AES-256, AES-128 Complete Guide to Encryption Algorithms (DES, AES, RSA, SHA)
Summary
This post compares and analyzes the core concepts and differences of symmetric-key (DES, SEED, AES), asymmetric-key (Diffie-Hellman, RSA, ECC), and hash (MD5, SHA) encryption algorithms that frequently appear in the Information Processing Engineer practical exam, and provides practice questions.
💡 Short-answer practice problems for the Information Processing Engineer exam are at the end of this post. It is recommended to solve the problems multiple times.
1. Symmetric-Key Encryption Algorithms 🔑
Symmetric-key encryption uses the same key for both encryption and decryption. Key management is crucial since there is only one key, but it has the advantage of fast encryption speeds.
Key Algorithm Comparison
| Category | DES (Data Encryption Standard) | SEED | AES (Advanced Encryption Standard) |
|---|---|---|---|
| Developed by | IBM (1975) | KISA (Korea Internet & Security Agency, 1999) | Joan Daemen, Vincent Rijmen (2001) |
| Block Size | 64-bit | 128-bit | 128-bit |
| Key Length | 56-bit (actually 64-bit) | 128, 256-bit | 128, 192, 256-bit |
| Structure | Feistel Structure | Feistel Structure | SPN (Substitution-Permutation Network) |
| Security | Vulnerable. No longer recommended for use. | Secure. Used as a domestic standard in Korea. | Very secure. Widely used as the current standard. |
| Features | An early standard. Complemented by 3DES but replaced by AES. | South Korea's first standard encryption algorithm. (Replaced by ARIA in 2004) | The US standard that replaced DES. Most widely used. |
💡 Key Takeaways:
- DES: The first standard, but now vulnerable due to its short key length.
- AES: The most secure and widely used symmetric-key algorithm today.
- SEED: The first South Korean symmetric-key algorithm.
2. Asymmetric-Key (Public-Key) Encryption Algorithms 👥
Asymmetric-key encryption uses separate keys for encryption and decryption. One key is made public (public key), while the other is kept secret (private key). It is slower than symmetric-key encryption but has the significant advantage of allowing secure key exchange.
Key Algorithm Comparison
| Category | Diffie-Hellman | RSA (Rivest-Shamir-Adleman) | ECC (Elliptic Curve Cryptography) |
|---|---|---|---|
| Primary Use | Key Exchange | Encryption, Digital Signatures | Encryption, Digital Signatures |
| Underlying Principle | Discrete Logarithm Problem | Difficulty of Integer Factorization | Elliptic Curve Discrete Logarithm Problem |
| Key Length | Relatively long (e.g., 2048-bit) | Relatively long (e.g., 2048-bit) | Relatively short (e.g., 256-bit) |
| Performance | Moderate | Slow | Fast |
| Security | Secure | Secure | Very secure (high security with a short key) |
| Features | The first public-key algorithm. | The most widely used public-key algorithm. | An alternative to RSA, providing the same level of security with a shorter key. Advantageous for IoT and mobile environments. |
💡 Key Takeaways:
- Diffie-Hellman: The first public-key algorithm.
- RSA: Based on the difficulty of integer factorization and is the most popular asymmetric-key algorithm.
- ECC: An alternative to RSA that offers high security with a short key length, resulting in excellent performance. Suitable for mobile environments.
3. Hash Encryption Algorithms ⛓️
A hash algorithm is a one-way function that converts data of arbitrary length into a fixed-length hash value. It is irreversible and is mainly used for data integrity verification or password storage.
Key Algorithm Comparison
| Category | MD5 (Message-Digest Algorithm 5) | SHA-1 (Secure Hash Algorithm 1) | SHA-2 (SHA-256/384/512) |
|---|---|---|---|
| Developed by | Ronald Rivest (1991) | NSA (1995) | NSA (2001) |
| Hash Size | 128-bit | 160-bit | 256, 384, 512-bit |
| Security | Very vulnerable (collision found) | Vulnerable (collision found) | Secure |
| Features | Widely used in the past but now prohibited. | More secure than MD5, but its use is now discouraged. | The most widely used hash algorithm today. The number indicates the hash size. |
💡 Key Takeaways:
- MD5, SHA-1: Collision vulnerabilities have been found, so they should no longer be used.
- SHA-2 family (SHA-256, etc.): The most widely used and secure hash algorithm, currently the security standard, corresponding to AES key lengths.
📝 Exam Preparation Problems
Now, let's solve some practice problems based on what we've learned.
| Problem | The following are descriptions of symmetric-key and asymmetric-key encryption algorithms. Fill in the blanks with the most appropriate terms. ( ① ) is an encryption method where the same key is used for both encryption and decryption. On the other hand, ( ② ) is an encryption method where different keys are used for encryption and decryption, with the disadvantage of slower key generation and encryption/decryption speeds. |
| Your Answer | |
| Correct Answer | Reveal Answer |
| Problem | Developed by IBM in 1975, this was designated as the data encryption standard by the US Department of Defense. It has a block size of 64 bits and uses a 56-bit key. It is no longer recommended for use due to security vulnerabilities related to its key length. What is the encryption algorithm described? |
| Your Answer | |
| Correct Answer | Reveal Answer |
| Problem | This is a representative asymmetric-key encryption algorithm based on the difficulty of integer factorization. It provides not only encryption but also digital signature functions. It is the most widely used public-key encryption algorithm today. |
| Your Answer | |
| Correct Answer | Reveal Answer |