ZyXEL Communications PLA-470 V2 - V3.0.5 Instalační příručka stáhnout pdf (Strana 87)

Mixed-Key Cryptography

Mixed-key cryptography, illustrated in Figure 4.6, uses the two aforementioned

techniques, i.e. symmetric-key cryptography and public-key cryptography. It com-

bines in this way the advantages of the two techniques while avoiding their disad-

vantages. Their disadvantages are well known, as symmetric-key cryptography does

not enable secured key transmissions and the public-key cryptography uses algo-

rithms that are too slow for data encryption.

When sending data, the sender encrypts the message with a secret key using a

symmetric-key algorithm. At the same time, this secret key is encrypted by the

sender with the public key generated by the recipient. The secret key can be transmit-

ted reliably and securely in this way.

Encrypting a secret key on 128 bits using a public key algorithm is very fast con-

sidering the size of this key. It is then transmitted to the recipient. The recipient

decrypts the secret key of the sender with his or her private key. The recipient now

has the uncoded secret key and can use it to decrypt the message.

Another advantage of this technique is that it is no longer necessary to encrypt a

message several times when it is intended for several recipients. As the encrypted

message is transmitted with its secret key, all you have to do is encrypt this key with

the various public keys of the recipients.

Electronic Signatures

The electronic signature is used to identify and authenticate the data sender. It is also

used to check that the data transmitted over the network has not been changed.

68 Security

Figure 4.6 Mixed-key cryptography

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ZyXEL Communications PLA-470 V2 - V3.0.5 Instalační příručka Strana 87