Symmetric Key Algorithm

Symmetric Key Algorithm

1. Symmetric-Key Algorithm
Prof. Neerj Bhargava
Mrs. Shubha Chaturvedi
Department of Computer Science, School of
Engineering & System Sciences
MDS University Ajmer, Rajasthan

2. Symmetric-Key Algorithms
•Symmetric-keyalgorithmsarealgorithmsforcryptography
thatusethesamecryptographkeysforboththeencryption
ofplaintextandthedecryptionofciphertext.
•Thekeysmaybeidentical,ortheremaybeasimple
transformationtogobetweenthetwokeys.
•Thekeys,inpractice,representasharedsecretbetween
twoormorepartiesthatcanbeusedtomaintainaprivate
informationlink.
•Therequirementthatbothpartieshaveaccesstothe
secretkeyisoneofthemaindrawbacksofsymmetric-key
encryption,incomparisontopublic-keyencryption(also
knownasasymmetric-keyencryption).

3. Types of Symmetric-Key Encryption
Symmetric-key encryption can use eitherstream
ciphersorblock ciphers.
Stream
Cipher
Block
Cipher

4. Stream ciphers
•Stream ciphers encrypt the digits (typicallybytes),
or letters (in substitution ciphers) of a message
one at a time.
•In stream cipher, one byte is encrypted at a time
while in block cipher ~128 bits are encrypted at a
time.
•Initially, a key(k) will be supplied as input to
pseudorandom bit generator and then it
produces a random 8-bit output which is treated
as keystream.

5. Block ciphers
•Incryptography a block cipheris adeterministic
algorithm operating on fixed-length groups
ofbits, calledblocks. It uses an unvarying
transformation, that is, it uses asymmetric key.
•Block ciphers take a number of bits and encrypt
them as a single unit, padding the plaintext so
that it is a multiple of the block size.

6. ASSIGNMENT
Q. Differentiate between Stream and Block
Cipher?