Cryptographic Security Cryptographic Mechanisms Mesbah Islam Operating Systems

Cryptographic Security Cryptographic Mechanisms Mesbah Islam– Operating Systems 1

Cryptographic Security Presentation Outline n n n n Introduction Security goals Symmetric algorithm Asymmetric algorithm Hashing algorithm Digital signature Summary and conclusions Q/A? Mesbah Islam– Operating Systems 2

Cryptographic Security Introduction n Cryptography is a branch of applied mathematics concerned with transformations of data for security. In cryptography, a sender transforms unprotected information (plaintext) into coded text (ciphertext). A receiver uses cryptography to either (a) transform the ciphertext back into plaintext, (b) verify the sender’s identity, (c) verify the data’s integrity, or some combination. Mesbah Islam– Operating Systems 3

Cryptographic Security Internet Security Issues n n n Eavesdropping. Information remains intact, but its privacy is compromised. Tampering. Information in transit is changed or replaced and then sent on to the recipient. Impersonation. Information passes to a person who poses as the intended recipient. Impersonation can take two forms: Spoofing. A person can pretend to be someone else. Misrepresentation. A person or organization can misrepresent itself. Mesbah Islam– CS 5204 – Operating Systems 4

Cryptographic Security Goals n Applicability of cryptography to support the basic security services privacy/confidentiality -information not disclosed to unauthorized entities ¨ integrity -information not altered deliberately or accidentally ¨ authentication -validation of identity of source of information ¨ non-repudiation -source of information can be objectively established ¨ Mesbah Islam– CS 5204 – Operating Systems 5

Cryptographic Security Symmetric Key Encryption for Confidentiality M A EA Ciphertext 01011 Sender DB B M Receiver Eavesdropper cannot read o Sender encrypts the plaintext using public key o Receiver decrypts the ciphertext using private key Mesbah Islam– CS 5204 – Operating Systems 6

Cryptographic Security Asymmetric Key Encryption n Asymmetric (also called Public-key encryption) involves a pair of keys-a public key and a private key-associated with an entity that needs to authenticate its identity electronically or to sign or encrypt data. Each public key is published, and the corresponding private key is kept secret. The sender encrypts the data with the receiver’s public key, and the receiver decrypts the ciphertext message with its own private key. Mesbah Islam– CS 5204 – Operating Systems 7

Cryptographic Security Asymmetric Key Encryption (contd. ) M A EB Ciphertext 01011 Sender DB B M Receiver Eavesdropper cannot read o Sender encrypts the plaintext using receiver’s public key o Receiver decrypts the ciphertext using receiver’s private key Mesbah Islam– CS 5204 – Operating Systems 8

Cryptographic Security Asymmetric Key Encryption (contd. ) n Compared with symmetric-key encryption, public-key encryption requires more computation and is therefore not always appropriate for large amounts of data. n However, it's possible to use public-key encryption to send a symmetric key. Mesbah Islam– CS 5204 – Operating Systems 9

Cryptographic Security Secure Hashing Algorithm n n The secure hash function takes a stream of data and reduces it to a fixed size through a one-way mathematical function. The result is called a message digest and can be thought of as a fingerprint of the data. The message digest can be reproduced by any party with the same stream of data, but it is virtually impossible to create a different stream of data that produces the same message digest. A message digest can be used to provide integrity. Mesbah Islam– CS 5204 – Operating Systems 10

Cryptographic Security Secure Hashing Algorithm (contd. ) Mesbah Islam– CS 5204 – Operating Systems 11

Cryptographic Security Secure Hashing Algorithm (contd. ) Mesbah Islam– CS 5204 – Operating Systems 12

Cryptographic Security Secure Hashing Algorithm (contd. ) n Digests are Fixed length ¨ Irreversible ¨ Unique ¨ Mesbah Islam– CS 5204 – Operating Systems 13

Cryptographic Security Digital Signature n n Digital signatures employ a type of asymmetric cryptography. For messages sent through a non-secure channel, a properly implemented digital signature gives the receiver reason to believe the message was sent by the claimed sender. Digital signatures are equivalent to traditional handwritten signatures in many respects; properly implemented digital signatures are more difficult to forge than the handwritten type. Digital signatures can also provide non-repudiating, meaning that the signer cannot successfully claim they did not sign a message, while also claiming their private key remains secret. Mesbah Islam– CS 5204 – Operating Systems 14

Cryptographic Security Digital Signature (contd. ) M A Enc(Bpub(Apriv(M))) Dec(Apub(Bpriv(C))) B M Receiver Sender Mesbah Islam– CS 5204 – Operating Systems 15

Cryptographic Security Summary and Conclusions Mechanism Confidentiality Integrity Authentication Nonrepudiation Symmetric Key Cryptography yes no no no Asymmetric Key Cryptography yes no no no Secure Hashing yes no no yes yes Digital Signature with Asymmetric Key Mesbah Islam– CS 5204 – Operating Systems 16

Cryptographic Security ? ? Mesbah Islam– CS 5204 – Operating Systems 17