What are secret-key and public-key signatures?

- Asymmetric cryptography is often referred to as the public-key cryptography. 

- It is a cryptographic algorithm which makes use of two individual keys namely the secret key and the public key. 

- The secret is kept private and the public key is open. 

- Even though these two keys are different, there is some mathematical link between the two. 

- The key which is used for the encryption of the plain text and verification of the digital signature is the public key. 

- So, the private key is one that is used for the decryption of the cipher text in to plain text or for creation of a digital signature. 

- Both these keys are contrast of each other unlike in the symmetric cryptography where the same key serves both the purposes. 

- The public keys are created based up on some mathematical problems for which presently there is no efficient solution such as the following:

Ø  Elliptic curve relationships

Ø  Discrete logarithms

Ø  Integer factorization

- Generating the public and the private key pair is computationally easy for the users. 

- The strength of the public keys lies in the fact that determining the private key from its public key is computationally in feasible or almost impossible. 

- Thus, without fearing any compromise with the security, the public key can be published whereas the private key is kept hidden from everyone so as not to reveal it to anyone who does not has authorization for performing the digital signatures or reading the messages. 

- Unlike for the symmetric key algorithms, a secure initial exchange of the secret keys is not required for the public key algorithms. 

- In the process of message authentication, a private key is used for processing a message for producing the digital signature. 

- After doing so, the signature can be verified by anyone by processing the value of the signature using the corresponding public key of the signer. 

- The result is then compared with the message. 

- The unmodified nature of the message is confirmed a success signal. 

- Also, it is presumed that the private key of the signer has been kept hidden from the others. 

- However, in practical applications, the message’s digest or hash is encrypted and used as the signature. 

- The fundamental security components of the cryptosystems, protocols and applications are the public key algorithms.

These systems underpin the following internet standards:

Ø  PGP

Ø  GPG

Ø  TLS or transport layer security

- Secrecy as well as Key distribution is provided by some of the public key algorithms such as the Diffie-Hellman key exchange algorithm while some algorithms like Digital signature algorithm provide the digital signature and some others offer both the things.

- An example of such algorithm is RSA. 

- All these algorithms have been widely accepted. 

- A pair of cryptographic keys (i.e., a public key for encryption and a private key for decryption) is provided to each of the users. 

- Similarly, for digital signatures the pair of keys consists of a private key for signing and a public key for verification. 

- The concept of the private key has been introduced so as to ensure the confidentiality. 

- The digital signatures can be verified by anyone possessing the corresponding public key. 

- With such a confirmation it is confirmed the private key is possessed by the sender. 

- This is also a way to confirm that no tampering has been done to the message. 

- If the message has been tampered, it will introduce changes in the encoded message digest. 

- Mail box having a mail slot and a personal wax seal can be taken as an analogy to public – key encryption and digital signatures respectively. 

What are different object oriented metrics in software measurement?

Object Oriented Metrics

Lines of code and Function point metrics can be used for object oriented projects but they do not provide enough granularity for schedule. Some object oriented metrics are as follows:

- Number of scenario scripts
A scenario script describes the interaction between user and application. It is directly related to application size and number of test cases developed to exercise the system.

- Number of key classes
Key classes are independent components. The number of key classes is the indication of the amount of effort that is required to develop the software and it also indicates the potential amount of reuse applied during system development. The key classes are directly related to problem domain.

- Number of support classes
Support classes are not directly related to problem domain. Support classes can be developed for key class. Number of support classes indicates amount of effort required to develop software and potential amount of reuse to be applied.

- Number of subsystems
Subsystem is gathering of classes supporting a function visible to the end user. A schedule is laid out in which work on subsystem is partitioned.

- Average number of support classes per key class
Estimation becomes easy and simplified if average number of support classes per key class is known.

As database grows, relationships between object oriented measures and project measures provides metrics for project estimation.

Nanotechnology - a key for enhancing fuel cell performance

Nanotechnology is being used to reduce the cost of catalysts used in fuel cells to produce hydrogen ions from fuel such as methanol and to improve the efficiency of membranes used in fuel cells to separate hydrogen ions from other gases such as oxygen.

