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21 Νοε 2013 (πριν από 4 χρόνια και 6 μήνες)

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4. Clarify the basic concepts of PKI (Public Key Infrastructure).

A PKI (public key infrastructure) enables users in an unsecured network such as the
Internet to securely and privately exchange data, records, or money through the use of a public
and a pr
ivate cryptographic key pair that is obtained and shared through a trusted authority. The
public key infrastructure provides for a digital certificate that can identify an individual or an
organization and directory service that can store and, when necessa
ry, revoke the certificates.
Although the components of a PKI are generally understood, a number of different vendor
approaches and services are emerging. Meanwhile, an Internet standard for PKI is being worked

The public key infrastructure assumes t
he use of public key cryptography, which is the
most common method on the Internet for authenticating a message sender or encrypting a
message. Traditional cryptography has usually involved the creation and sharing of a secret key
for the encryption and de
cryption of messages. This secret or private key system has the
significant flaw that if the key is discovered or intercepted by someone else, messages can easily
be decrypted. For this reason, public key cryptography and the public key infrastructure is t
preferred approach on the Internet. (The private key system is sometimes known as symmetric
cryptography and the public key system as asymmetric cryptography.)

A public key infrastructure consists of:

A certificate authority (CA) that issues and ver
ifies digital certificate. A certificate includes
the public key or information about the public key.

A registration authority (RA) that acts as the verifier for the certificate authority before a
digital certificate is issued to a requestor.

One or more

directories where the certificates (with their public keys) are held

A certificate management system

PKI provides three primary services:


The assurance to the recipient that the sender is who the sender claims to be.
This is achieved by

means of digital signature.


The assurance to the recipient that data has not been altered during Internet
communication. This is achieved by means of digital signature.


The assurance to a sender and recipient that no one ca
n read a particular
piece of data except the intended recipient. This is achieved by means of encryption.

Who Provides the Infrastructure?

A number of products are offered that enable a company or group of companies to implement
a PKI. The acceleration o
f e
commerce and business
business commerce over the Internet has
increased the demand for PKI solutions. Related ideas are the virtual private network (VPN) and
the IP Security (IPsec) standard. Among PKI leaders are:

RSA, which has developed the mai
n algorithms used by PKI vendors

Verisign, which acts as a certificate authority and sells software that allows a company to
create its own certificate authorities

GTE CyberTrust, which provides a PKI implementation methodology and consultation
service t
hat it plans to vend to other companies for a fixed price

Xcert, whose Web Sentry product that checks the revocation status of certificates on a server,
using the Online Certificate Status Protocol (OCSP)

Netscape, whose Directory Server product is said
to support 50 million objects and process
5,000 queries a second; Secure E
Commerce, which allows a company or extranet manager
to manage digital certificates; and Meta
Directory, which can connect all corporate
directories into a single directory for secu
rity management.