Advanced Encryption Standard, Multiple Encryption and Triple DES, Block Cipher Modes of
operation, Stream Ciphers and RC4, Confidentiality using Symmetric Encryption, Introduction
to Number Theory: Prime Numbers, Fermat’s and Euler’s Theorems, Testing for Primality, The
Chinese Remainder Theorem, Discrete Logarithms, Public-Key Cryptography and RSA
Introduction: OSI Security Architecture, Security attacks, ,Security Services, Security
Mechanisms, Model for Network Security, Fundamentals of Abstract Algebra : Groups, Rings,
Fields, Modular Arithmetic, Euclidean Algorithm, Finite Fields of the form GF(p),Polynomial
Arithmetic, Finite Fields of the form GF(2n),Classical Encryption techniques, Block Ciphers and
Data Encryption Standard.
Key Management, Diffie-Hellman Key Exchange, Elliptic Curve Arithmetic, Elliptic Curve
Cryptography, Message Authentication and Hash Functions, Hash and MAC Algorithms
Digital Signatures and Authentication Protocols
Introduction: OSI Security Architecture, Security attacks, ,Security Services, Security
Mechanisms, Model for Network Security, Fundamentals of Abstract Algebra : Groups, Rings,
Fields, Modular Arithmetic, Euclidean Algorithm, Finite Fields of the form GF(p),Polynomial
Arithmetic, Finite Fields of the form GF(2n),Classical Encryption techniques, Block Ciphers and
Data Encryption Standard.
Key Management, Diffie-Hellman Key Exchange, Elliptic Curve Arithmetic, Elliptic Curve
Cryptography, Message Authentication and Hash Functions, Hash and MAC Algorithms
Digital Signatures and Authentication Protocols
Key Management, Diffie-Hellman Key Exchange, Elliptic Curve Arithmetic, Elliptic Curve
Cryptography, Message Authentication and Hash Functions, Hash and MAC Algorithms
Digital Signatures and Authentication Protocols
Key Management, Diffie-Hellman Key Exchange, Elliptic Curve Arithmetic, Elliptic Curve
Cryptography, Message Authentication and Hash Functions, Hash and MAC Algorithms
Digital Signatures and Authentication Protocols
ASIC Implementation of Triple Data Encryption Algorithm (3DES)Kevin Xiao Xiao
The Triple DES Encryption is a data encryption algorithm which will be used to protect confidential data against unauthorized access. This algorithm can be used to encrypt and decrypt files, which applies the triple data encryption standard (3DES). The project is designed to enhance the security of data stored inside the devices. It enhances the privacy of the user and also able to protect user’s identity. Anyone who wants to read the data file inside the device needs to have the right keys in order to decrypt the file. Businesses may use it to protect corporate secrets, governments use it to secure classified information, and many individuals use it to protect personal information to guard against things like identity theft. The 3DES algorithm makes this design unique and important since it is hard to break. This project is more appropriate for an ASIC design because the project needed to be customized to implement a chip with application-specific logic for a particular use. This kind of task is more suitable for the ASIC rather than microcontroller since microcontroller usually needs more time delay and consumes much more power than ASIC design.The Triple DES Encryptor will track all bytes being transferred to a certain device and then applies bitwise operation for the encryption/decryption algorithm. FPGA will be used to off load the encryption algorithm onto the FPGA from the Atom/Linux, then the block that does the encryption will have to write over the Avalon bus to the FPGA.
Project consists of individual modules of encryption and decryption units. Standard T-DES algorithm is implemented. Presently working on to integrate DES with AES to develop stronger crypto algorithm and test the same against Side Channel Attacks and compare different algorithms.
Public Key Cryptography and RSA algorithmIndra97065
Public Key Cryptography and RSA algorithm.Explanation and proof of RSA algorithm in details.it also describer the mathematics behind the RSA. Few mathematics theorem are given which are use in the RSA algorithm.
Implementation is the stage of the project when the theoretical design is turned out into a working system. Thus it can be considered to be the most critical stage in achieving a successful new system and in giving the user, confidence that the new system will work and be effective.
The implementation stage involves careful planning, investigation of the existing system and it’s constraints on implementation, designing of methods to achieve changeover and evaluation of changeover methods.
Main Modules:-
1. User Module:
In this module, Users are having authentication and security to access the detail which is presented in the ontology system. Before accessing or searching the details user should have the account in that otherwise they should register first.
2. Secure DeDuplication System:
To support authorized deduplication, the tag of a file F will be determined by the file F and the privilege. To show the difference with traditional notation of
tag, we call it file token instead. To support authorized access, a secret key kp will be bounded with a privilege p to generate a file token. Let ϕ′ F;p = TagGen(F, kp) denote the token of F that is only allowed to access by user with privilege p. In another word, the token ϕ′ F;p could only be computed by the users with privilege p. As a result, if a file has been uploaded by a user with a duplicate token ϕ′
F;p, then a duplicate check sent from another user will be successful if and only if he also has the file F and privilege p. Such a token generation function could be
easily implemented as H(F, kp), where H(_) denotes a cryptographic hash function.
