# Caesars Cipher And Symmetric Encryption Computer Science Essay

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In cryptography, Caesars cipher also is known as the shift code which is simplest code example of a substitution cipher. It is most widely known encryption techniques. With Caesars cipher, each letter in the plaintext is replaced by a letter which is fixed positions down to the alphabet to create a form of code.

## For example:

Caesars cipher with shift +4

Plain: ABCDEFGHIJKLMNOPQRSTUVWXYZ

Cipher: EFGHIJKLMNOPQRSTUVWXYZABCD

Plaintext: Hello

Cipher: MJPPS

The encryption that is performed by a Caesar cipher is usually combined as part of more complex schemes. Also Caesar cipher can be broken easily and in practice, it is not meet safety requirements in communication security.

## Symmetric Encryption

Symmetric encryption is a symmetric algorithm which uses the same key for encrypting and decrypting data. Also the people who have a copy of the key can encrypt and decrypt the same data. Symmetric algorithm provides confidentiality by encrypting data. It works well when the user must provide confidentiality and the user can keep the key secret. With symmetric encryption, the users don't need to share the key with others and they can easily safeguard a single key. But symmetric encryption does not work well when the users have to solve the problem of key distribution. Symmetric encryption also called single-key and private-key encryption. The users can use either the private key or public key and the user to encrypt data and use other key to perform the decryption operation. Both server and client must be known in order to encode and decode data successfully. Some commonly used symmetric encryption includes the following:

- The Advanced Encryption Standard (AES),

- RC4,

- Blowfish,

- IDEA (International Data Encryption Algorithm)

- DES (Data Encryption Standard)

- 3DES (Triple DES)

## For example:

I have encrypted my data by using my own key. When I send this data to my friend, I also need to give him my key to decrypt the data as well.

## Asymmetric Encryption

Asymmetric encryption uses different keys to encrypt and decrypt the data or message. With asymmetric encryption, the decryption key is very hard and private. The decryption key only allows the receiver be able to decrypt that data or message. But the encryption key is different. It is public to allow every one be able to encrypt a data or message. To use the asymmetric encryption, the both sender and receiver must have the same software. The receiver needs to make a pair of keys (public key and private key) which can be unlocked with a single password.

## For example:

I and my friend have the own public key and private key. Then I give him my public key and he gives me his public key as well. So I can use my friend's public key to encrypt and send my data or my message to him. After my received my data, he can use his private key to decrypt it.

## Hash function

Hash function is one way functions which can be used to create a hash that is used indentify a message or file. It is a type of encryption. The users can use hash to determine whether data has been changed by computing the hash at two different times and comparing the results. The users also can use hash when they are sending the email because hashes have a fixed length so that an attacker cannot deduce the length of the original data from the hash. The users can not reconstruct the message from the hash but they can use the hash to determine whether data has been changed since the hash was created. Hash function is usually used to security data integrity. It is also used to store passwords. Many OS store hashes instead of passwords because it is increase the security. Hash function is a one-way characteristic so it is impossible to determine a password from a hash. The only method to determine the corresponding password is by performing a brute-force attack.

## For example:

From the password, Microsoft Window OS will create a hash and store it to database. So when the user enters the password to logs on, the Window OS will perform the same hashing operation on this password. If the both hashes are matched which means the user enters the correct password then they can log on to the computer system.

## Digital Signature

Digital signature is a way that the user can use the public key encryption to authenticate an email massage or file. It encrypts the data with the private key of sender. Then anyone who wants to decrypt the massage or data, they need to use the public key of sender. If the message is decrypted successful, the receiver can massage came from the correct sender because only the sender's public key can be used to decrypt the message which is signed with their own private key. It is non-repudiation.

## For example

I create a hash of my email message and then I sign this hash by encrypt it with my own private key. I send this hash to my friend. After he received this hash he can use my public key to decrypt it. If it is successful to decrypt the hash with my public key, my friend can know that I am a person who sent this message. Also, my friend can perform an identical hash function and compares the resulting has with the hash that I send with this message. If both hashes match, my friend can be assured that the message has not been changed since I signed it.

## Public key cryptography

The area that public key encryption can be used are emailing and soliciting bids from supplier and customer. Encryption uses a pairing of a private and public key to create a digital signature. The user can encrypt data by using either the private key or public key and the user then uses other key to perform the decryption operation. The public key made freely available to lock data and the private key kept safely in order to decrypt. Public key cryptography can provide confidentiality, data integrity, authentication and non repudiation. The public key made freely available to lock data and the private key kept safely in order to decrypt. Public key cryptography can provide confidentiality, data integrity, authentication and non repudiation. Because the different encryption methods have different advantages, so the applied cryptography often combines them. Hash functions and public key cryptography are most often combined for signing. Symmetric encryption and public key encryption are most often combined exchange data confidentially. In the business environment, public key encryption can be used for emailing and soliciting bids from supplier and customer.

## For example

I have my own private key and public key. I will give my public key to my friend. He will use this key to encrypt the message or data that he want to send me. After I received the encrypted message from him, I will use my private key to decrypt it.