Cryptographic Algorithms

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Cryptographic Algorithms
By Kirti Chawla
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• Introduction
• Classification
• Algorithms
• Vis-à-Vis
• Looking back

What is a Cipher or Crypto-algorithm ?
A method or system for transforming given
information in order to conceal its meaning.
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Prologue

• Introduction
• Classification
• Algorithms
• Vis-à-Vis
• Looking back

Transposition ciphers

Transposition
Computers Can Only Execute Answers
CCOEAoan xnmnlesp _ycwu__u et__tre_ _ess____
Substitution ciphers

Substitution
Computers Can Only Execute Answers
Frpsxwhuv Fdq Rqob Hahfxwh Dqvzhuv
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Algorithms Genealogy

• Introduction
• Classification
• Algorithms
• Vis-à-Vis
• Looking back

Algorithms
Ciphers
Authenticators
Asymmetric
Symmetric
DES\3DES AES IDEA RC6 BlowFish
RSA ELGAMAL
SHA MD5
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Algorithmic Parlance

• Introduction
• Classification
• Algorithms
• Vis-à-Vis
• Looking back

Strong
Open
Key-oriented
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At the heart of Algorithms

• Introduction
• Classification
• Algorithms
• Vis-à-Vis
• Looking back

Methods
to do
Categories
Deciding Operations

• Simple XOR
• Modular Arithmetic with Polynomials
• Relative Prime Factors

• S-boxes P-boxes
• Inversion
• Data distribution/redundancy

Controlled Chaos Creation

• Self generation or ask from user
• Key organization
• Key protection

Key Management

• Buffer management
• Padding and boundary cases
• State management

Anomalous Behavior Handling

• Hash or One time PADs
• Bi-directionality

Directional Behavior
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Deciding Operations
Simple XOR

• Introduction
• Classification
• Algorithms
• Vis-à-Vis
• Looking back

This is secret message
This is key
Axaw sa dawawt sazawcsr
Modular arithmetic with polynomials
This is secret message
X7 x5 x2 1
This is key
Axaw sa dawawt sazawcsr
Relative prime factors
This is secret message
Factorized key1
Axaw sa dawawt sazawcsr
Factorized key2
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Controlled Chaos Creation
S-box
P-box

• Introduction
• Classification
• Algorithms
• Vis-à-Vis
• Looking back

Inversion
Data distribution/redundancy
1010 (data) 001 1010 001 1010 0101(data) 1010
001 1010 001
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Key Management
Self-generation
Ask from user

• Introduction
• Classification
• Algorithms
• Vis-à-Vis
• Looking back

1010 (data) 1010 XOR 11 1001 0101
(data) 0101 XOR 11 0110
Key organization
Key protection
1010 0000 1010 1111 0000 1011 (key) 1010 0000
1010 (key)
1010 0000 1010 1111 0000 1011 (key) 1010 0000
1010 1111 0000 1010 1010
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Anomalous Behavior Handling

• Introduction
• Classification
• Algorithms
• Vis-à-Vis
• Looking back

Buffer management
Padding

• 1010 1000 0010 1100
• 1000 1001 Overflow
• Capture of 1010 1000 0010 1100 as
• plain-text from buffer on which
• algorithm operate

If the input data or key are not exactly
fulfilling the algorithm requirements, lets say
required input is of multiple of 2 and gt 512 bit,
but user does not provide !
Boundary cases
State management
U/SIGN-INT U/SIGN-INT gt 65536/32768
If the algorithm works in various stages, each
stage signifying a state and regurgitating
partially (weak) cipher-text and hence
making possible interleaving !
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Directional Behavior

• Introduction
• Classification
• Algorithms
• Vis-à-Vis
• Looking back

Hash or one time PADs

• Use one character once only for
• substitution.
• Destroy or delete encryption
• mechanism.
• Destroy or delete decryption
• mechanism.
• Hash differs from one time PADs in
• a way of producing output.

Bi-directionality

• Given the single algorithm, the
• enciphering and deciphering
• operations should be inverse of
• each other.
• Bi-directional nature of algorithm is
• there, because of need to get original
• data back.

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Symmetric Ciphers

• A single key for enciphering and deciphering
  operations.
• More the number of bits of key, more secure your
  data.
• Algorithms are usually characterized as stream
  or block ciphers.
• Algorithmic proclivity to certain weak keys can
  create problem.
• Used generally for protecting data.

• Introduction
• Classification
• Algorithms
• Vis-à-Vis
• Looking back

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Asymmetric Ciphers

• One key for enciphering and another key for
  deciphering
• operation.
• More the distance between mutually prime nos.
  (here they are key),
• more secure your data.
• Used generally for protecting data as well for
  making sure its
• authentication.

• Introduction
• Classification
• Algorithms
• Vis-à-Vis
• Looking back

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Authenticators

• Hash functions gives a fixed-length output for a
  arbitrary-length
• message.
• Strength of algorithm is measured by collision
  resistance.
• Uni-directionality is innate capability of
  authentication algorithms.
• Authentication is achieved by re-computing hash
  and compared
• with stored hash value.

• Introduction
• Classification
• Algorithms
• Vis-à-Vis
• Looking back

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DES/ algorithms

• Introduction
• Classification
• Algorithms
• Vis-à-Vis
• Looking back

Enigma
Cipher cylinders
Caesar cipher
Egyptian pictorial substitution