Compression
A compression function mixes two fixed length inputs and produces a single fixed length output of the same size as one of the inputs. This can also be seen as that the compression function transforms one large fixed-length input into a shorter, fixed-length output.
For instance, input A might be 128 bits, input B 128 bits and they are compressed together to a single output of 128 bits. This is the same thing as if one single 256-bit input is compressed together to a single output of 128 bits.
Some compression functions have different size of the two inputs but the output usually is the same size as one of the inputs. For instance, input A might be 256 bits, input B 128 bits and they are compressed together to a single output of 128 bits. That is, a total of 384 input bits are compressed together to 128 output bits.
The mixing is done in such a way that full avalanche effect is achieved. That is, every output bit depends on every input bit.
Read more about this topic: One-way Compression Function
Famous quotes containing the word compression:
“Do they [the publishers of Murphy] not understand that if the book is slightly obscure it is because it is a compression and that to compress it further can only make it more obscure?”
—Samuel Beckett (1906–1989)
“The triumphs of peace have been in some proximity to war. Whilst the hand was still familiar with the sword-hilt, whilst the habits of the camp were still visible in the port and complexion of the gentleman, his intellectual power culminated; the compression and tension of these stern conditions is a training for the finest and softest arts, and can rarely be compensated in tranquil times, except by some analogous vigor drawn from occupations as hardy as war.”
—Ralph Waldo Emerson (1803–1882)