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Unit 12: Security Solution

Aside from key length and encryption approach, other factors and variables impact the success of Notes
a cryptographic system. For example, different cipher modes, in coordination with initialization
vectors and salt values, can be used to modify the encryption method. Cipher modes defi ne 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.

12.2 How Encryption Works?

Encryption or encoding information helps prevent it by unauthorized user. Both the sender and
receiver have to know what set of rules (called cipher) was used to transform original information
in to its cipher text (code) form – cipher text.
Simple cipher might to be add an arbitrary number of characters to all the character in the
message.

Example: Say “Udupa”—is the original name
“Irida”—is the cipher text (arbitrary no. chosen is “!2”)
1 2 3 4 5 6 7 8 9 10 11 12

A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
The decrypt (decode) “Irido”, First, start counting letter “I” & replace the letter “I” in the coded
text with the letter which comes after the count 12. So, “I” is replaced by “U”, similarly for other
letters to get back the original name “udupa” It is clear from the above example that both the
sender and recipient has to know the arbitrary number chosen in order to encrypt & decrypt the
original message.
Basically encryption has two parts:
1. Algorithm-a cryptographic algorithm is mathematical function.
2. Key-string of digit.
In the above example counting forward (to decrypt) & backward (encrypt) is the algorithm part.
Key used is 12.
Cryptographic algorithm combines the plain text or other intelligible information with a string
of digit called key’s to produce unintelligible cipher text. But some encryption algorithms does
not use a key.
Encryption on key-based system offers two important advantages.

1. It is difficult to come up with new-algorithm each time to communicate privately with
new correspondent. By using a key, same algorithm can be used with many people with
different key for each correspondent.
2. It is easy to change the key in case of any mal-practice rather than going for a new
algorithm.
The number of keys each algorithm can support depends on the number of bits in the key. Ex-8
8
bit key allows only 256 possible numeric combinations, each key is called a key of 2 . Hence more
the digits (bit – length) more the possible keys and more difficult to crack an encrypted message.

For example, to unlock a physical number zero and nine, at one stage the lock-gets unlocked.
If it is a three digit decimal number, the p[ossible combinations vary from 000-999. Similarly if
a 1000 bit (binary) key wre used on a computer which is capable of guessing one million keys
every second could still take many centuries to discover the right key hence the security of the
encryption algorithm correlates with the length of the key. Trying each possible key to fi nd the
right one to get back original message is called Brute—force method.

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