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Se refiere a que es un diseño de estructura para los algoritmos de cifrado de bloque, se utiliza en lo que sería varios sistemas de cifrado como el DES. También se refiere a que es una estructura que divide el bloque de datos en dos mitades y realiza múltiples rondas de transformaciones matemáticas con la ayuda de una función de permutación y una clave secreta.

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Originally published by TokenEx here. Written by Valerie Hare, Content Marketing Specialist, TokenEx.
Quick Hits:

Feistel cipher is a design model designed to create different block ciphers, such as DES.

The model uses substitution and permutation alternately.

This cipher structure is based on the Shannon model proposed in 1945.

What Is a Feistel Cipher?

The Feistel cipher is a design model or structure used to build various symmetric block ciphers, such as DES. This design model can have invertible, non-invertible, and self-invertible components. Additionally, the Feistel block cipher uses the same encryption and decryption algorithms.

The Feistel structure is based on the Shannon structure proposed in 1945, demonstrating the confusion and diffusion implementation processes. Confusion produces a complex relationship between the ciphertext and encryption key, which is done by using a substitution algorithm. On the other hand, diffusion creates a complex relationship between plain text and cipher text by using a permutation algorithm.

The Feistel cipher proposed the structure that implements substitution and permutation alternately. Substitution replaces plain text elements with ciphertext. Permutation changes the order of the plain text elements rather than being replaced by another element as done with substitution.

Feistel Cipher Encryption Example

The Feistel cipher encryption process involves numerous rounds of processing plain text. Each round includes the substitution step and then the permutation step. Check out the following example describing the encryption structure used for this design model.

Step 1 - The first step involves the plain text being divided into blocks of a fixed size, with only one block being processed at a time. The encryption algorithm input consists of a plain text block and a key K.

Step 2 - The plain text block is divided into two halves. The left half of the plain text block will be represented as LE0, and the right half of the block will be RE0. Both halves of the plain text block (LE0 and RE0) will go through numerous rounds of processing plain text to produce the ciphertext block.

For every round, the encryption function is applied on the right half REi of the plain text block plus the key Ki. The function results are then XORed with the left half LEj. XOR is a logical operator used in cryptography that compares two input bits and produces one output bit. The XOR function results become the new right half for the next round RE i+1. The previous right half REi becomes the new left half LEi+1 for the next round.

Every round will execute the same function, in which a substitution function is implemented by using the round function to the right half of the plain text block. The result of this function is XORed by using the left half of the block. Then, a permutation function is used by switching the two halves. The permutation results are provided for the next round. Indeed, this is how the Feistel cipher model implements the substitution and permutation steps alternately, similar to the Shannon structure mentioned above.

Block size - Block ciphers are considered more secure when the block size is larger. Though, larger block sizes reduce the execution speed for the encryption and decryption process. Typically, block ciphers have a block size of 64-bits, but modern blocks like AES (Advanced Encryption Standard) are 128-bits.

Easy analysis - Block ciphers should be easy to analyze, which can help identify and address any cryptanalytic weaknesses to create more robust algorithms.

Key size - Like the block size, larger key sizes are considered more secure at the cost of potentially slowing down the time it takes to finish the encryption and decryption process. Modern ciphers use a 128-bit key, which has replaced the earlier 64-bit version.

The number of rounds - The number of rounds can also impact the security of a block cipher. While more rounds increase security, the cipher is more complex to decrypt. Thus, the number of rounds depends on a business's desired level of data protection.

Round function - A complex round function helps boost the block cipher's security.

Subkey generation function - The more complex a subkey generation function is, the more difficult it is for expert cryptanalysts to decrypt the cipher.

Quick software encryption and decryption - It's helpful to use a software application that can help produce faster execution speeds for block ciphers.

Feistel cipher design features that are considered when using block ciphers:

Feistel Cipher Decryption Example

It may be surprising that the Feistel cipher model uses the same algorithm for encryption and decryption. There are a couple of key rules to consider during the decryption process:

As shown in the figure above, the cipher text block contains two halves, the left (LD0) and the right (RD0).

