Today we’re going to talk about how to keep information secret, and this isn’t a new goal. From as early as Julius Caesar’s Caesar cipher to Mary, Queen of Scots, encrypted messages to kill Queen Elizabeth in 1587, theres has long been a need to encrypt and decrypt private correspondence. This proved especially critical during World War II as Allan Turing and his team at Bletchley Park attempted to decrypt messages from Nazi Enigma machines, and this need has only grown as more and more information sensitive tasks are completed on our computers. So today, we’re going to walk you through some common encryption techniques such as the Advanced Encryption Standard (AES), Diffie-Hellman Key Exchange, and RSA which are employed to keep your information safe, private, and secure.

Note: In October of 2017, researchers released a viable hack against WPA2, known as KRACK Attack, which uses AES to ensure secure communication between computers and network routers. The problem isn't with AES, which is provably secure, but with the communication protocol between router and computer. In order to set up secure communication, the computer and router have to agree through what's called a "handshake". If this handshake is interrupted in just the right way, an attacker can cause the handshake to fault to an insecure state and reveal critical information which makes the connection insecure. As is often the case with these situations, the problem is with an implementation, not the secure algorithm itself.

What is culture? How do we define it and how does it change? We’ll explore different categories of culture, like low culture, high culture, and sub-cultures. We'll also revisit our founding theories to consider both a structural functionalist and a conflict theory perspective on what cultures mean for society.

Cybersecurity is a set of techniques to protect the secrecy, integrity, and availability of computer systems and data against threats. In today’s episode, we’re going to unpack these three goals and talk through some strategies we use like passwords, biometrics, and access privileges to keep our information as secure, but also as accessible as possible. From massive Denial of Service, or DDos attacks, to malware and brute force password cracking there are a lot of ways for hackers to gain access to your data, so we’ll also discuss some strategies like creating strong passwords, and using 2-factor authentication, to keep your information safe.

This week we build on our naked eye observations from last week and take a look at the cyclical phenomena that we can see at work in the universe.

Chapters:
Introduction
Cycles in the Sky
The Zodiac
Planetary Movement
The Earth's Axis
Precession
Things We've Learned From Naked Eye Observations
Review

Hexagons appear all over the natural world from honeycomb to bubbles, and they even appear in organic chemistry! In this episode of Crash Course Organic Chemistry, we're learning all about cyclohexanes, including how rings pucker to relieve strain, the boat and chair conformations, and how ring flips can switch substituents from axial to equatorial. We'll practice a lot of chair flips, but don't flip an actual chair just yet! Lots of practice is key to understanding organic chemistry's favorite manifestation of the hexagon.

Batteries power much of your daily life, so today we're going to talk about how they work. We're also explaining how terminal voltage results from the natural internal resistance of every real battery. We'll get into both series and parallel circuit configurations, and how the laws of conservation affect the current and voltage for each.

Hank imagines himself breaking into the Hot Pockets factory to steal their secret recipes and instruction manuals in order to help us understand how the processes known as DNA transcription and translation allow our cells to build proteins.

Chapters:
1) Transcription
A) Transcription Unit
B) Promoter
C) TATA Box
D) RNA Polymerase
E) mRNA
F) Termination signal
G) 5' Cap & Poly-A Tail
2) RNA Splicing
A) SNuRPs & Spliceosome
B) Exons & Introns
3) Translation
A) mRNA & tRNA
B) Triplet Codons & Anticodons
4) Folding & Protein Structure
A) Primary Structure
B) Secondary Structure
C) Tertiary Structure
D) Quaternary Structure

Your DNA contains all the instructions your body needs to function. In this episode of Crash Course Biology, we’ll figure out what this giant instruction manual looks like and how this three-billion-letter code gets copied into your trillions of cells through DNA replication.
Chapters:
Introduction: DNA & The Human Genome
The Structure of DNA
Chromosomes
DNA Replication
How DNA Replication Works
Mutations
The Okazakis
Review & Credits
Credits

Hank introduces us to that wondrous molecule deoxyribonucleic acid - also known as DNA - and explains how it replicates itself in our cells.

