Cryptographic Key Exchange Authentication
ABSTRACT
Key exchange (also known as "key establishment") is any method in cryptography by which cryptographic keys are exchanged between users, allowing use of a cryptographic algorithm. If sender and receiver wish to exchange encrypted messages, each must be equipped to encrypt messages to be sent and decrypt messages received. The nature of the equipping they require depends on the encryption technique they might use. If they use a code, both will require a copy of the same codebook. If they use a cipher, they will need appropriate keys. If the cipher is a symmetric key cipher, both will need a copy of the same key. If an asymmetric key cipher with the public/private key property, both will need the other's public key. The key exchange problem is how to exchange whatever keys or other information are needed so that no one else can obtain a copy. Historically, this required trusted couriers, diplomatic bags, or some other secure channel. With the advent of public key / private key cipher algorithms, the encrypting key could be made public, since no one without the decrypting Key could exchange the message. In 1976, Whitfield Diffie and Martin Hellman published a cryptographic protocol called the Diffie–Hellman key exchange (D–H) based on concepts developed by Hellman's PhD student Ralph Merkle. The protocol enables users to securely exchange secret keys even if an opponent is monitoring that communication channel. The D–H key exchange protocol, however, does not by itself address authentication (i.e. the problem of being sure of the actual identity of the person or 'entity' at the other end of the communication channel). Authentication is crucial when an opponent can both monitor and alter messages within the communication channel (aka man-in-the-middle or MITM attacks) and was addressed in the fourth section of the 1976 paper.
Existing System
Earlier password-based authentication systems transmitted a cryptographic hash of the password over a public channel which makes the hash value accessible to an attacker. When this is done, and it is very common, the attacker can work offline, rapidly testing possible passwords against the true password’s hash value. Studies have consistently shown that a large fraction of user-chosen passwords are readily guessed automatically.
Disadvantage:
The hash value accessible to an attacker.
The attacker can work offline, rapidly testing possible passwords against the true password’s hash value.
Proposed System:
Recent research advances in password-based authentication have allowed a client and a server mutually to authenticate with a password and meanwhile to establish a cryptographic key for secure communications after authentication. In general, current solutions for password based
authentication follow two models.
The first model, called PKI-based model, assumes that the client keeps the server’s public key in addition to share a password with the server. In this setting, the client can send the password to the server by public key encryption. Gong et al. were the first to present this kind of
authentication protocols with heuristic resistant to offline dictionary attacks, and Halevi and Krawczyk were the first to provide formal definitions and rigorous proofs of security for PKI-based model.
The second model is called password-only model. Bellovin and Merritt were the first to consider authentication based on password only, and introduced a set of so-called “encrypted key exchange” protocols, where the password is used as a secret key to encrypt random numbers for key exchange purpose. Formal models of security for the password-only authentication were first
given independently by Bellare et al. and Boyko et al.. Katz et al. were the first to give a password-only authentication protocol which is both practical and provably secure under standard cryptographic assumption.
Advantages:
Establish a cryptographic key for secure communications after authentication.
Problem Statement
In most of existing two-server PAKE protocols such as , it is assumed or implied that the discrete logarithm of g2 to the base g1 is unknown to anyone. Otherwise, their protocols are insecure. Our initialization can ensure that nobody is able to know the discrete logarithm of g2 to the base g1 unless the two servers collude. It is well known that the discrete logarithm problem is hard, and our model assumes that the two servers never collude.
The two secure channels are necessary for all two server PAKE protocols, where a password is split into two parts, which are securely distributed to the two servers, respectively, during registration. Although we refer to the concept of public key cryptosystem, the encryption key of one server should be unknown to another server and the client needs to remember a password only after registration.
Scope:
Our protocol provides explicit authentication in the sense that each party know that other parties have established their secret session keys correctly if the message authentication by the party succeeds. If the client C accepts the messages M4 and M5, the client C is confirmed that the servers S1 and S2 will compute their secret session keys with the client C correctly. If the server S1 accepts the message M6, the server S1 is confirmed that the client C has computed the same secret session key SK1, and the client C and the server S2 have established their secret session key correctly.
Architecture:
MODULES”
1. Diffie-Hellman Key Exchange Protocol .
2. ElGamal Encryption Scheme .
3. Initialization.
4. Registration.
Modules Description
1. Diffie-Hellman Key Exchange Protocol
The Diffie-Hellman key exchange protocol was invented by Diffie and Hellman in 1976. It was the first practical method for two users to establish a shared secret key over an unprotected communications channel. Although it is a non authenticated key exchange protocol, it provides the basis for a variety of authenticated protocols. Diffie-Hellman key exchange protocol was followed shortly afterward by RSA, the first practical public key cryptosystem.
2. ElGamal Encryption Scheme
Each user has a private key x
Each user has three public keys: prime modulus p, generator g and public Y = gxmod p
Security is based on the difficulty of DLP
Secure key size > 1024 bits ( today even 2048 bits)
Elgamal is quite slow, it is used mainly for key authentication protocols
3. Initialization
The two peer servers S1 and S2 jointly choose a cyclic group G of large prime order q with a generator g1 and a secure hash function H : {0; 1}*->Zq, which maps a message of arbitrary length into an l-bit integer, where l= log2 q. Next, S1 randomly chooses an integer s1 from Zq and S2 randomly chooses an integer s2 from Zq , and S1 and S2 exchange g1s1 and g1s2 . After that, S1 and S2 jointly publish public system parameters G; q; g1; g2;H where g2 = gs1s2 .
4. Registration
The two secure channels are necessary for all twoserver PAKE protocols, where a password is split into two parts, which are securely distributed to the two servers, respectively, during registration. Although we refer to the concept of public key cryptosystem, the encryption key of one server should be unknown to another server and the client needs to remember a password only after registration.
System Configuration:-
H/W System Configuration:-
Processor - Pentium –III
Speed - 1.1 Ghz
RAM - 256 MB (min)
Hard Disk - 20 GB
Floppy Drive - 1.44 MB
Key Board - Standard Windows Keyboard
Mouse - Two or Three Button Mouse
Monitor - SVGA
S/W System Configuration:-
v Operating System :Windows95/98/2000/XP
v Technology : JAVA, JFC(Swing),J2me
v Database : Mysql
v Database Connectivity : JDBC.
CONCLUSION
In this paper, we have presented a symmetric protocol for two-server password-only authentication and key exchange. Security analysis has shown that our protocol is secure against passive and active attacks in case that one of the two servers is compromised. Performance analysis has shown that our protocol is more efficient than existing symmetric and asymmetric two-server PAKE protocols.
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