This document provides an overview of cryptography and its applications. It discusses the history of cryptography beginning in ancient Egypt. It defines basic cryptography terminology like plaintext, ciphertext, cipher, key, encryption, decryption, cryptography, and cryptanalysis. It describes classical ciphers like the Caesar cipher and substitution ciphers. It also discusses cryptanalysis techniques, transposition ciphers, modern symmetric ciphers, public key cryptography including RSA, key distribution methods, and hybrid encryption.
The Diffie-Hellman algorithm was developed by Whitfield Diffie and Martin Hellman in 1976.
This algorithm was devices not to encrypt the data but to generate same private cryptographic key at both ends so that there is no need to transfer this key from one communication end to another.
Diffie – Hellman algorithm is an algorithm that allows two parties to get the shared secret key using the communication channel, which is not protected from the interception but is protected from modification.
The Diffie-Hellman algorithm was developed by Whitfield Diffie and Martin Hellman in 1976.
This algorithm was devices not to encrypt the data but to generate same private cryptographic key at both ends so that there is no need to transfer this key from one communication end to another.
Diffie – Hellman algorithm is an algorithm that allows two parties to get the shared secret key using the communication channel, which is not protected from the interception but is protected from modification.
Today in modern era of internet we share some sensitive data to information transmission. but need to ensure security. So we focus on Cryptography modern technique for secure transmission of information over network.
Cryptography is the science of using mathematics to encrypt and decrypt data.
Cryptography enables you to store sensitive information or transmit it across insecure networks so that it cannot be read by anyone except the intended recipient.
Key management: Introduction, How public key distribution done, Diffie Hellman Key Exchage Algorithm,Digital Certificate. Key Management using Digital certificate is done etc. wireshark screenshot showing digital cetificate.
An introduction to asymmetric cryptography with an in-depth look at RSA, Diffie-Hellman, the FREAK and LOGJAM attacks on TLS/SSL, and the "Mining your P's and Q's attack".
In cryptography, a block cipher is a deterministic algorithm operating on ... Systems as a means to effectively improve security by combining simple operations such as .... Finally, the cipher should be easily cryptanalyzable, such that it can be ...
USER AUTHENTICATION
MEANS OF USER AUTHENTICATION
PASSWORD AUTHENTICATION
PASSWORD VULNERABILITIES
USE OF HASHED PASSWORDS – IN UNIX
PASSWORD CRACKING TECHNIQUES
USING BETTER PASSWORDS
TOKEN AUTHENTICATION
BIO-METRIC AUTHENTICATION
Slides for a college cryptography course at CCSF. Instructor: Sam Bowne
Based on: Understanding Cryptography: A Textbook for Students and Practitioners by Christof Paar, Jan Pelzl, and Bart Preneel, ISBN: 3642041000 ASIN: B014P9I39Q
See https://samsclass.info/141/141_F17.shtml
Cryptography is the practice and study of techniques for conveying information security.
The goal of Cryptography is to allow the intended recipients of the message to receive the message securely.
The most famous algorithm used today is RSA algorithm
This is a Presentation On use of AES Algorithm To Encrypt Or Decrypt a Text File. This Algorithm is the latest and better than DES. It is a Networking Presentation. Thank You.
Easy for the signer to sign a message
There is no point in having a digital signature scheme that involves the signer needing to use slow and complex operations to compute a digital signature.
Easy for anyone to verify a message
Similarly we would like the verification of a digital signature to be as efficient as possible.
Hard for anyone to forge a digital signature
It should be practically impossible for anyone who is not the legitimate signer to compute a digital signature on a message that appears to be valid. By “appears to be valid” we mean that anyone who attempts to verify the digital signature is led to believe that they have just successfully verified a valid digital signature on a message.
Today in modern era of internet we share some sensitive data to information transmission. but need to ensure security. So we focus on Cryptography modern technique for secure transmission of information over network.
Cryptography is the science of using mathematics to encrypt and decrypt data.
Cryptography enables you to store sensitive information or transmit it across insecure networks so that it cannot be read by anyone except the intended recipient.
