kono angou ha muzukasii.

A natural reading is:

Kono angō wa muzukashii.

More specifically:

• この = kono
• 暗号 = angō
• は = wa here
• 難しい = muzukashii

A rough pronunciation guide:

• kono = koh-noh
• angō = ahn-goh (with a long ō sound)
• wa = wah
• muzukashii = moo-zoo-kah-shee-ee

This is one of the first things learners notice.

The character は is normally read ha when it is part of a word. But when it is used as the topic particle, it is pronounced wa.

So in this sentence:

• この暗号は難しい。
• the は marks この暗号 as the topic
• and it is read wa

This is just a standard rule of Japanese grammar, not an exception specific to this sentence.

は marks the topic of the sentence.

Here, the topic is:

• この暗号 = this code / this cipher

Then the sentence says something about that topic:

• 難しい = is difficult

So the overall structure is basically:

• As for this code, it is difficult.

In natural English, we usually just say:

• This code is difficult.

But grammatically, Japanese is slightly more like:

• Speaking of this code, it’s difficult.

No, 暗号この is not correct.

この is a demonstrative determiner, meaning it must come directly before a noun.

So:

• この暗号 = this code

This works the same way as:

• この本 = this book
• この人 = this person

You cannot place この after the noun.

A helpful comparison:

• この + noun = this + noun
• これ = this on its own

So:

• この暗号 = this code
• これは暗号です = this is a code

They are related, but they are used differently.

• この must be followed by a noun
  
  • この暗号 = this code
• これ stands alone
  
  • これは難しい = this is difficult

So in your sentence, この is correct because 暗号 comes right after it.

You could say:

• この暗号は難しい。 = This code is difficult.
• これは難しい。 = This is difficult.

The second sentence is less specific unless the context already makes clear what this refers to.

難しい is an i-adjective.

That means it is a type of adjective that ends in -い in its dictionary form.

Examples of other i-adjectives:

• 大きい = big
• 小さい = small
• 新しい = new

In this sentence, 難しい works like the main predicate:

• この暗号は難しい。
• This code is difficult.

Unlike English, Japanese does not need a separate word like is here in casual/plain style. The adjective itself can finish the sentence.

Because Japanese grammar works differently from English.

In English, you need:

• This code is difficult.

In Japanese, an i-adjective like 難しい can act as the predicate by itself:

• この暗号は難しい。

So Japanese does not need a separate verb meaning is here.

If you want to make it more polite, you can add です:

• この暗号は難しいです。

That still means the same thing, but sounds more polite.

Yes, absolutely.

Both are correct:

• この暗号は難しい。 = plain / casual
• この暗号は難しいです。 = polite

The sentence without です is not wrong or incomplete. It is just less polite and more neutral/plain in tone.

This is very common in Japanese:

• dictionary/plain form in casual writing or speech
• です / ます forms in polite speech

暗号 often means:

• code
• cipher
• encrypted message
• sometimes password/code phrase, depending on context

So the exact English translation can vary.

For example:

• in a puzzle or cryptography context, cipher or code
• in a general secret-message context, secret code

In your sentence, This code is difficult is a very natural translation, but the exact nuance depends on context.

Japanese normally does not use spaces between words in ordinary writing.

So the sentence would usually be written as:

• この暗号は難しい。

Learner materials often add spaces like:

• この　暗号　は　難しい。

This is just to make the parts easier to see. It is not standard Japanese formatting.

Sometimes, yes, but the nuance changes.

• この暗号は難しい。
  = This code is difficult.
  This presents this code as the topic.

• この暗号が難しい。
  = This code is the difficult one / It is this code that is difficult.
  This can sound more contrastive or more focused on identifying which thing is difficult.

So は is the more neutral choice if you are simply talking about this code and describing it.

Yes. Depending on context, 難しい can mean:

• difficult
• hard
• complicated
• sometimes even tricky or problematic

So this sentence could imply:

• the code is hard to understand
• hard to solve
• hard to decode
• complicated in some way

The exact nuance depends on the situation.

Yes.

• 難しい暗号 = a difficult code

That is different from:

• この暗号は難しい。 = This code is difficult.

So compare:

1. 難しい暗号

   • adjective directly modifies noun
   • a difficult code

2. この暗号は難しい。

   • noun phrase is the topic, adjective is the predicate
   • This code is difficult.

Both are very common patterns in Japanese.