SM4GCM

SM4GCM is an authenticated encryption algorithm that combines the SM4 block cipher with the Galois/Counter Mode (GCM). It provides both confidentiality and data integrity by encrypting plaintext and generating an authentication tag for associated data and ciphertext.

SM4 is a 128-bit block cipher with a 128-bit key, standardized in China for governmental and commercial use. SM4 serves as the underlying cipher in SM4GCM, with the GCM mode handling both encryption and authentication. In SM4-GCM, encryption uses a counter-based keystream to transform plaintext, while a GHASH computation processes associated data and ciphertext to produce a 128-bit authentication tag.

The security properties of SM4GCM rely on the standard assumptions of GCM: a unique IV (nonce) for each encryption, an unpredictable or random IV, and a tag that ensures integrity once verification is performed. The tag is transmitted alongside the ciphertext and validated during decryption. As with other GCM-based schemes, reusing an IV can compromise confidentiality and authenticity, so proper IV management is essential. The typical tag length is 128 bits, offering strong authenticity guarantees when correctly implemented.

Applications and implementation of SM4GCM appear in Chinese cryptographic ecosystems, where SM4 and its authenticated modes are standardized and supported by various software libraries and hardware accelerators. It is used for secure communications and data protection in contexts that require alignment with national standards for cryptography. Compatibility with non-SM4 systems depends on the broader use of GCM, but SM4GCM specifically requires SM4 support as the underlying cipher.

See also: SM4, GCM, authenticated encryption.