Information and data security block cipher and the data encryption standard (...Mazin Alwaaly
Information And Data Security Block Cipher and the data encryption standard (DES) seminar
Mustansiriya University
Department of Education
Computer Science
Information and data security block cipher and the data encryption standard (...Mazin Alwaaly
Information And Data Security Block Cipher and the data encryption standard (DES) seminar
Mustansiriya University
Department of Education
Computer Science
There is great research in the field of data security these days. Storing information digitally in the cloud and transferring it over the internet proposes risks of disclosure and unauthorized access, thus users, organizations and businesses are adapting new technology and methods to protect their data from breaches. In this paper, we introduce a method to provide higher security for data transferred over the internet, or information based in the cloud. The introduced method for the most part depends on the Advanced Encryption Standard (AES) algorithm. Which is currently the standard for secret key encryption. A standardized version of the algorithm was used by The Federal Information Processing Standard 197 called Rijndael for the Advanced Encryption Standard. The AES algorithm processes data through a combination of Exclusive-OR operations (XOR), octet substitution with an S-box, row and column rotations, and a MixColumn operations. The fact that the algorithm could be easily implemented and run on a regular computer in a reasonable amount of time made it highly favorable and successful.
In this paper, the proposed method provides a new dimension of security to the AES algorithm by securing the key itself such that even when the key is disclosed, the text cannot be deciphered. This is done by enciphering the key using Output Feedback Block Mode Operation. This introduces a new level of security to the key in a way in which deciphering the data requires prior knowledge of the key and the algorithm used to encipher the key for the purpose of deciphering the transferred text.
Keywords: Keywords: Keywords: Keywords: Keywords: Keywords: Keywords:
Stream Cipher
Block Cipher
Stream Cipher and Block Cipher
The Feistel Cipher
Feistel Cipher Design Features
Data Encryption Standard (DES)
DES is a block cipher
THE AVALANCHE EFFECT
Block Cipher Design Principles
Performance Analysis of Data Encryption Standard DESijtsrd
Information security is becoming much more important in data storage and transmission with the fast progression of digital data exchange in electronic way. Cryptography has come up as a solution which plays a vital role in information security system against malicious attacks. The cryptography is most important aspect of communications security and becoming an important building block for computer security. This security mechanism uses some algorithms to scramble data into unreadable text which can be only being decoded or decrypted by party those possesses the associated key. To protect sent messages that some of the most commonly used cryptography methods with private key based algorithm are LOKI 89, 91, 97 , DES, triple DES, AES, Blowfish, etc. These algorithms also include several computational issues as well as the analysis of DES algorithm. The main features that specify and differentiate one algorithm from another are the ability to the speed of encryption and decryption of the input plain text. This paper analyzes the private key based algorithm DES and LOKI91 by computing index of coincidence IC and time efficiency. Thida Soe | Soe Soe Mon | Khin Aye Thu "Performance Analysis of Data Encryption Standard (DES)" Published in International Journal of Trend in Scientific Research and Development (ijtsrd), ISSN: 2456-6470, Volume-3 | Issue-5 , August 2019, URL: https://www.ijtsrd.com/papers/ijtsrd26650.pdfPaper URL: https://www.ijtsrd.com/computer-science/computer-security/26650/performance-analysis-of-data-encryption-standard-des/thida-soe
There is great research in the field of data security these days. Storing information digitally in the cloud and transferring it over the internet proposes risks of disclosure and unauthorized access, thus users, organizations and businesses are adapting new technology and methods to protect their data from breaches. In this paper, we introduce a method to provide higher security for data transferred over the internet, or information based in the cloud. The introduced method for the most part depends on the Advanced Encryption Standard (AES) algorithm. Which is currently the standard for secret key encryption. A standardized version of the algorithm was used by The Federal Information Processing Standard 197 called Rijndael for the Advanced Encryption Standard. The AES algorithm processes data through a combination of Exclusive-OR operations (XOR), octet substitution with an S-box, row and column rotations, and a MixColumn operations. The fact that the algorithm could be easily implemented and run on a regular computer in a reasonable amount of time made it highly favorable and successful.
In this paper, the proposed method provides a new dimension of security to the AES algorithm by securing the key itself such that even when the key is disclosed, the text cannot be deciphered. This is done by enciphering the key using Output Feedback Block Mode Operation. This introduces a new level of security to the key in a way in which deciphering the data requires prior knowledge of the key and the algorithm used to encipher the key for the purpose of deciphering the transferred text.
