Mod 5 Intro to Info Sec WGU ~ Cryptography

Decryption

the process of recovering the plaintext message from the ciphertext. The plaintext and ciphertext may also be generically referred to as the message.

Answer these questions.

1. What type of cipher is a Caesar cipher? 2. What is the difference between a block and a stream cipher? 3. ECC is classified as which type of cryptographic algorithm? 4. What is the key point of Kerckhoffs' principle? 5. What is a substitution cipher? 6. What are the main differences between symmetric and asymmetric key cryptography? 7. Explain how 3DES differs from DES. 8. How does public key cryptography work? 9. Decrypt this message: V qb abg srne pbzchgref. V srne gur ynpx bs gurz. -Vfnnp Nfvzbi. 10. How is physical security important when discussing cryptographic security of data?

Data Security

A great many solutions exist for protecting data at rest. The primary method we use to protect this type of data is encryption, particularly when we know that the storage media, or the media and the device in which it is contained, will be potentially exposed to physical theft, such as on a backup tape or in a laptop.An enormous number of commercial products are available that will provide encryption for portable devices, often focused on hard drives and portable storage devices, including products from large companies such as McAfee (presently owned by Intel), Symantec, and PGP (presently owned by Symantec), just to name a few. The features of such commercial products often include the ability to encrypt entire hard disks, known as full disk encryption, and a variety of removable media, as well as centralized management and other security and administrative features. There are also a number of free and/or open source encryption products on the market, such as TrueCrypt, BitLocker, which ships with some versions of Windows, dm-crypt, which is specific to Linux, and many others. We also need to be aware of the location where data of a sensitive nature for which we are responsible is being stored and need to take appropriate measures to ensure that it is protected there.

German-made Enigma machine

A more intricate example of a cryptographic machine. The Enigma was created by Arthur Scherbius in 1923 and was used to secure German communications during World War II. In fact, there were several models of Enigma machine, and a variety of accessories and add-ons that could be attached to them. The Enigma was based on a series of wheels, referred to as rotors, each with 26 letters and 26 electrical contacts on them, similar in general concept to the Jefferson Disk. The device also had a keyboard, on which the plaintext message was entered, and a set of 26 characters above the keyboard, each of which could be lit. To add further possible variations, some models also had a patch panel, allowing some or all the letters to be swapped by plugging cables into different positions. On each rotor, the ring containing the letters of the alphabet could also be rotated independently of the electrical contacts, in order to change the relationship between the character selected and the character output.

Collision

Although it is theoretically possible to engineer a matching hash for two different sets of data, called a collision, this is a very difficult task indeed, and generally requires that the hashing algorithm be broken in order to accomplish. Some algorithms, such as Message-Digest algorithm 5 (MD5), have been attacked in this fashion, although producing a collision is still nontrivial. When such cases occur, the compromised algorithm usually falls out of common use. Hashing algorithms such as SHA-2 and the soon-to-arrive SHA-3 have replaced MD5 in cases where stringent hash security is required.Many other hash algorithms exist and are used in a variety of situations, such as MD2, MD4, and RACE

Asymmetric cryptography

Although symmetric key cryptography makes use of only one key, asymmetric key cryptography, also known as public key cryptography, utilizes two keys: a public key and a private key. The public key is used to encrypt data sent from the sender to the receiver and is shared with everyone. We see public keys included in e-mail signatures, posted on servers that exist specifically to host public keys, posted on Web pages, and displayed in a number of other ways. Private keys are used to decrypt data that arrives at the receiving end and are very carefully guarded by the receiver. Complex mathematical operations are used to create the private and public keys. These operations are, at present, difficult enough that the means do not exist to reverse the private key from the public key. Asymmetric key cryptography was first described by Martin Hellman and Whitfield Diffie in their 1976 paper, "New Directions in Cryptography."3

Protecting the Connection

Another approach we might choose to take is to encrypt all our network traffic with a virtual private network (VPN) connection. VPN connections use a variety of protocols to make a secure connection between two systems. We might use a VPN when we are connecting from a potentially insecure network, such as the wireless connection in a hotel, to the internal resources that are secure behind our company firewalls.Although a variety of protocols can be used to secure a VPN connection, and many have been developed and used over the years, two main methods are used at present: Internet Protocol Security (IPsec) VPNs and SSL VPNs. These two types of VPN connections can be configured to a nearly identical set of features and functionality, from the perspective of the user, but they require a slightly different set of hardware and software to set up. Typically, an IPsec VPN requires a more complex hardware configuration on the back end and a software client to be installed, whereas an SSL VPN often operates from a lightweight plug-in downloaded from a Web page and a less complex hardware configuration on the back end. From a security footing standpoint, the two methods are relatively equivalent in terms of encryption. It is possible that the SSL VPN client might be downloaded to a public computer or other random computer, due to its ease of installation, and provide an avenue for data leakage or attack because of the potentially insecure state of the system