Key management: Introduction, How public key distribution done, Diffie Hellman Key Exchage Algorithm,Digital Certificate. Key Management using Digital certificate is done etc. wireshark screenshot showing digital cetificate.
An introduction to asymmetric cryptography with an in-depth look at RSA, Diffie-Hellman, the FREAK and LOGJAM attacks on TLS/SSL, and the "Mining your P's and Q's attack".
In cryptography, a block cipher is a deterministic algorithm operating on ... Systems as a means to effectively improve security by combining simple operations such as .... Finally, the cipher should be easily cryptanalyzable, such that it can be ...
USER AUTHENTICATION
MEANS OF USER AUTHENTICATION
PASSWORD AUTHENTICATION
PASSWORD VULNERABILITIES
USE OF HASHED PASSWORDS – IN UNIX
PASSWORD CRACKING TECHNIQUES
USING BETTER PASSWORDS
TOKEN AUTHENTICATION
BIO-METRIC AUTHENTICATION
Slides for a college cryptography course at CCSF. Instructor: Sam Bowne
Based on: Understanding Cryptography: A Textbook for Students and Practitioners by Christof Paar, Jan Pelzl, and Bart Preneel, ISBN: 3642041000 ASIN: B014P9I39Q
See https://samsclass.info/141/141_F17.shtml
Cryptography is the practice and study of techniques for conveying information security.
The goal of Cryptography is to allow the intended recipients of the message to receive the message securely.
The most famous algorithm used today is RSA algorithm
This is a Presentation On use of AES Algorithm To Encrypt Or Decrypt a Text File. This Algorithm is the latest and better than DES. It is a Networking Presentation. Thank You.
Easy for the signer to sign a message
There is no point in having a digital signature scheme that involves the signer needing to use slow and complex operations to compute a digital signature.
Easy for anyone to verify a message
Similarly we would like the verification of a digital signature to be as efficient as possible.
Hard for anyone to forge a digital signature
It should be practically impossible for anyone who is not the legitimate signer to compute a digital signature on a message that appears to be valid. By “appears to be valid” we mean that anyone who attempts to verify the digital signature is led to believe that they have just successfully verified a valid digital signature on a message.
When collection of thing belongs to certain definition, it is known as Set. When these set shows a degree of membership, it is known as Fuzzy Set. Fuzzy Set theory was given by the Professor Lofti Zadeh , University of California 1965. Copy the link given below and paste it in new browser window to get more information on Fuzzy Set:- http://www.transtutors.com/homework-help/statistics/fuzzy-set.aspx
Fuzzy logic is often heralded as a technique for handling problems with large amounts of vagueness or uncertainty. Since its inception in 1965 it has grown from an obscure mathematical idea to a technique used in a wide variety of applications from cooking rice to controlling diesel engines on an ocean liner.
This talk will give a layman's introduction to the topic and explore some of the real world applications in control and human decision making. Examples might include household appliances, control of large industrial plant, and health monitoring systems for the elderly. We will look at where the field might be going over the next ten years, highlighting areas where DMU's specialist expertise drives the way.
How can you deal with Fuzzy Logic. Fuzzy logic is a form of many-valued logic; it deals with reasoning that is approximate rather than fixed and exact. In contrast with traditional logic theory, where binary sets have two-valued logic: true or false, fuzzy logic variables may have a truth value that ranges in degree
between 0 and 1
Flexible querying of relational databases fuzzy set based approach 27-11Adel Sabour
(حلقة تكنولوجية) فى موضوعات حديثة منتقاه فى مجال نظم وتكنولوجيا المعلومات وعلوم الحاسب
يوم الجمعة الساعة الثامنة والنصف مساءًا بتوقيت مصر - كل أسبوع (مباشرة Live) - اليوم
على youtube.com/AdelSabour
https://link.springer.com/chapter/10.1007/978-3-319-13461-1_42
This presentation introduces the Basics of Cryptography and Network Security concepts. Heavily derived from content from William Stalling's book with the same title.