Keywords: Keywords: Keywords: Keywords: Keywords: Keywords: Keywords:
Stream Cipher
Block Cipher
Stream Cipher and Block Cipher
The Feistel Cipher
Feistel Cipher Design Features
Data Encryption Standard (DES)
DES is a block cipher
THE AVALANCHE EFFECT
Block Cipher Design Principles
Performance Analysis of Data Encryption Standard DESijtsrd
Information security is becoming much more important in data storage and transmission with the fast progression of digital data exchange in electronic way. Cryptography has come up as a solution which plays a vital role in information security system against malicious attacks. The cryptography is most important aspect of communications security and becoming an important building block for computer security. This security mechanism uses some algorithms to scramble data into unreadable text which can be only being decoded or decrypted by party those possesses the associated key. To protect sent messages that some of the most commonly used cryptography methods with private key based algorithm are LOKI 89, 91, 97 , DES, triple DES, AES, Blowfish, etc. These algorithms also include several computational issues as well as the analysis of DES algorithm. The main features that specify and differentiate one algorithm from another are the ability to the speed of encryption and decryption of the input plain text. This paper analyzes the private key based algorithm DES and LOKI91 by computing index of coincidence IC and time efficiency. Thida Soe | Soe Soe Mon | Khin Aye Thu "Performance Analysis of Data Encryption Standard (DES)" Published in International Journal of Trend in Scientific Research and Development (ijtsrd), ISSN: 2456-6470, Volume-3 | Issue-5 , August 2019, URL: https://www.ijtsrd.com/papers/ijtsrd26650.pdfPaper URL: https://www.ijtsrd.com/computer-science/computer-security/26650/performance-analysis-of-data-encryption-standard-des/thida-soe
Automobile Management System Project Report.pdfKamal Acharya
The proposed project is developed to manage the automobile in the automobile dealer company. The main module in this project is login, automobile management, customer management, sales, complaints and reports. The first module is the login. The automobile showroom owner should login to the project for usage. The username and password are verified and if it is correct, next form opens. If the username and password are not correct, it shows the error message.
When a customer search for a automobile, if the automobile is available, they will be taken to a page that shows the details of the automobile including automobile name, automobile ID, quantity, price etc. “Automobile Management System” is useful for maintaining automobiles, customers effectively and hence helps for establishing good relation between customer and automobile organization. It contains various customized modules for effectively maintaining automobiles and stock information accurately and safely.
When the automobile is sold to the customer, stock will be reduced automatically. When a new purchase is made, stock will be increased automatically. While selecting automobiles for sale, the proposed software will automatically check for total number of available stock of that particular item, if the total stock of that particular item is less than 5, software will notify the user to purchase the particular item.
Also when the user tries to sale items which are not in stock, the system will prompt the user that the stock is not enough. Customers of this system can search for a automobile; can purchase a automobile easily by selecting fast. On the other hand the stock of automobiles can be maintained perfectly by the automobile shop manager overcoming the drawbacks of existing system.
COLLEGE BUS MANAGEMENT SYSTEM PROJECT REPORT.pdfKamal Acharya
The College Bus Management system is completely developed by Visual Basic .NET Version. The application is connect with most secured database language MS SQL Server. The application is develop by using best combination of front-end and back-end languages. The application is totally design like flat user interface. This flat user interface is more attractive user interface in 2017. The application is gives more important to the system functionality. The application is to manage the student’s details, driver’s details, bus details, bus route details, bus fees details and more. The application has only one unit for admin. The admin can manage the entire application. The admin can login into the application by using username and password of the admin. The application is develop for big and small colleges. It is more user friendly for non-computer person. Even they can easily learn how to manage the application within hours. The application is more secure by the admin. The system will give an effective output for the VB.Net and SQL Server given as input to the system. The compiled java program given as input to the system, after scanning the program will generate different reports. The application generates the report for users. The admin can view and download the report of the data. The application deliver the excel format reports. Because, excel formatted reports is very easy to understand the income and expense of the college bus. This application is mainly develop for windows operating system users. In 2017, 73% of people enterprises are using windows operating system. So the application will easily install for all the windows operating system users. The application-developed size is very low. The application consumes very low space in disk. Therefore, the user can allocate very minimum local disk space for this application.
Explore the innovative world of trenchless pipe repair with our comprehensive guide, "The Benefits and Techniques of Trenchless Pipe Repair." This document delves into the modern methods of repairing underground pipes without the need for extensive excavation, highlighting the numerous advantages and the latest techniques used in the industry.