Protecting Data in Motion

Another major concern to protecting our data comes when it is in motion over a network of some variety. This might be over a closed WAN or LAN, over a wireless network, over the Internet, or in other ways. The primary method of securing data from exposure on network media is encryption, and we may choose to apply it in one of two main ways: by encrypting the data itself to protect it or by protecting the entire connection

_________________ corroborates the identity of an entity, whether is is the sender, the sender's computer, some device, or some information.

Authentication

Cryptographic Machines

Before the advent of the modern computer, machines existed that simplified the use of encryption and made more complex encryption schemes feasible. Initially, such devices were simple mechanical machines, but as technology progressed, we began to see the inclusion of electronics and considerably more complex systems.

cryptography is one of the main tools that have allowed us to become a very network-centric society

Buying, selling, conducting business transactions, playing games, email, social networking tools such as social media, and internet browsing through a variety of interfaces and devices, and connect to wireless networks and we do almost all of this in a secure fashion through the use of cryptography.

Caesar Cipher

Caesar cipher is a classic example of ancient cryptography and is said to have been used by Julius Caesar. The Caesar cipher is based on transposition and involves shifting each letter of the plaintext message by a certain number of letters, historically three. The ciphertext can be decrypted by applying the same number of shifts in the opposite direction. This type of encryption is known as a substitution cipher, due to the substitution of one letter for another in a consistent fashion. A more recent variation of the Caesar cipher can be found in the ROT13 cipher. ROT13 uses the same mechanism as the Caesar cipher but moves each letter 13 places forward. The convenience of moving 13 places lies in the fact that applying another round of encryption with ROT13 also functions as decryption, as two rotations will return us to the original starting place in the alphabet. Utilities for performing ROT13 can be found in the basic set of tools that ship with many Linux and UNIX operating systems. There are a number of simple systems that are built around simple transposition

An Algorithm used for Cryptographic purposes is known as a

Cipher

Several other asymmetric algorithms exist, including

ElGamal, Diffie-Hellman, and Digital Signature Standard (DSS). We can also see a variety of protocols and applications that are based on asymmetric cryptography, including Pretty Good Privacy (PGP) for securing messages and files, SSL and Transport Layer Security (TLS) for several kinds of traffic including Web and e-mail, and some Voice over IP (VoIP) for voice conversations. Asymmetric cryptography has allowed many of the modern methods of secure communication to exist and will likely continue to be the basis of them for some time.

For anyone interested in getting hands-on experience with a classic item of cryptographic history that the Enigma represents, there are several modern options.

For the DIY inclined, a kit is available that recreates the functionality of the Enigma using modern electronics components. Additionally, a variety of software-based Enigma simulators exist. Software simulators are particularly instructive in showing a visual representation of the relationships between the rotors and how the path through them changes with each character entered.When a key was pressed on the keyboard, one or more of the rotors would physically rotate, depending on its configuration, thereby changing the orientation of the electrical contacts between the rotors. Current would flow through the entire series of disks and then back through them again to the original disk. The scrambled equivalent of the letter would light on the series of characters above the keyboard and be recorded.In order for two Enigma machines to communicate, they needed to be configured identically. The rotors needed to be the same and in the same position, the rings marked with the alphabet on each rotor needed to be in the same position, the rotors needed to be set to the same starting position, and any plugs in the plugboard needed to be configured in the same fashion. Between the inherent strengths of the device and the knowledge of the required configuration needed for decryption, the Enigma posed quite a difficult task for those attempting to break the messages generated by it.

Lapses in physical security are a very common starting point for security issues

If we do not take steps to ensure that our important assets are protected from a physical standpoint, we may nullify the rest of our very carefully planned security measures. Physical security should be at the core of all our security planning discussions.We also need to be aware of the areas we cannot physically protect and need to limit the data that leaves our protected spaces. In an office building, we have a fairly limited area to protect, and we can apply even more layers of physical security to areas that might need them, such as the data center in which our servers sit. If sensitive data leaves such areas, we are very limited in what we can do to physically protect it, outside of using encryption.

