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  • Ch 1:Tng quan v M ha thng tin v ng dng

  • M u

  • M uKhoa hc mt m ra i t hng nghn nm. Trong sut nhiu th k, cc kt qu ca lnh vc ny hu nh khng c ng dng trong cc lnh vc dn s thng thng ca i sng x hi m ch yu c s dng trong lnh vc qun s, chnh tr, ngoi giao... Ngy nay, cc ng dng m ha v bo mt thng tin ang c s dng ngy cng ph bin trong cc lnh vc khc nhau trn th gii, t cc lnh vc an ninh, qun s, quc phng, cho n cc lnh vc dn s nh thng mi in t, ngn hng

  • Mt m hcMt m (Cryptography) l ngnh khoa hc nghin cu cc k thut ton hc nhm cung cp cc dch v bo v thng tin.W. Stallings (2003), Cryptography and Network Security: Principles and Practice, Third Edition, Prentice Hall

  • Mt s thut ngCryptographyCryptanalysisCryptology = Cryptography + CryptanalysisSecuritySteganography

  • Cc vn chnh trong Mt m hc

  • Mt m hc???Cch hiu truyn thng: gi b mt ni dung trao iAlice v Bob trao i vi nhau trong khi Eve tm cch nghe lnAliceBobEve

  • Mt s vn chnh trong bo v thng tin Bo mt thng tin (Secrecy): m bo thng tin c gi b mt.Ton vn thng tin (Integrity): bo m tnh ton vn thng tin trong lin lc hoc gip pht hin rng thng tin b sa i.Xc thc (Authentication): xc thc cc i tc trong lin lc v xc thc ni dung thng tin trong lin lc. Chng li s thoi thc trch nhim (Non-repudiation): m bo mt i tc bt k trong h thng khng th t chi trch nhim v hnh ng m mnh thc hin

  • Xc thc (Authentication)V d:Bob ch Alice xc nhn khi n thi im thc hin cng vicCn m bo rng Eve khng can thip to xc nhn giXc thc (Authentication), nh danh (identification)


  • Tnh ton vn thng tin (Integrity)V d:Bob cn m bo l nhn chnh xc ni dung m Alice giCn m bo rng Eve khng can thip sa ni dung thng ip m Alice gi cho BobTnh ton vn thng tin (Integrity)


  • Chng li s thoi thc trch nhimV d:Bob nhn c 1 thng ip m Alice giAlice khng th chi rng khng gi thng ip ny cho BobChng li s thoi thc trch nhim (Non-repudiation)AliceBob

  • Cc gii phpAuthentication (Identity verification)Access control (Authorization)Data confidentiality (Privacy)Data integrity (Tamper-proofing)Non-repudiation (Proof of transaction)

  • AuthenticationKim tra danh tnhm bo rng mt ngi dng ( c th l mt t chc, mt phn mm, ...) phi chng minh c mnh l ai.Ngn nga hin tng gi mo danh tnh (Identity interception) v hin tng s dng username v password dng clear-text ca ngi khc do dm ng c trn mng vo mc ch xu xa (Masquerading)Gii phpCh k in t

  • Access Control (Authorization)Cho php mt ngi dng hp l ng nhp vo h thng v thc hin cc chc nng tng ng vi vai tr ca mnhAccess Control c th hin thc bng cc dch v File v databaseGii phpACLs (Access Control Lists): danh sch cc ngi dng, thuc v cc nhm no , v quy nh v cc quyn tng ng cho tng nhm trn LDAP server.

  • Data Confidentiality (Privacy)Bo v thng tin trn ng truyn khi nhng con mt lic ngang lic dcGii phpM ha d liu (M ha i xng v m ha bt i xng)

  • Data Integrity (Tamper- Proofing)Ngn nga d liu b thay i trn ng truynm bo d liu t ngi gi n ngi nhn phi ging nhauGii phpHm bm mt m (Message Digest)

  • Non-repudiation (Proof of Transaction)Chng minh vi t chc th 3 mt giao tc no tht s xy raBo v c ngi gi ln ngi nhnGii phpCh k in t

  • Lch s pht trin ca Mt m hc

  • S lc lch s pht trin ca mt m hcNgun: http://www.cqrsoft.com/history/scytale.htm

  • Dn nhpn/con du c s dng ng ln cc ti liu quan trngMt khu (Password) c s dng nh danh ngi trong t chcNgun: http://images.encarta.msn.com/xrefmedia/sharemed/targets/images/pho/t025/T025102A.jpg

  • M ha thi k c iPhng php m ha Atbash:c s dng trong ting Hebrew c = Phng php CaesarBt k ai bit c quy tc m ha ny d dng gii m thng ip


  • M ha thi k c iC phng php Atbash v Shift Cipher u l trng hp c bit ca phng php tng qut c s dng trong thi c i: Phng php Thay th n k t (MonoAlphabetic Substitution Cipher)Phng php Caesar l mt trng hp c bit ca phng php m ha bng cch dch chuyn (Shift Ciphers). Phng php Shift Cipher: cc k t c xoay vng i K v tr trong bng ch ci. K c xem l kha gii m


