Sankar jayam
- 1. CRYPTOGRAPHYPresenting by: J.P.S.M.K
- 2. What is CryptographyCryptography
- 3. In a narrow sense
- 4. Mangling information into apparent unintelligibility
- 5. Allowing a secret method of un-mangling
- 6. In a broader sense
- 7. Mathematical techniques related to information security
- 8. About secure communication in the presence of adversaries
- 10. The study of methods for obtaining the meaning of encrypted information without accessing the secret information
- 11. Cryptology
- 12. Cryptography + cryptanalysisSecurity AttacksPassive attacks
- 15. Active attacks
- 16. Masquerade of one entity as some other
- 18. Modify messages in transmit
- 20. Denial of serviceObjectives of Information SecurityConfidentiality (secrecy)
- 21. Only the sender and intended receiver should be able to understand the contents of the transmitted message
- 22. Authentication
- 23. Both the sender and receiver need to confirm the identity of other party involved in the communication
- 24. Data integrity
- 25. The content of their communication is not altered, either maliciously or by accident, in transmission.
- 26. Availability
- 27. Timely accessibility of data to authorized entities.Objectives of Information SecurityNon-repudiation
- 28. An entity is prevented from denying its previous commitments or actions
- 29. Access control
- 30. An entity cannot access any entity that it is not authorized to.
- 31. Anonymity
- 32. The identity of an entity if protected from others.Types of Cryptographic FunctionsSecret key functions
- 34. Hash functionsSecret Key CryptographyencryptionplaintextciphertextkeyciphertextplaintextdecryptionUsing a single key for encryption/decryption.The plaintext and the ciphertext having the same size.Also called symmetric key cryptography
- 35. SKC: Security UsesTransmitting over an insecure channelThe transmitted message is encrypted by the sender and can be decrypted by the receiver, with the same keyPrevent attackers from eavesdroppingSecure storage on insecure mediaData is encrypted before being stored somewhereOnly the entities knowing the key can decrypt it
- 36. SKC: Security UsesAuthenticationStrong authentication: proving knowledge of a secret without revealing it.AliceBobchallenger AresponserA encrypted with KA,Br BrB encrypted with KA,B
- 37. SKC: Security UsesIntegrity CheckNoncryptographic checksumUsing a well-known algorithm to map a message (of arbitrary length) to a fixed-length checksumProtecting against accidental corruption of a messageExample: CRCCryptographic checksumA well-know algorithmGiven a key and a messageThe algorithm produces a fixed-length message authentication code (MAC) that is sent with the message
- 38. Public Key CryptographyencryptionplaintextciphertextPublic keyPrivate keyciphertextplaintextdecryptionEach individual has two keysa private key (d): need not be reveal to anyone a public key (e): preferably known to the entire worldPublic key crypto is also called asymmetric crypto.
- 39. PKC: Security UsesTransmitting over an insecure channelAliceBobencrypt mA using dBencrypt mA using eBSecure storage on insecure mediaData is encrypted with the public key of the source, before being stored somewhereNobody else can decrypt it (not knowing the private key of the data source)
- 40. PKC: Security UsesAuthenticationAliceBobencrypt rusing eBdecrypt to rusing dBr
- 41. PKC: Security UsesDigital SignaturesProving that a message is generated by a particular individualNon-repudiation: the signing individual can not be denied, because only him/her knows the private key. signingplaintextSigned messagePrivate keyPublic keySigned messageplaintextverification
- 42. Hash FunctionsCryptographic hash functionA mathematical transformation that takes a message of arbitrary length and computes it a fixed-length (short) number.Properties( Let the hash of a message m be h(m) )For any m, it is relatively easy to compute h(m)Given h(m), there is no way to find an m that hashes to h(m) in a way that is substantially easier than going through all possible values of m and computing h(m) for each one.It is computationally infeasible to find two values that hash to the same thing.
