In today’s technology-driven world, computers have penetrated all walks of our life, and more of our personal and corporate data is available electronically than ever. Unfortunately, the same technology that provides so many benefits can also be used for destructive purposes. In recent years, individual hackers, who previously worked mostly for personal gain, have organized into groups working for financial gain, making the threat of personal or corporate data being stolen for unlawful purposes much more serious and real. Malware infests our computers and redirects our browsers to specific advertising web sites depending on our browsing context. Phishing emails entice us to log into web sites that appear real but are designed to steal our passwords. Viruses or direct attacks breach our networks to steal passwords and data. As Big Data, analytics, and machine learning push into the modern enterprise, the opportunities for critical data to be exposed and harm to be done rise exponentially.

If you want to counter these attacks on your personal property (yes, your data is your personal property) or your corporate property, you have to understand thoroughly the threats as well as your own vulnerabilities. Only then can you work toward devising a strategy to secure your data, be it personal or corporate.

Think about a scenario where your bank’s investment division uses Hadoop for analyzing terabytes of data and your bank’s competitor has access to the results. Or how about a situation where your insurance company decides to stop offering homeowner’s insurance based on Big Data analysis of millions of claims, and their competitor, who has access (by stealth) to this data, finds out that most of the claims used as a basis for analysis were fraudulent? Can you imagine how much these security breaches would cost the affected companies? Unfortunately, only the breaches highlight the importance of security. To its users, a good security setup—be it personal or corporate—is always transparent.

This chapter lays the foundation on which you can begin to build that security strategy. I first define a security engineering framework. Then I discuss some psychological aspects of security (the human factor) and introduce security protocols. Last, I present common potential threats to a program’s security and explain how to counter those threats, offering a detailed example of a secure distributed system. So, to start with, let me introduce you to the concept of security engineering.

Introducing Security Engineering

Security engineering is about designing and implementing systems that do not leak private information and can reliably withstand malicious attacks, errors, or mishaps. As a science, it focuses on the tools, processes, and methods needed to design and implement complete systems and adapt existing systems.

Security engineering requires expertise that spans such dissimilar disciplines as cryptography, computer security, computer networking, economics, applied psychology, and law. Software engineering skills (ranging from business process analysis to implementation and testing) are also necessary, but are relevant mostly for countering error and “mishaps”—not for malicious attacks. Designing systems to counter malice requires specialized skills and, of course, specialized experience.

Security requirements vary from one system to another. Usually you need a balanced combination of user authentication, authorization, policy definition, auditing, integral transactions, fault tolerance, encryption, and isolation. A lot of systems fail because their designers focus on the wrong things, omit some of these factors, or focus on the right things but do so inadequately. Securing Big Data systems with many components and interfaces is particularly challenging. A traditional database has one catalog, and one interface: SQL connections. A Hadoop system has many “catalogs” and many interfaces (Hadoop Distributed File System or HDFS, Hive, HBase). This increased complexity, along with the varied and voluminous data in such a system, introduces many challenges for security engineers.

Securing a system thus depends on several types of processes. To start with, you need to determine your security requirements and then how to implement them. Also, you have to remember that secure systems have a very important component in addition to their technical components: the human factor! That’s why you have to make sure that people who are in charge of protecting the system and maintaining it are properly motivated. In the next section, I define a framework for considering all these factors.

Security Engineering Framework

Good security engineering relies on the following five factors to be considered while conceptualizing a system:

• Strategy: Your strategy revolves around your objective. A specific objective is a good starting point to define authentication, authorization, integral transactions, fault tolerance, encryption, and isolation for your system. You also need to consider and account for possible error conditions or malicious attack scenarios.
• Implementation: Implementation of your strategy involves procuring the necessary hardware and software components, designing and developing a system that satisfies all your objectives, defining access controls, and thoroughly testing your system to match your strategy.
• Reliability: Reliability is the amount of reliance you have for each of your system components and your system as a whole. Reliability is measured against failure as well as malfunction.
• Relevance: Relevance decides the ability of a system to counter the latest threats. For it to remain relevant, especially for a security system, it is also extremely important to update it periodically to maintain its ability to counter new threats as they arise.
• Motivation: Motivation relates to the drive or dedication that the people responsible for managing and maintaining your system have for doing their job properly, and also refers to the lure for the attackers to try to defeat your strategy.

Figure 1-1 illustrates how these five factors interact.