  • Ceasar Shift CiphersVD: dch chuyn 3 k t trong bng ch ci, ta c:M ha cm t: Attack at Down

  • Qu trnh m ha v gii mM haGii m

  • Using a key to shift alphabetS dng kha l mt t no , v d WORDm bo nh x mt-mtC1 W O R D A B C E F G H I J K L M N P Q S T U V X Y ZEncrypted Message:??Message:

    Bob, I love you. Alice



  • Monoalphabetic Substitution CipherMi k t thay th bng 1 k t khc duy nht trong bng ch ciEncrypted Message:Nkn, s gktc wky. mgsbcMessage:

    Bob, I love you. Alice



  • M ha thi k c iKhng phi tt c cc phng php m thi c i u s dng phng php thay th.Thit b m ha u tin: Spartan scytaleNgun: http://plus.maths.org/issue34/features/ekert/S dng thit b ny, cc ch ci trong thng ip khng b thay i, m ch thay i v tr xut hin ca cc thng ip (Transposition)

  • Columnar TranspositionSp xp cc k t ca d liu plaintext vo cc ctNu cc k t ca plaintext khng l bi s ca ct, thay bng cc k t t xut hin nh x, z.T H I S I S A M E SS A G E TO S H O W H O W A C O L U M N A R T R A N S P O S I T I O N W O R K ST S S O HO A N I WH A A S OL R S T OI M G H WU T P I R S E E O A M R O O KI S T W CN A S N SPlain TextCipher Text

  • M ha thi k c iTheo cc ti liu ghi nhn li, phng php phn tch tn s s dng c s dng t th k th 9http://en.wikipedia.org/wiki/Caesar_cipherhttp://plus.maths.org/issue34/features/ekert/M ha Chu u gn nh t c s pht trin t thi c i n th k 14!!!

  • M ha thi k phc hng , cng nh cc nc Chu u khc, mt m hc bt u c pht trin tr liCc quc gia, cc thnh ph bt u tm kim cc chuyn gia v mt m v ph m m ha v gii m cc bc th.Phng php m ha giai on ny thng l Thay th a k t (PolyAlphabetic Substitution Cipher).Nhiu dng c m ha c ch to v s dng

  • Polyalphabetic Substitution CipherS dng mt chui Monoalphabetic CipherC1, C2, C2, C1, C2V dEncrypted Message:Ghu, n etox dhz.tenvjMessage:

    Bob, I love you. Alice



  • M ha thi k phc hngPhng php m ha bng cch thay th a k t c th c xem nh s dng nhiu ln thay th n k t lin tip nhau.Thng dng dng c Cipher Disk, hoc dng bng tra gip m ha v gii mK thut chnh (kinh in) dng ph v h m Thay th a k t gm 2 bc:Tm ra di ca chu kp dng k thut phn tch (cho phng php m ha thay th n k t) + thng tin thu c t cc k t trc

  • M ha trong th k 19 v u th k 20M ha c s dng ph bin trong Th chin IS pht trin ca sng v tuyn v in i gip vic lin lc trong qun i c thc hin d dng v nhiu hn.i hi cc thit b h tr vic m ha v gii m Cc my m ha ra i

  • M ha trong th k 19 v u th k 20Th chin th 2: cuc chin trn lnh vc khoa hc, trong c c khoa hc mt m.My m ha Enigma (ca c) b qun i Anh gii m My m ha Purple ca Nht b qun i M gii m

  • H thng m ha

  • H thng m haBo m mt mu tin x c m ha bng lut m ha ek c th c gii m chnh xc bng lut dk

  • H thng m ha i xng

  • M ha kha cng cng

  • M i xng VS m bt i xngM kha ngnTc x l nhanhM kha diTc x l chmTrao i m khad dngKh trao i m kha

  • Trng Zm

  • Khi nim v ZmZm c nh ngha l tp hp {0, 1, , m-1}, c trang b php cng (k hiu +) v php nhn (k hiu l ). Php cng v php nhn c thc hin trong Zm tng t nh trong Z, ngoi tr kt qu tnh theo modulo m V d: Gi s ta cn tnh gi tr trong Z16. Trong Z, ta c kt qu ca php nhn 11 13=143 Do 14315 (mod 16) nn 11 13 = 15 trong Z16.

  • Tnh cht ca Zm

  • Tnh cht ca Zm (tt)

    Cryptography is the study of mathematical techniques related to the design of ciphers Cryptanalysis is the study of breaking them Cryptology (or crypto) is the study of both Crypto building blocks are otherwise known as cryptographic primitivese.g. hash functions, block cyphers, stream cyphers, digital signatures

    ******** Many of the encrypted messages in this period use nomenclature. Using substitution ciphers to encode messages using these codes, code breaking becomes harder. Consider the issue of recognizing the fact that youve actually broken the code.nomenclature naming conventions that are a combination of a code and a simple compression technique. Different leaders and cities, professions and commodities get a 2-3 letter code.

    **Cryptography in the 19th and 20th Centauries Telegraph and Morse code revolutionize communications. Many mechanical and electro-mechanical devices invented for encrypted communications. Telegraphy and flags used in American civil war extensively, but relatively few interesting codes were used.