Kerckhoffs' Principle

In 1883, the Journal des Sciences Militaires published an article by Auguste Kerckhoffs titled "la cryptographie militaire." In the article, Kerckhoffs outlined six principles around which a cryptographic system should be based : 1. The system must be substantially, if not mathematically, undecipherable. 2. The system must not require secrecy and can be stolen by the enemy without causing trouble. 3. It must be easy to communicate and remember the keys without requiring written notes, and it must be easy to change or modify the keys with different participants. 4. The system ought to be compatible with telegraph communication. 5. The system must be portable, and its use must not require more than one person. 6. Finally, regarding the circumstances in which such system is applied, it must be easy to use and must require neither the stress of mind nor the knowledge of a long series of rules. Although several of these principles have become outmoded with the advent of computers to aid in cryptography, the second principle has become a tenet of cryptographic algorithms. This idea was later restated by Claude Shannon as "the enemy knows the system". Both versions of this concept mean that cryptographic algorithms should be robust enough that, even though someone may know every bit of the system with the exception of the key itself, he or she should still not be able to break the encryption. This idea represents the opposite approach to "security through obscurity" and is one of the underlying principles for many modern cryptographic systems.

Data at rest breach example

In August 2013, the Advocate Medical Group in Park Ridge, Illinois, announced that it had a breach of personal information due to the theft of four computers containing unencrypted storage media. The media contained sensitive information such as names, addresses, Social Security numbers, and dates of birth on more than 4 million patients. Had the group taken the necessary steps to protect its data at rest by encrypting it, not only would it have not had such a large security incident, but it may have been spared from having to publicly disclose that the incident had occurred, thus saving quite a bit of embarrassment. Other examples is data on smart phones, tablets, and USB drives, if they are lost or stolen and the data was not encrypted it must be assumed to be compromised. Key management across all these systems that includes things like the ability to lookup key for backup tapes put into storage years ago, key recovery for users who forgot it and ability to change keys when users leave the organization is critical.

Example of Data in Use Breach

In June 2013, it was discovered that classified information containing details on the US National Security Agency (NSA) PRISM program, ostensibly designed to collect and review terrorism-related communications flowing through, in, and out of the United States, had been deliberately leaked to news agencies by a government contractor named Edward Snowden [9]. Clearly this is a case of extremely sensitive data being lost, but we can also see many examples of companies that hold and work with data sensitive to businesses and individuals on a regular basis.

Certificates

In addition to hashes and digital signatures, we have another construct by which we can scale up the use of message signing, in the form of digital certificates, commonly known as certificates. Certificates are created to link a public key to a particular individual and are often used as a form of electronic identification for that particular person. A certificate is typically formed by taking the public key and identifying information, such as a name and address, and having them signed by a certificate authority (CA). A CA is a trusted entity that handles digital certificates. One well-known CA, at present, is VeriSign. Additionally, some large organizations, such as the US Department of Defense (DoD), that utilize a large number of certificates may choose to implement their own CA in order to keep costs down.

Hashes cannot be used to discover the contents of the original message, or any of its other characteristics, but can be used to determine whether the message has changed.

In this way, hashes provide integrity, but not confidentiality. Hashes can be used on programs (to determine if someone modified an application you want to download), open text messages or operating system files. Hashes are very useful when distributing files or sending communications, as the hash can be sent with the message so that the receiver can verify its integrity. The receiver simply hashes the message again using the same algorithm, then compares the two hashes. If the hashes match, the message has not changed. If they do not match, the message has been altered.

One-way problems

One-way problems are generally easy to perform in one direction but very difficult to perform in the other direction. Factorization of very large numbers is an example of a one-way problem. Such problems form the basis of many modern cryptographic systems.

A few main protocols secure much of this traffic for us

SSL/TLS encrypts quite a bit of our network traffic including e-mail, Web browsing, VoIP, and others. SSL/TLS can use a variety of algorithms, including AES. When we use VPNs to encrypt entire connections, we generally see either IPsec or SSL used to encrypt the VPN connection. IPsec can again use a variety of algorithms. Depending on how exactly it is configured, we might find AES, MD5, SHA-1, 3DES, or even DES in use

Symmetric key algorithms

Some of the cryptographic algorithms that are more recognizable to the general public are symmetric key algorithms. Several of these, such as DES, 3DES, and AES, are or have been in regular use by the US government and others as standard algorithms for protecting highly sensitive data.

