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Encryption

These are the principal types of encryption.

Symmetric Encryption:

A single fundamental is used to encrypt and decrypt the bulletin sent between two parties. Symmetric encryption is fast, and effective but when a central is kept absolutely clandestine between ii parties.

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Sit-in of Caesar Encryption using CrypTool

In this CrypTool demonstration, we will use Caesar, one of the oldest encryption algorithms.

Encryption

1. Open the Cryptool UI and the document that needs to be encrypted.

   

2. Click Encrypt/Decrypt > Symmetric (classic) > Caesar

1. Select Caesar way and the "alphabet grapheme" is "N." That means that the text will have characters replaced starting with N. So A >North, B>M, and so on. Click on "encrypt."

   

2. The certificate is encrypted as per the configured policy. This is a very basic example of how symmetric encryption works.

Decryption procedure

Perform the following steps to decrypt the encrypted document.

1. Open the encrypted certificate, and click on "Encrypt.Decrypt" >Symmetric >Caesar.
2. Enter "Due north" as the alphabet character. This is the shared secret that both parties must know in order to encrypt and decrypt.
3. Click on decrypt.

Block Cipher

Block cipher is the process in which n- bits of plaintext is converted into n-bits of ciphertext using 10-bits of key with block ciphers, message encryption and decryption happens in blocks. The most mutual mode of performance is cipher cake chaining.

Source: Wikipedia

In this mode of operation, an initialization vector is needed, which is used to perform a XOR performance on plaintext. The XOR role takes 2 inputs and produces ane result. Below is a brief explanation on how Bitwise XOR operation works.

Input 1	Input 2	Operation	Result
0	0	XOR	0
0	1	XOR	ane
ane	0	XOR	1
1	one	XOR	0

As we can see in the above chart in XOR operation, Same $.25 (0-0 , one-1) results in an output flake of 0 and different bits (0-1,1-0) results in an output scrap of 1.

Afterward the XOR performance, Iv is and then encrypted with the key to produce a cake of ciphertext. The same ciphertext block is used to perform an XOR operation with next block of plaintext and so on. In the decryption process, for the first cake the ciphertext is decrypted using the key, and XORed using the same IV to produce the first block of plaintext. For the remaining blocks, after the outset ciphertext is decrypted, it is then XORed with the previous block of ciphertext to produce the final cake of plaintext.

Other examples of cake cipher modes are electronic codebook (ECB), propagating cipher cake chaining (PCBC), cypher feedback (CFB), output feedback (OFB), and counter (CTR). I encourage users to sympathize these modes to proceeds a skillful understanding of block ciphers.

Hither'south a demonstration of a DES nothing in CBC mode.

Well-nigh Data Encryption Standard (DES): DES is the archetypal block zip — an algorithm that takes a stock-still-length string of plaintext bits and transforms it through a series of complicated operations into some other ciphertext bitstring of the same length. In the case of DES, the block size is 64 $.25. DES also uses a central to customize the transformation, so that decryption tin can supposedly only be performed by those who know the particular key used to encrypt. The key ostensibly consists of 64 bits; all the same, simply 56 of these are really used past the algorithm. Eight $.25 are used solely for checking parity, and are thereafter discarded. Hence the effective key length is 56 $.25, and it is always quoted as such.

Sit-in of DES(CBC) using CrypTool

In this section, we will perform DES encryption in CBC mode.

1. Click on Encrypt > Symmetric (modern) > DES (CBC).
2. Enter a hexadecimal character between 0-9,A-F to perform encryption, and click on encrypt.
3. Modify whatsoever chip with the selected hexadecimal character. In the image beneath I have selected the characters '0' and 'one'.

1. Here's the encrypted document.

Now perform decryption.

1. Click on Click on Decrypt > Symmetric (modern) > DES (CBC).
2. Click on decrypt.

What happened? Did yous get this fault message?

The fault is because the key used for encryption and decryption is not the same.

