Encryption

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The purpose of my question is get an better idea about reasonable amount of time the generation of the RSA public/private keypair should take? To be less vague let me specify the question and define I would use these commands to generate the keypair on an laptop running a recent 3.2.xx linux kernel. Select Caesar mode and the “alphabet character” is “N.” That means that the text will have characters replaced starting with N. So A N, BM, and so on. Click on “encrypt.”. The document is encrypted as per the configured policy.

These are the main types of encryption.

Symmetric Encryption:

A single key is used to encrypt and decrypt the message sent between two parties. Symmetric encryption is fast, and effective only when a key is kept absolutely secret between two parties.

Demonstration of Caesar Encryption using CrypTool

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

Encryptionhttps://treebud159.weebly.com/blog/xdcam-codec-quicktime-mac-download.

1. Open the Cryptool UI and the document that needs to be encrypted.
2. Click Encrypt/Decrypt > Symmetric (classic) > Caesar

1. Select Caesar mode and the “alphabet character” is “N.” That means that the text will have characters replaced starting with N. So A >N, B>M, and so on. Click on “encrypt.”
2. The document is encrypted as per the configured policy. This is a very basic example of how symmetric encryption works.

Decryption process

Perform the following steps to decrypt the encrypted document.

1. Open the encrypted document, and click on “Encrypt.Decrypt” >Symmetric >Caesar.
2. Enter “N” 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 x-bits of key with block ciphers, message encryption and decryption happens in blocks. The most common mode of operation is cipher block chaining.

Source: Wikipedia

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

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

After the XOR operation, IV is then encrypted with the key to produce a block 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 block 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 first ciphertext is decrypted, it is then XORed with the previous block of ciphertext to produce the final block of plaintext.

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

Here’s a demonstration of a DES cipher in CBC mode.

About Data Encryption Standard (DES): DES is the archetypal block cipher — an algorithm that takes a fixed-length string of plaintext bits and transforms it through a series of complicated operations into another ciphertext bitstring of the same length. In the case of DES, the block size is 64 bits. DES also uses a key to customize the transformation, so that decryption can supposedly only be performed by those who know the particular key used to encrypt. The key ostensibly consists of 64 bits; however, only 56 of these are actually used by the algorithm. Eight bits are used solely for checking parity, and are thereafter discarded. Hence the effective key length is 56 bits, and it is always quoted as such.

Demonstration 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. Change any bit with the selected hexadecimal character. In the image below I have selected the characters ‘0’ and ‘1’.

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 you get this error message?

The error 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

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

This proves that both the parties must possess same secret key.

Now put the same key in to decrypt the document.

Stream Cipher

A stream cipher 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 corresponding digit of the keystream, to give a digit of the ciphertext stream. There are various examples of stream ciphers, like RC4, AES etc. The procedure for encryption and decryption for stream ciphers is the same as is done for block ciphers.

Block Ciphers vs Stream Ciphers

The below section will illustrate the main advantages and disadvantages of stream and block ciphers.

• Since stream ciphers work bit 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.
• One of the biggest advantage of block ciphers over stream ciphers is that they do not require padding.
• Because block ciphers encrypt a whole block at a time (and furthermore have “feedback” modes which are most recommended), they are more susceptible to noise in transmission, that is if you mess up one part 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 support for interruptions on the line.
• stream ciphers do not provide integrity protection or authentication, whereas some block ciphers (depending on mode) can provide integrity protection, in addition 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. Private 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’s public key(since public key is visible to everyone) and send the message to B.
• Since a public key encryption can only be decrypted using its related private key, so the encrypted packet from A can be only decrypted by B since it possess the private key.
• After decrypting the message, if B wants to send the message to A, then B will encrypt the message using A’s public key which can only be decrypted by A’s private key, which only A possesses. that only B can decrypt the message with their private key. After decrypting the message, B will encrypt the message with A’s public key. Only A can decrypt it using their private key.

  Sounds like a good solution! Well as far as secrecy is concerned it is, but when it comes to real world applications, asymmetric encryption is pretty slow. The keys involved in this process can be as large as 1024 bits or more. After the initial handshake, for subsequent requests even more overhead is incurred. What can we do? A hybrid approach is used, called public key infrastructure (PKI), which we will discuss later. First let’s 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. First, we’ll create RSA keys. Click on “Indiv procedures” >PKI >Generate keys.
2. Select the RSA algorithm, with a bit length of 1024.
3. Enter the details for the key pair to be created. They are the public and private key pair.