Notice the relationships, such as strategy for relevance, implementation of a strategy, implementation of relevance, reliability of motivation, and so on.

Consider Figure 1-1’s framework through the lens of a real-world example. Suppose I am designing a system to store the grades of high school students. How do these five key factors come into play?

With my objective in mind—create a student grading system—I first outline a strategy for the system. To begin, I must define levels of authentication and authorization needed for students, staff, and school administrators (the access policy). Clearly, students need to have only read permissions on their individual grades, staff needs to have read and write permissions on their students’ grades, and school administrators need to have read permissions on all student records. Any data update needs to be an integral transaction, meaning either it should complete all the related changes or, if it aborts while in progress, then all the changes should be reverted. Because the data is sensitive, it should be encrypted—students should be able to see only their own grades. The grading system should be isolated within the school intranet using an internal firewall and should prompt for authentication when anyone tries to use it.

My strategy needs to be implemented by first procuring the necessary hardware (server, network cards) and software components (SQL Server, C#, .NET components, Java). Next is design and development of a system to meet the objectives by designing the process flow, data flow, logical data model, physical data model using SQL Server, and graphical user interface using Java. I also need to define the access controls that determine who can access the system and with what permissions (roles based on authorization needs). For example, I define the School_Admin role with read permissions on all grades, the Staff role with read and write permissions, and so on. Last, I need to do a security practices review of my hardware and software components before building the system.

While thoroughly testing the system, I can measure reliability by making sure that no one can access data they are not supposed to, and also by making sure all users can access the data they are permitted to access. Any deviation from this functionality makes the system unreliable. Also, the system needs to be available 24/7. If it’s not, then that reduces the system’s reliability, too. This system’s relevance will depend on its impregnability. In other words, no student (or outside hacker) should be able to hack through it using any of the latest techniques.

The system administrators in charge of managing this system (hardware, database, etc.) should be reliable and motivated to have good professional integrity. Since they have access to all the sensitive data, they shouldn’t disclose it to any unauthorized people (such as friends or relatives studying at the high school, any unscrupulous admissions staff, or even the media). Laws against any such disclosures can be a good motivation in this case; but professional integrity is just as important.

Psychological Aspects of Security Engineering

Why do you need to understand the psychological aspects of security engineering? The biggest threat to your online security is deception: malicious attacks that exploit psychology along with technology. We’ve all received phishing e-mails warning of some “problem” with a checking, credit card, or PayPal account and urging us to “fix” it by logging into a cleverly disguised site designed to capture our usernames, passwords, or account numbers for unlawful purposes. Pretexting is another common way for private investigators or con artists to steal information, be it personal or corporate. It involves phoning someone (the victim who has the information) under a false pretext and getting the confidential information (usually by pretending to be someone authorized to have that information). There have been so many instances where a developer or system administrator got a call from the “security administrator” and were asked for password information supposedly for verification or security purposes. You’d think it wouldn’t work today, but these instances are very common even now! It’s always best to ask for an e-mailed or written request for disclosure of any confidential or sensitive information.

Companies use many countermeasures to combat phishing:

• Password Scramblers: A number of browser plug-ins encrypt your password to a strong, domain-specific password by hashing it (using a secret key) and the domain name of the web site being accessed. Even if you always use the same password, each web site you visit will be provided with a different, unique password. Thus, if you mistakenly enter your Bank of America password into a phishing site, the hacker gets an unusable variation of your real password.
• Client Certificates or Custom-Built Applications: Some banks provide their own laptops and VPN access for using their custom applications to connect to their systems. They validate the client’s use of their own hardware (e.g., through a media access control, or MAC address) and also use VPN credentials to authenticate the user before letting him or her connect to their systems. Some banks also provide client certificates to their users that are authenticated by their servers; because they reside on client PCs, they can’t be accessed or used by hackers.
• Two-Phase Authentication: With this system, logon involves both a token password and a saved password. Security tokens generate a password (either for one-time use or time based) in response to a challenge sent by the system you want to access. For example, every few seconds a security token can display a new eight-digit password that’s synchronized with the central server. After you enter the token password, the system then prompts for a saved password that you set up earlier. This makes it impossible for a hacker to use your password, because the token password changes too quickly for a hacker to use it. Two-phase authentication is still vulnerable to a real-time “man-in-the-middle” attack (see the “Man-in-the-Middle Attack” sidebar for more detail).

