SM4 (国密) Encrypt & Decrypt

A: Standard Origin: SM4 is a commercial cryptography standard released by China's State Cryptography Administration (2012), AES is a federal standard released by the U.S. NIST (2001). Key Length: SM4 only supports 128-bit keys, AES supports 128/192/256 bits. Algorithm Structure: SM4 is based on Feistel structure (32 rounds), AES is based on SPN structure (10/12/14 rounds). Security: SM4 has comparable security to AES-128, both with 2^128 complexity. Performance: AES performs better on platforms with hardware acceleration, SM4 has comparable performance in software implementations. Compliance: In China's critical sectors, SM4 complies with Cryptography Law requirements, AES does not. Recommendation: Use SM4 for critical sectors within China, use AES for international applications.

A: According to the Cryptography Law of the People's Republic of China (effective January 1, 2020) and related industry regulations: Mandatory Use: Commercial cryptography products involving national security, national economy and people's livelihood, and social public interests must be certified by the State Cryptography Administration and use national cryptography algorithms (including SM4). Recommended Use: Critical sectors such as finance (banking, securities, insurance), government (e-government, electronic licenses), telecommunications (mobile communications, IoT), energy (electricity, petroleum), and transportation (railways, civil aviation). Optional Use: General commercial applications and personal applications can choose independently, but using national cryptography algorithms helps improve security and compliance. Note: Specific requirements are subject to the latest laws, regulations, and industry standards.

A: SM4's choice of a 128-bit key was based on balancing security and performance considerations. Sufficient Security: The breaking complexity of a 128-bit key is 2^128 (approximately 3.4×10^38), would take billions of years even using all computers globally. Performance Advantage: 128-bit keys perform better than 256-bit keys, with faster encryption speeds. International Standard: AES-128 is also a widely used standard, proving that 128-bit keys are sufficiently secure. Future Extension: If higher security is needed in the future, variants or upgraded versions of SM4 can be used. Practical Application: For the vast majority of application scenarios, SM4's 128-bit key already provides sufficient security.

A: Compatibility Considerations: SM4 is primarily used in China with limited international support. If the application needs to be internationalized, it's recommended to support both SM4 and AES. Dual Algorithm Approach: 1) Negotiation Mechanism: Client and server negotiate the algorithm to use (SM4 within China, AES abroad). 2) Dual Encryption: Use both SM4 and AES encryption simultaneously to ensure decryption both domestically and internationally. 3) Algorithm Identification: Identify the algorithm used in the data, and select the algorithm based on the identifier during decryption. Library Support: OpenSSL 1.1.1+ supports SM4, GmSSL is a specialized national cryptography algorithm library.

A: SM4, SM2, and SM3 are three core components of the national cryptography algorithm system, often used together. SM4: Symmetric encryption algorithm, used for data encryption, fast speed, suitable for large amounts of data. SM2: Asymmetric encryption and digital signature algorithm, used for key exchange and signing, high security but slower speed. SM3: Hash algorithm, used for data integrity verification and message digests. Combined Use: Typical workflow is to use SM2 to exchange SM4 keys, use SM4 to encrypt data, use SM3 to verify integrity, and use SM2 for signing. National Cryptography Suite: SM2-SM3-SM4 is a complete national cryptography algorithm suite, similar to the RSA-SHA256-AES suite. Application: National cryptography SSL certificates use the SM2-SM3-SM4 suite, replacing the traditional RSA-SHA256-AES suite.

A: Standard Test Vectors: The GM/T 0002-2012 standard provides official test vectors. For example, using specific keys and plaintext, SM4 should produce specific ciphertext. Comparison Tools: Use multiple independent implementations (such as OpenSSL, GmSSL, this tool) to encrypt the same data and compare results for consistency. Decryption Verification: Decrypt immediately after encryption to check if the original data can be recovered. Certified Products: If used for commercial cryptography products, use cryptographic modules certified by the State Cryptography Administration. Open Source Implementation: GmSSL (GitHub) is an authoritative open-source implementation of national cryptography algorithms and can be used as a reference.