!!! Overview[1]
[{$pagename}] (Galois/Counter Mode) ([GCM]) is a [Block Cipher] Mode of operation that uses universal hashing over a binary Galois field to provide [authenticated|authentication] [encryption].

[{$pagename}] is a mode of operation for [Symmetric Key] cryptographic [Block Ciphers] that has been widely adopted because of its efficiency and performance. [{$pagename}] throughput rates for state of the art, high speed communication channels can be achieved with reasonable hardware resources. 

The operation is an [authenticated] [Encryption] [algorithm] designed to provide both data [integrity] and [confidentiality]. [{$pagename}] is defined for [Block Ciphers] with a block size of 128 bits. 

[Galois Message Authentication Code] ([GMAC]) is an [authentication]-only variant of the [{$pagename}] which can be used as an incremental [Message Authentication Code] ([MAC]). Both [GCM] and [GMAC] can accept [Initialization Vectors] of arbitrary length.

Different [Block Cipher] modes of operation can have significantly different performance and efficiency characteristics, even when used with the same block cipher. [{$pagename}] can take full advantage of parallel processing and implementing GCM can make efficient use of an instruction pipeline or a hardware pipeline. In contrast, the [Cipher Block Chaining] ([CBC]) mode of operation incurs significant pipeline stalls that hamper its efficiency and performance.

!! More Information
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* [#1] - [The Galois/Counter Mode of Operation (GCM)|http://csrc.nist.gov/groups/ST/toolkit/BCM/documents/proposedmodes/gcm/gcm-spec.pdf|target='_blank'] - based on information obtained 2013-04-10