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27. Diffie-Hellman Key Exchange

Key exchange is any method in cryptography by which cryptographic keys are exchanged between two parties, allowing the use of a cryptographic algorithm. If the sender and receiver wish to exchange encrypted messages, each must be equipped to encrypt messages to be sent and decrypt messages received.

The nature of the equipment they require depends on the encryption technique they might use. If they use a code, both will require a copy of the same code book. If they use a cipher, they will need appropriate keys. If the cypher is a symmetric key cipher, both will need a copy of the same key. Both will require the other public key if it is an asymmetric key cypher with the public private key property. The key exchange problem is how to exchange whatever keys or other information are needed so that no one else can obtain a copy. Historically, before the invention of public key cryptography, symmetric key cryptography utilised a secret key to encrypt and decrypt information. For two parties to communicate confidentially, they must first exchange the secret key so that each party can read encrypted messages as well as send them.

This process is known as the key exchange. The overarching problem with symmetrical cryptography or single-key cryptography is that it can require a secret key to be communicated through a trusted channel. If the two parties cannot establish a secure initial key exchange, they cannot communicate securely without the risk of the key being compromised. Let's say, for example, that Amy and Billare want to communicate with each other. They want to make sure that their communication is confidential and that they are, in fact, communicating with each other. In other words, the other person is authenticated. When Amy randomly selects her secret key, she has to somehow send it to Bill. But she doesn't yet have a secure channel to communicate with Bill, so she can't encrypt the key if she sends it by email or some other unencrypted means. A third party like Mal might intercept the key in transit and use the key to eavesdrop on all subsequent communications between Amy and Bill.

To compound the problem, what would Bill do once he received the key from Amy? He has no way of verifying that the letter sent to him was, in fact, from Amy. If Mall is clever, he could impersonate Bill and send a fake key to Amy, then impersonate Amy and send a fake key to Bill. So this would have the same effect as intercepting the key that Amy was originally sending to Bill legitimately, and Mao would be able to eavesdrop on all their communications. The solution to this would be to use an outbound key exchange. This simply means that Amy and Bill can use a different channel that they both trust. For example, if they are familiar with each other's appearance, they may arrange a face-to-face meeting at a local coffee shop. Or if they are familiar with each other's voices, they may call each other. These options, however, present their own set of challenges. For example, what if Amy and Bill live in two different cities? Arranging a face-to-face meeting in that instance would not be feasible. The alternative solution is to use an inbound key exchange. In an inbound key exchange, the key exchange is done digitally, and one way this can be done is through the Diffie-Hellman algorithm, which we will discuss next.

28. Key Escrow

Diffie-Hellman Key Exchange, also called Exponential Key Exchange, is a method of digital encryption that uses numbers raised to specific powers to produce encryption keys on the basis of components that are never directly transmitted, making the task of a would-be codebreaker mathematically impossible. The Diffie-Hellman key exchange is a method of securely exchanging cryptographic keys over a public channel and was one of the first public key protocols.

As originally conceptualised by Ralph Markle and named after Whitfield Defy and Martin Hellman, DIFY Hellman is one of the earliest practical examples of public key exchange implemented within the field of cryptography. We will definitely look at the math behind the Diffie-Hellman key exchange, but before we do that, I'd like to share a very simplified analogy using colors, which may help those students that are better visual learners. The concept of Diffie-Hellman is much easier to understand with this colour analogy.

Let's say Alice and Bob want to agree on a common secret colour that no one else should know about. Here's how they might do this: First, Alice sends a message to Bob, telling him a common colour they might use. Let's say that Alice selects green and tells Bob the colour by email. Next, Alice and Bob each select a secret colour of paint that they don't tell each other. Alice's secret colour is red, and Bob's secret colour is blue.

Alice and Bob then each take the common green colour and mix it with their secret color. For Alice, green and red make yellow, and for Bob, green and blue make cyan. Alice then sends the message to Bob and tells him that her results are yellow. And Bob tells Alice that he got cyan for his results. Alice and Bob now have two colours created by mixing their shared green colour with their partner's secret color. They then mix their own secret colour with their partners' shared color. For Alice, she mixes cyan and red to get teal. For Bob, he mixes yellow and blue to get teal.

Both of these colours are identical and were created by mixing together the same three colors: green, red, and blue. Now, let's assume that a malicious person is watching all of the messages that Alice and Bob exchanged. What would he know? Well, he knows that they started with the colour green and that they exchanged the colours cyan and yellow.

