| Cryptography is the science of transforming | | | | same key to encrypt and decrypt the blocks. DES |
| messages to make them secure and immune to | | | | encrypts a 64-bit plaintext block using a 64-bit key. It is |
| attack. The literal meaning of cryptography is "secret | | | | widely used in military, aerospace and intelligence |
| writing". If the original message is sent through a | | | | institutions because of its fast operation and security. |
| network, then any hacker can get access and change | | | | Triple DES - It is advanced from DES since three keys |
| its meaning. To ensure the security of the message, | | | | are used in succession to encrypt a message. It has |
| the original message is transformed to ciphertext using | | | | also increased the key size to 112 bits. |
| an encryption algorithm by the sender. And the | | | | AES (Advanced Encryption Standard) - AES is a very |
| receiver uses a decryption algorithm to transform the | | | | complex round cipher with three different key sizes: |
| ciphertext back into plaintext. | | | | 128, 192, or 156 bits. |
| Encryption and decryption algorithms are called ciphers. | | | | IDEA (International Data Encryption Algorithm) - It was |
| And those algorithms operate on a set of numbers | | | | developed by Xuejia Lai and james Massey. The |
| called Key. To encrypt a message, we need an | | | | block size is 64 bits and key size is 128 bits. |
| encryption algorithm, encryption key and the plain text. | | | | Blowfish - It was developed by Bruce Schneier. The |
| These create the ciphertext. Similarly to decrypt a | | | | block size is 64 and key size between 32 and 448. |
| message, we need a decryption algorithm, decryption | | | | CAST-128 - It was developed by Carlisle Adams and |
| key and the ciphertext. These reveal the plaintext. In | | | | Stafford Tavares. The block size is 64 bits and key |
| cryptography three characters (Alice, Bob, and Eve) | | | | size is 128 bits. |
| are very popular. Alice is the person who sends | | | | RC5 - RC5 was designed by Ron Rivest. It has |
| message and Bob is the recipient. Eve disturbs this | | | | different block size and key sizes. |
| communication by intercepting message to uncover | | | | Asymmetric-Key Cryptography |
| the data. | | | | This uses two keys: a private key and a public key. |
| There are 2 types of ciphers (cryptography | | | | Public key is used to encrypt to message whereas |
| algorithms) | | | | private key is used to decrypt. The public encryption |
| 1- Symmetric-key or Secret key Cryptography | | | | key is made available to whoever wants to use it, but |
| 2- Asymmetric-key or Public key Cryptography | | | | the private key is kept secret by the key owner. The |
| Symmetric-Key Cryptography | | | | process is explained below: |
| In Symmetric-Key Cryptography, the same key is | | | | - If A wants to send a message to B, the message is |
| used by both sender and receiver. So the key must | | | | encrypted by A using B's public key. |
| be known to both parties. The traditional ciphers are | | | | - If B receives the message, the message is |
| substitution cipher and transposition cipher. A | | | | decrypted by using B's private key. No other recipient |
| substitution cipher substitutes one symbol with another. | | | | can decrypt the message. |
| For example, we can replace character B with G and | | | | RSA - It is most commonly used public key algorithm. It |
| F with X. In a transposition cipher, location of a | | | | is named by its inventors name Rivest, Shamir, and |
| character is changed in the ciphertext. Let's discuss | | | | Adelman (RSA). It uses two numbers as the public and |
| some important symmetric ciphers. | | | | private keys. RSA is useful for short messages and |
| DES (Data Encryption Standard) - DES is a | | | | also used in digital signatures. But it is very slow if the |
| symmetric-key block cipher designed by IBM. A block | | | | message size is long. |
| cipher divides the plaintext into blocks and uses the | | | | |