2. Security Protocols
• A security protocol can be defined as a security
procedure for regulating data transmission
between computers.
• If sensitive data is transmitted over the network in
clear text, then anyone can read the data if they
intercept it intentionally or accidentally.
• To preserve the data confidentiality, we use
different encryption techniques.
3. Methods of Encryption
At a broad level, regardless of the technique used for
encryption, the generation of ciphers from the plaintext itself
can be done in two ways:
Stream Ciphers
Block Ciphers
Stream Cipher
It involves the encryption of one plaintext bit at a time. The
decryption also happens one bit at a time
Block Cipher
It involves the encryption of one block of text at a time. Decryption
also takes one block of encrypted text at a time.
4. Stream Cipher
Is one of the simplest way to encrypt data
When it is employed each bit of the data is encrypted
using one bit of the key
Faster than block cipher.
Can encrypt the same message twice and the cipher
text will be different
To make a stream cipher more difficult to crack, you
can use a crypto key that varies in length
The process of continually varying the crypto key is
known as One-time pad
5. Block Cipher
Unlike Stream Cipher which encrypts every single bit, Block
Cipher encrypts data in chunks of specific size
It specifies how much data should be encrypted on each pass
and what size key should be applied to each block
E.g DES specifies that DES encrypted data should be processed in
64-bit blocks using a 56-bit key
You can use a number of algorithms when processing block
cipher
The most basic is to simply take the data and break it into
blocks while applying the key to each
A better solution is to take the earlier resultants from the
algorithm and combine them with later keys
6. XOR Operation
An interesting property of XOR is that when used twice, it
produces the original data
Example:
Two binary numbers A=101, B=110
C = A XORB
C = 101 XOR110 = 011
Now, if we perform C XOR A, we will get B
011 XOR101 = 110 = B
Now, if we perform C XOR B, we will get A
011 XOR110 = 101 = A
This reversibility of XOR operations has many implications
in cryptographic algorithms
8. Data Encryption Standard
DES is a symmetric key encryption standard
Published in 1977 by the U.S. National Institute of
Standards and Technology (NIST)
It is developed by IBM
NIST states the goal of DES as
The goal is to completely scramble the data and key so
that every bit of the ciphertext depends on every bit of
data and every bit of key.
With a good algorithm, there should be no correlation
between the ciphertext and either the original data or key
9. Data Encryption Standard
It was widely adopted by the industry for use in
security products
a de facto standard
It takes as an input data blocks of 64-bits length and
generates 64-bit cipher blocks
56-bit key size
Today, DES is not considered secure in its original
form, but in its modified form (3DES) it is still
considered secure
10. DES Basic Operation
The algorithm, which is parameterized by a 56-bit key, has
16 distinct stages
It involves 16 rounds of plaintext transformations, including breaking
the plain text into two 32 bit chunks that are swapped repeatedly
during rounds
Each round expands 32bit block to 48bits,which are XORd with 48bit
sub-key
The sub-key has been generated by a “key schedule”
An algorithm that creates the 48-bit sub-key based on the original
56bit key
After XORing with sub-key, 48-bit text is divided into 6-bit chunks
(S-boxes), which then output 4-bit blocks
Reducing the overall plaintext block back to its original 32 bits
11. Data Encryption Standard
most widely used block cipher in world
adopted in 1977 by NBS (now NIST)
as FIPS PUB 46
encrypts 64-bit data using 56-bit key
has widespread use
has seen considerable controversy over
its security
12. DES History
IBM developed Lucifer cipher
by team led by Feistel
used 64-bit data blocks with 128-bit key
then redeveloped as a commercial cipher with
input from NSA and others
in 1973 NBS issued request for proposals for
a national cipher standard
IBM submitted their revised Lucifer which
was eventually accepted as the DES
13. DES Design Controversy
although DES standard is public
had considerable controversy over design
in choice of 56-bit key
and because design criteria were classified
subsequent events and public analysis show in
fact design was appropriate
DES has become widely used, especially in
financial applications
15. Strength of DES –Key Size
56-bit keys have 256
= 7.2 x 1016
values
brute force search looks hard
recent advances have shown is possible
in 1997 on Internet in a few months
in 1998 on dedicated h/w (EFF) in a few days
in 1999 above combined in 22hrs!
still must be able to recognize plaintext
16. DES Encryption Strength
The strength of any encryption algorithm lies in the
fact that it would take a long time to guess the used
key
DES is 56 bits, that is the key to decrypt DES will be 56
bits in length
56 bit is made up of 8 bytes with 7 data bits (8*7=56)
Thus we can have 128 (27
) values to choose from each
character
Possible number of combinations through some simple
math:
(128)8
= 72 thousand plus billion combinations
17. DES Weaknesses
DES is considered non secure for very
sensitive encryption.
It is crack able in a short period of time.
The short key length makes it easy to break
To overcome the weaknesses of DES, Triple
DES is developed from original DES.
19. Triple-DES
In Triple-DES, the DES algorithm is applied three
times using two or three different 56-bit keys
This approach produces Ciphertext that is scrambled
to the equivalent of a 112-bit or 168-bit key
(2)168
= 3.7 * (10)50
370 trillion, trillion, trillion, trillion combinations
Looking at the name, it may seem that 3DES makes
your encryption three times more difficult to break
3DES actually makes your encryption five billion,
trillion, trillion times harder to break that is 5 *(10)33
20. Advanced Encryption Standard (AES)
In 1990s, the U.S. Government wanted to standardize a
cryptographic algorithm, which was to be used universally.
Many proposals were submitted, and after a lot of debate, an
algorithm called Rijndaelwas accepted
The need for coming up with a new algorithm is actually
because of the perceived weakness in DES.
The 56-bit keys of DES were no longer considered safe
against attacks based on exhaustive key searches, and the 64
bit blocks were also considered as weak
AES was based on 128 bits blocks, with 128-bit key
21. IDEA
International Data Encryption
Standard
Takes input of 64-bits plain text blocks
Produces output of 64-bits cipher text
Key Length: 128 bits
22. AES
Worldwide a new cryptographic protocol standard
was needed because:
Key used in DES was too small (56-bit)
Triple DES (3-DES) was too slow
IDEA was patent protected and slow
Advanced Encryption Standard
NIST chose an algorithm that supports a variety of Data
Blockand Key Sizes
Two parameters (block size and key) can be chosen
independently from 128, 160, 192, 224 and 256 bit sizes
23. AES
According to AES Designers, the main
features of AES are
Symmetric and parallel structure
Adapted to modern processors
Suited to smart cards
After seeing the review of IETF protocols( SSL,
S/MIME, SSH) will have now modifications to
accommodate these algorithms
24. AES –The Advanced Encryption
Standard
Rules for AES proposals
1. The algorithm must be a symmetric block cipher.
2. The full design must be public.
3. Key lengths of 128, 192, and 256 bits supported.
4. Both software and hardware implementations
required
5. The algorithm must be public or licensed on
nondiscriminatory terms.
