What is a modern symmetric key cipher?

3. 5-1 MODERN BLOCK CIPHERS. A symmetric-key modern block cipher encrypts an n-bit block of plaintext or decrypts an n-bit block of ciphertext. The encryption or decryption algorithm uses a k-bit key.

Why is the length of the symmetric key important in modern ciphers?

Indeed, most symmetric-key algorithms are designed to have security equal to their key length. This is important for asymmetric-key algorithms, because no such algorithm is known to satisfy this property; elliptic curve cryptography comes the closest with an effective security of roughly half its key length.

How can the security of transposition ciphers be increased?

The security of transposition ciphers can be further improved by re-encrypting the resulting cipher using another transposition. Because the product of the two transpositions is also a transposition, the effect of multiple transpositions is to further increase the complexity of the route through the matrix.

What are some of the common modern symmetric ciphers?

Some popular symmetric encryption algorithms are: AES, ChaCha20, CAST, Twofish, IDEA, Serpent, RC5, RC6, Camellia and ARIA. All these algorithms are considered secure (when configured and used correctly).

How does modern ciphers achieve high confusion and diffusion properties?

For example, diffusion ensures that any patterns in the plaintext, such as redundant bits, are not apparent in the ciphertext. Block ciphers achieve this by “diffusing” the information about the plaintext’s structure across the rows and columns of the cipher.

How is symmetric ciphertext created?

Like all forms of cryptography, the general process of symmetric key cryptography is to first encrypt a message. This encryption algorithm will turn any plaintext data into ciphertext, an unreadable code. Then, that ciphertext is transmitted to another party who decrypts it to find the original message.

How do you solve permutation ciphers?

To decrypt a ciphertext encoded with the Permutation Cipher, we have to write out the ciphertext in columns (the same number as the length of the keyword). We then order the keyword alphabetically, and write the ordered keyword at the top of the columns.

How does product cipher achieve diffusion and confusion?

The simplest way to achieve both diffusion and confusion is a substitution-permutation network. In these systems, the plaintext and the key often have a very similar role in producing the output, hence it is the same mechanism that ensures both diffusion and confusion.

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