Cryptography - Ciphertext, Masking, Hash

Encryption and hashing that I write because I get confused

I want to organize the cryptography unit I learned while studying for the information security engineer exam before I forget it.

What is Cryptography

Linguistic and mathematical methodologies for protecting information (wikipedia says)

In any field, you learn the history of that discipline in the overview stage. When learning computer history in computer introduction, I slept on the desk, but cryptography history is about the fierce brain battles of geniuses, so it feels like reading an interesting novel.

However, what I want to organize today is not the history of cryptography, but the theoretical and practical aspects of cryptography. If you're curious about the history related to cryptographic technology, check out the article written by KISA.

Plaintext and Ciphertext

Plaintext is the original message before encryption occurs, and ciphertext is the message after plaintext has been encrypted by something. In cryptography, plaintext is abbreviated as P (Plain Text) PyoungMoon, and ciphertext is abbreviated as C (Cipher Text).

Confusion and Diffusion

'Confusion' and 'diffusion' are essential for encryption. Confusion is hiding the correlation between ciphertext and plaintext. Diffusion is spreading statistical properties throughout the ciphertext to hide them. What does this mean?

Let's say P = 'I LOVE JIAE SEO'. I changed this plaintext to 'I LOVA JIEA SAO'. If you look carefully, I changed E to A and A to E. Like this, you can implement confusion by changing the plaintext.

Again, let's say P = 'I LOVE JIAE SEO'. I changed this plaintext to 'I EVOL EAIJ OES'. If you look carefully, I changed the spelling order of each word. Like this, you can implement diffusion by changing the position of plaintext.

This is also the concept of substitution and transposition that frequently appear in cryptography. Substitution is among the methods to implement confusion, and transposition is among the methods to implement diffusion.

Encryption and Hashing

Regarding encryption and hashing, there's something people get confused about if they haven't learned it. It's the difference between encryption and hashing.

Encryption (Two-way encryption)

The key to encryption is that others can't understand it, but I can. The original data must be provided timely and intact through the decryption process.

Hashing (One-way encryption)

The key to hashing is that neither others nor I can understand it. Let's say there are plaintext1 and plaintext2. When these two plaintexts go through the process called hashing, result1 and result2 are generated.

In this case, neither you nor I nor anyone can recover the original data, but since the two hashing results are different, we can know that original 1 and original 2 are different. (assuming no hash collision occurs)

Utilizing the characteristic that the original cannot be recovered but can only be distinguished, it's often used when servers store passwords by going through a hashing process, and then verify during login whether the password is correct or incorrect.

Masking

The key to masking is that neither others, nor I, nor even Jesus can understand it. If I mask the plaintext 'I LOVE JIAE SEO' with * characters, the result is '***************'. Even Jesus can't understand this.