1. This message will appear if you’re successful.
2. Click on “Show Key Pair” to see the key pair and the associated public certificate. The public certificate of the key pair is shown below.

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To enable RSA encryption:

1. Choose the previously created key and click on Encrypt.

1. Here’s the encrypted document.

To decrypt:

1. Select the key pair to be decrypted and provide the key used during generation.

1. Click on decrypt.

Key generation is the process of generating keys in cryptography. A key is used to encrypt and decrypt whatever data is being encrypted/decrypted.

A device or program used to generate keys is called a key generator or keygen.

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Generation in cryptography[edit]

Modern cryptographic systems include symmetric-key algorithms (such as DES and AES) and public-key algorithms (such as RSA). Symmetric-key algorithms use a single shared key; keeping data secret requires keeping this key secret. Public-key algorithms use a public key and a private key. The public key is made available to anyone (often by means of a digital certificate). A sender encrypts data with the receiver's public key; only the holder of the private key can decrypt this data.

Since public-key algorithms tend to be much slower than symmetric-key algorithms, modern systems such as TLS and SSH use a combination of the two: one party receives the other's public key, and encrypts a small piece of data (either a symmetric key or some data used to generate it). The remainder of the conversation uses a (typically faster) symmetric-key algorithm for encryption.

Computer cryptography uses integers for keys. In some cases keys are randomly generated using a random number generator (RNG) or pseudorandom number generator (PRNG). A PRNG is a computeralgorithm that produces data that appears random under analysis. PRNGs that use system entropy to seed data generally produce better results, since this makes the initial conditions of the PRNG much more difficult for an attacker to guess. Another way to generate randomness is to utilize information outside the system. veracrypt (a disk encryption software) utilizes user mouse movements to generate unique seeds, in which users are encouraged to move their mouse sporadically. In other situations, the key is derived deterministically using a passphrase and a key derivation function.

Many modern protocols are designed to have forward secrecy, which requires generating a fresh new shared key for each session.

Classic cryptosystems invariably generate two identical keys at one end of the communication link and somehow transport one of the keys to the other end of the link.However, it simplifies key management to use Diffie–Hellman key exchange instead.

The simplest method to read encrypted data without actually decrypting it is a brute-force attack—simply attempting every number, up to the maximum length of the key. /activation-key-generator-for-pes-2017-for-pc.html. Therefore, it is important to use a sufficiently long key length; longer keys take exponentially longer to attack, rendering a brute-force attack impractical. Currently, key lengths of 128 bits (for symmetric key algorithms) and 2048 bits (for public-key algorithms) are common.

Generation in physical layer[edit]

Wireless channels[edit]

A wireless channel is characterized by its two end users. By transmitting pilot signals, these two users can estimate the channel between them and use the channel information to generate a key which is secret only to them.^[1] The common secret key for a group of users can be generated based on the channel of each pair of users.^[2]

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Optical fiber[edit]

A key can also be generated by exploiting the phase fluctuation in a fiber link.^{[clarification needed]}

See also[edit]

• Distributed key generation: For some protocols, no party should be in the sole possession of the secret key. Rather, during distributed key generation, every party obtains a share of the key. A threshold of the participating parties need to cooperate to achieve a cryptographic task, such as decrypting a message.

References[edit]

1. ^Chan Dai Truyen Thai; Jemin Lee; Tony Q. S. Quek (Feb 2016). 'Physical-Layer Secret Key Generation with Colluding Untrusted Relays'. IEEE Transactions on Wireless Communications. 15 (2): 1517–1530. doi:10.1109/TWC.2015.2491935.
2. ^Chan Dai Truyen Thai; Jemin Lee; Tony Q. S. Quek (Dec 2015). 'Secret Group Key Generation in Physical Layer for Mesh Topology'. 2015 IEEE Global Communications Conference (GLOBECOM). San Diego. pp. 1–6. doi:10.1109/GLOCOM.2015.7417477.

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