- 43. Hash Functions: Security UsesPassword hashingThe system store a hash of the password (not the password itself)When a password is supplied, it computes the password’s hash and compares it with the stored value.Message integrityUsing cryptographic hash functions to generate a MACBobAlicesecret=?messagehashhashsecret
- 44. Hash Functions: Security UsesMessage fingerprintSave the message digest of the data on a tamper-proof backing storePeriodically re-compute the digest of the data to ensure it is not changed.Downline load securityUsing a hash function to ensure a download program is not modifiedImproving signature efficiencyCompute a message digest (using a hash function) and sign that.
- 45. Cryptographic Algorithms: AgendaAttacks on cryptographic algorithmsDefinition of securitySome cryptographic algorithms: basic facts
- 46. Attacks: TypesBrute force searchAssume either know/recognize plaintextSimply try every keyCryptoanalysisCiphertext onlyWith the ciphertext Plaintext is recognizableKnown plaintext<cipher, plaintext> pairs are knownChosen plaintextSelect plaintext and obtain ciphertext to attack
- 47. Birthday AttacksPrincipleAssume: A function yields any of n different outputs with equal probability, where n is sufficiently large.After evaluating the function for about 1.2*squart(n) arguments, we expect to find a pair of different arguments, x1 and x2, such that f(x1)=f(x2). Attack: message replaySolution: increase the size of the output
- 48. Meet-in-the-Middle AttacksPrinciplebuild a table of keysCompute f(k,m) for every keyf is an encryption function, m is a known messageEavesdrop a value f(k’,m)If f(k’,m)=f(k,m), then there is a good chance k’=k.
- 49. Meet-in-the-Middle AttacksAn attack exampleAssume:a new encryption function: F(k1,k2,m)=f(k1,f(k2,m))A pair (P,C) is knownAttacker:Encrypt P, i.e., computing f(k2,P), for all possible values of k2; store the values in a tableDecrypt C, i.e., computing f-1(k1,C), for all possible values of k1, and for each result check the table A match reveals a possible combination of the keys
- 50. Security DefinitionUnconditional SecurityThe system cannot be defeated, no matter how much power is available by the adversary.Computational securityThe perceived level of computation required to defeat the system using the best known attack exceeds, by a comfortable margin, the computational resources of the hypothesized adversary.e.g., given limited computing resources, it takes the age of universe to break cipher.
- 51. Security DefinitionProvable securityThe difficulty of defeating the system can be shown to be essentially as difficult as solving a well-known and supposedly difficult problem (e.g., integer factorization) Ad hoc securityClaims of security generally remain questionableUnforeseen attacks remain a threat
- 52. Secret Key Cryptographic AlgorithmsDES (Data Encryption Standard)3DES (Triple DES)IDEA (International Data Encryption Algorithm)AES (Advanced Encryption Standard)
- 53. DES (Data Encryption Standard)Authors: NSA & IBM, 1977Data block size: 64-bit (64-bit input, 64-bit output)Key size: 56-bit keyEncryption is fastDES chipsDES software: a 500-MIP CPU can encrypt at about 30K octets per secondSecurityNo longer considered secure: 56 bit keys are vulnerable to exhaustive search
- 54. Triple-DES (3DES)C = DESk3(DESk2(DESk1(P))). Data block size: 64-bitKey size: 168-bit key; effective key size: 112 (due to man-in-the-middle attack)Encryption is slower than DESSecurer than DES
- 55. IDEA (International Data Encryption Algorithm)Authors: Lai & Massey, 1991Data block size: 64-bitKey size: 128-bitEncryption is slower than DESSecurityNobody has yet published results on how to break itHaving patent protection
- 56. AES (Advanced Encryption Standard)Authors: Daemen & RijmenBlock size:128-bitKey size: 128-bit, 192-bit, 256-bitEncryption is fastSecurityAs of 2005, no successful attacks are recognized.NSA stated it secure enough for non-classified data.