Overview of encryption

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Overview of encryption
Type of encryption algorithm (Symmetric and
Asymmetric) Hash - one way function Digital
Signature Virus
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Cryptography

• Cryptography (today is a goodday ? xfssfsf sdfs
  erwezyw89df)
• a science of protecting info by encoding it into
  an unreadable format.
• Confidentiality ( access by few people)
• Ensuring info is accessible only to those
  authorized to have access (encryption)
• Data integrity
• Ensuring infos accuracy and completeness
• (digest or check-pattern)
• Authentication
• Ensuring that authorized users have access to
  information (proof of identity)

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Cryptographic Techniques

• Plain text
• Message in an understandable/readable form, same
  as Clear text
• Cipher text
• encrypted text.
• Symmetric key cryptography (classical)
• Cryptographic technique where the same key is
  used for encryption and decryption operations.
• Substitution cipher
• Transposition cipher
• Asymmetric Key Cryptography
• Cryptographic technique where a key pair is used
  for encryption and decryption operations.

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Symmetric key cryptography

• Same key used for encryption and decryption
• Secrecy resides solely in the key, thus it must
  be kept absolutely secret
• Same key can be used for several messages, but
  should be changed periodically ? secure key
  distribution problem

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Symmetric key cryptography

• Symmetric Algorithms
• also known as secret key algorithm
• use single key on encrypt and decrypt
• usually hardware assisted
• Advantages
• efficient, take less time to encrypt a message
• smaller key size
• Fast and well proven technology

Disadvantages Key needed to be transmitted in the
first place. Both party must have a secret key,
distribution of key is very difficult. Same key
can be used for several messages, but should be
changed periodically
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Typical Symmetric algorithms

• Substitution cipher
• Transposition cipher
• Typical symmetric algorithm DES, 3DES, AES
• DES used a combination of above cipher techniques
• AES - Advanced Encryption Standard
• to replace DES gt winner of the algorithm (in
  1998) gt Rijndael (by Rimmen and Daemen)

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Substitution cipher

• Substitution cipher
• abcdefghijklmnopqrstuvwxyz
• poiyutrewqasdfghjmlknbvczx
• replace each plaintext character in message with
  matching ciphertext character
• nxex e ? ????
• plaintext Charlotte, my love
• ciphertext mmy-cheung, yr boss

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Transposition ciphers

• Transposition cipher move characters or bits to
  another place within the message block instead of
  substituting them with another value.
  (Permutation.)
• Eg. Simple Columnar Transposition
• Place the plaintext in a 2-dimensional matrix
• (left to right, top to bottom).
• Output column order
• (top to bottom, left to right)

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The Data Encryption Standard (DES)

• Symmetric system
• DES is a block cipher.
• break the plaintext message into several blocks
  of bits and then work on the individual blocks
  one at a time.The algorithm puts the bits within
  these blocks through several rounds of
  substitution and transposition.
• The plaintext is processed in 64- bit blocks
• The key is 56- bits in length.
• 56 Bit Key Big enough?
• 256 72,057,594,037,927,900

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The Data Encryption Standard (DES)

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Other symmetric algorithms

• Triple DES (3DES)
• RSA algorithms
• Symmetric key block encryption algorithm,
  involving variable length keys.
• RC2 block mode, 64-bit blocks, variable key
  length
• RC5 block mode, variable block size, variable
  key length
• Rijindael
• block cipher supports 128, 192 and 256 bit
• US government has selected Rijindael to replace
  DES as the Advanced Encryption Standard (AES)

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Triple DES
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Asymmetric Key Cryptography

• Public Key systems are also known as asymmetric
  key ciphers
• There are two different keys one for encryption
  and one for decryption
• Knowing one key can not compromise the other
• Things encrypted with the private key may only be
  decrypted with the public key
• Things encrypted with the public key may only be
  decrypted with the private key
• A public key is used to encrypt a message that
  can be decrypted only by the matching private
  key.
• M ? Pub ? ? Pri ? M
• M ? Pri ? ( ? Pub ? M

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Asymmetric Key Cryptography

• One problem with a single key system involves the
  distribution of the key
• Key is sent to many people.
• If only one person expose the key and the
  security of all messages is lost
• In a two key system, the encryption key can be
  made public while the decryption key remains
  secret

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Asymmetric Key Cryptography

• E.g.

