> # Cisco TrustSec FC Link Encryption Terminology

> The following Cisco TrustSec FC Link Encryption-related terms are used in this chapter:

> - Galois Counter Mode (GCM)—A block cipher mode of operation providing confidentiality and data-origin authentication.
> - Galois Message Authentication Code (GMAC)—A block cipher mode of operation providing only data-origin authentication. It is the authentication-only variant of GCM.
> - Security Association (SA)—A connection that handles the security credentials and controls how they propagate between switches. The SA includes parameters such as salt and keys.
> - Key—A 128-bit hexadecimal string that is used for frame encryption and decryption. The default value is zero.
> - Salt —A 32-bit hexadecimal number that is used during encryption and decryption. The same salt must be configured on both sides of the connection to ensure proper communication. The default value is zero.
> - Security Parameters Index (SPI) number—A 32-bit number that identifies the SA to be configured to the hardware. The range is from 256 to 4,294,967,295.

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