1. Operating Systems Concepts
Lecture 44,45 – Security Techniques

2. Operating System Facilities
Authentication
Authentication is a process of verifying whether a person is a legitimate user or not.
Authentication can be achieved in following three ways.
A secret, known only to that user (password) 
Some thing possessed only by that user (An Artifact such as magnetic badge)
Some human characteristics of the user (handwritten signatures, fingerprints, retina images)

3. Means of Authentication
Traditionally listed as three factors
Something you know
Password, PIN
Something you have
Card, RFID badge
Something you are
Biometrics
All of these methods, properly implemented and used, can provide secure user authentication.
However, each method has problems.
An adversary may be able to guess or steal a password.
or may be able to forge or steal a token.
or a user may forget a password or lose a token.
Further, there is a significant administrative overhead for managing password and token information on systems and securing such information on systems.
With respect to biometric authenticators, there are a variety of problems, including dealing with false positives and false negatives, user acceptance, cost, and convenience.

4. Biometrics expanded
Recently Biometrics (something you are) has been expanded into:
Something the individual is
Static Biometrics: Fingerprint, face
Something the individual does
Dynamic Biometrics: handwriting, voice recognition, typing rhythm

5. Operating System Facilities
File Access Control
Since the data held within the file system is the principal interest of the computer’s security system. It is not surprising to find that operating systems generally include facilities for the protection of files.
Dictates what types of access are permitted, under what circumstances, and by whom.
For various objects, operating system allows different Access Rights for different subjects. For example, for a file, these access rights can be Own, Write, Append, Read, and Execute (OWARE), as in AOS/VS of Data General Machines. UNIX has only Read, Write and eXecute (RWX) access rights.
For a printer as device, the access rights can be ‘Write’ or ‘None’ only. In general, we can list different access rights that can be granted as shown in the table

6. Contd. List of Access Rights Serial no Access Rights Code No Access N
No Access N 1
Execute Only E 2
Read Only R 3
Append Only A 4
Update U 5
Modify Protection M 6
Delete D

7. Cryptography
Encoding and decoding data so that it can be interpreted only by the intended recipients
Cryptography is associated with the process of converting ordinary plain text into unintelligible text and vice-versa. It is a method of storing and transmitting data in a particular form so that only those for whom it is intended can read and process it.
The process involves two things: Encryption, which means changing the original data to some other form so that nobody can make out anything about it, and Decryption, which means recovering the data in the original form.

8. Contd.
Encryption is the conversion of data in some intelligent format into an unintelligible format (cipher text) to prevent the data from being understood if read by an unauthorized party. A reverse operation, Decryption, converts the encrypted data back to its original form.
The most common scheme in use involves an encryption algorithm a decryption algorithm and a Key value. The key is some arbitrary bit string value, which is used in the algorithms.
The data before encryption is called plaintext and the data after encryption is called ciphertext.

9. Private Key Cryptography
Also known as symmetric cryptography
Uses the same secret key to encrypt and decrypt a message
Sender
Encrypts a message using the secret key
Sends encrypted message to the intended recipient
Recipient
Decrypts the message using the same secret key
Limitation of private-key cryptography
Before two parties can communicate securely, they must find a secure way to exchange the secret key

11. Asymmetric Key or Public Key Cryptography
Solves the problem of securely exchanging symmetric keys
Asymmetric
Employs two inversely related keys:
Public key
Freely distributed
Private key
Kept secret by its owner
If the public key encrypts a message, only the corresponding private key can decrypt it

13. Thank You!