Cryptography and network security Nit701Amit Pathak
Cryptography and network security descries the security parameter with the help of public and private key. Digital signature is one of the most important area which we apply in our daily life for transferring the data.
traditional private/secret/single key cryptography uses one key
Key is shared by both sender and receiver
if the key is disclosed communications are compromised
also known as symmetric, both parties are equal
hence does not protect sender from receiver forging a message & claiming is sent by sender
Improved Caesar Cipher with Random Number Generation Technique and Multistage...ijcisjournal
Secured Communication involves Encryption process at the sending end and Decryption process at the receiving end of the communication system. Many Ciphers have been developed to provide data security . The efficiency of the Ciphers that are being used depends mainly on their throughput and memory requirement. Using of large key spaces with huge number of rounds with multiple complex operations may provide security but at the same time affects speed of operation. Hence in this paper we have proposed a method to improve Caesar cipher with random number generation technique for key generation operations. The Caesar cipher has been expanded so as to include alphabets, numbers and symbols. The original Caesar cipher was restricted only for alphabets. The key used for Caesar Substitution has been derived using a key Matrix Trace value restricted to Modulo 94. The Matrix elements are generated using recursive random number generation equation, the output of which solely depends on the value of seed selected . In this paper, we made an effort to incorporate modern cipher properties to classical cipher. The second stage of encryption has been performed using columnar transposition with arbitrary random order column selection. Thus the proposed Scheme is a hybrid version of classical and modern cipher properties. The proposed method provides appreciable Security with high throughput and occupies minimum memory space. The Method is resistant against brute-force attack with 93! Combinations of keys, for Caesar encryption.
Improved Caesar Cipher with Random Number Generation Technique and Multistage...ijcisjournal
Secured Communication involves Encryption process at the sending end and Decryption process at the receiving end of the communication system. Many Ciphers have been developed to provide data security . The efficiency of the Ciphers that are being used depends mainly on their throughput and memory requirement. Using of large key spaces with huge number of rounds with multiple complex operations may provide security but at the same time affects speed of operation. Hence in this paper we have proposed a method to improve Caesar cipher with random number generation technique for key generation operations. The Caesar cipher has been expanded so as to include alphabets, numbers and symbols. The original Caesar cipher was restricted only for alphabets. The key used for Caesar Substitution has been derived using a key Matrix Trace value restricted to Modulo 94. The Matrix elements are generated using recursive random number generation equation, the output of which solely depends on the value of seed selected . In this paper, we made an effort to incorporate modern cipher properties to classical cipher. The second stage of encryption has been performed using columnar transposition with arbitrary random order column selection. Thus the proposed Scheme is a hybrid version of classical and modern cipher properties. The proposed method provides appreciable Security with high throughput and occupies minimum memory space. The Method is resistant against brute-force attack with 93! Combinations of keys, for Caesar encryption.
Hierarchical Digital Twin of a Naval Power SystemKerry Sado
A hierarchical digital twin of a Naval DC power system has been developed and experimentally verified. Similar to other state-of-the-art digital twins, this technology creates a digital replica of the physical system executed in real-time or faster, which can modify hardware controls. However, its advantage stems from distributing computational efforts by utilizing a hierarchical structure composed of lower-level digital twin blocks and a higher-level system digital twin. Each digital twin block is associated with a physical subsystem of the hardware and communicates with a singular system digital twin, which creates a system-level response. By extracting information from each level of the hierarchy, power system controls of the hardware were reconfigured autonomously. This hierarchical digital twin development offers several advantages over other digital twins, particularly in the field of naval power systems. The hierarchical structure allows for greater computational efficiency and scalability while the ability to autonomously reconfigure hardware controls offers increased flexibility and responsiveness. The hierarchical decomposition and models utilized were well aligned with the physical twin, as indicated by the maximum deviations between the developed digital twin hierarchy and the hardware.
Water scarcity is the lack of fresh water resources to meet the standard water demand. There are two type of water scarcity. One is physical. The other is economic water scarcity.
About
Indigenized remote control interface card suitable for MAFI system CCR equipment. Compatible for IDM8000 CCR. Backplane mounted serial and TCP/Ethernet communication module for CCR remote access. IDM 8000 CCR remote control on serial and TCP protocol.
