Page 111 - DCAP309_INFORMATION_SECURITY_AND_PRIVACY

Unit 8: Cryptography and Encryption

A key in cryptography is a long sequence of bits used by encryption/decryption algorithms. Notes

Example: The following represents a hypothetical 40-bit key:
00001010 01101001 10011110 00011100 01010101
A given encryption algorithm takes the original message, and a key, and alters the original
message mathematically based on the key’s bits to create a new encrypted message. Likewise, a
decryption algorithm takes an encrypted message and restores it to its original form using one
or more keys.

When a user encodes a file, another user cannot decode and read the file without the decryption
key. Adding a digital signature, a form of personal authentication, ensures the integrity of the
original message.
To encode plaintext, an encryption key is used to impose an encryption algorithm onto the data.
To decode cipher, a user must possess the appropriate decryption key.

A decryption key consists of a random string of numbers, from 40 through 2,000 bits in length.
The key imposes a decryption algorithm onto the data. This decryption algorithm reverses the
encryption algorithm, returning the data to plaintext. The longer the encryption key is, the
more difficult it is to decode. For a 40-bit encryption key, over one trillion possible decryption
keys exist.
There are two primary approaches to encryption: symmetric and public-key. Symmetric
encryption is the most common type of encryption and uses the same key for encoding and
decoding data. Public-key encryption uses two different keys, a public key and a private key.
One key encodes the message and the other decodes it. The public key is widely distributed
while the private key is secret.
Aside from key length and encryption approach, other factors and variables impact the success
of a cryptographic system.

Example: Different cipher modes, in coordination with initialization vectors and salt
values, can be used to modify the encryption method.
Cipher modes define the method in which data is encrypted. The stream cipher mode encodes
data one bit at a time. The block cipher mode encodes data one block at a time. Although block
cipher tends to execute more slowly than stream cipher.

Task Discuss the use of Secure Sockets Layer.

Did u know? What is session key?
Symmetric encryption is the most common type of encryption and uses the same key for
encoding and decoding data. This key is known as a session key.
Self Assessment

Fill in the blanks:
1. ........................... cryptosystems use the same key for the functions of both encryption and
decryption.

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