# Cryptography — An Art of Information Security.

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Cryptography is an art of securing information and communication, where only the sender and the intended recipient can view the content of the information. The term Cryptography is derived from the Greek word **kryptos*** **and ***graphy ***,*where kryptos means “Hidden” and graphy means “Art of writing”. The term Crypto has become verypopular after the introduction of crypto currencies like Bitcoin, Ethereum, etc. Cryptography is basically used to secure the electronic transaction where the sender encrypts the message and sends it over the network and the receiver decrypts the message to get the original content.

# Components of Cryptography

**Plaintext:** A text message, image or binary content that needs to be secured during the communication. It is the unencrypted or non-tempered data sent from sender to the receiver.

**Encryptions:** A process where plaintext is converted to an unreadable format which can be converted back to plaintext by the receiving party. Encryption algorithm users’ cipher the message and use a secret key. The receiving party cannot decrypt the message without the secret key.

**Ciphers:** A set of steps for encrypting and decrypting a message together are known as cipher.

**Secret Key:** A set of numbers on which the cipher works to convert the plaintext to ciphertext and vice versa.

**Ciphertext:** The plaintext which is converted to unreadable format is known as ciphertext. It can be easily decrypted based on the secret key and a decryption algorithm.

**Decryption:** A process where ciphertext is converted back to the plaintext using the secret key. The key might be different, based on type of encryption used like for symmetric key encryption, same key will be used to decrypt whereas for asymmetric, there will be different keys.

# Objectives

**Confidentiality / Privacy :** Only intended recipient of the message should be able to decrypt the message.

**Reliability / Integrity :** The message sent to the receiver cannot be modified in transit or at rest.

**Non-repudiation :** Sender of the message cannot deny the fact that the message was sent by him.

**Authenticity :** At any point of time, both sender and receiver of the message can verify the identities of each other.

# Types of Cryptography

## Symmetric Key Cryptography

Symmetric Key Cryptography is a cryptographic algorithm where same key is used for encryption and decryption of the content. This is also known as private or secret key cryptography where the same key is shared between sender and the receiver.

Some examples of symmetric key algorithms are:

· AES (Advanced Encryption Standard)

· DES (Data Encryption Standard)

· Blowfish

## Asymmetric Key Cryptography

Asymmetric Key Cryptography is also known as Public-key Cryptography where different keys are used for encryption and decryption. One key which is kept private is known as the “Private Key” and a key shared with all the parties is known as “Public Key”. The mathematical computation is such that the private key cannot be derived from the public key, but public key can be derived from private key.

When a sender wants to send some content, they encrypt the message using the public key of the recipient. After receiving the message, the receiver can decrypt the content by using their own private key. Anyone snooping in on the content in middle can’t decrypt the message as the private key of intended recipient is unknown.

Some examples of Asymmetric key algorithms are:

· RSA (Rivest–Shamir–Adleman)

· DSA (Digital Signature Algorithm)

· ECC (Elliptic-curve cryptography)

## Hash Function

Hash functions are one-way functions used to protect the content at the cost of not being able to get the original plaintext. Hash functions convert the text in a fix length string, the only way to verify the content is to try all the possible input on a hash function till both the stored hash match.

Some examples of Hash functions algorithms are:

· MD5 (Message-Digest algorithm 5)

· SHA-1 (Secure Hash Algorithm 1)

· SHA-2 (Secure Hash Algorithm 2)

# Do we really use Cryptography?

Yes, cryptography has become a standard for day-to-day data transfer. Many of us use the messaging apps for sending messages to friends, family or intended recipients. There apps safeguard our messages by encrypting the content in transit and rest. When we configure these apps, a pair of keys are generated and registered with the server to help us in message transfer.

Some more examples are:

· Authentication / digital signature service

· Data time stamping service

· Secure network communication

· Email services

· Data storage

# Conclusion

The current technological advancement generates a lot of data which is sensitive and more associated with an individual’s information like Personal Identifiable Information (PII) or geolocation, etc. Securing this information is very important as it can be harmful if exposed to public networks. Cryptography is a means of securing this information and ensuring that only intended recipients can make use of it.