Block vs. stream ciphers

Symmetric key cryptography makes use of two types of ciphers: block ciphers and stream ciphers. A block cipher takes a predetermined number of bits, known as a block, in the plaintext message and encrypts that block. Blocks are commonly composed of 64 bits but can be larger or smaller depending on the particular algorithm being used and the various modes in which the algorithm might be capable of operating. A stream cipher encrypts each bit in the plaintext message, 1 bit at a time. It is also possible for a block cipher to act as a stream cipher by setting a block size of 1 bit. A large majority of the encryption algorithms in use at present are block ciphers. Although block ciphers are often slower than stream ciphers, they tend to be more efficient. Since block ciphers operate on larger blocks of the message at a time, they do tend to be more resource intensive and are more complex to implement in hardware or software. Block ciphers are also more sensitive to errors in the encryption process as they are working with more data. An error in the encryption process of a block cipher may render unusable a larger segment of data than what we would find in a stream cipher, as the stream cipher would only be working with 1 particular bit.

Symmetric-key cryptography

Symmetric key cryptography, also known as private key cryptography, utilizes a single key for both encryption of the plaintext and decryption of the ciphertext. The key itself must be shared between the sender and the receiver, and this process, known as key exchange, constitutes an entire subtopic of cryptography. The symmetric in symmetric key cryptography is a reference to the use of a single key. One of the chief weaknesses of symmetric key cryptography lies in the use of one key. If the key is exposed beyond the sender and the receiver, it is possible for an attacker who has managed to intercept it to decrypt the message or, worse to decrypt the message, alter it, then encrypt it once more and pass it on to the receiver in place of the original message. Since such issues are present, symmetric key cryptography by itself provides only confidentiality, and not integrity, as we would not be aware that the message in our example had been altered.

Jefferson Disk

The Jefferson Disk, invented by Thomas Jefferson in 1795, is a purely mechanical cryptographic machine. It is composed of a series of disks, each marked with the letters a to z around its edge. On each disk, the letters are arranged in a different order; each disk is also marked with a unique designator to facilitate arranging them in a particular order. The device built by Jefferson contained 36 disks, with each disk representing one character in the message. In order to encrypt a message, we would line up the characters in a row across the set of disks to create the message in plaintext, as shown in row A of picture, and then choose a different row of characters to use as the ciphertext, as shown in row B.

Asymmetric key algorithms

The RSA algorithm, named for its creators Ron Rivest, Adi Shamir, and Leonard Adleman, is an asymmetric algorithm used all over the world, including in the Secure Sockets Layer (SSL) protocol, which is used to secure many common transactions such as Web and e-mail traffic. RSA was created in 1977 and is still one of the most widely used algorithms in the world to this day.

The use of cryptography is

The chief security measure that allows us to make use of such technologies is cryptography—in the form of encryption. It's an integral part of computing, networking, and the vast set of transactions that take place over such devices on a daily basis. We depend on cryptography when we have conversations on our cell phones, check our e-mail, buy things from online retailers, file our taxes, and do other activities.

Jefferson Disk layout

The key to this form of cipher is in the order of the disks. As long as the encrypting and decrypting devices have disks with the characters in the same order, and the disks themselves are in the same order, all we need to do to decrypt the message is to line up the disks in the same order as the ciphertext and then look over the rows to find the plaintext message. This is, of course, merely a more complex version of a substitution cipher, made possible through the use of a mechanical aid.

Protecting Data in use

The last category of protecting data involves securing it while it is being used. Although we can use encryption to protect data while it is stored or moving across a network, we are somewhat limited in our ability to protect data while it is being used by those who legitimately have access to it. Authorized users can print files, move them to other machines or storage devices, e-mail them, share them on peer-to-peer (P2P) file-sharing networks, and generally make a mockery of our carefully laid security measures.

