# Contemporary symmetric ciphers. What is meant by modern symmetric ciphers? 2022-10-26

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Contemporary symmetric ciphers are cryptographic algorithms that use a single secret key to both encrypt and decrypt data. They are an important tool for secure communication, allowing individuals or organizations to transmit sensitive information without fear of interception or tampering.

One of the most widely used contemporary symmetric ciphers is the Advanced Encryption Standard (AES). Developed by the National Institute of Standards and Technology (NIST) in the late 1990s, AES has become the de facto standard for symmetric encryption due to its strong security and efficiency. It uses a fixed block size of 128 bits and supports key sizes of 128, 192, and 256 bits.

Another popular symmetric cipher is the Blowfish algorithm, developed by Bruce Schneier in the early 1990s. Blowfish is a fast and secure cipher that uses a variable-length key and is well-suited for both encryption and decryption. It has a block size of 64 bits and supports key sizes ranging from 32 bits to 448 bits.

Symmetric ciphers have a number of advantages over their public key counterparts. They are generally faster and more efficient, as they do not require the use of complex mathematical operations such as factorization or discrete logarithms. They are also less computationally intensive, making them well-suited for use in resource-constrained environments.

However, symmetric ciphers also have some limitations. One of the main challenges is key management – the secret key must be securely shared between the sender and the recipient of the message. This can be difficult in situations where the sender and recipient are not in close proximity, or when the key needs to be shared with a large number of people.

In summary, contemporary symmetric ciphers are an important tool for secure communication, offering strong security and efficiency. While they do have some limitations, they remain a widely used and effective means of protecting sensitive information in a variety of contexts.

## Contemporary Symmetric Ciphers (Double

It uses block sizes of 128 bits and keys sizes of up to 256 bits. What is block cipher principles? Intuitively speaking, first applying a permutation and then another permutation is the same as applying a permutation that is the combination of the two permutations. This process uses some sort of key in the encryption and decryption algorithms. Typically this key is only a series of both the encryption and decryption algorithm. Similar to DES, each round uses a different key.

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## Symmetric Ciphers

In the United States, AES was announced by the NIST as U. Consequently, we examine the alternate application of substitutions and permutations. All the substitutions and transformations done depend on the secret key. So, a pseudo-random sequence is used. Criteria from RueppelThe RC4 key schedule initializes the state S to the numbers 0. Confusion means that each bit of the ciphertext should depend on several parts of the key. Due to these pros, however, there are a number of important symmetric ciphers in production today.

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## Modern Symmetric Ciphers Flashcards

The use of AES is ubiquitous, and the algorithm enjoys strong support in the cryptographic community. It's S-boxes, unlike in DES, are key-dependent, so they are generated dynamically. The amount of the rotation is the secret key. National Security Agency NSA for top secret information when used in an NSA approved cryptographic module. The most popular of these is Advanced Encryption Standard AES.

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## Chapter 6: Contemporary Symmetric Ciphers

However, as with the substitution, it is used as a building block for more complex encryption algorithms. Consequently, applying multiple permutations or multiple substitutions directly in sequence does not increase the security of the encryption algorithm. The result is one permutation and only one xor operation with a modified key derived from k0 and k1. For the double-DES 1. Because ECB encrypts identical plaintext blocks into identical ciphertext blocks, it does not hide data patterns well.

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## What is meant by modern symmetric ciphers?

The historical predecessor of permutations in cryptography is the so-called skytale. Because we rotate on each round, each bit is only used in approximately 14 out of the 16 rounds. There is no way to substitute this construction with simpler operations. In the advanced encryption standard AES the number of rounds is 10, 12, or 14 depending on the key length. If the key would be integrated in the substitutions or the permutations, different keys would offer different security levels. If an encryption routine is defined by simply xoring the key onto the plaintext the resulting algorithm is vulnerable.

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## Design of Modern Symmetric Ciphers

It produces plain text as output. This figure shows a construction with three rounds and four round keys. RC4 is widely used, in SSL for secure web transactions amongst other uses. In modern times, this building block is called a substitution box or simply S-box. ECB is not recommended for use in cryptographic protocols Cipher Block Chaining CBC From CBC diagram Initialization Vectors From An initialization vector IV is a block of bits that is used by several modes to randomize the encryption and hence to produce distinct ciphertexts even if the same plaintext is encrypted multiple times. Consequently, their outputs change as well. .

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## Modern Symmetric Ciphers

This key is usually decided at random to heighten security. For encrypting longer messages consisting of multiple blocks, the encrypted single blocks are chained using a so-called operation mode of the cipher. Chapter 6: Contemporary Symmetric Ciphers. Block Cipher Modes BCM of Operation The Use of Block Ciphers From A block cipher by itself is only suitable for the secure cryptographic transformation encryption or decryption of one fixed-length group of bits called a block. AES key , modes. For our purposes, define the key as consisting of two parts: k0 and k1. An initialization vector has different security requirements than a key, so the IV usually does not need to be secret.

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## INCS 741 CRYPTOGRAPHY Chapter 6 Contemporary Symmetric Ciphers

Like DES, it is a 16-round Fiestel cipher. The following figure shows a typical notation of such a network consisting of substitutions and permutations. Regarding diffusion, if a single letter of the plaintext changes then the single corresponding letter in the ciphertext changes. This property obscures the connection between the plaintext and the ciphertext. However, in symmetric cryptography, strict mathematical security proofs are hard to find.

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