MODULE 2: CRYPTOGRAPHY

Introduction to Cryptography

Cryptography

Start in Ancient Greeks and Romans.

Caesar Cipher

Shifting each letter to plaintext message by a certain number of letters

Caesar Cipher

Shifting each letter to

plaintext message by a certain number of

letters. It can be decrypted by applying the

same number of shifts in the opposite

direction..

Substitution Cipher

substituting one letter for another in a consistent fashion.

Jefferson Disk

called his invention the “wheel cypher.” It had 36 wooden

disks, each with 26 letters in random order (“jumbled

and without order,”) along the edge, like the ridges of a coin.

Wheel Cypher

It had 36 wooden disks, each with 26 letters in random order (“jumbled and without order,” according to Jefferson [2]) along the edge, like the ridges of a coin.

Cryptography

A method of protecting information and communications through the use of codes, so that only those for whom the information is intended can read and process it.

Cryptography

to secure information and communication techniques derived from mathematical concepts

and a set of rule-based calculations called algorithms, to transform messages in ways that are

hard to decipher. -TechTarget-

"hidden" or "vault"

"crypt-" means ____ or ____

"writing."

"-graphy" stands for

Cryptography and steganography

The actual implementation of security goals needs some techniques. Two techniques are

prevalent today:

Cryptography

a word with Greek origins, means “secretwriting.” However,

we use the term to refer to the science and art of transforming messages to make them

secure and immune to attacks.

steganography

with origin in Greek, means “coveredwriting,”

in contrast with cryptography, which means “secretwriting”

Computer Security

Tools that protect data and thwart hackers.

Network Security

Measures protecting data during transmission.

Internet Security

Protects data across interconnected networks.

Plain Text

The original, intelligible message.

Cipher text

The transformed, unintelligible message.

Cipher

Algorithm transforming plaintext into cipher text.

Key

Critical information used by the cipher, known only to sender & receiver.

Encipher

Converting plaintext to cipher text using a cipher and key.

Decipher

Converting cipher text back into plaintext.

Cryptanalysis

Breaking cipher text without knowledge of the key —

code breaking.

Cryptology

Both cryptography and cryptanalysis combined.

Symmetric Encryption and Asymmetric Encryption

Two Types of Cryptosystem

Substitution

Each element is mapped to another

element.

Transposition

Elements are rearranged in position.

Symmetric Key

Sender & receiver use the same single

key.

Public Key

Sender & receiver use two different keys.

Block Cipher

Processes input one block at a time.

Stream Cipher

Processes input continuously, one

element at a time.

Symmetric Cryptography

Also known as private key cryptography

Symmetric Cryptography

It uses single key

Symmetric Cryptography

Key itself must be shared between the sender and receiver(key exchange)

SYMMETRIC CRYPTOGRAPHY

Weakness:

★ It uses only one key

★ If the key exposed beyond the sender

and receiver , it is possible for an

attacker who has managed to intercept

it to decrypt message and alter

★ Provides confidentiality not integrity

Block Cipher

takes a predetermined number of bits known

as block in the plaintext message and encrypts

that block

Block Cipher

can use 64 bits but can larger or smaller

depending on the algorithm

Electronic CodeBook(ECB) MODE

The input data is padded out to a multiple of

the block size, broken into a integer number

of blocks, each of which is encrypted

independently using the key(for small

message).

Cipher Block Chaining

Each block of plaintext is XOR-ed with

the prior block of ciphertext. After

decryption, the output of the cipher must

then be XOR-ed with the previous

ciphertext to recover the original

plaintext.

Cipher Block Chaining

It uses Initialization Vector(message

uniques). It is generated randomly

Stream Cypher

Encrypt each bit in the plain

text message, 1 bit at a time.

True

it is possible for a block cipher

to act as a stream cipher by

setting a block size of 1 bit.

T/F

True

block cipher uses for often

T/F

True

block is often slower but more efficient

T/F

False

Stream is more sensitive to errors in the encryption process.

T/F

Data Encryption Standard(1976)

56 bit key

Advanced Encryption Standard

• Symmetric key symmetric block cipher

• 128-bit data, 128/192/256-bit keys

• Stronger and faster than Triple-DES

• Provide full specification and design details

• Software implementable in C and Java

Advanced Encryption Standard (AES)

is an iterative rather than Feistel cipher. It is based on

‘substitution–permutation network’. It comprises of a

series of linked operations, some of which involve

replacing inputs by specific outputs (substitutions) and

others involve shuffling bits around (permutations).

Asymmetric Key

Utilize two(2) keys-Public and

Private key

Public Key

Used to encrypt data sent from the sender to

received and shared to everyone.

it was included in email signature posted on

servers that exist.

Private Key

Used to decrypt data that arrives in the

receiving end and are carefully guarded by the

receiver.

• loss the need to distribute key

• Secret keys are exchanged over the Internet or a large network.

• A public key is made freely available to

anyone who might want to send you a message. The

second private key is kept a secret so that you can

only know.

Rivest Shamir Adleman (RSA) algorithms

Uses in Secure Socket Layer(SSL)

Elliptic Curve Cryptography (ECC)

is a key-based technique for encrypting data. Focuses on pairs of public and private keys for decryption

and encryption of web traffic.

Elliptic Curve Cryptography

- generates security between key pairs for public key

encryption by using the mathematics of elliptic curves.

Pretty Good Privacy(PGP)-

SSL and Transport Layer Security(TLS)

Protocols and Application that used asymmetric

HASH FUNCTION

• refers as message digest

• do not use key instead create a largely unique and fixed length hash value based on the original message(fingerprint)

• determine that the message has changed.

• provide confidentiality but not integrity

Hash Function

MD5.SHA2,SHA3

Digital Signature

-it allows the message to sign in order to enable detect

changes in message content to ensure that it was

legitimately sent by the expected party.

Digital Signature

-generate a hash of message and use the private key to

encrypt the hash.

Certificates

-it was created to link a public key to a

particular individual and are often used as a

form of electronic identification for the

particular identification.

Certificates

-it allows us to verify that the public key is

truly associated with a particular individual

PNPKI

it is a branding to distinguish the service that was provided by the

Philippine Government.

Public Key Infrastructure (PKI)

an infrastructure that secures

communications among individuals

and government agencies which is

being offered by the Department of

Information and Communications

Technology(DICT)

Public Key Cryptography

The Process of encrypting and decrypting data using two pairs of keys: Public and Private key

Digital Certificate + Public Key

-A small file that issued by

Certificate Authority as proof of

individual's identity
-It will be associated with Public

and Private Key

Sender Side

The document from the sender

will create a hash(green label)

Receiver side

When the receiver receives the

digitally signed document it will

create a hash and compare it to

the original hash

-If it didn't match, it means that

the documents was tampered.