Example of failure to protect data in both the physical and data security sense

US Department of Veterans Affairs (VA) breach that was reported in May 2010. In this case, a laptop containing unencrypted information, including Social Security numbers, on 616 veterans, was stolen from the personal vehicle of a contractor working for the VA. What makes this incident particularly unfortunate is that the VA suffered a similar breach in 2006, once again because of an unencrypted laptop stolen from a personal vehicle. In this case, the breach was much more severe because the set of data lost related to 28.5 million veterans and service members, ultimately costing the VA $48 million to clean up. In the words of George Santayana, "Those who cannot remember the past are doomed to repeat it"

several block modes can be used with an algorithm based on a block cipher to detect and compensate for such errors.

We can see such modes in use with algorithms such as the Data Encryption Standard (DES) and Advanced Encryption Standard (AES), and we will look at some of these modes in the next section when we talk about the algorithms that use them.Typically, block ciphers are better for use in situations where the size of the message is fixed or known in advance, such as when we are encrypting a file or have message sizes that are reported in protocol headers. Stream ciphers are often better for use in situations where we have data of an unknown size or the data is in a continuous stream, such as we might see moving over a network.

Protecting the Data itself

We can take a variety of approaches to protect the data we are sending over the network, depending on what data we are sending and the protocols over which we are sending it. SSL and TLS are often used to protect information sent over networks and over the Internet, and they operate in conjunction with other protocols such as Internet Message Access Protocol (IMAP) and Post Office Protocol (POP) for e-mail, Hypertext Transfer Protocol (HTTP) for Web traffic, VoIP for voice conversations, instant messaging, and hundreds of others. SSL is actually the predecessor of TLS, and TLS is based heavily on the last version of SSL. The terms are often used interchangeably, and they are nearly identical to each other. Both methods are still in common use. When SSL/TLS is used, it encrypts a connection between two systems communicating over a network but is generally specific to a particular application or protocol. So, although we might be using SSL/TLS to encrypt our communications with the server that holds our e-mail, this does not necessarily mean the connections made through our Web browser enjoy the same level of increased security. Many common applications are capable of supporting SSL/TLS, but they generally need to be configured to do so independently.

A new challenge that the security team is facing is movement to cloud infrastructure

When deciding who to outsource all the originations data to physical security of the devices that will store the data should be part of the evaluation

Elliptic curve cryptography (ECC)

a class of cryptographic algorithms, although it is sometimes referred to as though it were an algorithm in and of itself. ECC is named for the type of mathematical problem on which its cryptographic functions are based. ECC has several advantages over other types of algorithms. It has a higher cryptographic strength with shorter keys than many other types of algorithms, meaning that we can use shorter keys with ECC while still maintaining a very secure form of encryption. It is also a very fast and efficient type of algorithm, allowing us to implement it on hardware with a more constrained set of resources, such as a cell phone or portable device, more easily. We can see ECC implemented in a variety of cryptographic algorithms, including Secure Hash Algorithm 2 (SHA-2) and Elliptic Curve Digital Signature Algorithm (ECDSA).

The specifics of the process used to encrypt the plaintext or decrypt the ciphertext is referred to as

a cryptographic algorithm. Cryptographic algorithms generally use a key, or multiple keys, in order to encrypt or decrypt the message, this being roughly analogous to a password. The range of all possible values for the key is referred to as the keyspace. The larger the keyspace, the harder it is to decrypt the message. We may also refer to the cryptosystem, a concept that covers a given algorithm and all possible keys, plaintexts, and ciphertexts

AES

a set of symmetric block ciphers endorsed by the US government through NIST, and now used by a variety of other organizations, and is the replacement for DES as the standard encryption algorithm for the US federal government. AES uses three different ciphers: one with a 128-bit key, one with a 192-bit key, and one with a 256-bit key, all having a block length of 128 bits. A variety of attacks have been attempted against AES, most of them against encryption using the 128-bit key, and most of them unsuccessful, partially successful, or questionable altogether. At the time of this writing, the US government still considers AES to be secure. AES shares the same block modes that DES uses and also includes other modes such as XEX-based Tweaked CodeBook (TCB) mode.

Digital signatures are

an extension of hash functions that allow us to not only create a hash to ensure that the message has not been altered but also encrypt the hash with the public key of an asymmetric algorithm to ensure that the message was sent by the expected party and to provide for nonrepudiation.