Learn about the cost savings, reduced environmental impact, and minimal disruption associated with trenchless technology. Discover detailed explanations of popular techniques such as pipe bursting, cured-in-place pipe (CIPP) lining, and directional drilling. Understand how these methods can be applied to various types of infrastructure, from residential plumbing to large-scale municipal systems.
Ideal for homeowners, contractors, engineers, and anyone interested in modern plumbing solutions, this guide provides valuable insights into why trenchless pipe repair is becoming the preferred choice for pipe rehabilitation. Stay informed about the latest advancements and best practices in the field.
Vaccine management system project report documentation..pdfKamal Acharya
The Division of Vaccine and Immunization is facing increasing difficulty monitoring vaccines and other commodities distribution once they have been distributed from the national stores. With the introduction of new vaccines, more challenges have been anticipated with this additions posing serious threat to the already over strained vaccine supply chain system in Kenya.
Overview of the fundamental roles in Hydropower generation and the components involved in wider Electrical Engineering.
This paper presents the design and construction of hydroelectric dams from the hydrologist’s survey of the valley before construction, all aspects and involved disciplines, fluid dynamics, structural engineering, generation and mains frequency regulation to the very transmission of power through the network in the United Kingdom.
Author: Robbie Edward Sayers
Collaborators and co editors: Charlie Sims and Connor Healey.
(C) 2024 Robbie E. Sayers
Final project report on grocery store management system..pdfKamal Acharya
In today’s fast-changing business environment, it’s extremely important to be able to respond to client needs in the most effective and timely manner. If your customers wish to see your business online and have instant access to your products or services.
Online Grocery Store is an e-commerce website, which retails various grocery products. This project allows viewing various products available enables registered users to purchase desired products instantly using Paytm, UPI payment processor (Instant Pay) and also can place order by using Cash on Delivery (Pay Later) option. This project provides an easy access to Administrators and Managers to view orders placed using Pay Later and Instant Pay options.
In order to develop an e-commerce website, a number of Technologies must be studied and understood. These include multi-tiered architecture, server and client-side scripting techniques, implementation technologies, programming language (such as PHP, HTML, CSS, JavaScript) and MySQL relational databases. This is a project with the objective to develop a basic website where a consumer is provided with a shopping cart website and also to know about the technologies used to develop such a website.
This document will discuss each of the underlying technologies to create and implement an e- commerce website.
Courier management system project report.pdfKamal Acharya
It is now-a-days very important for the people to send or receive articles like imported furniture, electronic items, gifts, business goods and the like. People depend vastly on different transport systems which mostly use the manual way of receiving and delivering the articles. There is no way to track the articles till they are received and there is no way to let the customer know what happened in transit, once he booked some articles. In such a situation, we need a system which completely computerizes the cargo activities including time to time tracking of the articles sent. This need is fulfilled by Courier Management System software which is online software for the cargo management people that enables them to receive the goods from a source and send them to a required destination and track their status from time to time.
Quality defects in TMT Bars, Possible causes and Potential Solutions.PrashantGoswami42
Maintaining high-quality standards in the production of TMT bars is crucial for ensuring structural integrity in construction. Addressing common defects through careful monitoring, standardized processes, and advanced technology can significantly improve the quality of TMT bars. Continuous training and adherence to quality control measures will also play a pivotal role in minimizing these defects.
Quality defects in TMT Bars, Possible causes and Potential Solutions.
CNS2 unit 2.pdf
1. Feistel Block Cipher
Feistel Cipher is not a specific scheme of block cipher. It is a design model from which
many different block ciphers are derived. DES is just one example of a Feistel Cipher.
A cryptographic system based on Feistel cipher structure uses the same algorithm for
both encryption and decryption.
Encryption Process
The encryption process uses the Feistel structure consisting multiple rounds of
processing of the plaintext, each round consisting of a “substitution” step followed by
a permutation step.
Feistel Structure is shown in the following illustration −
The input block to each round is divided into two halves that can be denoted as
L and R for the left half and the right half.
2. In each round, the right half of the block, R, goes through unchanged. But the
left half, L, goes through an operation that depends on R and the encryption
key. First, we apply an encrypting function ‘f’ that takes two input − the key K
and R. The function produces the output f(R,K). Then, we XOR the output of the
mathematical function with L.
In real implementation of the Feistel Cipher, such as DES, instead of using the
whole encryption key during each round, a round-dependent key (a subkey) is
derived from the encryption key. This means that each round uses a different
key, although all these subkeys are related to the original key.