3. Security Of Duplicate Check Token :
We consider several types of privacy we need protect, that is, i) unforgeability of duplicate-check token: There are two types of adversaries, that is, external adversary and internal adversary. As shown below, the external adversary
can be viewed as an internal adversary without any privilege. If a user has privilege p, it requires that the adversary cannot forge and output a valid duplicate token with any other privilege p′ on any file F, where p does not match p′. Furthermore, it also requires that if the adversary does not make a request of token with its own privilege from private cloud server, it cannot forge and output a valid duplicate token with p on any F that has been queried.
4. Send Key:
Once the key request was received, the sender can send the key or he can decline it. With this key and request id which was generated at the time of sending key request the receiver can decrypt the message.
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
Advanced Encryption Standard, Multiple Encryption and Triple DES, Block Cipher Modes of
operation, Stream Ciphers and RC4, Confidentiality using Symmetric Encryption, Introduction
to Number Theory: Prime Numbers, Fermat’s and Euler’s Theorems, Testing for Primality, The
Chinese Remainder Theorem, Discrete Logarithms, Public-Key Cryptography and RSA
Security Analysis of AES and Enhancing its Security by Modifying S-Box with a...IJCNCJournal
Secured and opportune transmission of data alwaysis a significant feature for any organization. Robust
encryption techniques and algorithms always facilitate in augmenting secrecy, authentication and
reliability of data. At present, Advanced Encryption Standard (AES) patronized by NIST is the most secure
algorithm for escalating the confidentiality of data. This paper mainly focuses on an inclusive analysis
related to the security of existing AES algorithm and aim to enhance the level security of this algorithm.
Through some modification of existing AES algorithm by XORing an additional byte with s-box value, we
have successfully increased the Time Security and Strict Avalanche Criterion. We have used random
additional key for increasing security. Since this key is random, result of security measurement sometimes
fluctuates.
Block Ciphering
Confusion and Diffusion Theory
Understand the algebra of AES e.g. finding inverse etc.
AES and its importance in security
Efficient implementation of AES.
Implementation of AES
Register Organization of 8086, Architecture, Signal Description of 8086, Physical Memory
Organization, General Bus Operation, I/O Addressing Capability, Special Processor Activities,
Minimum Mode 8086 System and Timings, Maximum Mode 8086 System and Timings.
Addressing Modes of 8086.
Machine Language Instruction Formats – Instruction Set of 8086-Data transfer
instructions,Arithmetic and Logic instructions,Branch instructions,Loop instructions,Processor
Control instructions,Flag Manipulation instructions,Shift and Rotate instructions,String
instructions, Assembler Directives and operators,Example Programs,Introduction to Stack,
STACK Structure of 8086, Interrupts and Interrupt Service Routines, Interrupt Cycle of 8086,
Non-Maskable and Maskable Interrupts, Interrupt Programming, MACROS.
Network Security: Authentication Applications, Electronic Mail Security, IP Security, Web
Security, System Security: Intruders, Malicious Software, Firewalls
Network Security: Authentication Applications, Electronic Mail Security, IP Security, Web
Security, System Security: Intruders, Malicious Software, Firewalls
Registers - Serial in serial out, Serial in Parallel out, Parallel in serial out, Parallel in Parallel
out registers, Bidirectional shift registers, universal shift registers.
Counters - Synchronous and asynchronous counters, UP/DOWN counters, Modulo-N
Counters, Cascaded counter, Programmable counter, Counters using shift registers, application
of counters.
Introduction: OSI Security Architecture, Security attacks, ,Security Services, Security
Mechanisms, Model for Network Security, Fundamentals of Abstract Algebra : Groups, Rings,
Fields, Modular Arithmetic, Euclidean Algorithm, Finite Fields of the form GF(p),Polynomial
Arithmetic, Finite Fields of the form GF(2n),Classical Encryption techniques, Block Ciphers and
Data Encryption Standard.
Number systems - Efficiency of number system, Decimal, Binary, Octal, Hexadecimalconversion
from one to another- Binary addition, subtraction, multiplication and division,
representation of signed numbers, addition and subtraction using 2’s complement and I’s
complement.
Binary codes - BCD code, Excess 3 code, Gray code, Alphanumeric code, Error detection
codes, Error correcting code.Deepak john,SJCET-Pala
2024.06.01 Introducing a competency framework for languag learning materials ...Sandy Millin
http://sandymillin.wordpress.com/iateflwebinar2024
Published classroom materials form the basis of syllabuses, drive teacher professional development, and have a potentially huge influence on learners, teachers and education systems. All teachers also create their own materials, whether a few sentences on a blackboard, a highly-structured fully-realised online course, or anything in between. Despite this, the knowledge and skills needed to create effective language learning materials are rarely part of teacher training, and are mostly learnt by trial and error.