• Remote control: Parallel or serial interface.
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• Remote control system for accessing CCR and allied system over serial or TCP.
• Indigenized local Support/presence in India.
• Easy in configuration using DIP switches.
Technical Specifications
Indigenized remote control interface card suitable for MAFI system CCR equipment. Compatible for IDM8000 CCR. Backplane mounted serial and TCP/Ethernet communication module for CCR remote access. IDM 8000 CCR remote control on serial and TCP protocol.
Key Features
Indigenized remote control interface card suitable for MAFI system CCR equipment. Compatible for IDM8000 CCR. Backplane mounted serial and TCP/Ethernet communication module for CCR remote access. IDM 8000 CCR remote control on serial and TCP protocol.
• Remote control: Parallel or serial interface
• Compatible with MAFI CCR system
• Copatiable with IDM8000 CCR
• Compatible with Backplane mount serial communication.
• Compatible with commercial and Defence aviation CCR system.
• Remote control system for accessing CCR and allied system over serial or TCP.
• Indigenized local Support/presence in India.
Application
• Remote control: Parallel or serial interface.
• Compatible with MAFI CCR system.
• Compatible with IDM8000 CCR.
• Compatible with Backplane mount serial communication.
• Compatible with commercial and Defence aviation CCR system.
• Remote control system for accessing CCR and allied system over serial or TCP.
• Indigenized local Support/presence in India.
• Easy in configuration using DIP switches.
Industrial Training at Shahjalal Fertilizer Company Limited (SFCL)MdTanvirMahtab2
This presentation is about the working procedure of Shahjalal Fertilizer Company Limited (SFCL). A Govt. owned Company of Bangladesh Chemical Industries Corporation under Ministry of Industries.
Student information management system project report ii.pdfKamal Acharya
Our project explains about the student management. This project mainly explains the various actions related to student details. This project shows some ease in adding, editing and deleting the student details. It also provides a less time consuming process for viewing, adding, editing and deleting the marks of the students.
2. The History of Cryptography
Cryptography has roots that
begin around 2000 B.C. in Egypt
used to decorate tombs to tell
the life story of the deceased
not so much about hiding the
messages themselves; rather, the
hieroglyphics were intended to
make the life story seem more
noble, ceremonial, and majestic
3. Some Basic Terminology
plaintext - original message
ciphertext - coded message
cipher - algorithm for transforming plaintext to ciphertext
key - info used in cipher known only to sender/receiver
encipher (encrypt) - converting plaintext to ciphertext
decipher (decrypt) - recovering ciphertext from plaintext
cryptography - study of encryption principles/methods
cryptanalysis (codebreaking) - study of principles/
methods of deciphering ciphertext without knowing key
cryptology - field of both cryptography and cryptanalysis
3
4. Classical Substitution Ciphers
where letters of plaintext are replaced by other letters or by
numbers or symbols
or if plaintext is viewed as a sequence of bits, then substitution
involves replacing plaintext bit patterns with ciphertext bit patterns
4
5. Caesar Cipher
earliest known substitution cipher
by Julius Caesar
first attested use in military affairs
replaces each letter by 3rd letter on
a b c d e f g h i j k l m n o p q r s t u v w
x y z
D E F G H I J K L M N O P Q R S T U V W X Y Z A
B C
example:
meet me after the toga party
PHHW PH DIWHU WKH WRJD SDUWB
5
6. Caesar Cipher
mathematically give each letter a number
