**WHAT IS CRYPTOGRAPHY?**

**Definition: **Cryptography is associated with the process of converting ordinary plain text into unintelligible text and vice-versa. It is a method of storing and transmitting data in a particular form so that only those for whom it is intended can read and process it. Cryptography not only protects data from theft or alteration, but can also be used for user authentication.

Cryptography, or cryptology, is also the practice and study of techniques for secure communication in the presence of third parties called adversaries

** **Earlier cryptography was effectively synonymous with encryption but nowadays cryptography is mainly based on mathematical theory and computer science practice.

*Modern cryptography concerns with:*

Confidentiality – Information cannot be understood by anyone

Integrity – Information cannot be altered.

Non-repudiation – Sender cannot deny his/her intentions in the transmission of the information at a later stage

Authentication – Sender and receiver can confirm each

Cryptography is used in many applications like banking transactions cards, computer passwords, and e- commerce transactions.

**What is cryptography used for?**

Modern **cryptography** uses sophisticated mathematical equations (algorithms) and secret keys to encrypt and decrypt data. Today, **cryptography** is **used to** provide secrecy and integrity to our data, and both authentication and anonymity to our communications.

* Types of cryptographic techniques used in general*.

1. Symmetric-key cryptography

2. Hash functions.

3. Public-key cryptography

**Symmetric-key Cryptography:** Both the sender and receiver share a single key. The sender uses this key to encrypt plaintext and send the cipher text to the receiver. On the other side the receiver applies the same key to decrypt the message and recover the plain text.

**Public-Key Cryptography:** This is the most revolutionary concept in the last 300-400 years. In Public-Key Cryptography two related keys (public and private key) are used. Public key may be freely distributed, while its paired private key, remains a secret. The public key is used for encryption and for decryption private key is used.

**Hash Functions: **No key is used in this algorithm. A fixed-length hash value is computed as per the plain text that makes it impossible for the contents of the plain text to be recovered. Hash functions are also used by many operating systems to encrypt passwords.

**WHAT IS CRYPTOGRAPHIC ALGORITHM**

Cryptographic algorithms are used for important tasks such as data encryption, authentication, and digital signatures, but one problem has to be solved to enable these algorithms: binding cryptographic keys to machine or user identities. Public key infrastructure (PKI) systems are built to bridge useful identities (email addresses, Domain Name System addresses, etc.) and the cryptographic keys used to authenticate or encrypt data passing among these identities.

**What is the best cryptographic algorithm?**

…**Specific Encryption Algorithms**

- AES. …
- Triple DES. …
- RSA. …
- Blowfish. …
- Twofish. …
- Rivest-Shamir-Adleman (RSA).

**How do cryptographic algorithms work?**

A **cryptographic algorithm works** in combination with a key — a word, number, or phrase — to encrypt the plaintext. The same plaintext encrypts to different ciphertext with different keys. … A **cryptographic algorithm**, plus all possible keys and all the protocols that **make** it **work** comprise a cryptosystem

## Classes of Cryptographic Algorithms

There are three general classes of NIST-approved cryptographic algorithms, which are defined by the number or types of cryptographic keys that are used with each.

### Hash functions

A cryptographic hash function does not use keys for its basic operation. This function creates a small digest or “hash value” from often large amounts of data through a one-way process. Hash functions are generally used to create the building blocks that are used in key management and provide security services such as:

- Providing source and integrity authentication services by generating message authentication codes (MACs)
- Compressing messages for generating and verifying digital signatures
- Deriving keys in key-establishment algorithms
- Generating deterministic random numbers

### Symmetric-key algorithms

Also referred to as a secret-key algorithm, a symmetric-key algorithm transforms data to make it extremely difficult to view without possessing a secret key.

The key is considered symmetric because it is used for both encrypting and decrypting. These keys are usually known by one or more authorized entities. Symmetric key algorithms are used for:

- Providing data confidentiality by using the same key for encrypting and decrypting data.
- Providing Message Authentication Codes (MACs) for source and integrity authentication services. The key is used to create the MAC and then to validate it.
- Establishing keys during key-establishment processes
- Generating deterministic random numbers

### Asymmetric-key algorithms

Also referred to as public-key algorithms, asymmetric-key algorithms use paired keys (a public and a private key) in performing their function. The public key is known to all, but the private key is controlled solely by the owner of that key pair. The private key cannot be mathematically calculated through the use of the public key even though they are cryptographically related. Asymmetric algorithms are used for:

- Computing digital signatures
- Establishing cryptographic keying material
- Identity Management

## Cryptography – Benefits

Cryptography is an essential information security tool. It provides the four most basic services of information security −

**Confidentiality**− Encryption technique can guard the information and communication from unauthorized revelation and access of information.**Authentication**− The cryptographic techniques such as MAC and digital signatures can protect information against spoofing and forgeries.**Data Integrity**− The cryptographic hash functions are playing vital role in assuring the users about the data integrity.**Non-repudiation**− The digital signature provides the non-repudiation service to guard against the dispute that may arise due to denial of passing message by the sender.

All these fundamental services offered by cryptography has enabled the conduct of business over the networks using the computer systems in extremely efficient and effective manner.

## Cryptography – Drawbacks

Apart from the four fundamental elements of information security, there are other issues that affect the effective use of information −

- A strongly encrypted, authentic, and digitally signed information can be
**difficult to access even for a legitimate user**at a crucial time of decision-making. The network or the computer system can be attacked and rendered non-functional by an intruder. **High availability,**one of the fundamental aspects of information security, cannot be ensured through the use of cryptography. Other methods are needed to guard against the threats such as denial of service or complete breakdown of information system.- Another fundamental need of information security of
**selective access control**also cannot be realized through the use of cryptography. Administrative controls and procedures are required to be exercised for the same. - Cryptography does not guard against the vulnerabilities and
**threats that emerge from the poor design of systems,**protocols, and procedures. These need to be fixed through proper design and setting up of a defensive infrastructure. - Cryptography comes at cost. The cost is in terms of time and money −
- Addition of cryptographic techniques in the information processing leads to delay.
- The use of public key cryptography requires setting up and maintenance of public key infrastructure requiring the handsome financial budget.

- The security of cryptographic technique is based on the computational difficulty of mathematical problems. Any breakthrough in solving such mathematical problems or increasing the computing power can render a cryptographic technique vulnerable