64gcm

64gcm is a designation related to encryption algorithms and modes of operation. Specifically, it refers to the use of the Galois/Counter Mode (GCM) with a 64-bit block size. GCM is a widely adopted authenticated encryption mode that provides both confidentiality and integrity for data. It combines a counter mode encryption with a Galois field multiplication-based authentication tag.

The block size of an encryption algorithm refers to the fixed-size chunk of data that the algorithm processes at a time. Common block sizes include 128 bits. While 128-bit block sizes are prevalent, GCM can theoretically be implemented with different block sizes, though 128 bits is the standard and most common configuration. A 64-bit block size would imply that the underlying block cipher operates on 64 bits of data, which is less common in modern symmetric encryption standards compared to 128-bit blocks.

The use of GCM provides strong security guarantees. Confidentiality is achieved through the counter mode, which encrypts a unique counter value for each block. Integrity and authenticity are provided by the Galois field multiplication, which generates an authentication tag that can be verified by the recipient. If the data is tampered with, the tag will not match, indicating a compromise.

The choice of block size can have implications for performance and security. However, when discussing 64gcm, it's important to note that GCM is standardized for a 128-bit block size. Implementations or discussions involving a 64-bit block size might be non-standard or relate to specific legacy or experimental contexts. Standard GCM, as specified in NIST SP 800-38D, operates with a 128-bit block size.