ZyXEL Communications PLA-470 V2 - V3.0.5 Guía de instalación descargar pdf (Pagina 86)

As with symmetric-key cryptography, various algorithms are used, in particular

RSA (Rivest, Shamir, Adelman) and Diffie-Hellman.

Though this technique makes it possible to compensate for the shortcomings of

symmetric cryptography, i.e., key transmission, it is much slower than symmetric

cryptography.

RSA (Rivest, Shamir, Adelman)

This public-key algorithm is named after its three inventors, Ron Rivest, Adi

Shamir, and Leonard Adelman. RSA, which was created in 1977, was the first pub-

lic-key algorithm. Its strength resides in the supposed difficulty to factorize large

numbers.

RSA uses keys with a variable length (512, 1,024, and 2,048 bits). 512-bit keys

are not considered to be very reliable. RSA is still used nowadays by SSL, IPsec, and

many other applications. RSA is deemed reliable with reasonable key lengths until

future mathematical advances are made.

Diffie-Hellman

This other public-key algorithm, which was invented by Whitfield Diffie and Mar-

tin Hellman, was the first encryption algorithm put on the market. As it is vulnera-

ble to some types of attacks, it is preferably used with the help of a certification

authority.

One of its characteristics is to enable two people to share a secret without

requiring a safe transmission. It is still used today.

Overview of Network Security Issues 67

Figure 4.5 Public-key cryptography

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ZyXEL Communications PLA-470 V2 - V3.0.5 Guía de instalación Pagina 86