Okay, I need to write a professional Wikipedia-style document about ChaCha20 in Korean Let me start by understanding the and requirements.

First, the main is Technology, subcategory Encryption, specifically Symmetric Encryption. The title is ChaCha20. The document needs to have clear H1 title, an overview section, several detailed sections with H2 and H3 headers, and references section if needed. It should be at least 800 characters long, which in Korean would be around 400-500 words. The content must be accurate, objective, with appropriate depth, easy to read, and use professional terms with explanations.

I'll start with the H1 title: # ChaCha20

Next, the overview section. I should introduce ChaCha2 as a stream cipher, its purpose, who developed it, and its adoption. Mention Daniel J. Bernstein, the year (2008), and its use in TLS 1.3, SSH, etc. Also, note its advantages like speed and resistance to side-channel attacks.

Then, detailed sections. Let's think of possible H2 sections. Maybe "기본 원리" (Basic Principles), "특징 및 장점" (Features and Advantages), "보안성" (Security), "응용 분야" (Applications), and "ChaCha20-Poly1305". Each H2 can have H3 subsections if needed.

Under "기본 원리", explain the structure: 256-bit key, 32-bit nonce, 32-bit block counter. How it generates keystream in 512-bit blocks. The ARX approach (Addition, Rotation, XOR). Maybe mention the rounds (20 rounds) and the permutation function.

"특징 및 장점" can include speed in software, especially on devices without hardware AES support. Resistance to timing attacks, simplicity in implementation, and widespread adoption.

"보안성" should discuss cryptanalysis results, any known attacks, and why it's considered secure. Mention the lack of successful attacks on full 20 rounds.

"응용 분야" covers where ChaCha20 is used: TLS/SSL, SSH, WiFi 6, cryptocurrency wallets. Maybe include specific protocols like TLS 1.3 and QUIC.

"ChaCha20-Poly1305" needs to explain the AEAD construction, combining ChaCha20 with Poly1305 for authentication. Benefits of AEAD, like preventing tampering.

References section can include IETF RFCs, Bernstein's papers, NIST documents, and other relevant sources.

I need to ensure that technical terms are explained. For example, when mentioning ARX, define it as Addition-Rotation-XOR. Also, clarify what a stream cipher is if necessary, but since the audience is in the symmetric encryption category, maybe assume some knowledge.

Check for accuracy: ChaCha20 was indeed designed by Bernstein, replaced Salsa20. The key and nonce sizes are correct. The ARX operations are right. The adoption in TLS 1.3 and other protocols is accurate.

Make sure the markdown structure is correct: H1, H2, H3 headers, bullet points where appropriate, code blocks if needed (though maybe not necessary here). Use emphasis (**) for key terms when first mentioned.

Avoid any subjective statements, keep it factual. Length should be sufficient, so each section needs enough detail without being too verbose. Maybe around 500-600 words in Korean.

I'll start drafting each section, ensuring smooth transitions and logical flow. Check for any errors in technical details. Maybe verify the number of rounds (20) and the block size. Also, mention that ChaCha20 is often used with Poly1305 for authenticated encryption, which is part of its common implementation.

Finally, review the document to meet all the user's requirements and ensure clarity and professionalism.