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- **No, AES-256 is *not* fully quantum-resistant**, but it is considered **relatively resistant** compared to other symmetric encryption schemes.
- ### Here's why:
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- ### 🔒 **Quantum Impact on Symmetric Encryption (like AES):**
- Quantum computers can speed up brute-force attacks using **Grover’s algorithm**, which provides a **quadratic speedup** over classical brute-force:
- * **Classical brute-force on AES-256**:
- $2^{256}$ operations.
- * **Quantum brute-force with Grover’s algorithm**:
- $2^{128}$ operations — still **infeasible with any foreseeable quantum hardware**.
- ---
- ### 🔐 AES Key Size and Quantum Resistance:
- | AES Key Size | Classical Security | Quantum Security (Grover’s) |
- | ------------ | ------------------ | --------------------------- |
- | AES-128 | 128 bits | \~64 bits |
- | AES-256 | 256 bits | \~128 bits |
- So, **AES-256 provides \~128 bits of post-quantum security**, which is currently considered **safe** against quantum adversaries.
- ---
- ### 🧠 Summary:
- * **AES-256 is not quantum-proof**, but it is **quantum-resistant** in the sense that even with quantum computers, breaking it would still require **astronomical effort**.
- * For **long-term security**, AES-256 is preferred over AES-128.
- * AES will likely **remain useful even in a post-quantum world**, particularly if used in combination with quantum-safe key exchange algorithms.
- ---
- If you're concerned about **quantum security** in general, the **main focus** should be on replacing **asymmetric cryptography** (RSA, ECC) with **post-quantum algorithms**, since those are far more vulnerable to quantum attacks (e.g., via Shor’s algorithm).
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