a b c d e f g h i j k l m n o p q r s t u v w x y
z
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24
25
then have Caesar cipher as:
c = E(p) = (p + k) mod (26)
p = D(c) = (c – k) mod (26)
6
7. Cryptanalysis of Caesar Cipher
only have 26 possible ciphers
A maps to A,B,..Z
could simply try each in turn
given ciphertext, just try all shifts of letters
do need to recognize when have plaintext
eg. break ciphertext "GCUA VQ DTGCM"
7
9. Transposition Ciphers
now consider classical transposition or permutation ciphers
these hide the message by rearranging the letter order
without altering the actual letters used
can recognise these since have the same frequency distribution as
the original text
28
10. Row Transposition Ciphers
a more complex transposition
write letters of message out in rows over a specified number of
columns
then reorder the columns according to some key before reading off
the rows
Key: 4 3 1 2 5 6 7
Plaintext: a t t a c k p
o s t p o n e
d u n t i l t
w o a m x y z
Ciphertext: TTNAAPTMTSUOAODWCOIXKNLYPETZ
30
11. scytale cipher
Around 400 B.C., the Spartans
would write a message on a sheet
of papyrus (a type of paper) that
was wrapped around a staff (a
stick or wooden rod), which was
then delivered and wrapped
around a different staff by the
recipient. The message was only
readable if it was wrapped around
the correct size staff, which made
the letters properly match up
13. Product Ciphers
ciphers using substitutions or transpositions are not
secure because of language characteristics
hence consider using several ciphers in succession to
make harder, but:
two substitutions make a more complex substitution
two transpositions make more complex transposition
but a substitution followed by a transposition makes a new
much harder cipher
this is bridge from classical to modern ciphers
33
15. Block and Stream Ciphers
BLOCK CIPHERS WORK ON
BLOCKS OF BITS
STREAM CIPHERS, WHICH WORK
ON ONE BIT AT A TIME
16. Initialization Vectors
•Random values that are used with algorithms to ensure patterns are not
created during the encryption process.
•(If IVs are not used, then two identical plaintext values that are
encrypted with the same key will create the same ciphertext. )
•They are used with keys
•Do not need to be encrypted when being sent to the destination.
17. Key Distribution
• 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 relay key between A & B
18. Strengths and Weaknesses
Strengths
Much faster (less computationally intensive) than asymmetric
systems.
Hard to break if using a large key size.
Weaknesses
Requires a secure mechanism to deliver keys properly.
Each pair of users needs a unique key, so as the number of individuals
increases, so does the number of keys, possibly making key
management overwhelming.
Provides confidentiality but not authenticity or nonrepudiation
19. Types of Symmetric Systems
•Data Encryption Standard (DES)
•3DES (Triple DES)
•Blowfish
•Twofish
•IDEA (International Data Encryption Algorithm)
•RC4, RC5, RC6
•AES (Advanced Encryption Standard)
•SAFER (Secure and Fast Encryption Routine)
•Serpent
21. RSA
by Rivest, Shamir & Adleman of MIT in 1977
best known & widely used public-key scheme
based on exponentiation in a finite (Galois) field over
integers modulo a prime
nb. exponentiation takes O((log n)3) operations (easy)
uses large integers (eg. 1024 bits)
security due to cost of factoring large numbers
nb. factorization takes O(e log n log log n) operations (hard)
22. Ideas...
Given a big number n, a message M (that is converted to
integer value), if we can choose e and d that satisfy the
following conditions:
C=Me mod n for all M<n
M=Cd mod n=Med mod n
or Med ≡ M mod n (denote Med conguence M modulo n)
It is infeasible to dermine d given e and n.