Digital signatures

are a great example of where the hash function is used. Digital signatures allow us to sign a message in order to enable detection of changes to the message contents, to ensure that the message was legitimately sent by the expected party, and to prevent the sender from denying that he or she sent the message, known as nonrepudiation. To digitally sign a message, the sender would generate a hash of the message, and then use his private key to encrypt the hash, thus generating a digital signature. The sender would then send the digital signature along with the message, usually by appending it to the message itself.When the message arrives at the receiving end, the receiver would use the sender's public key to decrypt the digital signature, thus restoring the original hash of the message. The receiver can then verify the integrity of the message by hashing the message again and comparing the two hashes. Although this may sound like a considerable amount of work to verify the integrity of the message, it is often done by a software application of some kind and the process typically is largely invisible to the end user. A digital signature is considered legally binding and if it is lost or stolen must be revoked

The science of breaking through the encryption used to create the ciphertext is referred to as

cryptanalysis. The overarching field of study that covers cryptography and cryptanalysis is referred to as cryptology.

DES

first came into use in 1976 in the United States and has since been used by a variety of parties globally. DES is a block cipher based on symmetric key cryptography and uses a 56-bit key. Although DES was considered to be very secure for some period of time, it is no longer considered to be so. In 1999, a distributed computing project was launched to break a DES key by testing every possible key in the entire keyspace, and the project succeeded in doing so in a little more than 22 h. This weakness brought about by the short key length was compensated for a period of time through the use of 3DES (pronounced triple DES), which is simply DES used to encrypt each block three times, each time with a different key. DES can operate in several different block modes, including Cipher Block Chaining (CBC), Electronic CodeBook (ECB), Cipher Feedback (CFB), Output Feedback (OFB), and Counter Mode (CTR). Each mode changes the way encryption functions and the way errors are handled.

There are a large number of other well-known symmetric block ciphers

including Twofish, Serpent, Blowfish, CAST5, RC6, and IDEA, as well as stream ciphers, such as RC4, ORYX, and SEAL.

Protecting data at rest

is an area in which security is often lax and is a particularly bad area in which we choose not to emphasize security. Data is generally considered to be at rest when it is on a storage device of some kind and is not moving over a network, through a protocol, and so forth. Somewhat illogically, data at rest on media can also be in motion; for example, we might ship a load of backup tapes containing sensitive data, carry in our pocket a flash drive containing a copy of our tax forms, or leave in the back seat of our car a laptop containing the contents of a customer database

Physical Security

is another important step in protecting data at rest. If we make it more difficult for attackers to physically access or steal the storage media on which our sensitive data is contained, we have solved a large portion of our problem. In many cases, large businesses have databases, file servers, and workstations that contain customer information, sales forecasts, business strategy documents, network diagrams, and large amounts of other data they do not wish to become public or fall into the hands of their competitors. If the physical security at the location where such data rests is weak, an attacker might be able to simply enter the building and steal a laptop, paper documentation, flash drive, or disk from a server and walk right out with the system and the data on it.

In general, cryptography provides us with a mechanism to

protect data at rest, in motion, and, to a certain extent, in use. It provides the core of many of the basic security mechanisms that enable us to communicate and carry out transactions when the data involved is of a sensitive nature and we would prefer that it not be exposed to the general public or to attackers.

We can divide practical uses of cryptography into two major categories:

protecting data at rest and protecting data in motion. Protecting data at rest is important because of the large amount of stored data that can be found on devices such as backup tapes, flash drives, and hard drives in portable devices such as laptops. Protecting data in motion is vital as well because of the enormous amount of business that is conducted over the Internet, including financial transactions, medical information, tax filings, and other similarly sensitive exchanges

Hash Functions

represent a third cryptography type alongside symmetric and asymmetric cryptography, what we might call keyless cryptography. Hash functions, also referred to as message digests, do not use a key, but instead create a largely unique and fixed-length hash value, commonly referred to as a hash, based on the original message, something along the same lines as a fingerprint. Any slight change to the message will change the hash.

Symmetric vs. Asymmetric Cryptography

symmetric key cryptography versus asymmetric key cryptography, we do not have a situation in which one is necessarily better overall than the other for all situations. Instead, each has a set of strengths and weaknesses when used in a given situation. In many cases, symmetric key cryptography is much faster than asymmetric, but symmetric cryptography brings with it the issue of key exchange so it was difficult to determine which was best to use when designing a secure infrastructure.