The permutation step at the end of each round swaps the modified L and
unmodified R. Therefore, the L for the next round would be R of the current
round. And R for the next round be the output L of the current round.
Above substitution and permutation steps form a ‘round’. The number of rounds
are specified by the algorithm design.
Once the last round is completed then the two sub blocks, ‘R’ and ‘L’ are
concatenated in this order to form the ciphertext block.
The difficult part of designing a Feistel Cipher is selection of round function ‘f’. In order
to be unbreakable scheme, this function needs to have several important properties
that are beyond the scope of our discussion.
Decryption Process
The process of decryption in Feistel cipher is almost similar. Instead of starting with a
block of plaintext, the ciphertext block is fed into the start of the Feistel structure and
then the process thereafter is exactly the same as described in the given illustration.
The process is said to be almost similar and not exactly same. In the case of
decryption, the only difference is that the subkeys used in encryption are used in the
reverse order.
The final swapping of ‘L’ and ‘R’ in last step of the Feistel Cipher is essential. If these
are not swapped then the resulting ciphertext could not be decrypted using the same
algorithm.
Number of Rounds
The number of rounds used in a Feistel Cipher depends on desired security from the
system. More number of rounds provide more secure system. But at the same time,
more rounds mean the inefficient slow encryption and decryption processes. Number
of rounds in the systems thus depend upon efficiency–security tradeoff.
Block Cipher Design Principles
Block ciphers are built in the Feistel cipher structure. Block cipher has a
specific number of rounds and keys for generating ciphertext. For defining
the complexity level of an algorithm few design principles are to be
considered.
These are explained as following below :
3. 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.
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.
Key schedule algorithm –
In Feistel Block cipher structure, each round would generate a sub-key for
increasing the complexity of cryptanalysis. The Avalanche effect makes it
more complex in deriving sub-key. Decryption must be done very carefully
to get the actual output as the avalanche effect is present in it.
Triple DES
The speed of exhaustive key searches against DES after 1990 began to
cause discomfort amongst users of DES. However, users did not want to replace DES
as it takes an enormous amount of time and money to change encryption algorithms
that are widely adopted and embedded in large security architectures.
The pragmatic approach was not to abandon the DES completely, but to change the
manner in which DES is used. This led to the modified schemes of Triple DES
(sometimes known as 3DES).
Incidentally, there are two variants of Triple DES known as 3-key Triple DES (3TDES)
and 2-key Triple DES (2TDES).
3-KEY Triple DES
Before using 3TDES, user first generate and distribute a 3TDES key K, which consists
of three different DES keys K1, K2 and K3. This means that the actual 3TDES key has
length 3×56 = 168 bits. The encryption scheme is illustrated as follows −
4. The encryption-decryption process is as follows −
Encrypt the plaintext blocks using single DES with key K1.
Now decrypt the output of step 1 using single DES with key K2.
Finally, encrypt the output of step 2 using single DES with key K3.
The output of step 3 is the ciphertext.
Decryption of a ciphertext is a reverse process. User first decrypt using K3, then
encrypt with K2, and finally decrypt with K1.
Due to this design of Triple DES as an encrypt–decrypt–encrypt process, it is possible
to use a 3TDES (hardware) implementation for single DES by setting K1, K2, and K3 to
be the same value. This provides backwards compatibility with DES.
Second variant of Triple DES (2TDES) is identical to 3TDES except that K3is replaced
by K1. In other words, user encrypt plaintext blocks with key K1, then decrypt with key
K2, and finally encrypt with K1 again. Therefore, 2TDES has a key length of 112 bits.
Triple DES systems are significantly more secure than single DES, but these are
clearly a much slower process than encryption using single DES.
International Data Encryption Algorithm (IDEA)
In cryptography, block ciphers are very important in the designing of many
cryptographic algorithms and are widely used to encrypt the bulk of data in
chunks. By chunks, it means that the cipher takes a fixed size of the plaintext
in the encryption process and generates a fixed size ciphertext using a fixed-
length key. An algorithm’s strength is determined by its key length.
5. The Simplified International Data Encryption Algorithm (IDEA) is
a symmetric key block cipher that:
uses a fixed-length plaintext of 16 bits and
encrypts them in 4 chunks of 4 bits each
to produce 16 bits ciphertext.
The length of the key used is 32 bits.
The key is also divided into 8 blocks of 4 bits each.
