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CryptographyPROFESSIONAL PRACTICE

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Content(Present By)

1.Introduction www.Aask24.com Purpose of cryptography

2.Types of cryptography www.Aask24.com3.Strength Of Cryptosystems4.Putting the Pieces to Work www.Aask24.com5.Basic Terms of cryptography6.Example Of Cryptography www.Aask24.com8. Summary

Introduction

Cryptography is a technique used to hide the meaning of a message and is derived from the Greek word kryptos (hidden). This is different from steganograhic techniques in that one is not hiding the actual message, only the meaning of the message. If a message were to fall into the hands of the wrong person, cryptography should ensure that, that message could not be read. Typically the sender and receiver agree upon a message scrambling protocol beforehand and agree upon methods for encrypting and decrypting messages. Cryptography is further divided into two implementation techniques and those include transposition and substitiution.

Purpose Of Cryptography

Cryptography is the science of writing in secret code and is an ancient art the first documented use of cryptography in writing dates back to 1900 B.C. when an Egyptian scribe used non-standard hieroglyphs in an inscription. Some experts argue that cryptography appeared spontaneously sometime after writing was invented, with applications ranging from diplomatic missives to war-time battle plans. It is no surprise, then, that new forms of cryptography came soon after the widespread development of computer communications. In data and telecommunications, cryptography is necessary when communicating over any untrusted medium, which includes just about any network, particularly the Internet.

Purpose of cryptography (cont.)

Within the context of any application-to-application communication, thereare some specific security requirements, including:i. Authentication: The process of proving one's identity. (The primary forms of host-to-host authentication on the Internet

today are name- based or address-based, both of which are notoriously weak.)

ii. Privacy/confidentiality: Ensuring that no one can read the message except the intended receiver.iii. Integrity: Assuring the receiver that the received message has not been altered in any way from the original.iv. Non-repudiation: A mechanism to prove that the sender really sent this message.

Purpose of cryptography (cont.)

Cryptography, then not only protects data from theft or alteration, but can also be used for user authentication. There are, in general, three types of cryptographic schemes typically used to accomplish these goals: secret key (or symmetric) cryptography, public-key (or asymmetric) cryptography, and hash functions, each of which is described below. In all cases, the initial unencrypted data is referred to as plaintext. It is encrypted into cipher text, which will in turn (usually) be decrypted into usable plaintext.

Strength Of Cryptosystems

A strong cryptosystem is considered strong only until it’s been cracked.

That might sound like common sense, but you can never prove that a cryptosystem is strong or unbreakable—you can simply ensure that certain properties are present within it. Each defeat of an attempt to crack a cryptosystem strengthens the belief in its ability to secure. Similar to monetary currency, a cryptosystem has value because its users believe in its worth. If that worth is proven to be unfounded, the cryptosystem collapses and no one relies on it anymore.The most popular commercial cryptosystems found in software products have similar characteristics. Their algorithms are made readily available to the public (through published standards and public posting), and the strength of the algorithm rests in the keys used to encrypt and decrypt (in general, the longer the key, the better). The basic idea is to keep the keys, not the algorithm, secret. Many government cryptosystems are kept secret and are not

intended for public or commercial use.

Type of Cryptography

There are, in general, three types of cryptographic schemes

typically used to accomplish these goals• Secret key (or symmetric) cryptography• Public-key (or asymmetric) cryptography• Hash functions

In all these cases, the initial unencrypted data is referred to as plaintext. It is encrypted into ciphertext, which will in turn (usually) be decrypted into usable plaintext.

Type of Cryptography (Cont.)

Secret Key Cryptography (SKC): Uses a single key for both encryption and decryptionPublic Key Cryptography (PKC): Uses one key for encryption and another for decryptionHash Functions: Uses a mathematical transformation to

irreversibly "encrypt" information

Basic Terms and Concepts

• Cryptosystems disguise messages, allowing only selected peopleto see through the disguise• Cryptography is the science (or art) of designing,

building, and using cryptosystems• Cryptanalysis is the science (or art) of breaking a

cryptosystem• Cryptology is the umbrella study of

cryptography and cryptanalysis

Basic Terms and Concepts (cont.)

Cryptographers rely on two basicmethods:

• Transposition: letters are rearranged into a different order

• Substitution: letters are replaced by other letters and/or symbols.

Plaintext is the message that is passed through an encryption algorithm and becomes ciphertext, When ciphertext is passed through a decryption algorithm, it becomes plaintext again

Putting the Pieces to Work

Background Technologies• A hash is a transformation of data into distilled forms that are

unique to the data• With a computer program, a document is run through a one-way

hashing formula to produce a small numeric value that’s unique but easily repeatable for that exact stream of data

• This process is also called digesting data or creating a message digest

Digital Envelope

K is a random session key and Es is a symmetric encryption algorithm and EA is an asymmetric encryption algorithm. The receiver recovers the secret key from the digital envelope using his/her private key. He/she then uses the secret key to decrypt the message.

KM

KR(pub)K

ES

EA

How is a digital signature generated?

DS is used to provide authentication service for sendingmessage from one user to another. Two steps are needed:• Using hash algorithm to generate a digest from the

message to be sent.• Using sender's private key to encrypt the digest. The

encrypteddigest then becomes the sender's digital signature.

Example of Cryptography

Can anyone understand the following word?

fcjjm

Sender sends the message to

receiver Like fcjjm with a shift

of two

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

Now understand that msg we need to use this pattern

The key for this Message is skip 2 Step forwardfcjjm

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

“Hello“

Summary

Cryptography is needed by computer applications to implement the privacy and security that users demandThe strength of a cryptosystem rests in the size and means used to protect cryptographic keysThe same key can be used to both encrypt and decrypt information and is called a symmetric key, or different keys can be used for encryption and decryption are called asymmetric keysCryptography relies on two basic methods: transposition and substitutionDigital signatures are used in asymmetric key cryptography to support authentication, integrity and non-repudiation services