Like the encryption algorithm, the round function is executed on the right half of the cipher block with the key K16. The function's result is XORed with the left half of the cipher text block. The XOR function's output becomes the new right half (RD1), while RD0 switches with LD0 for the next round. Indeed, every round uses the same function, and once the fixed number of rounds is executed, the plain text block is achieved.

Final Points

The Feistel cipher is a well-known cryptography design model that organizations can use to help secure their sensitive data. Even if a hacker knows the cipher algorithm, a strong encryption cipher should prevent the criminal from deciphering the cipher plain text without having the key or sets of keys. In addition to this cipher model, businesses should adopt a layered cybersecurity strategy to help prevent threat actors from stealing or exposing their sensitive information. Tokenization is an effective solution that replaces original data with unique, randomly generated numbers called tokens. Tokenized data can be stored and managed via a secure cloud platform. If a breach impacts an organization, hackers will only be left with tokens that lack valuable information.

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The Feistel cipher is a well-known cryptography design model that organizations can use to help secure their sensitive data.

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Su funcionamiento es que primero de un bloque de datos se divide en dos mitades iguales, denominadas como L y R. Después se nos dice que en cada ronda se realiza una serie de transformaciones sobre estas mitades, además de que se aplica una función de cifrado a la mitad derecha y luego se combina el resultado con la mitad izquierda mediante una operación. Al final se repetirá durante varias rondas, para que las mitades se recombinen para así formar el texto cifrado.

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Originally published by TokenEx here. Written by Valerie Hare, Content Marketing Specialist, TokenEx.
Quick Hits:

Feistel cipher is a design model designed to create different block ciphers, such as DES.

The model uses substitution and permutation alternately.

This cipher structure is based on the Shannon model proposed in 1945.

What Is a Feistel Cipher?

The Feistel cipher is a design model or structure used to build various symmetric block ciphers, such as DES. This design model can have invertible, non-invertible, and self-invertible components. Additionally, the Feistel block cipher uses the same encryption and decryption algorithms.

The Feistel structure is based on the Shannon structure proposed in 1945, demonstrating the confusion and diffusion implementation processes. Confusion produces a complex relationship between the ciphertext and encryption key, which is done by using a substitution algorithm. On the other hand, diffusion creates a complex relationship between plain text and cipher text by using a permutation algorithm.

The Feistel cipher proposed the structure that implements substitution and permutation alternately. Substitution replaces plain text elements with ciphertext. Permutation changes the order of the plain text elements rather than being replaced by another element as done with substitution.

Feistel Cipher Encryption Example

The Feistel cipher encryption process involves numerous rounds of processing plain text. Each round includes the substitution step and then the permutation step. Check out the following example describing the encryption structure used for this design model.

Step 1 - The first step involves the plain text being divided into blocks of a fixed size, with only one block being processed at a time. The encryption algorithm input consists of a plain text block and a key K.

Step 2 - The plain text block is divided into two halves. The left half of the plain text block will be represented as LE0, and the right half of the block will be RE0. Both halves of the plain text block (LE0 and RE0) will go through numerous rounds of processing plain text to produce the ciphertext block.

For every round, the encryption function is applied on the right half REi of the plain text block plus the key Ki. The function results are then XORed with the left half LEj. XOR is a logical operator used in cryptography that compares two input bits and produces one output bit. The XOR function results become the new right half for the next round RE i+1. The previous right half REi becomes the new left half LEi+1 for the next round.

Every round will execute the same function, in which a substitution function is implemented by using the round function to the right half of the plain text block. The result of this function is XORed by using the left half of the block. Then, a permutation function is used by switching the two halves. The permutation results are provided for the next round. Indeed, this is how the Feistel cipher model implements the substitution and permutation steps alternately, similar to the Shannon structure mentioned above.

Block size - Block ciphers are considered more secure when the block size is larger. Though, larger block sizes reduce the execution speed for the encryption and decryption process. Typically, block ciphers have a block size of 64-bits, but modern blocks like AES (Advanced Encryption Standard) are 128-bits.

