Okay, I need create a markdown document about 3 based on the given structure and requirements. Let's start by understanding the user's. The main category is, subcategory encryption specifically symmetric encryption, and the topic is 3DES.

First, the document should have a title (H1). the title will be "DES: 트리 데이터 암호화 표준". Then an overview section. I'll need to explain what 3DES is, its purpose, and why it was developed. Maybe mention that it's improvement over DES because DES vulnerable to brute-force attacks.

Next, detailed sections. Let's break it down. H2 sections could include "3DES의 작동 원리", "보안성과 한계", "응용 분야", "3DES vs AES". Under "작동 원리", I should explain the encryption process, the three stages with keys, and the keying options. Maybe use a list or a table for keying options. Also mention the EDE process (Encrypt-Decrypt-Encrypt).

For "보안성과 한계", discuss how 3DES is more secure than DES but still has issues like smaller block size, vulnerability to meet-in-the-middle attacks, and why it's considered obsolete now. Mention the effective key length and how it's not as secure as it seems.

In "응용 분야", list where 3DES is still used, like in finance, legacy systems, and some ISO standards. But note that it's being phased out in favor of AES.

The comparison with AES should highlight why AES is better: key size, efficiency, block size. Maybe a table comparing 3DES and AES.

I need to ensure technical terms are explained. For example, explain what a block cipher is, or meet-in-the-middle attack briefly. Also, use code blocks if there's any technical code, but maybe not necessary here.

The document should be in Korean, so I need to translate terms properly. Check for accuracy in technical terminology. Also, include references or related links at the end, like NIST publications or related algorithms.

Make sure the structure flows well, each section logically follows the previous. Avoid overly technical jargon where possible, but maintain professionalism. Check that the content meets the 800-character minimum. Let me start drafting each section, ensuring each part addresses the points mentioned. Also, use markdown syntax correctly: headers, lists, tables, bold/italic where needed. Maybe add some emphasis on key points like security issues and key lengths.

Wait, the user mentioned using code blocks for technical content. Since 3DES is more about explanation than code examples, maybe not necessary unless there's a pseudocode. Probably safe to skip unless I can think of a relevant example. Otherwise, stick to descriptions.

Also, ensure that the document is objective, just presenting facts without bias. Mention that 3DES is deprecated but still used in some legacy systems. Don't make it sound too negative, just state the facts.

Let me outline each section step by step, then flesh them out. Make sure each subsection under H2 has enough detail. For example, in the working principle, explain each of the three encryption steps, the key sizes, and how the keying options affect security. Then in security, discuss the meet-in-the-middle attack's impact on effective security, block size issues, and why it's not recommended anymore.

In applications, provide specific examples like financial services, EMV, etc., and note that its use is declining. The comparison with AES should clearly show why AES is preferred now.

Finally, add a references section with links to NIST, Wikipedia, or other authoritative sources. Maybe also mention related algorithms like DES and AES for context.

Check for any missing elements from the user's requirements. Ensure the markdown formatting is correct, with proper headers, no markdown in code. Use appropriate Korean terms where possible. Avoid errors in technical details. For example, confirm the key length of 3DES (effective 112 bits with two keys, or 168 with three keys), and that the block size is 64 bits. Also, note that 3DES has been deprecated by NIST since 2017 or 2023.

Once all sections are drafted, review for clarity and flow, ensuring each part connects logically. Check word count to meet the minimum requirement. Then finalize the document.