• Trusted Computing: This approach involves installing a TPM (trusted platform module) security chip on PC motherboards. TPM is a dedicated microprocessor that generates cryptographic keys and uses them for encryption/decryption. Because localized hardware is used for encryption, it is more secure than a software solution. To prevent any malicious code from acquiring and using the keys, you need to ensure that the whole process of encryption/decryption is done within TPM rather than TPM generating the keys and passing them to external programs. Having such hardware transaction support integrated into the PC will make it much more difficult for a hacker to break into the system. As an example, the recent Heartbleed bug in OpenSSL would have been defeated by a TPM as the keys would not be exposed in system memory and hence could not have been leaked.
• Strong Password Protocols: Steve Bellovin and Michael Merritt came up with a series of protocols for encrypted key exchange, whereby a key exchange is combined with a shared password in such a way that a man in the middle (phisherman) can’t guess the password. Various other researchers came up with similar protocols, and this technology was a precursor to the “secure” (HTTPS) protocol we use today. Since use of HTTPS is more convenient, it was implemented widely instead of strong pass word protocol, which none of today’s browsers implement.
• Two-Channel Authentication: This involves sending one-time access codes to users via a separate channel or a device (such as their mobile phone). This access code is used as an additional password, along with the regular user password. This authentication is similar to two-phase authentication and is also vulnerable to real-time man-in-the-middle attack.

Introduction to Security Protocols

A security system consists of components such as users, companies, and servers, which communicate using a number of channels including phones, satellite links, and networks, while also using physical devices such as laptops, portable USB drives, and so forth. Security protocols are the rules governing these communications and are designed to effectively counter malicious attacks.

Since it is practically impossible to design a protocol that will counter all kinds of threats (besides being expensive), protocols are designed to counter only certain types of threats. For example, the Kerberos protocol that’s used for authentication assumes that the user is connecting to the correct server (and not a phishing web site) while entering a name and password.

Protocols are often evaluated by considering the possibility of occurrence of the threat they are designed to counter, and their effectiveness in negating that threat.

Multiple protocols often have to work together in a large and complex system; hence, you need to take care that the combination doesn’t open any vulnerabilities. I will introduce you to some commonly used protocols in the following sections.

The Needham–Schroeder Symmetric Key Protocol

The Needham–Schroeder Symmetric Key Protocol establishes a session key between the requestor and authenticator and uses that key throughout the session to make sure that the communication is secure. Let me use a quick example to explain it.

A user needs to access a file from a secure file system. As a first step, the user requests a session key to the authenticating server by providing her nonce (a random number or a serial number used to guarantee the freshness of a message) and the name of the secure file system to which she needs access (step 1 in Figure 1-2). The server provides a session key, encrypted using the key shared between the server and the user. The session key also contains the user’s nonce, just to confirm it’s not a replay. Last, the server provides the user a copy of the session key encrypted using the key shared between the server and the secure file system (step 2). The user forwards the key to the secure file system, which can decrypt it using the key shared with the server, thus authenticating the session key (step 3). The secure file system sends the user a nonce encrypted using the session key to show that it has the key (step 4). The user performs a simple operation on the nonce, re-encrypts it, and sends it back, verifying that she is still alive and that she holds the key. Thus, secure communication is established between the user and the secure file system.

The problem with this protocol is that the secure file system has to assume that the key it receives from authenticating server (via the user) is fresh. This may not be true. Also, if a hacker gets hold of the user’s key, he could use it to set up session keys with many other principals. Last, it’s not possible for a user to revoke a session key in case she discovers impersonation or improper use through usage logs.

To summarize, the Needham–Schroeder protocol is vulnerable to replay attack, because it’s not possible to determine if the session key is fresh or recent.

Kerberos

A derivative of the Needham–Schroeder protocol, Kerberos originated at MIT and is now used as a standard authentication tool in Linux as well as Windows. Instead of a single trusted server, Kerberos uses two: an authentication server that authenticates users to log in; and a ticket-granting server that provides tickets, allowing access to various resources (e.g., files or secure processes). This provides more scalable access management.

What if a user needs to access a secure file system that uses Kerberos? First, the user logs on to the authentication server using a password. The client software on the user’s PC fetches a ticket from this server that is encrypted under the user’s password and that contains a session key (valid only for a predetermined duration like one hour or one day). Assuming the user is authenticated, he now uses the session key to get access to secure file system that’s controlled by the ticket-granting server.