Chapters:
1) Nucleic Acids
2) DNA
-A) Polymers
-B) Three Ingredients
-C) Base Pairs
-D) Base Sequences
3) Pop Quiz
4) RNA
-A) Three Differences from DNA
5) Biolography
6) Replication
-A) Helicase and Unzipping
-B) Leading Strand
-C) DNA Polymerase
-D) RNA Primase
-E) Lagging Strand
-F) Okazaki Fragments
-F) DNA Ligase
Review

Watch. Dime. Develop. Powder. Pantry. Dirt. That's right, it's time for a dip into the random, because we're talking about the Dada theater that grew out of Symbolism, and the Surrealist theater that followed Dada. You'll learn about Maurice Maeterlinck, Paul Fort, Lugne Poe, Andre Breton, and Alfred Jarry and his infamous play, Ubu Roi. Along the way, you'll pick up lots of interesting facts. For instance, Jarry's favorite cocktail was made up of absinthe, vinegar, and ink. We don't want to boss you around, but do not ever drink anything like that.

Today, Mike Rugnetta takes you from our beginnings in ancient Greek theater, and moves on to the development of Roman theater. Which, it turns out, is A LOT like Greek theater. Because the Romans were real Grecophiles, they modeled their plays on the Greeks.

John Green teaches you about the so-called Dark Ages, which it turns out weren't as uniformly dark as you may have been led to believe. While Europe was indeed having some issues, many other parts of the world were thriving and relatively enlightened. John covers European Feudalism, the cultural blossoming of the Islamic world, and the scientific and artistic advances in China, all during these "Dark Ages." Along the way, John will raise questions about the validity of Europe's status as a continent, reveal the best and worst years of his life, and frankly state that science and religion were once able to coexist.

Chapters:
Introduction: Europe
Why are they called The Dark Ages?
Feudalism in Medieval Europe
Dar al Islam and the Umayyad Dynasty
The Abbasids
An Open Letter to Science and Religion
Spanish Muslims in Cordoba
China's Golden Age
Credits

In this episode, the universe as we know it starts to come into focus. Dr. Katie Mack teaches John Green about the cosmic dark ages, the possibility of a multiverse, and the connection between the hot, dense early universe and today.

Chapters:
Introduction
CMB & The Cosmic Web
The Possibility of a Multiverse
The Inflaton Field
Viewing Early Galaxies
The Surface of Last Scattering
The Dark Ages of the Cosmos
Dark Matter & Cosmic Dawn
Feeling Awe

The majority of the universe is made up of a currently mysterious entity that pervades space: dark energy. We don’t know exactly what it is, but we do know that dark energy accelerates the expansion of space. We think this means the Universe will expand forever, even as our view of it shrinks while space expands faster all the time.

Chapters:
Introduction: The Expanding Universe
The Expansion of Space is Accelerating
What is Dark Energy?
Will the Universe Expand Forever? The Geometry of the Universe
The Cosmic Horizon of the Observable Universe
Review

Today on Crash Course Astronomy, Phil dives into some very dark matters. The stuff we can actually observe in the universe isn’t all there is. Galaxies and other large structures in the universe are created and shifted by a force we detect mostly indirectly, by observing its impact: DARK MATTER.

Chapters:
Introduction: Dark Matter
Discovery of Dark Matter
What is Dark Matter?
Axions
Gravitational Lensing and the Bullet Cluster
What Effect Does Dark Matter Have on the Universe?
Review

Propaganda! Misinformation! Disinformation! Today we’re talking about the dark – or, shall we say, darkER – side of media. Understanding these media bogeymen is essential to being a more media literate citizen.

"Survival of the Fittest" sounds like a great WWE show but today we're talking about that phrase as it relates to Charles Darwin and Alfred Wallace. Darwin and Wallace are at the heart of understanding evolution and natural selection. Today, Hank talks about their wonderful (if not seasick inducing) trips around the world.

Today we’re going to talk about on how we organize the data we use on our devices. You might remember last episode we walked through some sorting algorithms, but skipped over how the information actually got there in the first place! And it is this ability to store and access information in a structured and meaningful way that is crucial to programming. From strings, pointers, and nodes, to heaps, trees, and stacks get ready for an ARRAY of new terminology and concepts.

Over the next few episodes we’re going to talk about the history of video games. Today, we’re going to start with the first re-programmable computers in the 1940’s. Now, these computers were serious tools. They were for codebreaking and calculating artillery tables during World War II - but like most tools we human use, we eventually looked for ways to make them playthings. And over the next three decades the advances of computer technology and the tentative curiosity of many engineers and programmers would inspire a new culture and eventually the first true coin-operated video game in 1971.

As the Roman Empire fell, so did the theater. If there's anyone who hates theater and actors more than Romans, it's early Christians. As Christianity ascended in the west, theater declined. But, fear not. This isn't the end of the series. Theater would be back, and in the best subversive theater-y fashion, it would return via the Catholic mass!