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Key Determination Protocol in .NET Encoder qr-codes in .NET Key Determination Protocol

Key Determination Protocol generate, create qr-codes none for .net projects About QR Code IKE key determinat .net vs 2010 Denso QR Bar Code ion is a refinement of the Diffie-Hellman key exchange algorithm. Recall that Diffie-Hellman involves the following interaction between users A and B.

There is prior agreement on two global parameters: q, a large prime number; and a, a primitive root of q. A selects a random integer XA as its private key and transmits to B its public key A = aXA mod q. Similarly, B selects a random integer XB as its private key and transmits to A its public key B = aXB mod q.

Each side can now compute the secret session key: K = (. B) XA mod q = (. XB A). mod q = aXAXB mod q The Diffie-Hellman algorithm has two attractive features: Secret keys are created only when needed. There is no need to store secret keys for a long period of time, exposing them to increased vulnerability. The exchange requires no pre-existing infrastructure other than an agreement on the global parameters.

However, there are a number of weaknesses to Diffie-Hellman, as pointed out in [HUIT98]. It does not provide any information about the identities of the parties. It is subject to a man-in-the-middle attack, in which a third party C impersonates B while communicating with A and impersonates A while communicating with B.

Both A and B end up negotiating a key with C, which can then listen to and pass on traffic. The man-in-the-middle attack proceeds as 1. B sends his public key YB in a message addressed to A (see Figure 3.

13). 2. The enemy (E) intercepts this message.

E saves B s public key and sends a message to A that has B s User ID but E s public key YE. This message is. CHAPTER 8 / IP SECURITY sent in such a way that it appears as though it was sent from B s host system. A receives E s message and stores E s public key with B s User ID. Similarly, E sends a message to B with E s public key, purporting to come from A.

3. B computes a secret key K1 based on B s private key and YE. A computes a secret key K2 based on A s private key and YE.

E computes K1 using E s secret key XE and YB and computers K2 using XE and YA. 4. From now on, E is able to relay messages from A to B and from B to A, appropriately changing their encipherment en route in such a way that neither A nor B will know that they share their communication with E.

It is computationally intensive. As a result, it is vulnerable to a clogging attack, in which an opponent requests a high number of keys. The victim spends considerable computing resources doing useless modular exponentiation rather than real work.

IKE key determination is designed to retain the advantages of DiffieHellman, while countering its weaknesses. FEATURES OF IKE KEY DETERMINATION The IKE key determination algorithm is characterized by five important features: 1. It employs a mechanism known as cookies to thwart clogging attacks.

2. It enables the two parties to negotiate a group; this, in essence, specifies the global parameters of the Diffie-Hellman key exchange. 3.

It uses nonces to ensure against replay attacks. 4. It enables the exchange of Diffie-Hellman public key values.

5. It authenticates the Diffie-Hellman exchange to thwart man-in-the-middle attacks. We have already discussed Diffie-Hellman.

Let us look at the remainder of these elements in turn. First, consider the problem of clogging attacks. In this attack, an opponent forges the source address of a legitimate user and sends a public DiffieHellman key to the victim.

The victim then performs a modular exponentiation to compute the secret key. Repeated messages of this type can clog the victim s system with useless work. The cookie exchange requires that each side send a pseudorandom number, the cookie, in the initial message, which the other side acknowledges.

This acknowledgment must be repeated in the first message of the Diffie-Hellman key exchange. If the source address was forged, the opponent gets no answer. Thus, an opponent can only force a user to generate acknowledgments and not to perform the Diffie-Hellman calculation.

IKE mandates that cookie generation satisfy three basic requirements: 1. The cookie must depend on the specific parties. This prevents an attacker from obtaining a cookie using a real IP address and UDP port and then using it to swamp the victim with requests from randomly chosen IP addresses or ports.

2. It must not be possible for anyone other than the issuing entity to generate cookies that will be accepted by that entity. This implies that the issuing entity will use local secret information in the generation and subsequent verification of a.

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