Subject | Computer and Network Security |
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NU Year | Set: 1.(b) Marks: 2 Year: 2017 |

Symmetric encryption is
a form of computerized cryptography using a singular encryption key to guise an
electronic message. Its data conversion uses a mathematical algorithm along
with a secret key, which results in the inability to make sense out of a
message. Symmetric encryption is a two-way algorithm because the mathematical
algorithm is reversed when decrypting the message along with using the same
secret key.

Symmetric encryption is
also known as private-key encryption and secure-key encryption.

Asymmetric Encryption
is a form of Encryption where keys come in pairs. What one key
encrypts, only the other can decrypt.

Frequently (but not
necessarily), the keys are interchangeable, in the sense that if key A encrypts
a message, then B can decrypt it, and if key B encrypts a message, then key A
can decrypt it. While common, this property is not essential to asymmetric
encryption.

Asymmetric Encryption
is also known as Public Key Cryptography, since users typically create a
matching key pair, and make one public while keeping the other secret.

Users can
"sign" messages by encrypting them with their private keys. This is
effective since any message recipient can verify that the user's public key can
decrypt the message, and thus prove that the user's secret key was used to
encrypt it. If the user's secret key is, in fact, secret, then it follows that
the user, and not some impostor, really sent the message.

Users can send secret
messages by encrypting a message with the recipient's public key. In this case,
only the intended recipient can decrypt the message, since only that user
should have access to the required secret key.

The key to successful
use of Asymmetric Encryption is a Key Management system, which
implements a Public Key Infrastructure. Without this, it is difficult to
establish the reliability of public keys, or even to conveniently find suitable
ones.