•Information security means protecting information and information systems fromunauthorized access, use, disclosure, disruption, modification, or destructionCryptography (from Greek "hidden, secret") is the practice and study of hidinginformation•Information security is concerned with the confidentiality, integrity and availabilityof data regardless of the form the data may take: electronic, print, or otherforms.•Cryptography is used in applications present in technologically advanced societies;examples include the security of ATM cards, computer passwords, andelectronic commerce, which all depend on cryptography.
•Information security uses cryptography to transform usable informationinto a form that renders it unusable by anyone other than an authorizeduser; this process is called encryption•Encrypted information can be transformed back into its original form by anauthorized user, who possesses the cryptographic key, through the processof decryption•Cryptography is used in information security to protect information fromunauthorized users while the information is in transit and storage•Cryptography provides information security with improved authenticationmethods, message digests, digital signatures, and encrypted networkcommunications
Modern Information Security• Computer SecurityIt mainly focuses on shared system, such as time-sharing system andnecessary to provide some tools to protect file and other information storedon the computer• Network (Communication) SecurityIt mainly concerns distributed system, such as internet and its purpose is toprotect the information over the internetIt also focuses on measures to deter, prevent, detect and correct securityviolations that involve the transmission of information.
• Confidentiality : Information is accessible only for reading• Authentication : Information is correctly identified, with an assurancethat identity is not false• Integrity : Only authorized parties are able to modify computersystem assets and transmitted information• Nonrepudiation : Both the sender and receiver of message are unableto deny the transmission.• Access Control : Requires that access to information resources may becontrolled by or for the target system..
The art or science encompassing the principles and methods of transformingan intelligible message into unintelligible one, and then retransforming thatmessage back to original form.PlaintextCiphertextCipherKeycodeEncipher(encode)Decipher(decode)CryptanalysisCryptology
World War II brought about many advancements in information securityand mark the beginning of the professional field of information securityGerman Lorenz cipher machine
The development of digital computers andelectronics after WWII made possiblemuch more complex ciphersMany computer ciphers can be charact-erized by their operation on binary bitsequences,unlike classical andmechanical schemesThe Enigma machine, used, in severalvariants, by the German military betweenthe late 1920s and the end ofWorld War IIEnigma machine
Cryptography, then, not only protects data from theft or alteration, but canalso be used for user authentication. There are, in general, three types ofcryptographic schemes typically used to accomplish these goals•Secret key cryptography (or symmetric)•Public-key cryptography (or asymmetric)•Hash functions,
•In this form single key is used for both encryption and decryption•The sender uses the key to encrypt the plaintext and sends the ciphertextto the receiver. The receiver applies the same key to decrypt the messageand recover the plaintext•Because a single key is used for both functions, secret key cryptography isalso called symmetric encryption
•Secret key cryptography schemes are generally categorized as beingeither stream ciphers or block ciphers.•Stream ciphers operate on a single bit (byte or computer word) at a timeand implement some form of feedback mechanism so that the key isconstantly changing.• A block cipher is so-called because the scheme encrypts one block ofdata at a time using the same key on each block.• In general, the same plaintext block will always encrypt to the sameciphertext when using the same key in a block cipher whereas the sameplaintext will encrypt to different ciphertext in a stream cipher.
•PKC depends upon the existence of so-called one-way functions,thatare easy to computer whereas their inverse function is difficult to compute•It employs two keys that are mathematically related although knowledgeof one key does not allow someone to easily determine the other key•One key is used to encrypt the plaintext and the other key is used todecrypt the ciphertext
Hash functions, also called message digests and one-way encryption, arealgorithms that, in some sense, use no keyA fixed-length hash value is computed based upon the plaintext that makesit impossible for either the contents or length of the plaintext to berecovered.Hash algorithms are typically used to provide a digital fingerprint of a filescontents and are also commonly employed by many operating systems toencrypt passwords and then, provide a measure of the integrity of a file
Combines all functions to form a secure transmission comprising digital signature anddigital envelope
•Nearly all modern network operating systems employ passwords at thevery least to protect and authenticate users accessing computer andnetwork resources•But passwords are not typically kept on a host or server in plaintext, butare generally encrypted using some sort of hash scheme•As the passwords are not saved in plaintext on computer systemsprecisely,they cannot be easily compromised.•An even stronger authentication method uses the password to modify ashared secret between the client and server, but never allows thepassword in any form to go across the network.
•PGP can be used to sign or encrypt e-mail messages with the mereclick of the mouse•Depending upon the version of PGP, the software uses SHA or MD5for calculating the message hash; CAST, Triple-DES, or IDEA forencryption; and RSA or DSS/Diffie-Hellman for key exchange and digitalsignatures.•PGP is available as a plug-in for many e-mail clients, such as ClarisEmailer, Microsoft Outlook and Qualcomm Eudora•Pretty Good Privacy (PGP) is one of todays most widely used public keycryptography programs, developed by Philip Zimmermann in the early1990s
•In typical applications workstation are attached to LAN. The user canreach other hosts, workstations and servers in the same LAN that areinterconnected via bridges and routers.•Transmissions from station to station is visible on the LAN to allstation. Data is transmitted in the form of packets which containsource/destination Ids, and other information.•On this basis, an eavesdropper can monitor and capture trafficpackets. Eavesdropper needs not be a local LAN user; it could beanyone to whom the LAN offers a dial-up capacity.•Eavesdropping may also occur in any of the communication linkswhich provide connectivity to the system
Link EncryptionEach vulnerable communication link is equipped on both end with anencryption devicesEnd-to-End EncryptionData is encrypted only at the source node and decrypted at the destinationnodeProblemData consists of packets have a header portion and content portion. we can’tencrypt the header. So the data is secure and the traffic pattern is notSolutionUse a combination of above two approaches.