For encryption we used: 00 00 01 00 11 01 01 00

For decryption we used: 00 00 00 00 00 00 00 00

This proves that both the parties must possess same hush-hush fundamental.

Now put the aforementioned key in to decrypt the document.

Stream Zero

A stream naught is a symmetric key cipher where plaintext digits are combined with a pseudorandom cipher digit stream (keystream). In a stream cipher each plaintext digit is encrypted one at a time with the respective digit of the keystream, to give a digit of the ciphertext stream. In that location are various examples of stream ciphers, like RC4, AES etc. The procedure for encryption and decryption for stream ciphers is the aforementioned every bit is done for block ciphers.

Cake Ciphers vs Stream Ciphers

The below department volition illustrate the main advantages and disadvantages of stream and cake ciphers.

• Since stream ciphers piece of work flake by bit, stream ciphers are faster than block ciphers.
• Since block cipher work on block of data, so it requires more memory for computation than stream cipher.
• Ane of the biggest advantage of block ciphers over stream ciphers is that they do non crave padding.
• Considering block ciphers encrypt a whole cake at a time (and furthermore have "feedback" modes which are most recommended), they are more susceptible to racket in transmission, that is if you mess upward 1 role of the data, all the rest is probably unrecoverable. Whereas with stream ciphers are bytes are individually encrypted with not connection to other chunks of data (in most ciphers/modes), and often have back up for interruptions on the line.
• stream ciphers do not provide integrity protection or authentication, whereas some block ciphers (depending on style) can provide integrity protection, in improver to confidentiality.

Asymmetric Encryption

A pair of keys is used to encrypt and decrypt the message. The pair of keys are public and private keys. Individual keys are kept secret, known only by the owner, and the public key is visible to everyone. A and B want to communicate using asymmetric encryption. Below are the steps that happen in asymmetric encryption.

• So A encrypts the message with B'south public central(since public key is visible to everyone) and send the message to B.
• Since a public fundamental encryption can only be decrypted using its related private key, so the encrypted packet from A tin be merely decrypted past B since it possess the private cardinal.

• After decrypting the bulletin, if B wants to send the bulletin to A, then B will encrypt the message using A'southward public primal which tin can only exist decrypted by A's individual key, which just A possesses. that merely B tin decrypt the message with their individual key. After decrypting the message, B volition encrypt the message with A's public key. Just A can decrypt it using their individual primal.

  Sounds like a good solution! Well every bit far as secrecy is concerned it is, but when information technology comes to real globe applications, asymmetric encryption is pretty slow. The keys involved in this process tin be equally big as 1024 $.25 or more. Afterwards the initial handshake, for subsequent requests even more overhead is incurred. What tin can nosotros do? A hybrid approach is used, called public central infrastructure (PKI), which we volition discuss later. Start let'due south see how asymmetric keys are generated, using CrypTool.

We'll generate asymmetric keys using the RSA algorithm. RSA keys are generated with prime numbers.

Demonstration of Asymmetric Keys using CrypTool

1. Beginning, nosotros'll create RSA keys. Click on "Indiv procedures" >PKI >Generate keys.

2. Select the RSA algorithm, with a fleck length of 1024.

3. Enter the details for the cardinal pair to be created. They are the public and private key pair.

4. Click on Generate primal pair.

1. This message will announced if yous're successful.

   

2. Click on "Show Key Pair" to meet the key pair and the associated public certificate. The public certificate of the primal pair is shown below.

   

To enable RSA encryption:

1. Click on Encrypt > Asymmetric >RSA encryption.

2. Choose the previously created cardinal and click on Encrypt.

1. Here's the encrypted certificate.

To decrypt:

1. Click on Decrypt > Asymmetric >RSA decryption.

2. Select the primal pair to be decrypted and provide the fundamental used during generation.

1. Click on decrypt.

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Source: https://resources.infosecinstitute.com/topic/cryptography-fundamentals-part-2-encryption/

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