Knowledge and skills frameworks, generally called competency frameworks, for ELT teachers, trainers and managers have existed for a few years now. However, until I created one for my MA dissertation, there wasn’t one drawing together what we need to know and do to be able to effectively produce language learning materials.
This webinar will introduce you to my framework, highlighting the key competencies I identified from my research. It will also show how anybody involved in language teaching (any language, not just English!), teacher training, managing schools or developing language learning materials can benefit from using the framework.
Palestine last event orientationfvgnh .pptxRaedMohamed3
An EFL lesson about the current events in Palestine. It is intended to be for intermediate students who wish to increase their listening skills through a short lesson in power point.
The Roman Empire A Historical Colossus.pdfkaushalkr1407
The Roman Empire, a vast and enduring power, stands as one of history's most remarkable civilizations, leaving an indelible imprint on the world. It emerged from the Roman Republic, transitioning into an imperial powerhouse under the leadership of Augustus Caesar in 27 BCE. This transformation marked the beginning of an era defined by unprecedented territorial expansion, architectural marvels, and profound cultural influence.
The empire's roots lie in the city of Rome, founded, according to legend, by Romulus in 753 BCE. Over centuries, Rome evolved from a small settlement to a formidable republic, characterized by a complex political system with elected officials and checks on power. However, internal strife, class conflicts, and military ambitions paved the way for the end of the Republic. Julius Caesar’s dictatorship and subsequent assassination in 44 BCE created a power vacuum, leading to a civil war. Octavian, later Augustus, emerged victorious, heralding the Roman Empire’s birth.
Under Augustus, the empire experienced the Pax Romana, a 200-year period of relative peace and stability. Augustus reformed the military, established efficient administrative systems, and initiated grand construction projects. The empire's borders expanded, encompassing territories from Britain to Egypt and from Spain to the Euphrates. Roman legions, renowned for their discipline and engineering prowess, secured and maintained these vast territories, building roads, fortifications, and cities that facilitated control and integration.
The Roman Empire’s society was hierarchical, with a rigid class system. At the top were the patricians, wealthy elites who held significant political power. Below them were the plebeians, free citizens with limited political influence, and the vast numbers of slaves who formed the backbone of the economy. The family unit was central, governed by the paterfamilias, the male head who held absolute authority.
Culturally, the Romans were eclectic, absorbing and adapting elements from the civilizations they encountered, particularly the Greeks. Roman art, literature, and philosophy reflected this synthesis, creating a rich cultural tapestry. Latin, the Roman language, became the lingua franca of the Western world, influencing numerous modern languages.
Roman architecture and engineering achievements were monumental. They perfected the arch, vault, and dome, constructing enduring structures like the Colosseum, Pantheon, and aqueducts. These engineering marvels not only showcased Roman ingenuity but also served practical purposes, from public entertainment to water supply.
The Indian economy is classified into different sectors to simplify the analysis and understanding of economic activities. For Class 10, it's essential to grasp the sectors of the Indian economy, understand their characteristics, and recognize their importance. This guide will provide detailed notes on the Sectors of the Indian Economy Class 10, using specific long-tail keywords to enhance comprehension.
For more information, visit-www.vavaclasses.com
This is a presentation by Dada Robert in a Your Skill Boost masterclass organised by the Excellence Foundation for South Sudan (EFSS) on Saturday, the 25th and Sunday, the 26th of May 2024.
He discussed the concept of quality improvement, emphasizing its applicability to various aspects of life, including personal, project, and program improvements. He defined quality as doing the right thing at the right time in the right way to achieve the best possible results and discussed the concept of the "gap" between what we know and what we do, and how this gap represents the areas we need to improve. He explained the scientific approach to quality improvement, which involves systematic performance analysis, testing and learning, and implementing change ideas. He also highlighted the importance of client focus and a team approach to quality improvement.
Students, digital devices and success - Andreas Schleicher - 27 May 2024..pptxEduSkills OECD
Andreas Schleicher presents at the OECD webinar ‘Digital devices in schools: detrimental distraction or secret to success?’ on 27 May 2024. The presentation was based on findings from PISA 2022 results and the webinar helped launch the PISA in Focus ‘Managing screen time: How to protect and equip students against distraction’ https://www.oecd-ilibrary.org/education/managing-screen-time_7c225af4-en and the OECD Education Policy Perspective ‘Students, digital devices and success’ can be found here - https://oe.cd/il/5yV
Welcome to TechSoup New Member Orientation and Q&A (May 2024).pdfTechSoup
In this webinar you will learn how your organization can access TechSoup's wide variety of product discount and donation programs. From hardware to software, we'll give you a tour of the tools available to help your nonprofit with productivity, collaboration, financial management, donor tracking, security, and more.