Next, the user requests access to the secure file system from the ticket-granting server. If the access is permissible (depending on user’s rights), a ticket is created containing a suitable key and provided to the user. The user also gets a copy of the key encrypted under the session key. The user now verifies the ticket by sending a timestamp to the secure file system, which confirms it’s alive by sending back the timestamp incremented by 1 (this shows it was able to decrypt the ticket correctly and extract the key). After that, the user can communicate with the secure file system.

Kerberos fixes the vulnerability of Needham–Schroeder by replacing random nonces with timestamps. Of course, there is now a new vulnerability based on timestamps, in which clocks on various clients and servers might be desynchronized deliberately as part of a more complex attack.

Kerberos is widely used and is incorporated into the Windows Active Directory server as its authentication mechanism. In practice, Kerberos is the most widely used security protocol, and other protocols only have a historical importance. You will learn more about Kerberos in later chapters, as it is the primary authentication used with Hadoop today.

Burrows–Abadi–Needham Logic

Burrows–Abadi–Needham (BAN) logic provides framework for defining and analyzing sensitive information. The underlying principle is that a message is authentic if it meets three criteria: it is encrypted with a relevant key, it’s from a trusted source, and it is also fresh (that is, generated during the current run of the protocol). The verification steps followed typically are to

1. Check if origin is trusted,
2. Check if encryption key is valid, and
3. Check timestamp to make sure it’s been generated recently.

Variants of BAN logic are used by some banks (e.g., the COPAC system used by Visa International). BAN logic is a very extensive protocol due to its multistep verification process; but that’s also the precise reason it’s not very popular. It is complex to implement and also vulnerable to timestamp manipulation (just like Kerberos).

Consider a practical implementation of BAN logic. Suppose Mindy buys an expensive purse from a web retailer and authorizes a payment of $400 to the retailer through her credit card. Mindy’s credit card company must be able to verify and prove that the request really came from Mindy, if she should later disavow sending it. The credit card company also wants to know that the request is entirely Mindy's, that it has not been altered along the way. In addition, the company must be able to verify the encryption key (the three-digit security code from the credit card) Mindy entered. Last, the company wants to be sure that the message is new—not a reuse of a previous message. So, looking at the requirements, you can conclude that the credit card company needs to implement BAN logic.

Now, having reviewed the protocols and ways they can be used to counter malicious attacks, do you think using a strong security protocol (to secure a program) is enough to overcome any “flaws” in software (that can leave programs open to security attacks)? Or is it like using an expensive lock to secure the front door of a house while leaving the windows open? To answer that, you will first need to know what the flaws are or how they can cause security issues.

Securing a Program

Before you can secure a program, you need to understand what factors make a program insecure. To start with, using security protocols only guards the door, or access to the program. Once the program starts executing, it needs to have robust logic that will provide access to the necessary resources only, and not provide any way for malicious attacks to modify system resources or gain control of the system. So, is this how a program can be free of flaws? Well, I will discuss that briefly, but first let me define some important terms that will help you understand flaws and how to counter them.

Let’s start with the term program. A program is any executable code. Even operating systems or database systems are programs. I consider a program to be secure if it exactly (and only) does what it is supposed to do—nothing else! An assessment of security may also be decided based on program’s conformity to specifications—the code is secure if it meets security requirements. Why is this important? Because when a program is executing, it has capability to modify your environment, and you have to make sure it only modifies what you want it to.

So, you need to consider the factors that will prevent a program from meeting the security requirements. These factors can potentially be termed flaws in your program. A flaw can either be fault or a failure.

A fault is an anomaly introduced in a system due to human error. A fault can be introduced at the design stage due to the designer misinterpreting an analyst’s requirements, or at the implementation stage by a programmer not understanding the designer’s intent and coding incorrectly. A single error can generate many faults. To summarize, a fault is a logical issue or contradiction noticed by the designers or developers of the system after it is developed.

A failure is a deviation from required functionality for a system. A failure can be discovered during any phase of the software development life cycle (SDLC), such as testing or operation. A single fault may result in multiple failures (e.g., a design fault that causes a program to exit if no input is entered). If the functional requirements document contains faults, a failure would indicate that the system is not performing as required (even though it may be performing as specified). Thus, a failure is an apparent effect of a fault: an issue visible to the user(s).