He would not know either of the two secret colours that Alice and Bob selected, which are red and blue, or the common secret colour of feel, because those were never sent over the insecure channel. Diffie-Hellman is a way of generating a shared secret between two people in such a way that the secret can't be seen by observing the communication. That's an important distinction. You're not sharing information during the key exchange. You're creating a key together.

This is particularly useful because you can use this technique to create an encryption key with someone and then start encrypting your traffic with that key. And even if the traffic is recorded and later analyzed, there's absolutely no way to figure out what the key was, even though the exchanges that created it may have been visible. This is where "perfect forward secrecy" comes from. Nobody analysing the traffic at a later date can break in because the key was never saved, never transmitted, and never made visible anywhere. The way it works is reasonably simple. A lot of the math is the same as you see in public key crypto, in that a trapdoor function is used. While the X to the YMP business is traditionally solved using the discrete logarithm problem, the general process can be modified to use elliptic curve cryptography as well.

But even though it uses the same underlying principles as public key cryptography, this is not asymmetric cryptography because nothing is ever encrypted or decrypted during the exchange. It is, however, an essential building block and was, in fact, the base upon which asymmetric crypto was later built. The basic idea works like this: I'll come up with two prime numbers, G and P, and tell you what they are. You then pick a secret number, A, but you don't tell anyone. Instead, you compute G for the modulo plane and send that result back to me. We'll call that a capital A. Since it came from small A, I do the same thing, but we'll call my secret number small B and the computed number capital B.

So I compute G for the small B module and send you the result called capital B. Now you take the number I sent you and do the exact same operation with it. So that's from the capital B to the small A modulo p. Finally, I did the same operation with the result you sent me.

That is capital A to small B module p. The magic here is that the number I get in step five is the same number you got in step four. Now, it's not really magic. It's just math. And it comes down to the fancy property of modular exponents. Specifically, G to the A modulo p, all raced to the B modulo p, equals G to the AB modulo p, and G to the B modulo p, all raised to the A modulo p, equals G to the BA modulo p, which, if you examine closer, means that you'll get the same answer no matter which order you do the exponentiation in.

So I do it in one order, and you do it in another. I never know what secret number you use to get the same result, and you never know what number I use. but we still arrive at the same results. That result, that number we both stumbled upon in steps four and five, is our shared secret key. We can use that as our password for a yes-or-blowfish or any other algorithm that uses shared secrets. And we can be certain that nobody else—nobody but us—knows the key that we created together. So now we've worked with the Tiffy helmet in terms of mixed colors, and we've presented the basic idea of the formula.

Let's take a look at a real-world example. Instead of choosing a common starting color, Alice chooses two numbers represented by the variables p and g. P must be a prime number. Let's say that Alice sends a message to Bob, telling him to use 13 for p and seven for g. Next, Alice chooses a secret number. Let's say that she chooses five. We'll call that She then computes the value of uppercase A using the formula uppercase A equals G to the power modulo p of lowercase a. That's seven to the fifth power modulo 13, which gives us a value of eleven for A. Alice then sends the value of capital A, which is eleven, to Bob.

Bob then selects his own secret number. We'll call that a lowercase b. And let's say he chooses the number eight. Bob then performs a similar calculation to determine uppercase B using the formula uppercase B equals G to the lowercase B power modulo p. This gives us a value of three for Bob. Bob then sends the value of capital B, which is three, to Alice.

Alice then computes the shared secret. The formula S equals uppercase B to lowercase A power module p is used. This works out to three to the fifth power modulo 13, which is nine. Bob can then compute the same shared secret key using a different formula: s = uppercase A to lowercase B modulo p. That works out to eleven to the 8th power modulo 13, which is nine. And now Alice and Bob both have the same shared secret value of nine, which they can use as a symmetric encryption key. If a malicious person watched the entire communication between Alice and Bob, he wouldn't have enough information to reconstruct that key.

29. Trust Models

This lesson will go over escrow. useescrowy Escrow. Key Escro "fair," also known as a fair cryptosystem, is an arrangement in which the keys required to decrypt encrypted messages are held in escrow so that an authorized third party may gain access to those keys under certain authorized circumstances. These third parties may include individuals who want access to an employee's private files or communications, as well as governments who want to view the transmissions. The Clipper chip was an administration chip for the United States government. It was designed to be used as an encryption device by businesses for voice transmissions to the US government. The US government required a record of all communications between the US and countries other than the US.