Unit 8 - Information and Communication Technology (Paper I).pdfThiyagu K
This slides describes the basic concepts of ICT, basics of Email, Emerging Technology and Digital Initiatives in Education. This presentations aligns with the UGC Paper I syllabus.
2. Advanced Encryption Standard(AES)
Symmetric block cipher,designed by Rijmen-Daemen in Belgium and published
by National Institute of Standards and Technology (NIST) in December 2001.
Intended to replace DES and 3DES
DES is vulnerable to differential attacks
3DES has slow performances
NIST Evaluation Criteria
Security: The effort to crypt analyze an algorithm.
Cost: The algorithm should be practical in a wide range of applications.
Algorithm and Implementation Characteristics : Flexibility, simplicity etc.
3. Final evaluation criteria
General Security
Software Implementations
Hardware Implementations
Restricted-Space Environments
Attacks on Implementations
Encryption vs. Decryption
Key Agility
Potential for Instruction-Level Parallelism
Other versatility and Flexibility
4. AES Cipher
an iterative rather than Feistel cipher
processes data as block of 4 columns of 4 bytes
operates on entire data block in every round
designed to have:
resistance against known attacks
speed and code compactness on many CPUs
design simplicity
5. AES Structure
processes data as state array
Encryption/Decryption consists of 10 rounds of processing for 128-bit keys,12
rounds for 192-bit keys, and 14 rounds for 256-bit keys.
Except for the last round , all other rounds are identical.
Each round of processing includes
1. byte substitution (1 S-box; byte to byte substitution)
2. shift rows (permutation of bytes)
3. mix columns (substitution using matrix multiply of groups)
4. Add Round Key (XOR state with a portion of expended K)
The order in which these four steps are executed is different for encryption and
decryption
6. The input is a single 128 bit block both for decryption and encryption and is
known as the in matrix .
This block is copied into a state array which is modified at each stage of the
algorithm and then copied to an output matrix .
The key is expanded into an array of key schedule words (the w matrix).
Ordering of bytes within the in and w matrix is by column.
10. Byte Substitution
a simple substitution of each byte
uses S-box to perform a byte-by-byte
substitution of State
uses one table of 16x16 bytes containing a
permutation of all 256 8-bit values
each byte of state is replaced by byte indexed
by row (left 4-bits) & column (right 4-bits)
eg. byte {95} is replaced by byte in row 9
column 5
which has value {2A}
designed to be resistant to all known attacks
11. Shift Rows
a circular byte shift in each row
1st row is unchanged
2nd row does 1 byte circular shift to
left
3rd row does 2 byte circular shift to
left
4th row does 3 byte circular shift to
left
12. Mix Columns
operates at the column level;
it transforms each column of the state to a new column.
13. AddRoundKey
• adds a round key word with each state column matrix.
• Each column in the state matrix is XORed with a different word.
• proceeds one column at a time.
• the operation in AddRoundKey is matrix addition.
14. AES Key Expansion
create round keys for each round,
takes key and expands into array
of 44/52/60 32-bit words
start by copying key into first 4
words
15. AES Decryption
AES decryption is not identical to encryption since steps done in reverse.
Decryption algorithm uses the expanded key in reverse order.
All functions are easily reversible and their inverse form is used in decryption
Analysis of AES
the AES is secure against all known attacks.
Various aspects of its design incorporate specific features that help provide
security against specific attacks.
There are apparently no known attacks on AES.
16. Multiple Encryption & DES
clear a replacement for DES was needed
theoretical attacks that can break it
demonstrated exhaustive key search attacks
prior to this alternative was to use multiple encryption with DES implementations
Triple-DES is the chosen form
17. Double-DES
could use 2 DES encrypts on each block
C = EK2(EK1(P))
P = D(K1, D(K2, C))
Encryption sequence: E-E
Decryption sequence: D-D
and have “meet-in-the-middle” attack
since M = EK1(P) = DK2(C)
The attacker tries to break the two-part encryption method from both sides
simultaneously, a successful effort enables him to meet in the middle of the
block cipher.