This algorithm involves a series of 4 identical complete rounds and 1 half-
round. Each complete round involves a series of 14 steps that includes
operations like:
Bitwise XOR
Addition modulo
Multiplication modulo +1
After 4 complete rounds, the final “half-round” consists of only the first 4 out
of the 14 steps previously used in the full rounds. To perform these rounds,
each binary notation must be converted to its equivalent decimal notation,
perform the operation and the result obtained should be converted back to
the binary representation for the final result of that particular step.
Key Schedule: 6 subkeys of 4 bits out of the 8 subkeys are used in each
complete round, while 4 are used in the half-round. So, 4.5 rounds require 28
subkeys. The given key, ‘K’, directly gives the first 8 subkeys. By rotating the
main key left by 6 bits between each group of 8, further groups of 8 subkeys
are created, implying less than one rotation per round for the key (3
rotations).
6. Decryption
Decryption works like encryption, but the order of the round keys is inverted, and the subkeys for
the odd rounds are inversed. For instance, the values of subkeys K1–K4 are replaced by the
inverse of K49–K52 for the respective group operation, K5 and K6 of each group should be
replaced by K47 and K48 for decryption.
Weak keys
The very simple key schedule makes IDEA subject to a class of weak keys; some keys
containing a large number of 0 bits produce weak encryption.
These are of little concern in practice, being sufficiently rare that they are unnecessary to
avoid explicitly when generating keys randomly. A simple fix was proposed: XORing each
subkey with a 16-bit constant, such as 0x0DAE.
Larger classes of weak keys were found in 2002.
This is still of negligible probability to be a concern to a randomly chosen key, and some
of the problems are fixed by the constant XOR proposed earlier, but the paper is not certain
if all of them are. A more comprehensive redesign of the IDEA key schedule may be
desirable.
Advanced Encryption Standard
The more popular and widely adopted symmetric encryption algorithm likely to be
encountered nowadays is the Advanced Encryption Standard (AES). It is found at least
six time faster than triple DES.
A replacement for DES was needed as its key size was too small. With increasing
computing power, it was considered vulnerable against exhaustive key search attack.
Triple DES was designed to overcome this drawback but it was found slow.
The features of AES are as follows −
Symmetric key symmetric block cipher
128-bit data, 128/192/256-bit keys
Stronger and faster than Triple-DES
Provide full specification and design details
Software implementable in C and Java
Operation of AES
AES is an iterative rather than Feistel cipher. It is based on ‘substitution–permutation
network’. It comprises of a series of linked operations, some of which involve replacing
inputs by specific outputs (substitutions) and others involve shuffling bits around
(permutations).
Interestingly, AES performs all its computations on bytes rather than bits. Hence, AES
treats the 128 bits of a plaintext block as 16 bytes. These 16 bytes are arranged in
four columns and four rows for processing as a matrix −
7. Unlike DES, the number of rounds in AES is variable and depends on the length of
the key. AES uses 10 rounds for 128-bit keys, 12 rounds for 192-bit keys and 14
rounds for 256-bit keys. Each of these rounds uses a different 128-bit round key, which
is calculated from the original AES key.
The schematic of AES structure is given in the following illustration −
Encryption Process
Here, we restrict to description of a typical round of AES encryption. Each round
comprise of four sub-processes. The first round process is depicted below −
8. Byte Substitution (SubBytes)
The 16 input bytes are substituted by looking up a fixed table (S-box) given in design.
The result is in a matrix of four rows and four columns.
Shiftrows
Each of the four rows of the matrix is shifted to the left. Any entries that ‘fall off’ are re-
inserted on the right side of row. Shift is carried out as follows −
First row is not shifted.
Second row is shifted one (byte) position to the left.
Third row is shifted two positions to the left.
Fourth row is shifted three positions to the left.
The result is a new matrix consisting of the same 16 bytes but shifted with
respect to each other.
MixColumns
Each column of four bytes is now transformed using a special mathematical function.
This function takes as input the four bytes of one column and outputs four completely
new bytes, which replace the original column. The result is another new matrix
consisting of 16 new bytes. It should be noted that this step is not performed in the last
round.
Addroundkey
The 16 bytes of the matrix are now considered as 128 bits and are XORed to the 128
bits of the round key. If this is the last round then the output is the ciphertext.
Otherwise, the resulting 128 bits are interpreted as 16 bytes and we begin another
similar round.