So it proposed the Clipper 1993 Initiative in 1993. It was designed with this in mind, but due to public opposition, it was not implemented until 1996. The Clipper chip employs the "Askipjackialgorithm," which has been classified as secret by the US Agency, national NSA, or NSA Secret. It contained a chip, the Capstone chip, which provided processing and graphic processing. Telecommunications and communications companies in the United States adopted the Clipper chip. As a result, eavesdropping is prevented. Backdoor. There was a backdoor. The government had the key and was legally entitled to read all messages. Because of the potential for privacy abuse and possible abuse, the Clipper chip sparked public and from the public and the computer as a whole. Citizens were subjected to citizen surveillance, according to the Electronic Privacy Information Center and the Electronic Frontier Foundation.

legal surveillance. In addition, individuals and tight gets sector might get stuck with an intersystem. The public cannot evaluate encryption and secret classification as a clipper shifts. At end by the public. A data recovery windows usercrosoft Windows user who has been to decrypt the right t has been crypt data that was users. ted by other users. re is how it works the network administrator uses Microsoft Windows Group Policy in Active Directory to assign everyone a public key for encryption and their own personal private key for decryption. This ensures that users can only decrypt the content that they have created and no one else's. The data recovery agent, however, is assigned a private key capable of unlocking all content encrypted with the public key. In Windows 2000, the local administrator is the default Dr. In Windows XP Professional, Windows Seven, Windows Server 2003, and Windows Server 2008 R Two. There is no default VRA. Instead, the administrator must generate a recovery agent certificate, which grants the user permission to access encrypted resources. If the recovery agent certificate is created after the encryption of the resource, however, the resource cannot be decrypted by the DRM. Let's compare a key escrow with a recovery agent. A key escrow is used in cases where a third party needs access to encrypted data as defined by law.

So if you get a court order to decrypt data, for example, a "recovery" is someone who is permitted to decrypt another user's data in case of an emergency and has the key that can accomplish that decryption. So, in effect, the key keeper is someone who holds the key for each user, while the recovery agent has a master key.

30. Public Key Infrastructure (PKI) and Digital Certificates

In general, cryptographic systems assume some level of trust. A prime example of this would be a secure key exchange. In such an example, the parties involved must be confident that they are in fact communicating with the intended party and not someone else. Even beyond that, the parties would want to be confident that there is no eavesdropping on the communication by a third party. While key models such as Defy Hellman help prevent eavesdropping, they do not guarantee that we're not communicating with an imposter. A model such as the Defy helmet, for example, eliminates the need for eavesdropping protection. But it does not, however, imply that we are communicating with the intended party. So let's quickly recap the implications this has. The challenge of key exchange is that both parties must be confident that they are communicating with each other.

Two, they must be confident that neither is an imposter, and third, they must be sure that there is no eavesdropping on the exchange. Let's take this a step further to better understand the basic trust model. When two parties engage in a transaction, they must mutually trust each other's identity. They must trust that both parties are allowed to engage in the transaction. They must trust that no third party can know the details of the transaction. There must be basic trust that no third party can change any part of the transaction. Fifth, there must be trust that neither party can deny having engaged in that transaction, and sixth, there must be trust that the record of the transaction is kept. For future reference, we have clearly identified the challenges associated with the basic trust model.

So then, how do we ensure that we are in fact communicating with the intended individual? One possible solution would be through personal knowledge. For instance, the two parties could meet at a coffee shop and have an in-person key exchange. But is this really convenient and scalable? Probably not. Another option readily available is the Web of Trust, which we will discuss next. The public key infrastructure is the third option. A "web of trust" is a concept used in PGP and open PGP compatible systems to verify the authenticity of a public key's binding to its owner.

Its decentralised trust model is an alternative to the centralised trust model of public key infrastructure, which relies exclusively on a certificate authority or hierarchy of such, as with computer networks. There are numerous independent trust webs, and any user can be a part of one or more of them by using their identity certificate. A web of trust essentially works by having certificates signed by other users to endorse the association of that public key with the person or entity listed in the certificate. The drawback is that the user has to trust all those in the keychain to be honest, so it's often best suited to small user communities.