Easy analysis - Block ciphers should be easy to analyze, which can help identify and address any cryptanalytic weaknesses to create more robust algorithms.

Key size - Like the block size, larger key sizes are considered more secure at the cost of potentially slowing down the time it takes to finish the encryption and decryption process. Modern ciphers use a 128-bit key, which has replaced the earlier 64-bit version.

The number of rounds - The number of rounds can also impact the security of a block cipher. While more rounds increase security, the cipher is more complex to decrypt. Thus, the number of rounds depends on a business's desired level of data protection.

Round function - A complex round function helps boost the block cipher's security.

Subkey generation function - The more complex a subkey generation function is, the more difficult it is for expert cryptanalysts to decrypt the cipher.

Quick software encryption and decryption - It's helpful to use a software application that can help produce faster execution speeds for block ciphers.

Feistel cipher design features that are considered when using block ciphers:

Feistel Cipher Decryption Example

It may be surprising that the Feistel cipher model uses the same algorithm for encryption and decryption. There are a couple of key rules to consider during the decryption process:

As shown in the figure above, the cipher text block contains two halves, the left (LD0) and the right (RD0).

Like the encryption algorithm, the round function is executed on the right half of the cipher block with the key K16. The function's result is XORed with the left half of the cipher text block. The XOR function's output becomes the new right half (RD1), while RD0 switches with LD0 for the next round. Indeed, every round uses the same function, and once the fixed number of rounds is executed, the plain text block is achieved.

Final Points

The Feistel cipher is a well-known cryptography design model that organizations can use to help secure their sensitive data. Even if a hacker knows the cipher algorithm, a strong encryption cipher should prevent the criminal from deciphering the cipher plain text without having the key or sets of keys. In addition to this cipher model, businesses should adopt a layered cybersecurity strategy to help prevent threat actors from stealing or exposing their sensitive information. Tokenization is an effective solution that replaces original data with unique, randomly generated numbers called tokens. Tokenized data can be stored and managed via a secure cloud platform. If a breach impacts an organization, hackers will only be left with tokens that lack valuable information.

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The Feistel cipher is a well-known cryptography design model that organizations can use to help secure their sensitive data.

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¿Cuáles Son Sus Principios Y Conceptos Importantes?

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¿Cuáles Son Sus Principios Y Conceptos Importantes?

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Primero es que uno de sus principios es que feistel es un sistema simétrico, lo que significa que el mismo proceso se usa para cifrar y descifrar. También que el numero de rondas es un parámetro importante en la seguridad de un algoritmo feistel en donde cuantas mas rondas mayor aumenta la seguridad. Por ultimo es que la estructura feistel tiene la propiedad de que la misma función puede ser utilizada para el cifrado y el descifrado, lo que la hace eficiente ene términos de calculo.

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Block ciphers are built in the Feistel cipher structure. Block cipher has a specific number of rounds and keys for generating ciphertext.Block cipher is a type of encryption algorithm that processes fixed-size blocks of data, usually 64 or 128 bits, to produce ciphertext. The design of a block cipher involves several important principles to ensure the security and efficiency of the algorithm. Some of these principles are:

1. Number of Rounds - The number of Rounds is regularly considered in design criteria, it just reflects the number of rounds to be suitable for an algorithm to make it more complex, in DES we have 16 rounds ensuring it to be more secure while in AES we have 10 rounds which makes it more secure.

2. Design of function F - The core part of the Feistel Block cipher structure is the Round Function. The complexity of cryptanalysis can be derived from the Round function i.e. the increasing level of complexity for the round function would be greatly contributing to an increase in complexity. To increase the complexity of the round function, the avalanche effect is also included in the round function, as the change of a single bit in plain text would produce a mischievous output due to the presence of avalanche effect.

3. Confusion and Diffusion: The cipher should provide confusion and diffusion to make it difficult for an attacker to determine the relationship between the plaintext and ciphertext. Confusion means that the ciphertext should be a complex function of the key and plaintext, making it difficult to guess the key. Diffusion means that a small change in the plaintext should cause a significant change in the ciphertext, which makes it difficult to analyze the encryption pattern.