23. How RSA Works
Given two primes p, q, and two integers m, n, such that n=p.q
and 0<m<n, an arbitrary integer k. Because of Euler's
Theorem:
– mø(n)*k+1 ≡ m mod n (1)
in which, the totient ø(n) of a positive
integer n is defined to be the number of
positive integers less than or equal to n that
are coprime to n. ø(9)=6 since the six numbers
1, 2, 4, 5, 7 and 8 are coprime to 9
– We can have med ≡ m mod n, if
ed=ø(n)*k+1 or ed ≡ 1 mod ø(n)
according to rules of modular arithmetic, this
happens only if e (and therefore d) is
relative prime to ø(n). Or gcd(ø(n),e)=1
– Since p, q are two primes, we have
• ø(n)=(p-1)(q-1), it is easy to have e, and d
24. 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
note ø(n)=(p-1)(q-1)
selecting at random the encryption key e
where 1<e<ø(n), gcd(e,ø(n))=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}
25. 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
note that the message M must be smaller than the
modulus n (block if needed)
26. RSA Example - Key Setup
• Select primes: p=17 & q=11
• Compute n = pq =17 x 11=187
• Compute ø(n)=(p–1)(q-1)=16 x 10=160
• Select e: gcd(e,160)=1; choose e=7
• Determine d: de ≡1 mod 160 and d < 160 Value is
d=23 since 23x7=161= 10x160+1
• Publish public key PU={7,187}
• Keep secret private key PR={23,187}
27. RSA Example - En/Decryption
sample RSA encryption/decryption is:
given message M = 88 (nb. 88<187)
encryption:
C = 887 mod 187 = 11
decryption:
M = 1123 mod 187 = 88
28. RSA Security
possible approaches to attacking RSA are:
brute force key search (infeasible given big size of keys)
mathematical attacks (based on difficulty of computing
ø(n), by factoring modulus n)
timing attacks (on running of decryption)
29. Factoring Problem
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
currently believe all equivalent to factoring
Cryptanalysis have seen slow improvements over the years
currently assume 1024-2048 bit RSA is secure
ensure p, q of similar size and matching other constraints
30. Timing Attacks
developed by Paul Kocher in mid-1990’s
exploit timing variations in operations
eg. multiplying by small vs large number
or IF's varying which instructions executed
infer operand size based on time taken
RSA exploits time taken in exponentiation
countermeasures
use constant exponentiation time
add random delays
blind values used in calculations
31. Strengths and Weaknesses
Strengths
•Better key distribution than symmetric systems
•Better scalability than symmetric systems
•Can provide authentication and nonrepudiation
Weaknesses
•Works much more slowly than symmetric systems
•Mathematically intensive tasks
32. Key Management
public-key encryption helps address key distribution
problems
have two aspects of this:
distribution of public keys
use of public-key encryption to distribute secret keys
33. Distribution of Public Keys
can be considered as using one of:
public announcement
publicly available directory
public-key authority
public-key certificates
34. Public Announcement
users distribute public keys to recipients or broadcast
to community at large
eg. append PGP keys to email messages or post to news
groups or email list
major weakness is forgery
anyone can create a key claiming to be someone else and
broadcast it
until forgery is discovered can masquerade as claimed
user
35. Publicly Available Directory
can obtain greater security by registering keys with a
public directory
directory must be trusted with properties:
contains {name,public-key} entries
participants register securely with directory
participants can replace key at any time
directory is periodically published
directory can be accessed electronically
still vulnerable to tampering or forgery
36. Public-Key Authority
improve security by tightening control over
distribution of keys from directory
has properties of directory
and requires users to know public key for the
directory
then users interact with directory to obtain any
desired public key securely
does require real-time access to directory when keys are
needed
38. Public-Key Certificates
certificates allow key exchange without real-time
access to public-key authority
a certificate binds identity to public key
usually with other info such as period of validity, rights of
use etc
with all contents signed by a trusted Public-Key or
Certificate Authority (CA)
can be verified by anyone who knows the public-key
authorities public-key
40. Public-key infrastructure (PKI)
A public-key infrastructure (PKI) is a set of hardware, software, people,
policies, and procedures needed to create, manage, distribute, use,
store, and revoke digital certificates
PKI is an arrangement that binds public keys with respective user
identities by means of a certificate authority (CA)
41. Differences Between Symmetric
and Asymmetric Systems
Attribute Symmetric Asymmetric
Keys One key is shared between
two or more entities
One entity has a public key,
and the other entity has the
corresponding private key.
Key exchange Out-of-band through secure
mechanisms.
A public key is made available
to everyone, and a private key
is kept secret by the owner.
Speed Algorithm is less complex
and faster.
The algorithm is more
complex and slower.
Use Bulk encryption, which
means encrypting files and
communication paths.
Key distribution and digital
signatures.
