Cryptography -- Classical StylesOverviewSecurity problems of interestAttacksResponse?Model for cryptographyIssuesWhat’s cryptographyA few termsSlide 10Slide 11Slide 12TransformationsMore termsSteganographySlide 16Two crypto techniques“Staff” cipherThe ole alternation trickThe ole structured patterns trickThe ole mirror trickSlide 22Caesar cipher - substitution cipherSlide 24Substitution TechniqueCryptanalysis – break Caesar cipherMono-alphabetic SubstitutionLanguage regularitiesLanguage regularities - exampleCrypt algorithm developmentAlgorithm development (cont)Poly-alphabetic substitution cipherPoly-alphabetic exampleFrom letters to binaryOne time padRotor MachinesRotor machineSlide 38WW II crypto machinesNextBackup Notes cracking polyalphBackup Notes cracking polyalph (2)Slide 43Cryptography -- Classical StylesAnita JonesCS451 Information Security Copyright(C) Anita Jones9/2006 OverviewIntroductionA security modelWhat is cryptography?Some classical ciphersfrom days of olde …….up to World War II9/2006 Security problems of interestconfidentiality - protect info content from unwarranted observation integrity - protect info accuracy availability - ensure information delivery authentication - assure identity of user (sender) non-repudiation - protect from deniabilityaccess control - control access to info/resources Policies:Problems that arise in implementation:9/2006 Attacksinterception - of information-traffic, breaches confidentialityinterruption - of service, availabilitymodification - of information, i.e. loss of integrityfabrication - of information, destroys authenticity9/2006 Response?identify key assets evaluate threat posed to assets implement suitable countermeasures manage implementation cryptography is a key technologyNote – not a “perimeter defense” technology9/2006 Model for cryptographyPrincipalPrincipalMessageSecretInformationSecurityTransformSecurityTransformMessageSecretInformationTrusted 3rd Party(arbitrates, distributessecret information)OpponentInfo channel9/2006 IssuesTransformation algorithmWhat’s the secret information; How to generate itHow to distribute secret information Protocols -- disciplined interaction involving all parties9/2006 What’s cryptographycryptography is the study of secret (crypto-) writing (-graphy) concerned with developing algorithms which may be used to: conceal the content of a message from all except the sender & recipient (secrecy or confidentiality) verify the correctness of a message or its sender to the recipient (integrity & authentication) includes protocols solving many problems9/2006 A few termscryptography the art or science of transforming an intelligible message into one that is unintelligible, and then transforming that message back to original form plaintext the original intelligible message ciphertext the transformed message9/2006 A few termscipher an algorithm for transforming an intelligible message into one that is unintelligible key critical (secret) information used in the cipher & known only to the sender & receiver Symmetric – shared Asymmetric – public/private9/2006 A few termsencipher (encode) the process of converting plaintext to ciphertext using a cipher plus key decipher (decode) the process of converting ciphertext back into plaintext using a cipher plus key9/2006 A few termscryptanalysis (codebreaking) the study of methods for transforming an unintelligible message back into an intelligible message without knowledge of the keycode an algorithm for transforming an intelligible message into an unintelligible message using a code-book9/2006 Transformationsencryption applying a mathematical function mapping plaintext to ciphertext using the specified key: C = EK(P)decryption applying a mathematical function mapping ciphertext to plaintext using the specified key: P = EK-1(C) P = DK(C)9/2006 More termscryptographic system a single parameter family of invertible transformations with unique inverses where only the key is secretthe cryptographic system is typically made publickeys, of course, are secret9/2006 Steganographyembed message in innocuous settingMy Special Friend,Our speaker today in class today is exciting, & I know that the next speaker is even better. I need to report to you that next class the teacher will give the mid-term exam. Well, there is only one mid-term! YEAH!!! That is it for now. I’m awful at writing, but will keep trying ………...9/2006 Steganographyembed message in innocuous settingMy Special Friend,Our speaker today in class today is exciting, & I know that the next speaker is even better. I need to report to you that next class the teacher will give the mid-term exam. Well, there is only one mid-term! YEAH!!! That is it for now. I’m awful at writing, but will keep trying ………...Two crypto techniquesPermutationSubstitution9/2006 “Staff” cipheran early Greek transposition cipher:cut a narrow strip of paper long enough to write messagewind it around a staff so that adjacent edges abutwrite message horizontally down the shaft with a character on each wrappingunwindResult: long sequence of seemingly random letters9/2006 The ole alternation trickwrite message letters on alternate rows read off cipher by row Plain = “I CAME I SAW I CONQUERED” Plain: I A E S W C N U E C M I A I O Q R D Cipher: IAESW CNUE CMIAI OQRD9/2006 The ole structured patterns trickwrite message letters as a matrix read off cipher by some pattern Plain: I C A M E I S A W I C O N Q U E R E D A Cipher: diagonals, concentric circle, in and out, etc9/2006 The ole mirror trickwrite the message backwards Plain: I CAME I SAW I CONQUERED Cipher: DEREU QNOCI WASIE MACI………and speaking of J. CaesarTwo crypto techniquesPermutationSubstitution9/2006 Caesar cipher - substitution cipherJulius Caesar invented to transmit military information -- 2000 years agoMap each letter to another -- fixed offset -- called the translation alphabetAlphabets: Plain: A B C D E F G H I J K L M N O P Q R S T UCipher: E F G H I J K L M N O P Q R S T