Fortunately, not every fault results in a failure. For example, if the faulty part of the code is never executed or the faulty part of logic is never entered, then the fault will never cause the code to fail—although you can never be sure when a failure will expose that fault!

Broadly, the flaws can be categorized as:

• Non-malicious (buffer overruns, validation errors etc.) and
• Malicious (virus/worm attacks, malware etc.).

In the next sections, take a closer look at these flaws, the kinds of security breaches they may produce, and how to devise a strategy to better secure your software to protect against such breaches.

Non-Malicious Flaws

Non-malicious flaws result from unintentional, inadvertent human errors. Most of these flaws only result in program malfunctions. A few categories, however, have caused many security breaches in the recent past.

Buffer Overflows

A buffer (or array or string) is an allotted amount of memory (or RAM) where data is held temporarily for processing. If the program data written to a buffer exceeds a buffer’s previously defined maximum size, that program data essentially overflows the buffer area. Some compilers detect the buffer overrun and stop the program, while others simply presume the overrun to be additional instructions and continue execution. If execution continues, the program data may overwrite system data (because all program and data elements share the memory space with the operating system and other code during execution). A hacker may spot the overrun and insert code in the system space to gain control of the operating system with higher privileges.¹

Several programming techniques are used to protect from buffer overruns, such as

• Forced checks for buffer overrun;
• Separation of system stack areas and user code areas;
• Making memory pages either writable or executable, but not both; and
• Monitors to alert if system stack is overwritten.

Incomplete Mediation

Incomplete mediation occurs when a program accepts user data without validation or verification. Programs are expected to check if the user data is within a specified range or that it follows a predefined format. When that is not done, then a hacker can manipulate the data for unlawful purposes. For example, if a web store doesn’t mediate user data, a hacker may turn off any client JavaScript (used for validation) or just write a script to interact with the web server (instead of using a web browser) and send arbitrary (unmediated) values to the server to manipulate a sale. In some cases vulnerabilities of this nature are due to failure to check default configuration on components; a web server that by default enables shell escape for XML data is a good example.

Another example of incomplete mediation is SQL Injection, where an attacker is able to insert (and submit) a database SQL command (instead of or along with a parameter value) that is executed by a web application, manipulating the back-end database. A SQL injection attack can occur when a web application accepts user-supplied input data without thorough validation. The cleverly formatted user data tricks the application into executing unintended commands or modifying permissions to sensitive data. A hacker can get access to sensitive information such as Social Security numbers, credit card numbers, or other financial data.

An example of SQL injection would be a web application that accepts the login name as input data and displays all the information for a user, but doesn’t validate the input. Suppose the web application uses the following query:

"SELECT * FROM logins WHERE name ='" + LoginName + "';"

A malicious user can use a LoginName value of “' or '1'='1” which will result in the web application returning login information for all the users (with passwords) to the malicious user.

If user input is validated against a set of defined rules for length, type, and syntax, SQL injection can be prevented. Also, it is important to ensure that user permissions (for database access) should be limited to least possible privileges (within the concerned database only), and system administrator accounts, like sa, should never be used for web applications. Stored procedures that are not used should be removed, as they are easy targets for data manipulation.

Two key steps should be taken as a defense:

• Server-based mediation must be performed. All client input needs to be validated by the program (located on the server) before it is processed.
• Client input needs to be checked for range validity (e.g., month is between January and December) as well as allowed size (number of characters for text data or value for numbers for numeric data, etc.).

Time-of-Check to Time-of-Use Errors

Time-of-Check to Time-of-Use errors occur when a system’s state (or user-controlled data) changes between the check for authorization for a particular task and execution of that task. That is, there is lack of synchronization or serialization between the authorization and execution of tasks. For example, a user may request modification rights to an innocuous log file and, between the check for authorization (for this operation) and the actual granting of modification rights, may switch the log file for a critical system file (for example, /etc/password for Linux operating system).

There are several ways to counter these errors:

• Make a copy of the requested user data (for a request) to the system area, making modifications impossible.
• Lock the request data until the requested action is complete.
• Perform checksum (using validation routine) on the requested data to detect modification.

