CRYPTOGRAPHY

Cryptography – Science of Secret Writing

Algorithm – Mathematical functions / equations (which is Not Secret)

Key – How to carry out the mathematical function (which is Secret)

Algorithm:

a b c d e f g h I j k l m n o p q r s t u v w x y z

Key=2

Plain Text = RAJA → Cipher Text = TCLC

Symmetric Key:- {The Key for the Encryption in source is same as the Key for Decryption in destination}

Crypto System:- Implementation of cryptography which transforms a message from plain text to cipher text.

Cryptanalysis:- It is the practice of obtaining plain text from cipher text. (Breaching the Encryption)

Ceaser Cipher:-

Symmetric Cipher – Sender/Receiver uses the same Key

Key = 3 (spaces in the alphabet)

A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

D E F G H I J K L M N O P Q R S T U V W X Y Z A B C

Plain Text = RAJ → Cipher Text = UDM

Substitution Cipher:- It is a substitute which replaces text with another in reverse.

ABCDEFGHIJKLMNOPQRSTUVWXYZ

ZYXWVUTSRQPONMLKJIGHFEDCBA

Plain Text = RAJ → Cipher Text = JZR

Polyalphabetic Cipher:- It points each row corresponds to a Ceaser cipher.

Vigenere Table: {Import image}

Secret Key = “SECRET”

it is written like, SECRET SECRET SECRET SECRET

plain text, MYBANK PASSWO RDISMO HAN123

Cipher text, Encrypted cipher ---------→

Transposition Cipher:- It means changes / transpose.

Plain text - Corporate Company Services

Grouped Message - corporatecompanyservi

Order key is - 123451234512345123451

Key is - 245133152454123154324

Cipher text is - opocrtrcaeanompyivre

Cryto System:- There are two types of crypto system,

* Symmetric (which is similar)

* Asymmetric (which is different/not similar)

[Traditional form of cryptography known as single key/secret key/symmetric key cryptography]

[It uses Substitution of Transposition techniques]

Process of Encryption:

Plain text + Encryption = Cipher text

Cipher text + Decryption = Plain text

Process of Transforms:

P.T + Key = E.M || E.M + Key = P.T

[Key which is used to encrypt a msg and the key which is used to decrypt a msg are “ONE” and the “SAME”]

Difficult:-

- Key Maintenance

- Key distribution (Key has to be transmitted over secure channel)

Symmetric Algorithm:

The encryption algorithm can be applied on plain text messages in two methods,

* Block cipher

* Stream cipher

Block cipher:- It is used to make blocks to achieve cipher text.

Message/Plain text = My name is Mohanraj

Block cipher = MYNA MEIS MOHA NRAJ

B1 B2 B3 B4

Cipher messages = C1 C2 C3 C4

If block 1 and block 3 are identical, will get identical cipher. Attacker will get the pattern and deduce the original messages.

Stream Cipher:- It operates on bits and generates a key stream.

Key stream = 10011001101

Plain stream = 00110110001

XOR Result = 10101111100

Key stream {XOR} plain stream = Cipher text

DES (Data Encryption Standards):- It uses 16 rounds of Mathematical procedures.

In 1974, combined with NIST(national institute of standards and technology) and NSA (national security agency) invented a standard called DES.

Using DES, IBM has introduced an algorithm called “Lucifer”. Basically Lucifer is a 128 bit but NSA has altered and reduced to 64. From 64 bits, 8 bits goes for parity and hence it has only 56 bits.

After all the changes, the name has “DEA” - Data Encryption Algorithm.

DES Modes:-

a) – Cipher Feedback (CFB) – } Stream cipher, which are used in Hardware

b) – Output Feedback (OFB) – } Stream cipher, which are used in Hardware

c) – Electronic Code book (ECB) – } Block cipher, which are used in Software

d) – Cipher block chaining (CBC) – } Block cipher, which are used in Software

3DES – Triple DES Modes: It can do 3 rounds of encryption either with 2 or 3 keys.

1) DES – EEE3

2) DES – EDE3

3) DES – EEE2

4) DES – EDE2

AES – Advanced Encryption Standard:-

AES = ‘X’ bits

X are, 128, 192, 256

AES128, AES192 and AES256.

CBC – Cipher Block Chain

{import image which tells everything}

Asymmetric Cryptography:- It is also known as pubic key cryptography, which is introduced in 1976 by Whitefield Diffie & Martin Hellman.

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Algorithm:

a) Diffie Hellman Algorithm

b) RSA

c) Elgammal

Advantages of Asymmetric:

– No key distribution / Public key hosted in public

– Scalability

– Range of security services

Features:

– Privacy / Confidentiality || Encryption

– Authentication || Digital Signature / CA

– Data-Integrity || Hashing / MD

– Non-repudiation || Digital Signature

PKI – Public key infrastructure:- It provides full range of security services,

Pki is a combined with below,

- Public key

- Private key

- Digital signature

- Digital certificate

- Hashing

- Message Digest