31. Hash Functions

In this lesson, we will discuss the public key infrastructure, more commonly known as the PKI, and digital certificates. A public key infrastructure supports the distribution and identification of public encryption keys, enabling users and computers to both securely exchange data over networks such as the Internet and verify the identity of the other party. Without PKI, sensitive information can still be encrypted, ensuring confidentiality, and exchanged, but there would be no assurance of the identity or authentication of the other party. Any form of sensitive data exchange over the Internet is reliant on PKI for security. A typical PKI consists of hardware, software, policies, and standards to manage the creation, administration, distribution, and revocation of keys and digital certificates.

Digital certificates are at the heart of PKI, as they affirm the identity of the certificate subject and bind that identity to the public key contained in the certificate. A typical PKI includes the following key elements: a trusted party called a certificate authority, or CA, which acts as the root of trust and provides services that authenticate the identity of individuals, computers, and other entities.

A registration. authority, often called a subordinate CA, is certified by the root CA to issue certificates for specific uses permitted by the root. a certificate database that stores certificate requests, issues certificates, and revokes certificates; and a certificate store that resides on a local computer as a place to store issued certificates and private keys. A certificate authority, or CA, issues digital certificates to entities and individuals. After verifying their identities, it signs these certificates using its private key. Its public key is made available to all interested parties in a self-signed CA certificate. CAS uses this trusted root certificate to create a chain of trust. Many root certificates are embedded in web browsers, so they have built-in trust in those CAS.

Web servers, email clients, smartphones, and many other types of hardware and software also support PKI and contain trusted root certificates from the major CAS. along with an entity or individuals. Public-key digital certificates contain information about the algorithm used to create the signature. The person or entity identified the digital signature of the CA that verified the subject data and issued the certificate. The purpose of the public key, encryption signature, and certificate signing, as well as the date range during which the certificate can be considered valid, So what exactly is a certificate authority? A certificate authority, or CA, is a trusted entity that issues electronic documents that verify a digital entity's identity on the Internet. The electronic documents, which are called digital certificates, are an essential part of secure communication and play an important part in the public key infrastructure. Certificates typically include the owner's public key, the expiration date of the certificate, the owner's name, and other information about the public key.

Owner operating systems and browsers keep a list of trusted casual certificates on hand to verify the certificates issued and signed by a CA. So, in summary, a CA is an entity that issues digital certificates; it's a trusted third-party organization, and it verifies the identity of individuals and organisations and provides digital certificates containing the public key.

I have navigated here to the Identust.com website, and Identust.com provides IGC certificates. Obtaining a certificate is not a complicated process, but I thought I should share this piece of information for those who are interested. If you're interested in obtaining a certificate, this page has the frequently asked questions. You can basically submit your ID for verification. That identification will then be reviewed within a certain timeline, and a response will be given back to you once you've received that verified response. That certificate is basically your proof on the Internet that says you are who you are.

32. Digital Signatures and Digital Certificates

A core mechanism utilised to protect integrity is the concept of hashing.

A sample hash function looks like the one seen here. But what is hashing? Hash functions create message digests from larger files. Hashing is the process of converting a string of characters into a fixed-length value or key that represents the original string. It's used to index and retrieve items in a database because it's faster to find items using the shorter hash key than to find them using the original value. The values returned by hash functions are called hash values, hash codes, digests, or simply hashes. As mentioned, hashing is one of the core controls used to protect integrity.

It does this by utilising a mathematical algorithm. The unique digest that has been yielded from the algorithm serves as a fingerprint for the file. Any alterations to that file change the digest. In other words, if the short piece of data has changed, we know that the fingerprint of the file has changed, which means that there has been an alteration to that file. Let's take a closer look. I encourage you to practise along with me. If you go to the site listed here: www.miraclesalid.com web tools You will have access to the MD Five-hash generator if you use MD Five-dot PHP. I have gone ahead and opened up this link in my browser, and as you can see here, we have an input box where we can enter any string we want. We can simply copy and paste information here, or we can type in whatever we want.

For our example, I'm going to type a random sentence: I like to drink coffee. As you can see, the MD5 hash generator generates a hash that starts with the letter C and ends with the letter F. But what happens if I change the word "coffee" to "water"?As you can see, the whole hash changes now. Our hash begins with zero 90 and ends with two FB. By looking at the hash, we know that this file has been altered. But what happens if we go ahead and change the word "water" back to "coffee"? As you can see, we are right back to where we started. CC4 and F3F are the beginning and ending of our hash that's been generated. This is a very important concept because it indicates that any alteration or tampering of the file would be reflected in the changes in the hash.

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