Malicious Flaws

Malicious flaws produce unanticipated or undesired effects in programs and are the result of code deliberately designed to cause damage (corruption of data, system crash, etc.). Malicious flaws are caused by viruses, worms, rabbits, Trojan horses, trap doors, and malware:

• A virus is a self-replicating program that can modify uninfected programs by attaching a copy of its malicious code to them. The infected programs turn into viruses themselves and replicate further to infect the whole system. A transient virus depends on its host program (the executable program of which it is part) and runs when its host executes, spreading itself and performing the malicious activities for which it was designed. A resident virus resides in a system’s memory and can execute as a stand-alone program, even after its host program completes execution.
• A worm, unlike the virus that uses other programs as mediums to spread itself, is a stand-alone program that replicates through a network.
• A rabbit is a virus or worm that self-replicates without limit and exhausts a computing resource. For example, a rabbit might replicate itself to a disk unlimited times and fill up the disk.
• A Trojan horse is code with a hidden malicious purpose in addition to its primary purpose.
• A logic trigger is malicious code that executes when a particular condition occurs (e.g., when a file is accessed). A time trigger is a logic trigger with a specific time or date as its activating condition.
• A trap door is a secret entry point into a program that can allow someone to bypass normal authentication and gain access. Trap doors have always been used by programmers for legitimate purposes such as troubleshooting, debugging, or testing programs; but they become threats when unscrupulous programmers use them to gain unauthorized access or perform malicious activities. Malware can install malicious programs or trap doors on Internet-connected computers. Once installed, trap doors can open an Internet port and enable anonymous, malicious data collection, promote products (adware), or perform any other destructive tasks as designed by their creator.

How do we prevent infections from malicious code?

• Install only commercial software acquired from reliable, well-known vendors.
• Track the versions and vulnerabilities of all installed open source components, and maintain an open source component-security patching strategy.
• Carefully check all default configurations for any installed software; do not assume the defaults are set for secure operation.
• Test any new software in isolation.
• Open only “safe” attachments from known sources. Also, avoid opening attachments from known sources that contain a strange or peculiar message.
• Maintain a recoverable system image on a daily or weekly basis (as required).
• Make and retain backup copies of executable system files as well as important personal data that might contain “infectable” code.
• Use antivirus programs and schedule daily or weekly scans as appropriate. Don’t forget to update the virus definition files, as a lot of new viruses get created each day!

Securing a Distributed System

So far, we have examined potential threats to a program’s security, but remember—a distributed system is also a program. Not only are all the threats and resolutions discussed in the previous section applicable to distributed systems, but the special nature of these programs makes them vulnerable in other ways as well. That leads to a need to have multilevel security for distributed systems.

When I think about a secure distributed system, ERP (enterprise resource) systems such as SAP or PeopleSoft come to mind. Also, relational database systems such as Oracle, Microsoft SQL Server, or Sybase are good examples of secure systems. All these systems are equipped with multiple layers of security and have been functional for a long time. Subsequently, they have seen a number of malicious attacks on stored data and have devised effective countermeasures. To better understand what makes these systems safe, I will discuss how Microsoft SQL Server secures sensitive employee salary data.

For a secure distributed system, data is hidden behind multiple layers of defenses (Figure 1-3). There are levels such as authentication (using login name/password), authorization (roles with set of permissions), encryption (scrambling data using keys), and so on. For SQL Server, the first layer is a user authentication layer. Second is an authorization check to ensure that the user has necessary authorization for accessing a database through database role(s). Specifically, any connection to a SQL Server is authenticated by the server against the stored credentials. If the authentication is successful, the server passes the connection through. When connected, the client inherits authorization assigned to connected login by the system administrator. That authorization includes access to any of the system or user databases with assigned roles (for each database). That is, a user can only access the databases he is authorized to access—and is only assigned tables with assigned permissions. At the database level, security is further compartmentalized into table- and column-level security. When necessary, views are designed to further segregate data and provide a more detailed level of security. Database roles are used to group security settings for a group of tables.

In Figure 1-3, the user who was authenticated and allowed to connect has been authorized to view employee data in database DB1, except for the salary data (since he doesn’t belong to role HR and only users from Human Resources have the HR role allocated to them). Access to sensitive data can thus be easily limited using roles in SQL Server. Although the figure doesn’t illustrate them, more layers of security are possible, as you’ll learn in the next few sections.

