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# Data security in cloud computing - Part 2: Data encryption applications and limits

## 7/25/2011 11:49 AM EDT

Overview of Cryptographic Techniques

Introduced in Chapter 1 (Cloud Computing and Security: An Introduction), cryptography is a complex and esoteric field. In modern times, cryptography has expanded from protecting the confidentiality of private communications to including techniques for assuring content integrity, identity authentication, and digital signatures along with a range of secure computing techniques. Given that range of functional utility, cryptography has been recognized as being a critical enabling technology for security in cloud computing. Focusing on data security, cryptography has great value for cloud computing.

To effect cryptographic data confidentiality, plaintext is converted into cyphertext by numerous means, but the ones of practical value are all based on mathematical functions that must meet several requirements, including:

• The algorithm and implementation must be computationally efficient in converting plaintext to cyphertext, as well as in decryption.

• The algorithm must be open to broad analysis by a community of cryptographers and others.

• The resulting output must withstand the use of brute force attacks even by vast numbers of computers (such as in a computing grid or cloud).

In operation, plaintext is encrypted into cyphertext using an encryption key, and the resulting cyphertext is later decrypted using a decryption key. In Symmetric cryptography, these keys are the same (Figure 5.3).

FIGURE 5.3 Symmetric encryption.

Symmetric cryptography has broad applicability, but when it is used in communication between parties, the complexity of key management can become untenable since each pair of communicators should share a unique secret key. It is also very difficult to establish a secret key between communicating parties when a secure channel does not already exist for them to securely exchange a shared secret key.

By contrast, with asymmetric cryptography (also known as in public–private key cryptography), the encrypt key (public key) is different but mathematically related to the decrypt or private key (Figure 5.4).

FIGURE 5.4 Asymmetric encryption.

The primary advantage of asymmetric cryptography is that only the private key must be kept secret—the public key can be published and need not be secret. Although public–private key pairs are related, it is infeasible to computationally derive a private key from a public key.

This use of public–private keys is a great enabler for confidentiality in cloud computing, and not just for encryption of content. A private key can be used to authenticate a user or computational component, and it can also be used to initiate the negotiation of a secure channel or connection between communicating parties.

Going one level deeper in our background treatment of cryptography, for the purpose of this book, there are four basic uses of cryptography:

• Block Ciphers These take as input a key along with a block of plaintext and output a block of cyphertext. Because messages are generally larger than a defined block, this method requires some method to associate or knit together successive cyphertext blocks.

• Stream Ciphers These operate against an arbitrarily long stream of input data, which is converted to an equivalent output stream of cyphertext.

• Cryptographic Hash Functions Hash functions take an arbitrarily long input message and output a short, fixed length hash. A hash can serve various purposes, including as a digital signature or as a means to verify the integrity of the message.

• Authentication Cryptography is also widely used within authentication and identity management systems.

Although cryptography is a cornerstone of security, many an adopter has insecurely used it or worse attempted to implement cryptography to either save money or cut corners. The field of cryptography is well beyond the scope of this book, so the reader is encouraged to refer to widely available texts on cryptography in order to develop a better understanding of cryptography, its implementation, and secure application.

 TOOLS Sometimes you need to transfer files via secure physical media. When you do so, it is best to have the data secured on the media. To do this, you would typically create an encrypted image first and then copy it to the physical transfer media. However, you can also use encrypting media such as hardware encrypting USB flash drives. Two of the hallmarks of such devices are automated and integral encryption/decryption and hardware-based tamper resistance. They are very good as a backup for personal or sensitive data that you do not want to include in an unencrypted full disk backup. But these devices are excellent for transferring sensitive data in a highly protected manner when the transfer has to be physical. Since technology changes rapidly and vendors come and go, search for tamper resistant encrypting USB drive. Some of these products use very strong cryptography, and some have additional features.

EREBUS

7/25/2011 8:57 PM EDT

The only way you can control Cloud content and access is to implement a solid series of encrypted techniques throughout the architecture. Single techniques can be broken, but if you use a comprehensive layering approach, you can make it too difficult for the casual vandal to penetrate and you can quickly identify when someone is doing more than just using the system for their legitamate purposes.

Yes you will make it harder and more tedious to access the cloud, but I would bet that every common user would rather go through a little inconvience if they could be ensured of not having their data vandalized or stolen.

Just think of it, a web where we don't get overwhelmed with spam, no viruses, just a clean environment where we can do our work and go about our business without worrying about someone screwing everything up.

Now that would make a very pleasent web indeed.

Thanks,

prabhakar_deosthali

7/26/2011 7:22 AM EDT

It is very difficult to have a perfect world. So having a perfect Web with no viruses, no spy ware is something we can only hope for. Like all the physical security measures we take : most of them are prone for attack. The automatic teller machines have CCTV cameras to catch a person doing mis-deed. But we have cases where the thieves have covered the cameras with a cloth and stolen the whole machine itself . Combination locks are yet another security measures which can be decoded by a thief with sustained effort and sufficient amount of time.

So in case of data encryption you are never 100% sure that your encryption key code is broken into. The only way I see is to be able to detect that your security has been broken into as early as you can and contain the damage by a scheme of revolving keys, like the frequency hopping techniques used in secure communications

RWatkins

7/26/2011 9:47 AM EDT

As a student of cryptography since middle-school days, now over 45 years, a lot of what is spouted here is great to protect one from relatively weak decryption attacks or for relatively short periods of time. The use of "standard" encryption systems (available to civilians) has been outlawed for military applications requiring any level of security for decades and for very good reason. Any public/private key system by definition has a mathematical relationship between the public key and the private key. The "back door" is as simple as to derive said relationship. The statements made in this article propagate the wrong attitude that data can be shared in open interfaces and connected to open computational resources that contain decryption software, all safely. To be truly safe, somewhere there must be a proverbial funnel with a check valve to prevent hacking, extraction, or analysis attacks on data.
If your data is time critical and worthless in a matter of hours, all of this may not matter if you keep changing the algorithm, choose a good algorithm and sometimes vary it, and keep the key and algorithm away from prying software. However, if you really want to STORE information or keep information from competitors for longer periods of time, current techniques are a recipe for disaster. This is shown time and again in internet banking transactions where attacks have become increasingly sophisticated and fraud more and more prevalent.

przemek

8/1/2011 5:20 PM EDT

To RWatkins, who wrote "The use of standard encryption systems (available to civilians) has been outlawed for military applications requiring any level of security for decades"

On the contrary, the serious encryption is ONLY possible with standard methods that have been vetted thoroughly by professional cryptographers, and which depend on fundamental mathematical principles, not on some secret algorithm. Bruce Schneier put it nicely: "anyone can invent an encryption system that they themselves cannot break".

It is true that there may be a technological or mathematical discovery that breaks the current encryption, but the chance of that is small compared to the chance of leakage of an encryption based on a secret algorithm.