2. Definition
• An algorithm is basically a procedure or a formula for
solving a data snooping problem. An encryption
algorithm is a set of mathematical procedure for
performing encryption on data. Through the use of such
an algorithm, information is made in the cipher text and
requires the use of a key to transforming the data into its
original form.
• This brings us to the concept of cryptography that has
long been used in information security in communication
systems.
3. Cryptography
• Cryptography is a method of using advanced mathematical
principles in storing and transmitting data in a particular form
so that only those whom it is intended can read and process
it.
• Encryption is a key concept in cryptography – It is a process
whereby a message is encoded in a format that cannot be
read or understood by an eavesdropper. The technique is old
and was first used by Caesar to encrypt his messages using
Caesar cipher.
• A plain text from a user can be encrypted to a cipher text, then
send through a communication channel and no eavesdropper
can interfere with the plain text. When it reaches the receiver
end, the cipher text is decrypted to the original plain text.
4. Cryptography Terms
• Encryption: It is the process of locking up information
using cryptography. Information that has been locked
this way is encrypted.
• Decryption: The process of unlocking the encrypted
information using cryptographic techniques.
• Key: A secret like a password used to encrypt and
decrypt information. There are a few different types of
keys used in cryptography.
• Steganography: It is actually the science of hiding
information from people who would snoop on you. The
difference between steganography and encryption is
that the would-be snoopers may not be able to tell
there’s any hidden information in the first place.
5. Encoding
• Encoding is the process of converting data into a format
required for a number of information processing needs,
including:
Program compiling and execution
Application data processing, such as file conversion
The type of code used for converting characters is known as
American Standard Code for Information Interchange (ASCII), the
most commonly used encoding scheme for files that contain text.
ASCII contains printable and nonprintable characters that represent
uppercase and lowercase letters, symbols, punctuation marks and
numbers. A unique number is assigned to some characters
6. The standard ASCII scheme has only zero to 127 character
positions; 128 through 255 are undefined. The problem of
undefined characters is solved by Unicode encoding, which
assigns a number to every character used worldwide. Other
types of codes include BinHex, Uuencode (UNIX to UNIX
encoding) and Multipurpose Internet Mail Extensions (MIME).
Encoding is also used to reduce the size of audio and video
files. Each audio and video file format has a corresponding
coder-decoder (codec) program that is used to code it into the
appropriate format and then decodes for playback.
Encoding should not be confused with encryption, which hides
content. Both techniques are used extensively in the
networking, software programming, wireless communication
and storage fields
7. Decoding
• Decoding is the reverse process of encoding which is to
extract the information from the converted format.
• For example, decoding Binary Coded Decimal requires
some simple calculations in base-2 arithmetic. Decoding
ASCII values is a straightforward process since there is
a one to one mapping between characters and numbers.
The term decoding is also used for digital to analog
conversion. In the filed of communication, decoding is
the process of converting received messages in to a
message written using a specific language.
8. • This process is not straight forward as the previously
mentioned decoding schemes, since the message
could be tampered due to the noise in the channels
used for communication. Decoding methods such as
Ideal observer decoding, maximum likelihood
decoding, minimum distance decoding, etc are used
for decoding messages sent via noisy channels.
9. Types of Methods
• In encryption algorithm we have two types .They are
Symmetric Encryption
Asymmetric Encryption
10. Symmetric Encryption
• This is the simplest kind of encryption that involves only
one secret key to cipher and decipher information.
Symmetrical encryption is an old and best-known
technique.
• It uses a secret key that can either be a number, a word
or a string of random letters. It is a blended with the plain
text of a message to change the content in a particular
way. The sender and the recipient should know the
secret key that is used to encrypt and decrypt all the
messages
• .Blowfish, AES, RC4, DES, RC5, and RC6 are examples
of symmetric encryption
13. Definition
• A message that is encrypted using a public key can only
be decrypted using a private key, while also, a message
encrypted using a private key can be decrypted using a
public key. Security of the public key is not required
because it is publicly available and can be passed over
the internet. Asymmetric key has a far better power in
ensuring the security of information transmitted during
communication.
• Popular asymmetric key encryption algorithm includes
EIGamal, RSA, DSA, Elliptic curve techniques, PKCS.
14. 1. AES
• AES is an encryption standard chosen by the National
Institute of Standards and Technology(NIST) , USA to protect
classified information. It has been accepted world wide as a
desirable algorithm to encrypt sensitive data.
• It is a block cipher which operates on block size of 128 bits for
both encrypting as well as decrypting
Working:
• AES basically repeats 4 major functions to encrypt data. It
takes 128 bit block of data and a key and gives a cipher text
as output.
Sub Bytes
Shift Rows
Mix Columns
Add Key
15. • The number of rounds performed by the
algorithm strictly depends on the size of key
Key Size(in bits) Rounds
128.....................................10
192.....................................12
256.....................................14
The larger the number of keys the more secure will
be the data.
https://www.youtube.com/watch?v=nC0mjaUZd8w
16.
17.