18. Triple-DES with Two-Keys
hence must use 3 encryptions
would seem to need 3 distinct keys
Encryption sequence: E-D-E
Decryption sequence: D-E-D
but can use 2 keys with E-D-E sequence
C = EK1(DK2(EK1(P)))
P = D(K1, E(K2, D(K1, C)))
if K1=K2 then can work with single
DES
standardized in ANSI X9.17 & ISO8732
no current known practical attacks
19. Triple-DES with Three-Keys
although are no practical attacks on two-key Triple-DES have some indications
can use Triple-DES with Three-Keys to avoid even these
C = EK3(DK2(EK1(P)))
P=DK1 (EK2 (EK3 (C)))
E D E
20. Modes of Operation
block ciphers encrypt fixed size blocks
eg. DES encrypts 64-bit blocks with 56-bit key
NIST defines 5 possible modes to cover a wide variety of applications
1. Electronic CodeBook Mode (ECB)
2. Cipher Block Chaining Mode (CBC)
3. Cipher FeedBack Mode (CFB)
4. Output FeedBack Mode (OFB)
5. CounTeR Mode(CTR)
can be used with any block cipher
have block and stream modes
21. Electronic Code Book (ECB)
message is broken into independent
blocks which are encrypted
each block is a value which is
substituted, like a codebook,
each block is encoded independently
of the other blocks
Ci = EK1(Pi)
uses: secure transmission of single
values
22. Advantages and Limitations of ECB
message repetitions may show in cipher text
main use is sending a few blocks of data
23. Cipher Block Chaining (CBC)
message is broken into blocks
linked together in encryption
operation
each previous cipher blocks is
chained with current plaintext block,
use Initial Vector (IV) to start process
Ci = EK1(Pi XOR Ci-1)
Ci-1 = IV
uses: bulk data encryption,
authentication
24. Advantages and Limitations of CBC
a cipher text block depends on all blocks before it
any change to a block affects all following cipher text blocks
need Initialization Vector (IV)
which must be known to sender & receiver
hence IV must either be a fixed value
or must be sent encrypted in ECB mode before rest of message
25. Stream Modes of Operation
block modes encrypt entire block
may need to operate on smaller units
real time data
convert block cipher into stream cipher
cipher feedback (CFB) mode
output feedback (OFB) mode
counter (CTR) mode
use block cipher as some form of pseudo-random number generator
26. Cipher Feed Back (CFB)
message is treated as a stream of bits
added to the output of the block cipher
result is feed back for next stage
standard allows any number of bit (1,8, 64 or 128 etc) to be feed back
denoted CFB-1, CFB-8, CFB-64, CFB-128 etc
28. Advantages and Limitations of CFB
appropriate when data arrives in bits/bytes
most common stream mode
encryption mode used at both ends
29. Output Feed Back (OFB)
output of cipher is added to message
output is then feed back
feedback is independent of message
So feedback can be computed in advance
32. Counter (CTR)
must have a different key & counter value for every plaintext block (never
reused)
uses: high-speed network encryptions
33.
34. Advantages and Limitations of CTR
efficiency
can do parallel encryptions in h/w or s/w
can preprocess in advance of need
random access to encrypted data blocks
provable security (good as other modes)
but must ensure never reuse key/counter values, otherwise could break.
35. STREAM CIPHERS
Start with a secret key
process message bit by bit (as a stream)
have a pseudo random keystream
Combine the stream with the plaintext
to produce the ciphertext (typically by
XOR)
Ci = Mi XOR StreamKeyi
but must never reuse stream key
otherwise can recover messages
36. Stream Cipher Properties
some design considerations are:
long period with no repetitions
statistically random
depends on large enough key
properly designed, can be as secure as a block cipher
simpler & faster
37. RC4
A symmetric key encryption algorithm invented by Ron Rivest
Variable key size, byte-oriented stream cipher
Normally uses 64 bit and 128 bit key sizes.
Used in
SSL/TLS (Secure socket, transport layer security) between web browsers and
servers,
IEEE 802.11 wirelss LAN std: WEP (Wired Equivalent Privacy), WPA (WiFi
Protocol Access) protocol
38. RC4 Block Diagram
Plain Text
Secret Key
RC4
+
Encrypted
Text
Keystream
Cryptographically very strong and easy to implement
39. Consists of 2 parts:
Key Scheduling Algorithm (KSA):Generate State
array
Pseudo-Random Generation Algorithm
(PRGA):Generate keystream, XOR keystream
with the data to generate encrypted stream
KSA
PRGA
40. The KSA
Use the secret key to initialize and permutation of state vector S, done in two
steps
A variable-length key of from 1 to 256 bytes (8 to 2048 bits) is used to initialize a
256-byte state vector S, with elements S[0],S[1], Á ,S[255].
At all times, S contains a permutation of all 8-bit numbers from 0 through 255.
41.
42. The PRGA Generate key stream k , one by one
XOR S[k] with next byte of message to encrypt/decrypt
i = j = 0;
While (more_byte_to_encrypt)
i = (i + 1) (mod 256);
j = (j + S[i]) (mod 256);
swap(S[i], S[j]);
k = (S[i] + S[j]) (mod 256);
Ci = Mi XOR S[k];
Sum of shuffled pair selects "stream key" value from permutation
43. Decryption using RC4
Use the same secret key as during the encryption phase.