Security service
provided
Confidentiality. Authentication and
nonrepudiation
42. Types of Asymmetric Systems
The Diffie-Hellman Algorithm
RSA
El Gamal
Elliptic Curve Cryptosystems
LUC
Knapsack
Zero Knowledge Proof
44. Public-Key Distribution of Secret Keys
use previous methods to obtain public-key
can use for secrecy or authentication
but public-key algorithms are slow
so usually want to use private-key encryption to
protect message contents
hence need a session key
have several alternatives for negotiating a suitable
session
45. Simple Secret Key Distribution
proposed by Merkle in 1979
A generates a new temporary public key pair
A sends B the public key and their identity
B generates a session key K sends it to A encrypted using
the supplied public key
A decrypts the session key and both use
problem is that an opponent can intercept and
impersonate both halves of protocol
47. Hybrid Key Distribution
retain use of private-key KDC
shares secret master key with each user
distributes session key using master key
public-key used to distribute master keys
especially useful with widely distributed users
rationale
performance
backward compatibility
48. Diffie-Hellman Key Exchange
first public-key type scheme proposed
by Diffie & Hellman in 1976 along with the exposition
of public key concepts
note: now know that Williamson (UK CESG) secretly
proposed the concept in 1970
is a practical method for public exchange of a secret
key
used in a number of commercial products
49. Diffie-Hellman Key Exchange
a public-key distribution scheme
cannot be used to exchange an arbitrary message
rather it can establish a common key
known only to the two participants
value of key depends on the participants (and their private
and public key information)
based on exponentiation in a finite (Galois) field (modulo a
prime or a polynomial) - easy
security relies on the difficulty of computing discrete
logarithms (similar to factoring) – hard
50. Diffie-Hellman Setup
all users agree on global parameters:
large prime integer or polynomial q
–a being a primitive root mod q
each user (eg. A) generates their key
chooses a secret key (number): xA < q
compute their public key: yA = a
xA
mod q
each user makes public that key yA
51. Diffie-Hellman Key Exchange
shared session key for users A & B is KAB:
KAB = a
xA.xB
mod q
= yA
xB
mod q (which B can compute)
= yB
xA
mod q (which A can compute)
KAB is used as session key in private-key encryption scheme
between Alice and Bob
if Alice and Bob subsequently communicate, they will have the
same key as before, unless they choose new public-keys
attacker needs an x, must solve discrete log
52. Diffie-Hellman Example
users Alice & Bob who wish to swap keys:
agree on prime q=353 and a=3
select random secret keys:
A chooses xA=97, B chooses xB=233
compute respective public keys:
–yA=3
97
mod 353 = 40 (Alice)
–yB=3
233
mod 353 = 248 (Bob)
compute shared session key as:
–KAB= yB
xA
mod 353 = 248
97
= 160 (Alice)
–KAB= yA
xB
mod 353 = 40
233
= 160 (Bob)
53. Key Exchange Protocols
users could create random private/public D-H keys
each time they communicate
users could create a known private/public D-H key
and publish in a directory, then consulted and used
to securely communicate with them
both of these are vulnerable to a meet-in-the-
Middle Attack
authentication of the keys is needed
54. Kerckhoffs’ Principle
Auguste Kerckhoffs published a paper in 1883 stating that
•the only secrecy involved with a cryptography system should be the key.
•algorithm should be publicly known.
•if security were based on too many secrets, there would be more
vulnerabilities to possibly exploit.
55. Hash Functions
•condenses arbitrary message to fixed size
h = H(M)
•usually assume that the hash function is public and not keyed
•hash used to detect changes to message
•can use in various ways with message
•most often to create a digital signature
56. Requirements for Hash
Functions
•can be applied to any sized message M
•produces fixed-length output h
•is easy to compute h=H(M) for any message M
•given h is infeasible to find x s.t. H(x)=h
• one-way property
•given x is infeasible to find y s.t. H(y)=H(x)
• weak collision resistance
•is infeasible to find any x,y s.t. H(y)=H(x)
• strong collision resistance
58. Attacks Against One-Way Hash
Functions
If the algorithm does produce the same value for two distinctly different
messages, this is called a collision
An attacker can attempt to force a collision, which is referred to as a
birthday attack
How many people must be in the same room for the chance to be
greater than even that another person has the same birthday as you?
Answer: 253
How many people must be in the same room for the chance to be
greater than even that at least two people share the same birthday?
