Compression is a reduction in the number of bits needed to represent data.
Compressing data can save storage capacity, speed file transfer, and decrease
costs for storage hardware and network bandwidth.
One type of compression is lossless. Lossless compression doesn’t reduce the quality of the file at all.
No data is lost, so lossless compression allows a file to be recreated exactly as it was when originally
created. You can remember lossless by thinking that the data is not lost, lossless.
Another type of compression is Lossy. Lossy compression removes some of a file’s original data in
order to reduce the file size. This might mean reducing the numbers of colours in an image or
reducing the number of samples in a sound file. This can result in a small loss of quality of an image
or sound file.
Symmetric encryption’s job is to take readable data, scrambles it to make it unreadable then
unscramble it again when it’s needed. The most important thing to remember about symmetric
encryption is that both sides—the encrypter, and the decrypter—need access to the same key.
Asymmetric encryption also takes readable data, scrambles it, and unscrambles it again at the other
end, but there’s a twist: a different key is used for each end. Encrypters use a public key to scramble
the data, and decrypters use the matching private (secret) key on the other end to unscramble it
Hashing is what is actually happening when you hear about passwords being “encrypted”. Strictly
speaking, hashing is not a form of encryption, though it does use cryptography. Hashing takes data
and creates a hash out of it, a string of data with three important properties: 1.the same data will
always produce the same hash, 2. it’s impossible to reverse it back to the original data given knowledge
of only the hash, 3. it’s infeasible to create another string of data that will create the same hash (called
a “collision” in crypto parlance)