O slideshow foi denunciado.
Utilizamos seu perfil e dados de atividades no LinkedIn para personalizar e exibir anúncios mais relevantes. Altere suas preferências de anúncios quando desejar.
Cryptography,
Codes and Cipher,
Data Encryption
standard
Cryptography
• Cryptography is a method of storing and
transmitting data in a particular form so that
only those for whom ...
Some Basic Terminology
• plaintext - original message
• ciphertext - coded message
• cipher - algorithm for transforming p...
History – The Manual Era
• Dates back to at least 2000 B.C.
• Pen and Paper Cryptography
– Scytale – Spartan method involv...
History – The Mechanical Era
• Invention of cipher machines
• Examples
– Confederate Army’s Cipher Disk
– Japanese Red and...
History – The Modern Era
• Computers!
• Examples
– Lucifer
– Rijndael
– RSA
– ElGamal
Cryptosystem Services
• Confidentiality – Only authorized entities are
allowed to view
• Integrity – Ensures the message w...
Cryptographic Methods
• Symmetric
– Same key for encryption and decryption
– Key distribution problem
• Asymmetric
– Mathe...
Symmetric
• Fast
• Only provide confidentiality
• Need secure channel for key distribution
• Key management headaches from...
Symmetric or Private Key
Asymmetric
• Large mathematical operations make it slower
than symmetric algorithms
• No need for out of band key distribu...
Asymmetric or Public Key
Hybrid
• Combines strengths of both methods
• Asymmetric distributes symmetric key
– Also known as a session key
• Symmetr...
Key Distribution
• Given parties A and B have various key
distribution alternatives:
• A can select key and physically del...
Key Distribution Scenario
Ciphertext
• PCQ VMJYPD LBYK LYSO KBXBJXWXV BXV ZCJPO
EYPD KBXBJYUXJ LBJOO KCPK. CP LBO
LBCMKXPV XPV IYJKL PYDBL, QBOP KBO...
THE SOLUTION
Code
• X Z A V O I D B Y G E R S P C F H J K L M N Q T U W
• A B C D E F G H I J K L M N O P Q R S T U V W X ...
Plaintext
• Now during this time Shahrazad had borne
King Shahriyar three sons. On the thousand
and first night, when she ...
Data Encryption Standard (DES)
• The most widely used private key block cipher,
is the Data Encryption Standard (DES).
• I...
DES History
• IBM developed Lucifer cipher
– by team led by Feistel in late 60’s
– used 64-bit data blocks with 128-bit ke...
Multiple Encryption & DES
• clear a replacement for DES was needed
– theoretical attacks that can break it
– demonstrated ...
Double-DES?
• could use 2 DES encrypts on each block
– C = EK2(EK1(P))
• issue of reduction to single stage
• and have “me...
Triple-DES with Two-Keys
• hence must use 3 encryptions
– would seem to need 3 distinct keys
• but can use 2 keys with E-D...
Triple-DES with Three-Keys
• although no practical attacks on two-key Triple-
DES have some concerns
– Two-key: key length...
Triple DES
Public Key Infrastructure
• All components needed to enable secure
communication
– Policies and Procedures
– Keys and Algo...
PKI Components
• Digital Certificates
– Contains identity and verification info
• Certificate Authorities
– Trusted entity...
Class 17
Próximos SlideShares
Carregando em…5
×
Próximos SlideShares
Classical Encryption Techniques in Network Security
Avançar
Transfira para ler offline e ver em ecrã inteiro.

