From the course: Learning Cryptography and Network Security

Introducing cryptographic terminology

From the course: Learning Cryptography and Network Security

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Introducing cryptographic terminology

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When discussing cryptography, there are many terms. In this segment, we'll provide definitions for some common cryptographic concepts. I'll provide a broad definition of some key terms initially, and then we'll dive into more detail as the course progresses. For now, let's start with some basics. Encryption converts plaintext into ciphertext by using a key. Decryption converts ciphertext into plaintext and also uses a key. Ciphertext is an algorithm used to perform encryption or decryption. A cryptographic key is a string of numbers or letters used to either encrypt or decrypt data. The type of key used will depend on the type of encryption. Symmetric encryption uses a single shared secret key to encrypt and decrypt data. Asymmetric encryption uses a pair of keys: a public key and a private key, where one is used to encrypt data and the other is used to decrypt data. A digital signature is a cryptographic value created using data and a private key and is used to verify the authenticity and integrity of the data. And a hash is a one-way function that takes a variable-length input and produces a fixed-length output. Well, now that we've covered the basics, let's put it all together. One key concept in a hybrid cryptosystem is a trusted third party, which is an independent entity mutually trusted by two or more parties involved in a transaction. The role of the trusted third party is essential when exchanging keys during a transaction. Let's talk about why this is important. How do we trust all parties when interacting in a faceless, nameless environment such as the Internet while banking, shopping, or sending email? Well, most of these activities involve using encryption to ensure our transactions are secure. Encryption uses keys. Symmetric encryption uses a single key, but asymmetric encryption uses a pair of keys: a public key and a private key. The public key is shared for everyone to see and use during a transaction. When using someone's public key, we need to trust that the entity that provided the key is indeed the rightful owner. So when completing transactions on the Internet, we use certificates that provide proof of identity. For example, we'll go to google.com. And when you see the lock on the website, we know that the site is trusted. And we see here that it's verified by Google Trust Services. Now other examples that ensure this trust include GoDaddy, Verisign, DigiCert, and Thawte who provide certificate services and are considered a trusted third party. And finally, when we discuss cryptography, it's common to use themes much like the ones used in programming, such as Foo, Bar, and Hello World. In cryptography, we use the story of Bob and Alice. For example, I might start an explanation in the following manner: Alice needs to send Bob a secure message, but they must first obtain the same shared secret key. Now we can learn about Bob and Alice and other characters on this web page that provides a brief history on key cryptographic milestones. Now, in addition, I'm going to scroll down. We can see Bruce Schneier's book, Applied Cryptography. And I'll just show you here. We'll say Read More. And then down below, we see that Schneier created a list of his cast of characters. And I'll click on that, where we see a list of characters, including Mallory, a malicious man in the middle attacker; Eve, an eavesdropper; Trent is a trusted third party; or even Victor, the verifier. Using a story with characters helps explain technical topics in a fun way. And we will see more of Bob and Alice throughout our discussion on cryptography. Now let's test your knowledge. Define cryptographic terms such as encryption, symmetric, asymmetric, hashing, trusted third party, and digital signature. You can record your answer on the Challenge worksheet.

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