Generate keystream by running the KSA and PRGA.
XOR keystream with the encrypted text to generate the plain text.
Logic is simple :
(A xor B) xor B = A
A = Plain Text or Data
B = KeyStream
RC4 Security
claimed secure against known attacks
since RC4 is a stream cipher, must never reuse a key
44. Confidentiality using Symmetric Encryption
traditionally symmetric encryption is used to provide message confidentiality.
Placement of Encryption
have two major placement alternatives
link encryption
encryption occurs independently on every link
implies must decrypt traffic between links
requires many devices, but paired keys
end-to-end encryption
encryption occurs between original source and final destination
need devices at each end with shared keys
47. On the host side, the FEP accepts packets. The user data portion of the packet is
encrypted, while the packet header bypasses the encryption process. The resulting
packet is delivered to the network.
In the opposite direction, for packets arriving from the network, the user data
portion is decrypted and the entire packet is delivered to the host.
Red data are sensitive or classified data . Black data are encrypted data.
48. when using end-to-end encryption must leave headers in clear
so network can correctly route information
hence although contents protected, traffic pattern flows are not
ideally want both at once
end-to-end encryption protects data contents over entire path and provides
authentication
link encryption protects traffic flows from monitoring
can place encryption function at various layers in OSI Reference Model
link encryption occurs at layers 1 or 2
end-to-end can occur at layers 3, 4, 6, 7
49. Traffic Confidentiality
is related to the monitoring of communications flows between parties
link encryption approach
network-layer headers (e.g., frame or cell header) are encrypted, reducing the
opportunity for traffic analysis.
it is still possible for an attacker to assess the amount of traffic on a network and
to observe the amount of traffic entering and leaving each end system.
traffic padding
An effective countermeasure to traffic analysis
50. Traffic padding produces
cipher text output
continuously, even in the
absence of plaintext.
A continuous random data
stream is generated. When
plaintext is available, it is
encrypted and transmitted.
When input plaintext is not
present, random data are
encrypted and transmitted.
51. Key Distribution
symmetric schemes require both parties to share a common secret key
issue is how to securely distribute this key
system failure due to a break in the key distribution scheme
given parties A and B have various key distribution alternatives:
1. A can select key and physically deliver to B
2. third party can select & deliver key to A & B
3. if A & B have communicated previously can use previous key to encrypt a
new key
4. if A & B have secure communications with a third party C, C can deliver key
between A & B
52. Key Hierarchy
typically have a hierarchy of keys
session key
temporary key
used for encryption of data between users
for one logical session then discarded
master key
used to encrypt session keys
shared by user & key distribution center
54. 1. A issues a request to the KDC for a session key to protect a logical connection to
B. The message includes the identity of A and B and a unique identifier, N1, for
this transaction.
2. The KDC responds with a message encrypted using Ka Thus, A is the only one
who can successfully read the message. The message includes two items
intended for A,
A one-time session key(Ks) to be used for the session
The original request message.
The message includes two items intended for B;
The one-time session key, Ks to be used for the session
An identifier of A (e.g., its network address), IDA
These two items are encrypted with Kb (the master key that the KDC shares
with B). They are to be sent to B to establish the connection and prove A's
identity.
55. 3. A stores the session key for use in the upcoming session and forwards to B
the information that originated at the KDC for B, namely, E(Kb, [Ks || IDA]).
4. Using the newly minted session key for encryption, B sends a identifier N2, to A.
5. Also using Ks, A responds with f(N2), where f is a function that performs some
transformation on N2 (e.g., adding one).
56. Key Distribution Issues
hierarchies of KDC’s required for large networks, but must trust each other
session key lifetimes should be limited for greater security
use of automatic key distribution on behalf of users,
use of decentralized key distribution
controlling key usage
58. Decentralized Key Control
1. A issues a request to B for a session key and includes a identifier N1
2. B responds with a message that is encrypted using the shared master key(MKm).
The response includes the session key selected by B, an identifier of B, the value
f(N1), and another identifier, N2.
3. Using the new session key, A returns f(N2) to B.
59. Random Numbers
many uses of random numbers in cryptography
used in authentication protocols
session keys
public key generation
in all cases its critical that these values be
statistically random, uniform distribution, independent
unpredictability of future values from previous values
60. Pseudo Random Number Generators (PRNGs)
use algorithmic techniques to create “random numbers”
although are not truly random
can pass many tests of “randomness”
Linear Congruential Generator
common iterative technique using:
Xn+1 = (a Xn + c) mod m
If m, a, c, and X0 are integers,
Using Block Ciphers as PRNGs
for cryptographic applications, can use a block cipher to generate random
numbers
61. Introduction to Number Theory
Prime Numbers
prime numbers only have divisors of 1 and self
Prime Factorisation
to factor a number n is to write it as a product of other numbers: n=a x b x c .