Clear -text
Clear -text
Cipher -text
public
private
Clear -text
Clear -text
Cipher -text
public
private
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Asymmetric cryptographic system

• Based on the concepts of same cryptographic
  process but with the different secret keys pair,
  that is private key and public key

Cipher text
Cryptographic process
Cryptographic process
M
M
private key
Public key
different Cipher text
Cryptographic process
Cryptographic process
M
M
Public key
Private key
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Comparisons of Asymmetric and Symmetric
cryptographic system

• Symmetric
• 64 bit
• 112 bit
• 128 bit
• Same key to encrypt and decrypt
• Faster

• Asymmetric
• 512 bit
• 1792 bit
• 2304 bit
• Two keys public private
• 1 for encrypt another decrypt and vice versa.
• Slower

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Diffie-Hellman (DH) Key distribution

• DH is - most popular key exchange algorithm to
  address the problem of key exchange.
• Not covered in our syllabus

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Digital signature

• properties in e-commerce
• Integrity the received message is unmodified
• Confidentiality the message is seen by
  designated receiver
• Authentication receiver is sure of the senders
  identify and that an imposter has not sent the
  message
• Non-repudiation receiver can prove that a
  received message came from a specific sender and
  sender must not able to deny sending a message

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Hash

• MD is fixed length, used to verify the integrity
  of data
• Convert message into check pattern known as
  message digest
• Many algorithms (most common MD5)
• MD4 and MD5 are faster Based on the concept of
  one-way function (cannot get the message back)

AXSDKGVBNRQZ
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Generation of Digital Signature

• Digital Signature technique of appending a
  string of characters to an electronic message in
  order to authenticate the sender.
• One method is the encryption of MD with
  asymmetric key (senders private key)

How are U? I love U. Ill give U 10.
_at_
xyAA
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Verification of digital signature
verification at receiver site
How are U? I love U. Ill give U 100.
xyAA
xyAA
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Comparison of digests

• Hacker change message from 10 to 1000.

How are U? I love U. Ill give U 1000.
How are U? I love U. Ill give U 1000.
Hacker
xyKK
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Classification of Malicious Software
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Malicious Code
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Growth (virus) Reasons

• Increased access to computers
• More propagation mechanisms
• Programming ease
• Hacker information exchange
• Increased sophistication
• Viruses
• Program that can infect other programs by
  modifying them
• modification includes copy of virus program
• the infected program can infect other programs

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Virus Hoaxes

• Hoaxes are False warnings that contain incorrect
  information about malware or system events
• These warnings often describe impractical or
  impossible malware program characteristics that
  often fool the user into performing unwanted
  actions on their system or suggests that users
  should forward the warning to other users
• Hoaxes are not viruses, they are usually
  propagated by email and are designed deliberately
  to cause panic and alarm. They just add to the
  general confusion about viruses

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Viruses

• A computer virus is a self-replicating program
  segment that uses other programs or objects as
  hosts and, at some point, usually performs some
  action, which may be malicious
• First one written in 1983 by USC student Fred
  Cohen to demonstrate the concept
• There are now approx. 80,000 viruses that exist
  in cyberspace with about 600 to 700 new one being
  discovered per month (statistical data in 2002)

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Virus Structure

• Usually pre-pended or post-pended to executable
  program
• When program invoked, virus executes first then
  original program
• First seeks out uninfected executable files and
  infects them
• Then performs some action

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Virus and Worm

• A worm operates through networks, and a virus can
  spread through any medium (but usually uses
  copied program or data files).
• A worm spreads copies of itself as a stand-alone
  program, whereas the virus spreads copies of
  itself as a program that attaches to or embeds in
  other programs

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How Virus are Spread

• Via media (e.g. floppy diskette)
• Peer to peer networks
• Via email attachments
• FTP sites
• Chat and instant messaging
• Web surfing
• Commercial software
• Illegal software

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Types of Virus

• Viruses can be categorized by the types of files
  they infect, and by the manner in which they
  infect. Many viruses fit into more than one of
  these categories
• There are about six main types of viruses
• Boot sector viruses
• File viruses
• Multipartite viruses
• Polymorphic viruses
• Stealth viruses
• Macro viruses