There are three main categories of cryptographic algorithms:

symmetric key cryptography, also known as private key cryptography; asymmetric key cryptography, also known as public key cryptography; and hash functions that we might refer to as keyless cryptography. In private key cryptography, the key is used for both encryption and decryption and is shared by all parties that need to operate on the plaintext or ciphertext. In public key cryptography, we use a public and a private key. The sender encrypts the message with the receiver's public key, and the receiver decrypts the message with their private key. This resolves the problem of having to find a secure way to share a single private key between the receiver and the sender. Hash functions do not use a key at all but are used to create a theoretically unique fingerprint of the message so that we can tell if the message has been altered from its original form.

The advantage of having a certificate is

that it allows us to verify that a public key is truly associated with a particular individual. In the case of the digital signature we discussed in the preceding section, it might be possible that someone had falsified the keys being used to sign the message and that the keys did not actually belong to the original sender. If we have a digital certificate for the sender, we can easily check with the CA to ensure that the public key for the sender is legitimate.A CA is only a small part of the infrastructure that can be put in place to handle certificates on a large scale. This infrastructure is known as a public key infrastructure (PKI). A PKI is generally composed of two main components, although some organizations may separate some functions out into more than just these. In a PKI, we often find the CAs that issue and verify certificates and the registration authorities (RAs) that verify the identity of the individual associated with the certificate.

Cryptography

the art of protecting information by transforming it into an unreadable format, called cipher text. The science of keeping information secure (secure, in this case, in the sense of confidentiality and integrity (through hashing) Encryption itself is actually a subset of cryptography, referring specifically to the transformation of unencrypted data, called plaintext or cleartext, into its encrypted form, called ciphertext.

Kerberos is a somewhat complex network authentication protocol

the intimate details of which are beyond the scope of our discussion here, but it is nonetheless worthy of mention, as it is commonly used. Kerberos provides the basis of many single sign-on (SSO) implementations. SSO allows us to create a set of associated applications or systems that can all be accessed through a centralized login system. Kerberos also serves as the basis for Microsoft's Active Directory. As with many of the other cryptographic applications we have discussed, Kerberos can make use of a variety of cryptographic protocols.

The main advantage of asymmetric key cryptography over symmetric key cryptography is

the loss of the need to distribute the key. As we discussed earlier in this lesson, when we use a symmetric algorithm, we need to distribute the key in some way. We might do this by exchanging keys in person, sending a key in e-mail, or repeating it verbally over the phone, but we generally need to communicate the key in an out-of-band manner, meaning that we do not want to send the key with the message, as this would leave our message easily available to an eavesdropper. When we use asymmetric key cryptography, we have no need to share a single key. We simply make our public key easily available, and anyone who needs to send us an encrypted message makes use of it.

PGP, created by Phil Zimmerman

was one of the first strong encryption tools to reach the eye of the general public and the media. Created in the early 1990s, the original release of PGP was based on a symmetric algorithm and could be put to use in securing data such as communications and files. The original release of PGP was given away as free software, including the source code. At the time of its release, PGP was regulated as a munition under the US International Traffic in Arms Regulations (ITAR) law. Zimmerman spent several years under investigation for criminal activities, as he was suspected of exporting PGP out of the country, which was then illegal and encryption systems were included under arms trafficking regulations

In PKI

we also deal with the concept of certificate revocation, in the case where a certificate reaches its expiration date, the certificate is compromised, or another reason arises in which we need to ensure that the certificate can no longer be used. In this case, we will likely see the certificate added to a certificate revocation list (CRL). The CRL is a generally public list that holds all the revoked certificates for a certain period of time, depending on the organization in question. An example of the impact to trust relationships from certificates being compromised can be seen when DigiNotar had hundreds of SSL certificates stolen and used by hackers to sign malware with certificates from legitimate companies

Certificates allow us to link a public key to a particular identity so that

we can ensure that an encrypted message really represents a communication from a particular individual. The receiver can check with the issuer of the certificate, the CA, in order to determine whether the certificate presented is, in fact, legitimate. Behind the CA, we may find a PKI, which supports the issuing, verification, and revocation of certificates.

To secure communications between two machines,

we might see the Secure Shell (SSH) protocol in use, typically on port 22. The utilities that allow us to use SSH are generally installed by default on Linux- and UNIX-based systems, and are supported on most other operating systems as well. SSH is such a widely used tool that support for most any cryptographic algorithm can be found in one implementation or another, including 3DES, Blowfish, AES, Serpent, and IDEA, just to name a few . SSH can provide security for terminal connections, file transfers, remote desktop tools, VPN connectivity, Web browsing, and most any other application to which we might care to apply it.