the prime factorisation of a number n is when its written as a product of
primes
e.g. 91=71x131, 300=22x31x52
62. Relatively Prime Numbers & GCD
two numbers a, b are relatively prime if have no common divisors apart from 1
eg. 8 & 15 are relatively prime since factors of 8 are 1,2,4,8 and of 15 are
1,3,5,15 and 1 is the only common factor
can determine the greatest common divisor by comparing their prime
factorizations and using least powers
eg. 300=22x31x52 18=21x32 hence
GCD(18,300)=21x31x50=6
63. Fermat's Theorem
If p is prime and a is a positive integer not divisible by p, then
ap-1 ≡ 1 (mod p) also ap ≡ p (mod p)
useful in public key and primality testing
Proof : Consider the set of positive integers less than p
: {1, 2, ...., p - 1} and multiply each element by a mod p, to get the set X
X= {a mod p, 2a mod p, ...(p - 1)a mod p}
i.e ap-1(p - 1)! ≡ (p - 1)! (mod p)
We can cancel the ( P-1) ! term because it is relatively prime to P . This yields
ap-1 ≡ 1 (mod p)
65. Euler Totient Function ø(n)
defined as the number of positive integers less than n and relatively prime to n.
for example n=10, when doing arithmetic modulo n
complete set of residues is(0….n-1)= {0,1,2,3,4,5,6,7,8,9}
reduced set of residues is numbers which are relatively prime to n= {1,3,7,9}
number of elements in reduced set of residues is called the Euler Totient
Function ø(n)
67. Euler's Theorem
states that for every a and n that are relatively prime:
aø(n) ≡ 1 (mod n)
eg.
a=3;n=10; ø(10)=4;
hence 34 = 81 = 1 mod 10
a=2;n=11; ø(11)=10;
hence 210 = 1024 = 1 mod 11
68. Primality Testing
any positive odd integer n ≥ 3 can be expressed as
n - 1 = 2kq with k > 0, q odd
Miller-Rabin Algorithm
a test based on Fermat’s Theorem
The procedure TEST takes a candidate integer as input and returns the result
composite if is definitely not a prime, and the result inconclusive if may or may
not be a prime.
69.
70. Example 1: Prime number n=29
then (n - 1) = 28 = 22(7) = 2kq.
First, let us try a=10 .compute 107 mod 29 = 17 , which is neither 1 nor 28 , so
we continue the test.
The next calculation finds that (107)2 mod 29 = 28, and the test returns
inconclusive (i.e., 29 may be prime).
Let’s try again with a=2 .We have the following calculations: 27 mod 29 = 12;
214 mod 29 = 28 ; and the test again returns inconclusive.
If we perform the test for all integers in the range 1 through 28, we get the same
inconclusive result.
71. Example 2: composite number n = 13 * 17 = 221.
Then n-1 =220 = = 22(55) = 2kq.
Let us try a=5. Then we have 555 mod 221 = 112, which is neither 1 nor 220
(555)2 mod 221 = 168 .the test returns composite, indicating that 221 is definitely
a composite number.
suppose we had selected a=21 . Then we have 2155 mod 221 = 200;
(2155)2 mod 221 = 220 ; and the test returns inconclusive, indicating that 221
may be prime.
In fact, of the 218 integers from 2 through 219, four of these will return an
inconclusive result, namely 21, 47, 174, and 200.
72. Chinese Remainder Theorem
used to speed up modulo computations
Theorem: Let m1,…,mn > 0 be relative prime. Then the system of equations
x ≡ ai (mod mi) (for i=1 to n) has a unique solution modulo M = m1·…·mn.
73. Example: What’s x such that: x ≡ 2 (mod 3) ,x ≡ 3 (mod 5) and x ≡ 2 (mod 7)
So, a1 = 2, a2=3, a3=2 and m1 = 3 , m2=5, m3=7
Using the Chinese Remainder theorem:
M = 357 = 105
M1 = M/3 = 105/3 = 35 and M1
-1 = 2 (35 (mod 3))
M2 = M/5 = 105/5 = 21 and M2
-1 = 1 (21 (mod 5))
M3 = M/7 = 105/7=15 and M3
-1 = 1 (15 (mod 7))
So x ≡ a1 M1 M1
-1 + a2 M2 M2
-1 +…………+ ak Mk Mk
-1 (mod M)
≡ 2 × 2 × 35 + 3 × 1 × 21 + 2 × 1 × 15 = 233 ≡ 23 (mod 105)
So answer: x ≡ 23 (mod 105)
74. Public Key Cryptography and RSA
Public Key Cryptography
uses two keys – a public & a private key
asymmetric
developed to address two key issues:
key distribution – how to have secure communications in general without
having to trust a KDC with your key
digital signatures – how to verify a message comes intact from the claimed
sender
75. public-key/two-key/asymmetric cryptography involves the use of two keys:
a public-key, which may be known by anybody, and can be used to encrypt
messages, and verify signatures
a private-key, known only to the recipient, used to decrypt messages, and sign
(create) signatures
is asymmetric because
those who encrypt messages or verify signatures cannot decrypt messages or
create signatures
76.