Authentication

The first layer of security is authentication. SQL Server uses a login/password pair for authentication against stored credential metadata. You can also use integrated security with Windows, and you can use a Windows login to connect to SQL Server (assuming the system administrator has provided access to that login). Last, a certificate or pair of asymmetric keys can be used for authentication. Useful features such as password policy enforcement (strong password), date validity for a login, ability to block a login, and so forth are provided for added convenience.

Authorization

The second layer is authorization. It is implemented by creating users corresponding to logins in the first layer within various databases (on a server) as required. If a user doesn’t exist within a database, he or she doesn’t have access to it.

Within a database, there are various objects such as tables (which hold the data), views (definitions for filtered database access that may spread over a number of tables), stored procedures (scripts using the database scripting language), and triggers (scripts that execute when an event occurs, such as an update of a column for a table or inserting of a row of data for a table), and a user may have either read, modify, or execute permissions for these objects. Also, in case of tables or views, it is possible to give partial data access (to some columns only) to users. This provides flexibility and a very high level of granularity while configuring access.

Encryption

The third security layer is encryption. SQL Server provides two ways to encrypt your data: symmetric keys/certificates and Transparent Database Encryption (TDE). Both these methods encrypt data “at rest” while it’s stored within a database. SQL Server also has the capability to encrypt data in transit from client to server, by configuring corresponding public and private certificates on the server and client to use an encrypted connection. Take a closer look:

• Encryption using symmetric keys/certificate: A symmetric key is a sequence of binary or hexadecimal characters that’s used along with an encryption algorithm to encrypt the data. The server and client must use the same key for encryption as well as decryption. To enhance the security further, a certificate containing a public and private key pair can be required. The client application must have this pair available for decryption. The real advantage of using certificates and symmetric keys for encryption is the granularity it provides. For example, you can encrypt only a single column from a single table (Figure 1-4)—no need to encrypt the whole table or database (as with TDE). Encryption and decryption are CPU-intensive operations and take up valuable processing resources. That also makes retrieval of encrypted data slower as compared to unencrypted data. Last, encrypted data needs more storage. Thus it makes sense to use this option if only a small part of your database contains sensitive data.

• TDE: TDE is the mechanism SQL Server provides to encrypt a database completely using symmetric keys and certificates. Once database encryption is enabled, all the data within a database is encrypted while it is stored on the disk. This encryption is transparent to any clients requesting the data, because data is automatically decrypted when it is transferred from disk to the buffers. Figure 1-5 details the steps for implementing TDE for a database.

• Using encrypted connections: This option involves encrypting client connections to a SQL Server and ensures that the data in transit is encrypted. On the server side, you must configure the server to accept encrypted connections, create a certificate, and export it to the client that needs to use encryption. The client’s user must then install the exported certificate on the client, configure the client to request an encrypted connection, and open up an encrypted connection to the server.

Figure 1-6 maps the various levels of SQL Server security. As you can see, data can be filtered (as required) at every stage of access, providing granularity for user authorization.

Hadoop is also is a distributed system and can benefit from many of the principles you learned here. In the next two chapters, I will introduce Hadoop and give an overview of Hadoop’s security architecture (or the lack of it).

Summary

This chapter introduced general security concepts to help you better understand and appreciate the various techniques you will use to secure Hadoop. Remember, however, that the psychological aspects of security are as important to understand as the technology. No security protocol can help you if you readily provide your password to a hacker!

Securing a program requires knowledge of potential flaws so that you can counter them. Non-malicious flaws can be reduced or eliminated using quality control at each phase of the SDLC and extensive testing during the implementation phase. Specialized antivirus software and procedural discipline is the only solution formalicious flaws.

A distributed system needs multilevel security due to its architecture, which spreads data on multiple hosts and modifies it through numerous processes that execute at a number of locations. So it’s important to design security that will work at multiple levels and to secure various hosts within a system depending on their role (e.g., security required for the central or master host will be different compared to other hosts). Most of the times, these levels are authentication, authorization and encryption.

Last, the computing world is changing rapidly and new threats evolve on a daily basis. It is important to design a secure system, but it is equally important to keep it up to date. A security system that was best until yesterday is not good enough. It has to be the best today—and possibly tomorrow!

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¹Please refer to the IEEE paper “Beyond Stack Smashing: Recent Advances in Exploiting Buffer Overruns” by Jonathan Pincus and Brandon Baker for more details on these kind of attacks. A PDF of the article is available at http://classes.soe.ucsc.edu/cmps223/Spring09/Pincus%2004.pdf.