is one of the dominant peer to peer network used to share content over Internet. It is claimed to house more than 99% of copyright infringing contents.


provides a mean of verifying the identity of principals (e.g. a workstation user or a network server) on an open, unprotected network. This is accomplished without relying on authentication by the host operating system, without basing trust on host addresses, without requiring physical security of all the hosts on the network and under the assumption that packets traveling along the network can be read, modified and inserted at will.
Kerberos is a third party trusted host authentication system that uses secret key ciphers for encryption and authentication. It does not produce digital signatures, authenticate ownership of documents or provide for future third party verification of documents. The authentication server is a trusted third party central system that knows every user, system, client and server application and their associated passwords.The current version is 5.  The security model of Windows 2000 supports Kerberos

KERCKHOFFS (Principle of)

This French XIXth century cryptographer created one of the founding principles of cryptography. According to him, the strength of a cryptosystem must not rely on the fact that the attacker does not know inner working of the algorithm. This means that the secret relies on the keys rather than on the algorithm.

This is one of the most important law of security.  To often, the security of a system relies on the secrecy of its algorithm.  Proper design of cryptosystem relies on this principle.  The design is published.  Then, the cryptographic community attempts to break it.  After many years of iterative work, the algorithm may be considered as secure.

Key Escrow

is a Key recoverytechnique. It relies on the storage of private keys by the governments or by designated private entities.

Key management

is the action to generate, transmit, and store secret and public keys. All cryptosystems need key management.

Key recovery system

guarantees law enforcement agencies timely access, without user notice, to the plaintext of encrypted communication. Its essential elements are:

    • A mechanism external to the primary means of encryption and decryption, by which a third party can obtain covert access to the plaintext of encrypted data.
    • The existence of a highly sensitive secret key (or collection of keys) that must be secured for an extended period.

Key Escrow  is such a mechanism.


see Kleline


is a French start-up that handles electronic transactions. It has the role of authentication authority. Customers and merchants are registered by Kleline. When a customer orders something in a mall, the merchant sends a till ticket to Kleline. Kleline sends this till ticket to the customer for signature. Once the signed ticket is returned to Kleline, Kleline issues the corresponding cash voucher to the merchant who can then deliver the product. The system Klebox uses 512 bit keys with the customer, and 1024 bit keys with the merchant.
Following merchants used Klebox: 3 Suisses, Dégriftour, Météo France, AFP.

KNAPSACK cryptosystem

is a public key cryptosystem based on the subset-sum problems. Given a number of objects of given weights from a large set such as the sum of the weights is equal to a predefined weight.
The system has been cracked for all versions except CHAUM and RIVEST’s ones.

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