Fuel cells that are currently designed for transportation need rapid start-up periods for the practicality of consumer use. This process puts a lot of strain on the traditional polymer electrolyte membranes, which decreases the life of the membrane requiring frequent replacement. Using nanotechnology, engineers have the ability to create a much more durable polymer membrane, which addresses this problem. Nanoscale polymer membranes are also much more efficient in ionic conductivity. This improves the efficiency of the system and decreases the time between replacements, which lowers costs.

Modern fuel cells have the potential to revolutionize transportation. Like battery-electric vehicles, fuel cell vehicles are propelled by electric motors. But while battery electric vehicles use electricity from an external source and store it in a battery, fuel cells onboard a vehicle are electrochemical devices that convert a fuel's chemical energy directly to electrical energy with high efficiency and without combustion. These fuel cells run at relatively low temperature (<100°C) and therefore need catalysts to generate useful currents at high potential, especially at the electrode where oxygen is reduced (the cathode of the fuel.

Carbon Nanohorns provide a unique combination of strength, electrical conductivity, high surface area and open gas paths making them an ideal next generation electrode for various fuel cell applications. Nanotechnology is playing an increasing role in solving the world energy crisis. Platinum nano-particles produced and marketed under the trade name P-Mite are ideal candidates as a novel technology for low platinum automotive catalysts and for single-nanotechnology research. Lanthanum Nanoparticles, Cerium nanoparticles, Strontium Carbonate Nano-particles, Manganese Nanoparticles, Manganese Oxide Nanopowder, Nickel Oxide Nanopowder and several other nanoparticles are finding application in the development of small cost-effective Solid Oxide Fuel Cells (SOFC). And Platinum Nanoparticles are being used to develop small Proton Exchange Membrane Fuel Cells (PEM).

Entity - Relationship Model

The entity-relationship (ER) data model allows us to describe the data involved in a real-world enterprise in terms of objects and their relationships and is widely used to develop an initial database design. The ER model is important primarily for its role in database design. It provides useful concepts that allow us to move from an informal description of what users want from their database to a more detailed, and precise, description that can be implemented in a DBMS.

ENTITIES, ATTRIBUTES, AND ENTITY SETS
- A database can be modeled as:
o a collection of entities,
o relationship among entities.
- An entity is an object that exists and is distinguishable from other objects.
o Example: specific person, company, event, plant
- Entities have attributes.
o Example: people have names and addresses
- An entity set is a set of entities of the same type that share the same properties.
o Example: set of all persons, companies, trees, holidays.



- Attributes : An entity is represented by a set of attributes, that is descriptive properties possessed by all members of an entity set.
o E.g. Employee = (Name, Address, Age, Salary)



Types of Attributes
- SIMPLE attributes are attributes that are drawn from the atomic value domains.
E.g. Name = {John} ; Age = {23}
- COMPOSITE attributes: Attributes that consist of a hierarchy of attributes.
E.g. Address may consists of “Number”, “Street” and “Suburb” → Address = {59 + ‘Meek Street’ + ‘Kingsford’}
- SINGLE VALUED attributes: Attributes that have only one value for each entity.
E.g. Name, Age for EMPLOYEE
- MULTIVALUED attributes: Attributes that have a set of values for each entity.
E.g. Degrees of a person: ‘ BSc’ , ‘MIT’, ‘PhD’
- DERIVED attributes: Attributes Contain values that are calculated from other attributes.
E.g. Age can be derived from attribute DateOfBirth. In this situation, DateOfBirth might be called Stored Attribute.

- DOMAIN/VALUE SETS : Each simple attribute of an entity type is associated with a value set which specifies the set of values that may be assigned to that attribute for each individual entity.
- KEYS : An important constraint on the entities is the key. An entity type usually has an attribute whose values are distinct for each individual entity in the collection. Such an attribute is called a key attribute.
For example, for the entity SET EMPLOYEE = {EID, Name, Address, Age, Salary}
EID attribute is the unique key for entity set EMPLOYEE as no two employees can have two same EID. Some entity types have more than one key attribute. An entity type may also have no key.