Cryptography for everybody: Basics of Cryptology Series (correct ordering)

In 2020 I started my “Basics of Cryptology” series on my “Cryptography for everybody” YouTube channel.

Right now, the series consists of 23 different videos. The videos cover topics from the beginnings of cryptology and basic terminology up to modern cryptology (e.g. RSA and AES).

While creating the series I jumped with the focus and created videos, as the topics came into my mind. Thus, today, I tried to order the videos to a “correct” order. Here is my current list 🙂

Clearly, you can just watch the videos as they are present in the YouTube playlist 🙂
Maybe, in the future, I will create a single long video, a new playlist, or maybe even re-create all videos. When I started creating my videos, my YouTube channel was new and I had not so much experience as I have now.

Nevertheless, I hope you’ll find my videos in that series interesting and helpful. If you have any questions, ideas, or wishes, feel free to write below this blogpost or directly below my videos in the comment section 🙂

Nils

Cryptography for everybody: Let’s Create Our Own Homophonic Substitution Cipher

In our newest video on “Cryptography for everybody”, we create a homophonic substitution cipher using CrypTool 2.


The “Substitution component” of CrypTool 2 allows to create substitution ciphers. For that, we implemented an easy-to-use syntax based on plaintext and ciphertext alphabets. An “alphabet” is just a string (some text), which consists of our “symbols”. A symbol can be one or more UTF-8 characters.

Example (simple shift cipher):
– Plaintext alphabet=”ABCDEFG…Z”
– Ciphertext alphabet=”BCDEFGH…A”

Providing these two alphabets to the substitution component would create a simple shift cipher, where each letter of the plaintext alphabet is shifted one to the left in our corresponding ciphertext alphabet. In the substitution component, letters are substituted based on their corresponding positions in the given alphabets. The first letter of the plaintext alphabet is substituted by the first letter of the ciphertext alphabet, the second by the second, etc.

But the substitution component is much more powerful. It allows also to create alphabets consisting of “words” and also allows alternative substitutions to create “homophones”.

Example (homophonic substitution cipher):
– Plaintext alphabet=”ABCDEFG…Z”
– Ciphertext alphabet=”[01|02][03|04]…[999|555]”

In this example, the letter A can be substituted by either 01 or 02. The brackets tell the substitution component that it should use everything inside the brackets as a single ciphertext symbol. The pipe symbol tells the component that we want to create alternatives. Using this syntax, we are able to create a homophonic substitution cipher, where one plaintext letter will be replaced by one of the defined homophones.

But we are not only limited to use simple two or three digit combinations. We can also create mappings like [MAXIMILIAN] in the plaintext alphabet and [1001] in the ciphertext alphabet. Doing so, we can create so-called nomenclators. How this can be done in CrypTool 2 is part of the linked YouTube video. So if you are interested in more details, you should have a look at this 🙂

If you are interested in downloading the newest version of CrypTool 2 (I always recommend the nightly build, since it contains the newest components) go to https://www.cryptool.org/en/ct2/downloads

Nils

New blog software installed on my webserver :-)

This is the first post in wordpress. In future posts, I will write about cryptography, especially about CrypTool 2 and about retro computing.

Thus, this blog is mainly intended to be updated with news about my two YouTube channels:

My channel about cryptology: www.youtube.com/c/CrypTool 2

My channel about retro computing: www.youtube.com/c/NilsRetroHobbyRoom

Greetings,

Nils