77. 1. Each user generates a pair of keys to be used for the encryption and decryption
of messages.
2. Each user places one of the two keys in a public register or other accessible file.
This is the public key. The companion key is kept private. each user maintains a
collection of public keys obtained from others.
3. If Bob wishes to send a confidential message to Alice, Bob encrypts the message
using Alice’s public key.
4. When Alice receives the message, she decrypts it using her private key. No other
recipient can decrypt the message because only Alice knows Alice’s private key.
79. encrypting a message, using the sender’s private key. This provides the digital
signature.
encrypt again, using the receiver’s public key.
final cipher text can be decrypted only by the intended receiver, who alone has
the matching private key.
80. Public-Key Characteristics
Public-Key algorithms rely on two keys where:
it is computationally infeasible to find decryption key knowing only
algorithm & encryption key
it is computationally easy to en/decrypt messages when the relevant
(en/decrypt) key is known
either of the two related keys can be used for encryption, with the other used
for decryption (for some algorithms)
81. Public-Key Applications
can classify uses into 3 categories:
encryption/decryption (provide secrecy)
digital signatures (provide authentication)
key exchange (of session keys)
some algorithms are suitable for all uses, others are specific to one
82. Security of Public Key Schemes
brute force exhaustive search attack is always theoretically possible
but keys used are too large (>512bits)
requires the use of very large numbers
hence is slow compared to private key schemes
83. RSA
by Rivest, Shamir & Adleman of MIT in 1977
best known & widely used public-key scheme
is a block cipher in which the plaintext and cipher text are integers between 0 and
n - 1 for some n.
uses large integers (e.g. 1024 bits).
RSA makes use of an expression with exponentials.
Encryption and decryption are of the following form, for some plaintext block M
and ciphertext block C.
C = Me mod n
M = Cd mod n = (Me ) d mod n = Med mod n
84. RSA Key Setup
each user generates a public/private key pair by:
selecting two large primes at random p, q
computing their system modulus n= p . q
selecting at random the encryption key e
where 1<e<ø(n), gcd (e, ø(n))=1
note ø(n)=(p-1)(q-1)
solve following equation to find decryption key d
e.d=1 mod ø(n) and 0≤d≤n
publish their public encryption key: PU={e,n}
keep secret private decryption key: PR={d,n}
85. RSA Use
to encrypt a message M the sender:
obtains public key of recipient PU={e,n}
computes: C = Me mod n, where 0≤M<n
to decrypt the ciphertext C the owner:
uses their private key PR={d,n}
computes: M = Cd mod n
86. RSA Example - Key Setup
1. Select primes: p=17 & q=11
2. Compute n = pq =17 x 11=187
3. Compute ø(n)=(p–1)(q-1)=16 x 10=160
4. Select e: gcd(e,160)=1; choose e=7
5. Determine d: de=1 mod 160 and d < 160 Value is d=23 since
23x7=161= 10x160+1
6. Publish public key PU={7,187}
7. Keep secret private key PR={23,187}
87. RSA Example - En/Decryption
sample RSA encryption/decryption is:
given message M = 88
encryption:
C = 887 mod 187 = 11
decryption:
M = 1123 mod 187 = 88
88. Exponentiation
can use the Square and Multiply Algorithm
a fast, efficient algorithm for exponentiation
x11 mod n=
x11 = x1+2+8 = (x)(x2)(x8)
=[(x mod n) × (x2 mod n) × (x8 mod n)] mod n
e.g. 75 = 71 mod 11 × 74 mod 11 = 21 mod 11 = 10 mod 11
89.
90. Efficient Encryption and Decryption
encryption and decryption uses exponentiation to power e and power d
hence if e and d are small, the system will be faster
but if e and d are too small ,its not safe
91. RSA Security
possible approaches to attacking RSA are:
brute force key search (infeasible given size of numbers)
mathematical attacks.
timing attacks (on running of decryption)
chosen ciphertext attacks
92. Mathematical attack
mathematical approach takes 3 forms:
factor n=p.q, hence compute ø(n) and then d
determine ø(n) directly and compute d
find d directly
Timing Attacks
exploit timing variations in operations
eg. multiplying by small vs large number
countermeasures
use constant exponentiation time
add random delays
blind values used in calculations
93. Chosen Ciphertext Attacks
RSA is vulnerable to a Chosen Ciphertext Attack (CCA)
attackers chooses ciphertexts & gets decrypted plaintext back