4. Key Size: The key size should be large enough to prevent brute-force attacks. A larger key size means that there are more possible keys, making it harder for an attacker to guess the correct one. A key size of 128 bits is considered to be secure for most applications.

5. Key Schedule: The key schedule should be designed carefully to ensure that the keys used for encryption are independent and unpredictable. The key schedule should also resist attacks that exploit weak keys or key-dependent properties of the cipher.

6. Block Size: The block size should be large enough to prevent attacks that exploit statistical patterns in the plaintext. A block size of 128 bits is generally considered to be secure for most applications.

7. Non-linearity: The S-box used in the cipher should be non-linear to provide confusion. A linear S-box is vulnerable to attacks that exploit the linear properties of the cipher.

8. Avalanche Effect: The cipher should exhibit the avalanche effect, which means that a small change in the plaintext or key should cause a significant change in the ciphertext. This ensures that any change in the input results in a complete change in the output.

9. Security Analysis: The cipher should be analyzed for its security against various attacks such as differential cryptanalysis, linear cryptanalysis, and brute-force attacks. The cipher should also be tested for its resistance to implementation attacks, such as side-channel attacks.

Overall, a good block cipher design should be resistant to various attacks, efficient, and easy to implement.

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Block Cipher Design Principles - GeeksforGeeks

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A Computer Science portal for geeks. It contains well written, well thought and well explained computer science and programming articles, quizzes and practice/competitive programming/company interview Questions.

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Es un algoritmo de cifrado simétrico que utiliza un bloque de datos de 64 bits y una clave de 56 bits. DES realiza 16 rondas de transformaciones sobre el bloque de datos para cifrarlo.

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¿Qué es el DES? Si quieres descubrir realmente su significado, MSMK te aporta todo lo que necesitas, sigue leyendo en el enlace a la web!

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El efecto de avalancha en sí se refiere a un concepto de clave en criptografía que describe como un pequeño cambio en los datos de entrada (como lo que sería de un solo bit) debería producir un cambio significativo en el resultado como en el texto cifrado.

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The avalanche effect in cryptography refers to the phenomenon where a small change in the input of a cryptographic function, such as a hash function, results in a significant and seemingly unrelated change in the output. This property is desirable in cryptographic functions because it makes it difficult for an attacker to predict the output of the function based on partial knowledge of the input.

For example, consider a hash function that takes an input string and produces a fixed-size output. If the avalanche effect is strong, then making a small change to the input string, such as changing a single character, should result in a completely different output. This makes it difficult for an attacker to determine the original input by examining the output, as any change to the input will result in a significantly different output.

The avalanche effect is typically used as a measure of the quality of a cryptographic function. A function with a strong avalanche effect is considered to be more secure than a function with a weak avalanche effect, as it is more resistant to attacks that rely on predicting the output of the function based on partial knowledge of the input.

What is Cryptography?

Cryptography is the practice of secure communication in the presence of third parties. It is a mathematical science that uses techniques such as encryption and digital signing to protect the privacy and integrity of data and communications.

Encryption is the process of converting plaintext (unencrypted data) into ciphertext (encrypted data) using a secret key or password. Decryption is the reverse process, converting ciphertext back into plaintext using the same key or password. Encryption is used to protect data from unauthorized access or modification, as only someone with the correct key or password can decrypt and read the encrypted data.

Digital signing is a process that allows someone to verify the authenticity and integrity of a message or document. It involves the use of a private key to generate a unique digital signature, which is attached to the message or document. The signature can then be verified using the corresponding public key, which is available to anyone. Digital signing is used to ensure that a message or document has not been tampered with and to confirm the identity of the sender.

Cryptography is used in a wide range of applications, including email and messaging, online banking and shopping, and secure communication between servers. It is an essential tool for protecting sensitive information and maintaining the privacy and security of online communications.

What is Avalanche Effect?

The avalanche effect is a phenomenon that occurs in cryptographic functions, such as hash functions, where a small change in the input results in a significant and seemingly unrelated change in the output. This property is desirable in cryptographic functions because it makes it difficult for an attacker to predict the output of the function based on partial knowledge of the input.