18. Attacks in AES
• It is similar to the exhaustive key search attack(brute
force attack = trying all the possible set of keys) but it is
adaptive. It is 4 times better than the exhaustive key
search.
• There are more advanced attack on AES-256 bits like
the Related key Attack , which involves several distinct
keys linked together by a common relation which
reduces the keyspace to 99.5 which is also infeasible
19. 2.DES
• DES use symmetric system means both sender and
receiver side we used same key for encryption and
decryption
• It used 64 bits of block for encryption and decryption.
Sixteen rounds of transportation and substitution are
performed in order to achieve DES
20. DES Working
• It is a symmetric block encryption algorithm when 64-bit
blocks of plain text go in , 64-bit blocks of cipher text
come out.
• It uses a 64-bit key:56 bits make up the true key, and 8
bits are used for parity
• When it applied to data, it divides the message in to
blocks and operates on them one at a time .Then the
result is64-bit blocks of cipher text
21. DES Modes
• In Block ciphers have several modes of
operation. Each mode specifies how a block
cipher will operate
Electronic Code Book
Cipher Block Chaining
Cipher Feedback
Output Feedback
Counter Mode
22. Irrational Numbers
• These are similar to data
• Sequences generated form chaotic system, are
infinite and non-cyclic.
• Using irrational numbers to encrypt will
provide higher security without strict chaos
synchronization
25. 3.RC4, RC5, RC6
• A series of symmetric algorithms developed by RSA
Security
RC4 : A variable key-size stream cipher with byte-
oriented operations . The algorithm is based on the
random permutation
RC5 : a parameterized algorithm with a variable block
size, a variable key size, and a variable number of
rounds. Allowable choices for the block size are 32 bits
(for experimentation and evaluation purposes only), 64
bits (for use a drop-in replacement for DES), and 128
bits.
26. • The number of rounds can range from 0 to 255, while the
key can range from 0 bits to 2040 bits in size. RC5 has
three routines: key expansion, encryption, and
decryption
• RC6 -- a block cipher based on RC5. RC6 is a
parameterized algorithm where the block size, the key
size, and the number of rounds are variable. The upper
limit on the key size is 2040 bits. RC6 adds two features
to RC5: the inclusion of integer multiplication and the use
of four 4-bit working registers instead of RC5��s two 2-
bit registers.
27. 4.Kerberos
• Require that each client (each request for Service) prove
it’s identity.
• Does not require user to enter password every time a
service is requested.
• It uses Needham-Schroedar Algorithm
• Kerberos assumes that network connections (rather than
servers and work stations) are the weak link in network
security
• The Needham-Schroeder Public-key Protocol provides
mutual authentication
28.
29. 5.MD5
• The MD5 hashing algorithm was created in the early
1990’s, and is one of a family of Message-Digest
algorithms. Several of these were developed by Ronald
Rivest
• Ronald Rivest is a cryptographer with significant
contributions to the field. He is a professor at MIT. He’s
also one of the inventors of RSA Algorithm . He’s a giant
in the cryptography world
30. MD5 Working
• Md5 algorithm first divides the input into blocks of 512
bits each. 64 Bits recording the length of the original
input are inserted at the end of the last block. If the last
block is less than 512 bits, some extra bits are padded to
the end.
• The algorithm consists of a set of buffers and tables to
combine and shift the data through five computational
steps .Four rounds of computation are done to compute
the hash of the input value
• MD5 is quite computationally efficient, compared to other
hashing functions
31. MD5 Collisions
• In 1996, collisions were found in MD%. Further exploits
were demonstrated through the beginning of the 21st
Century.
• This led to search for other hashing algorithms, but MD5
is still in widespread use today
32. MD5 in Action
• MD5 is in widespread use in the Transport Layer Security(TLS)
protocol on which HTTPS is based
• In fact , even thought collisions were found with MD5 as early
as 1996, it was still included in TLS as late 2008. That said
MD5 was banned at that time in TLS Certificates but not for
other aspects of TLS
• Researchers have devised attacks taking advantages of these
weaknesses. Such technique are called Security Losses from
Obsolete and Truncated transcript Hashes, or SLOTH. With
significant but easily obtainable computing power ,
impersonation attacks can be conducted on TLS based
websites and applications
33. 6. SHA
• SHA Algorithm was developed by NIST along with NSA
• In 1993, SHA was published as a Federal Information
Processing Standard
• This algorithm uses Asymmetric Encryption
• It has following Versions:
SHA-1
SHA-256
SHA-384
SHA-526
36. 7.RSA
• RSA (Rivest–Shamir–Adleman) is an algorithm used
by modern computers to encrypt and decrypt messages.
It is an asymmetric cryptographic algorithm. Asymmetric
means that there are two different keys. This is also
called public key cryptography, because one of the keys
can be given to anyone. The other key must be kept
private. The algorithm is based on the fact that finding
the factors of a large composite number is difficult: when
the integers are prime numbers, the problem is called
prime factorization. It is also a key pair (public and
private key) generator.