Decryption Process
The process of decryption of an AES ciphertext is similar to the encryption process in
the reverse order. Each round consists of the four processes conducted in the reverse
order −
Add round key
Mix columns
Shift rows
Byte substitution
Since sub-processes in each round are in reverse manner, unlike for a Feistel Cipher,
the encryption and decryption algorithms needs to be separately implemented,
although they are very closely related.
AES Analysis
In present day cryptography, AES is widely adopted and supported in both hardware
and software. Till date, no practical cryptanalytic attacks against AES has been
discovered. Additionally, AES has built-in flexibility of key length, which allows a
9. degree of ‘future-proofing’ against progress in the ability to perform exhaustive key
searches.
However, just as for DES, the AES security is assured only if it is correctly
implemented and good key management is employed.
Block Cipher modes of Operation
Encryption algorithms are divided into two categories based on the input
type, as a block cipher and stream cipher. Block cipher is an encryption
algorithm that takes a fixed size of input say b bits and produces a ciphertext
of b bits again. If the input is larger than b bits it can be divided further. For
different applications and uses, there are several modes of operations for a
block cipher.
Electronic Code Book (ECB) –
Electronic code book is the easiest block cipher mode of functioning. It is
easier because of direct encryption of each block of input plaintext and
output is in form of blocks of encrypted ciphertext. Generally, if a message is
larger than b bits in size, it can be broken down into a bunch of blocks and
the procedure is repeated.
Procedure of ECB is illustrated below:
Advantages of using ECB –
Parallel encryption of blocks of bits is possible, thus it is a faster way of
encryption.
Simple way of the block cipher.
10. Disadvantages of using ECB –
Prone to cryptanalysis since there is a direct relationship between
plaintext and ciphertext.
Cipher Block Chaining(CBC) –
Cipher block chaining or CBC is an advancement made on ECB since ECB
compromises some security requirements. In CBC, the previous cipher block
is given as input to the next encryption algorithm after XOR with the original
plaintext block. In a nutshell here, a cipher block is produced by encrypting
an XOR output of the previous cipher block and present plaintext block.
The process is illustrated here:
Advantages of CBC –
CBC works well for input greater than b bits.
CBC is a good authentication mechanism.
Better resistive nature towards cryptanalysis than ECB.
Disadvantages of CBC –
Parallel encryption is not possible since every encryption requires a
previous cipher.
11. Cipher Feedback Mode (CFB) –
In this mode the cipher is given as feedback to the next block of encryption
with some new specifications: first, an initial vector IV is used for first
encryption and output bits are divided as a set of s and b-s bits.The left-hand
side s bits are selected along with plaintext bits to which an XOR operation is
applied. The result is given as input to a shift register having b-s bits to lhs,s
bits to rhs and the process continues. The encryption and decryption process
for the same is shown below, both of them use encryption algorithms.
Advantages of CFB –
Since, there is some data loss due to the use of shift register, thus it is
difficult for applying cryptanalysis.
Disadvantages of using ECB –
The drawbacks of CFB are the same as those of CBC mode. Both block
losses and concurrent encryption of several blocks are not supported by
the encryption. Decryption, however, is parallelizable and loss-tolerant.
12. Output Feedback Mode (OFB)–
The output feedback mode follows nearly the same process as the Cipher
Feedback mode except that it sends the encrypted output as feedback
instead of the actual cipher which is XOR output. In this output feedback
mode, all bits of the block are sent instead of sending selected s bits. The
Output Feedback mode of block cipher holds great resistance towards bit
transmission errors. It also decreases the dependency or relationship of the
cipher on the plaintext.
Advantages of OFB –
In the case of CFB, a single bit error in a block is propagated to all
subsequent blocks. This problem is solved by OFB as it is free from bit
errors in the plaintext block.
Disadvantages of OFB-
The drawback of OFB is that, because to its operational modes, it is more
susceptible to a message stream modification attack than CFB.
13. Counter Mode (CTR) –
The Counter Mode or CTR is a simple counter-based block cipher
implementation. Every time a counter-initiated value is encrypted and given
as input to XOR with plaintext which results in ciphertext block. The CTR
mode is independent of feedback use and thus can be implemented in
parallel.
Its simple implementation is shown below:
Advantages of Counter –
Since there is a different counter value for each block, the direct plaintext
and ciphertext relationship is avoided. This means that the same plain
text can map to different ciphertext.
Parallel execution of encryption is possible as outputs from previous
stages are not chained as in the case of CBC.
Disadvantages of Counter-
The fact that CTR mode requires a synchronous counter at both the
transmitter and the receiver is a severe drawback. The recovery of
plaintext is erroneous when synchronisation is lost.