For example, consider a hash function that takes an input string and produces a fixed-size output. If the avalanche effect is strong, then making a small change to the input string, such as changing a single character, should result in a completely different output. This makes it difficult for an attacker to determine the original input by examining the output, as any change to the input will result in a significantly different output.

The avalanche effect is typically used as a measure of the quality of a cryptographic function. A function with a strong avalanche effect is considered to be more secure than a function with a weak avalanche effect, as it is more resistant to attacks that rely on predicting the output of the function based on partial knowledge of the input.

Avalanche Effect examples

Here are some examples of the avalanche effect in cryptographic functions −

Hash functions − A hash function takes an input (called the message) and produces a fixed-size output (called the hash or message digest). If the avalanche effect is strong, then making a small change to the message should result in a completely different hash. For example, consider the following message and hash −

Message − "Hello World"

Hash − "86fb269d190d2c85f6e0468ceca42a20"

If we change just one character in the message, such as changing "o" to "O", the resulting hash should be completely different −

Message − "HellO World"

Hash − "8761d55f6a44d6b95f6e0468ceca42a6"

Block ciphers − A block cipher is a cryptographic function that takes a fixed-size block of plaintext as input and produces a block of ciphertext as output. If the avalanche effect is strong, then making a small change to the plaintext should result in a completely different ciphertext. For example, consider the following plaintext and ciphertext −

Plaintext − "Hello World"

Ciphertext − "9f1c9dbbf2d16a2c4918b2cc2f32d7a7"

If we change just one character in the plaintext, such as changing "o" to "O", the resulting ciphertext should be completely different −

Plaintext − "HellO World"

Ciphertext − "9f1c9dbb3cf8b1408e1d5a5b5a5b5b5b"

Stream ciphers − A stream cipher is a cryptographic function that generates a stream of key bits that are combined with the plaintext to produce the ciphertext. If the avalanche effect is strong, then making a small change to the plaintext should result in a completely different key stream, which in turn should result in a completely different ciphertext. For example, consider the following plaintext and ciphertext −

Plaintext − "Hello World"

Ciphertext − "9f1c9dbbf2d16a2c4918b2cc2f32d7a7"

If we change just one character in the plaintext, such as changing "o" to "O", the resulting ciphertext should be completely different −

Plaintext − "Hello World"

Ciphertext − "9f1c9dbb3cf8b1408e1d5a5b5a5b5b5b"

Get Started

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Avalanche Effect in Cryptography - The avalanche effect in cryptography refers to the phenomenon where a small change in the input of a cryptographic function, such as a hash function, results in a significant and seemingly unrelated change in the output.

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Define Y Clasifica Cuales Son Los Principios De Diseño De Cifrado De Bloque Principal

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Define Y Clasifica Cuales Son Los Principios De Diseño De Cifrado De Bloque Principal

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Confusión: Asegurar que la relación entre el texto plano y el texto cifrado sea compleja, es decir, que no haya una relación obvia entre ambos.

Difusión: Asegurar que los bits del texto plano se distribuyan de manera uniforme en el texto cifrado, dificultando la predicción de las características del mensaje original.

Seguridad: Utilizar claves secretas de tamaño adecuado para garantizar que sea difícil para un atacante descubrir.

Resistencia a ataques: Los algoritmos deben ser diseñados de tal forma que resistan ataques conocidos, como los ataques de texto conocido y el ataque de fuerza bruta.

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Block Cipher: A Comprehensive Guide For 2021 | UNext

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What is a block cipher? It is a data encryption method that takes in a block of plain text and generates a block of ciphertext of roughly the same size. A

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Es un algoritmo de cifrado por bloques que reemplazó lo que sería el DES como estándar en 2001. Utiliza tamaños clave de 128, 192 o 256 bits para cifrar bloques de 128 bits de datos.

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¿Qué es el cifrado AES? - Panda Security

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Te detallamos qué es el cifrado AES, cómo funciona y cómo Panda puede proporcionarte este valioso método de seguridad.

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Feistel Encoding (Cipher) made easy + step by step example ✅️