ancillary data necessary for the exchange, and identities. In addition the second message authenticates the responder. The third message authenticates the initiator and provides a proof of participation in the exchange. The graphic depictions of Aggressive Mode show the final payload in the clear; it need not be.
Exchanges in IKE are not open ended and have a fixed number of messages. Security Association negotiation is limited with Aggressive Mode. Due to message construction requirements the group in which the Diffie- Hellman exchange is performed cannot be negotiated.
In addition, different authentication methods may further constrain attribute negotiation. For example, authentication with public key encryption cannot be negotiated and when using the revised method of public key encryption for authentication the cipher and hash cannot be negotiated.
For situations where the rich attribute negotiation capabilities of IKE are required Main Mode may be required. This document does not proscribe such behavior on offers in phase 2 exchanges. There is no limit on the number of offers the initiator may send to the responder but conformant implementations MAY choose to limit the number of offers it will inspect for performance reasons.
During security association negotiation, initiators present offers for potential security associations to responders. If the initiator of an exchange notices that attribute values have changed or attributes have been added or deleted from an offer made, that response MUST be rejected. Four different authentication methods are allowed with either Main Mode or Aggressive Mode-- digital signature, two forms of authentication with public key encryption, or pre-shared key.
The values of 0, 1, and 2 above are represented by a single octet. As mentioned above, the negotiated authentication method influences the content and use of messages for Phase 1 Modes, but not their intent. When using public keys for authentication, the Phase 1 exchange can be accomplished either by using signatures or by using public key encryption if the algorithm supports it.
Following are Phase 1 exchanges with different authentication options. Main Mode with signature authentication is described as follows: However, this can be overridden for construction of the signature if the signature algorithm is tied to a particular hash algorithm e. The negotiated prf and hash function would continue to be used for all other prescribed pseudo- random functions. Since the hash algorithm used is already known there is no need to encode its OID into the signature.
One or more certificate payloads MAY be optionally passed. Each party's ability to reconstruct a hash proving that the other party decrypted the nonce authenticates the exchange.
In order to perform the public key encryption, the initiator must already have the responder's public key. In the case where the responder has multiple public keys, a hash of the certificate the initiator is using to encrypt the ancillary information is passed as part of the third message. In this way the responder can determine which corresponding private key to use to decrypt the encrypted payloads and identity protection is retained. In addition to the nonce, the identities of the parties IDii and IDir are also encrypted with the other party's public key.
If the authentication method is public key encryption, the nonce and identity payloads MUST be encrypted with the public key of the other party. Only the body of the payloads are encrypted, the payload headers are left in the clear. When using encryption for authentication, Main Mode is defined as follows. The payload length is the length of the entire encrypted payload plus header.
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The PKCS 1 encoding allows for determination of the actual length of the cleartext payload upon decryption. Using encryption for authentication provides for a plausably deniable exchange.
There is no proof as with a digital signature that the conversation ever took place since each party can completely reconstruct both sides of the exchange. In addition, security is added to secret generation since an attacker would have to successfully break not only the Diffie-Hellman exchange but also both RSA encryptions.
Note that, unlike other authentication methods, authentication with public key encryption allows for identity protection with Aggressive Mode. Unfortunately, this is at the cost of 4 public key operations-- two public key encryptions and two private key decryptions. This authentication mode retains the advantages of authentication using public key encryption but does so with half the public key operations.
In this mode, the nonce is still encrypted using the public key of the peer, however the peer's identity and the certificate if it is sent is encrypted using the negotiated symmetric encryption algorithm from the SA payload with a key derived from the nonce. This solution adds minimal complexity and state yet saves two costly public key operations on each side. In addition, the Key Exchange payload is also encrypted using the same derived key.
RFC - The Internet Key Exchange (IKE)
This provides additional protection against cryptanalysis of the Diffie-Hellman exchange. As with the public key encryption method of authentication section 5. In addition, the initiator my optionally send a certificate payload to provide the responder with a public key with which to respond. When using the revised encryption mode for authentication, Main Mode is defined as follows.
Only the body of the payloads are encrypted in both public key and symmetric operationsthe generic payload headers are left in the clear. The payload length includes that added to perform encryption.
The symmetric cipher keys are derived from the decrypted nonces as follows. The length of the value 0 in the computation of K1 is a single octet.
Save the requirements on the location of the optional HASH payload and the mandatory nonce payload there are no further payload requirements. Republished with permission from WatchGuard Technologies, Inc. LiveSecurity readers have responded enthusiastically to our articles specifically for beginners, but we're not about to neglect veteran network administrators, either.
We think this lengthy how-to provides valuable reference material intermediate and advanced users will want to save -- or anyone using Virtual Private Networks. But we'd love to know what you think. Feel free to sound off at lsseditor watchguard. Those organizations know that daily operations are more complicated when staff must contend with several different administrative interfaces.
Besides, discounts follow volume, so at least initially most organizations operate networks with one brand of router, firewall or VPN security gateway. But today, savvy organizations must plan ahead, anticipating a time when they will acquire a company, or be acquired, or when they must enter a business-to-business relationship with companies having different network equipment.
In those cases, tasks like building an IPsec VPN are not so simple, even when all the equipment involved implements accepted Internet Standards and has met desired levels of certification. With some careful planning and a good understanding of the IPsec capabilities of the VPN security gateways involved with firewalls, you can incorporate your Firebox into a multi-vendor VPN. Save yourself a lot of grief and test connectivity before you attempt to create VPN tunnels.
You need to document everything you can about the topology of the network and the configuration of your security gateways, including your Firebox with trusted, external and optional network addressingdefault routes, DNS and NTP servers. Begin by creating an overall topology map, one that illustrates all the networks that are to be connected using VPN tunnels. Identify the networks by domain name, IP address and subnet mask. These planning sheets will come in handy as you create a Security Policy Database on your Firebox and the remote security gateway.
IKE is also used for peer security gateway authentication.