**3.1 Public cloud**

*Cloud Computing Security - Concepts and Practice*

and compute purposes. There are basically three different service models (**Figure 1**)

In this model, various applications are hosted by a cloud service provider and publicized to the customers over internet, wherein end user can access the software using thin client through web browsers. Here all the software and relevant data are hosted centrally on the cloud server. CRM, Office Suite, Email, Games, Contact Data Management, Financial Accounting, Text Processing etc. are typically falls

A PaaS is typically is a programming platform for developers. This platform facilitates the ecosystem for the programmers/developers to create, test, run and manage the applications. It thus provides the access to the runtime environment for application development and deployment tools. Here developer does not have any access to underlying layers of OS and Hardware, but simply can run and deploy their own applications. Microsoft Azure, Salesforce and Google App Engine are

IaaS facilitates availability of the IT resources such as server, processing power, data storage and networks as an on demand service. Here user of this service can dynamically choose a CPU, memory storage configuration according to needs. A cloud user buys these virtualized and standardized services as and when required.

of offering high-volume low-cost services to the end user:

• Software as a Service (SaaS)

• Platform as a Service (PaaS)

**2.1 Software as a service (SaaS)**

**2.2 Platform as a service (PaaS)**

some of the typical examples of PaaS.

**2.3 Infrastructure as a service (IaaS)**

under this category.

**Figure 1.**

*Cloud service model.*

• Infrastructure as a Service (IaaS)

**2**

In the Public Cloud delivery mode, all the physical infrastructure are owned by the provider of the services which were provided off-site over the Internet hosted at cloud vendor's premises. Here the customer has no control and limited visibility over where the service is hosted as all these massive hardware installations are distributed throughout the country or across the globe seamlessly. This massive size enables economies of scale that permit maximum scalability to meet varying requirements of different customers and thus provides greatest level of efficiency, maximum reliability through shared resources but with rider cost of added vulnerability.