Compartilhar

Class 17

Baixar para ler offline

Class

Audiolivros relacionados

Gratuito durante 30 dias do Scribd

Ver tudo

Class 17

  1. 1. Cryptography, Codes and Cipher, Data Encryption standard
  2. 2. Cryptography • Cryptography is a method of storing and transmitting data in a particular form so that only those for whom it is intended can read and process it.
  3. 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
  4. 4. History – The Manual Era • Dates back to at least 2000 B.C. • Pen and Paper Cryptography – Scytale – Spartan method involved wrapping a belt around a rod of a given diameter and length – Atbash – Hewbrew cipher which mirrored the normal alphabet (shown in The DaVinci Code) – Caesar – Shift all letters by a given number of letters in the alphabet – Vignère – Use of a key and multiple alphabets to hide repeated characters in an encrypted message
  5. 5. History – The Mechanical Era • Invention of cipher machines • Examples – Confederate Army’s Cipher Disk – Japanese Red and Purple Machines – German Enigma
  6. 6. History – The Modern Era • Computers! • Examples – Lucifer – Rijndael – RSA – ElGamal
  7. 7. Cryptosystem Services • Confidentiality – Only authorized entities are allowed to view • Integrity – Ensures the message was not altered by unauthorized individuals • Authenticity – Validates the source of a message, to ensure the sender is properly identified • Nonrepudiation – Establishes sender identity so that the entity cannot deny having sent the message • Access Control – Access to an object requires access to the associated crypto keys in many systems (e.g. login)
  8. 8. Cryptographic Methods • Symmetric – Same key for encryption and decryption – Key distribution problem • Asymmetric – Mathematically related key pairs for encryption and decryption – Public and private keys
  9. 9. Symmetric • Fast • Only provide confidentiality • Need secure channel for key distribution • Key management headaches from large number of key pairs to maintain
  10. 10. Symmetric or Private Key
  11. 11. Asymmetric • Large mathematical operations make it slower than symmetric algorithms • No need for out of band key distribution (public keys are public!) • Scales better since only a single key pair needed per individual • Can provide authentication and nonrepudiation
  12. 12. Asymmetric or Public Key
  13. 13. Hybrid • Combines strengths of both methods • Asymmetric distributes symmetric key – Also known as a session key • Symmetric provides bulk encryption • Example: – SSL negotiates a hybrid method
  14. 14. Key Distribution • Given parties A and B have various key distribution alternatives: • A can select key and physically deliver to B • third party can select & deliver key to A & B • if A & B have communicated previously can use previous key to encrypt a new key • if A & B have secure communications with a third party C, C can relay key between A & B
  15. 15. Key Distribution Scenario
  16. 16. Ciphertext • PCQ VMJYPD LBYK LYSO KBXBJXWXV BXV ZCJPO EYPD KBXBJYUXJ LBJOO KCPK. CP LBO LBCMKXPV XPV IYJKL PYDBL, QBOP KBO BXV OPVOV LBO LXRO CI SX'XJMI, KBO JCKO XPV EYKKOV LBO DJCMPV ZOICJO BYS, KXUYPD: 'DJOXL EYPD, ICJ X LBCMKXPV XPV CPO PYDBLK Y BXNO ZOOP JOACMPLYPD LC UCM LBO IXZROK CI FXKL XDOK XPV LBO RODOPVK CI XPAYOPL EYPDK. SXU Y SXEO KC ZCRV XK LC AJXNO X IXNCMJ CI UCMJ SXGOKLU?' Any Guesses???
  17. 17. THE SOLUTION Code • X Z A V O I D B Y G E R S P C F H J K L M N Q T U W • 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
  18. 18. Plaintext • Now during this time Shahrazad had borne King Shahriyar three sons. On the thousand and first night, when she had ended the tale of Ma'aruf, she rose and kissed the ground before him, saying: 'Great King, for a thousand and one nights I have been recounting to you the fables of past ages and the legends of ancient kings. May I make so bold as to crave a favour of your majesty?’
  19. 19. Data Encryption Standard (DES) • The most widely used private key block cipher, is the Data Encryption Standard (DES). • It was adopted in 1977 by the National Bureau of Standards as Federal Information Processing Standard 46 (FIPS PUB 46). • DES encrypts data in 64-bit blocks using a 56- bit key. • The DES enjoys widespread use.
  20. 20. DES History • IBM developed Lucifer cipher – by team led by Feistel in late 60’s – used 64-bit data blocks with 128-bit key • then redeveloped as a commercial cipher with input from NSA and others • in 1973 NBS issued request for proposals for a national cipher standard • IBM submitted their revised Lucifer which was eventually accepted as the DES
  21. 21. Multiple Encryption & DES • clear a replacement for DES was needed – theoretical attacks that can break it – demonstrated exhaustive key search attacks • AES is a new cipher alternative – prior to this alternative was to use multiple encryption with DES implementations – Triple-DES is the chosen form
  22. 22. Double-DES? • could use 2 DES encrypts on each block – C = EK2(EK1(P)) • issue of reduction to single stage • and have “meet-in-the-middle” attack – works whenever use a cipher twice – since X = EK1(P) = DK2(C) – attack by encrypting P with all keys and store – then decrypt C with keys and match X value – takes O(256) steps
  23. 23. Triple-DES with Two-Keys • hence must use 3 encryptions – would seem to need 3 distinct keys • but can use 2 keys with E-D-E sequence – C = EK1(DK2(EK1(P))) – nb encrypt & decrypt equivalent in security – if K1=K2 then can work with single DES • standardized in ANSI X9.17 & ISO8732 • no current known practical attacks – several proposed impractical attacks might become basis of future attacks
  24. 24. Triple-DES with Three-Keys • although no practical attacks on two-key Triple- DES have some concerns – Two-key: key length = 56*2 = 112 bits – Three-key: key length = 56*3 = 168 bits • can use Triple-DES with Three-Keys to avoid even these – C = EK3(DK2(EK1(P))) • has been adopted by some Internet applications, eg PGP, S/MIME
  25. 25. Triple DES
  26. 26. Public Key Infrastructure • All components needed to enable secure communication – Policies and Procedures – Keys and Algorithms – Software and Data Formats • Assures identity to users • Provides key management features – Issuance – Revocation – Recovery – Distribution – History
  27. 27. PKI Components • Digital Certificates – Contains identity and verification info • Certificate Authorities – Trusted entity that issues certificates • Registration Authorities – Verifies identity for certificate requests • Certificate Revocation List (CRL)
  • AbilashKannan2

    Nov. 23, 2019
  • Roshnipaulk

    Jan. 21, 2016

Class

Vistos

Vistos totais

501

No Slideshare

0

De incorporações

0

Número de incorporações

8

Ações

Baixados

16

Compartilhados

0

Comentários

0

Curtir

2

×