Answer: 23
59. Message Authentication Code
(MAC)
•generated by an algorithm that creates a small fixed-sized block
• depending on both message and some key
• like encryption though need not be reversible
•appended to message as a signature
•receiver performs same computation on message and checks it
matches the MAC
•provides assurance that message is unaltered and comes from sender
63. Services of Cryptosystems
•Confidentiality Renders the information unintelligible except by
authorized
•entities.
•Integrity Data has not been altered in an unauthorized manner since it
was created, transmitted, or stored.
•Authentication Verifies the identity of the user or system that created
information.
•Nonrepudiation Ensures that the sender cannot deny sending the
message.
65. Link Encryption vs. End-to-End
Encryption
Link encryption encrypts all the data (except data link control messaging
information) along a specific communication path, as in a satellite link,
T3 line, or telephone circuit
end-to-end encryption happens within the applications
SSL encryption takes place at the transport layer.
66. HTTP Secure
HTTP Secure (HTTPS) is HTTP running over SSL (developed by Netscape)
SSL :
◦ it is not an open-community protocol
◦ works at the transport layer
◦ uses public key encryption
◦ provides data encryption, server authentication, message integrity, and
optional client authentication
The open-community version of SSL is Transport Layer Security (TLS)
67. Pretty Good Privacy
•Freeware e-mail security program and was released in 1991
•PGP is a complete cryptosystem that uses cryptographic protection to
protect e-mail and files.
•It can use RSA public key encryption for key management and use
•IDEA symmetric cipher for bulk encryption of data
•PGP uses “web of trust” in its key management approach
68. Secure Shell
SSH is a program and a set of protocols that work together to provide a
secure tunnel between two computers.
The two computers go through a handshaking process and exchange
(via Diffie-Hellman) a session key that will be used during the session to
encrypt and protect the data sent
SSH should be used instead of Telnet, FTP, rlogin, rexec, or rsh
69. Internet Protocol Security
(IPSec)
•IPSec uses two basic security protocols: Authentication Header (AH)
and Encapsulating Security Payload (ESP).
•AH is the authenticating protocol
•ESP is an authenticating and encrypting protocol that uses
cryptographic mechanisms to provide source authentication,
confidentiality, and message integrity
•IPSec can work in one of two modes:
◦ transport mode, in which the payload of the message is protected
◦ tunnel mode, in which the payload and the routing and header information
are protected
71. Steganography
an alternative to encryption
hides existence of message
using only a subset of letters/words in a longer message marked in
some way
using invisible ink
hiding in graphic image or sound file
has drawbacks
high overhead to hide relatively few info bits
91
72. Example
92
Removing all but the last 2 bits of each color component produces an almost
completely black image. Making that image 85 times brighter produces the image
on the right hand-side
.
73. 93
Jane S., a chief sub editor and editor, can always be found
hard at work in her cubicle. Jane works independently, without
wasting company time talking to colleagues. She never
thinks twice about assisting fellow employees, and she always
finishes given assignments on time. Often Jane takes extended
measures to complete her work, sometimes skipping
coffee breaks. She is a dedicated individual who has absolutely no
vanity in spite of her high accomplishments and profound
knowledge in her field. I firmly believe that Jane can be
classed as a high-caliber employee, the type which cannot be
dispensed with. Consequently, I duly recommend that Jane be
promoted to executive management, and a proposal will be
sent away as soon as possible.
Project Leader
Example 2: Letter of Recommendation
Jane S., a chief sub editor and editor, can always be found
hard at work in her cubicle. Jane works independently, without
wasting company time talking to colleagues. She never
thinks twice about assisting fellow employees, and she always
finishes given assignments on time. Often Jane takes extended
measures to complete her work, sometimes skipping
coffee breaks. She is a dedicated individual who has absolutely no
vanity in spite of her high accomplishments and profound
knowledge in her field. I firmly believe that Jane can be
classed as a high-caliber employee, the type which cannot be
dispensed with. Consequently, I duly recommend that Jane be
promoted to executive management, and a proposal will be
sent away as soon as possible.
Project Leader
(copied from http://gadgetopia.com/post/2278)