Encryption vs Hashing

Why they differ

Encryption can be reversed by whoever holds the key; hashing is one-way and can never give the original data back.

Networking

Scrambling data with a secret key so only someone holding the matching key can read it.

Formal

A mathematical process that uses a key to transform readable data into a form that cannot be read, such that only a holder of the matching key can turn it back. The key may be shared by both sides (symmetric) or split into a public and a private part.

In plain English

Like writing a letter in a secret code only you and a friend know - anyone who steals the letter sees only gibberish.

In practice

A nurse in a municipality's home care leaves her work laptop on the bus; its disk is encrypted, so whoever finds it cannot read the citizens' care notes without her password.

Why it matters

Data is copied, lost and overheard all the time; with encryption a stolen disk or tapped connection reveals nothing readable, which can turn a serious data breach into a minor incident - as long as the key stays safe.

Hashing

Cryptography

Turning any amount of data into a short, fixed-length value that changes completely if even one character changes.

Formal

A one-way calculation that maps input of any size to a value of fixed size. The same input always gives the same result, the result cannot be turned back into the input, and finding two inputs with the same result is practically impossible.

In plain English

Like a fingerprint - it identifies a person without containing the person, and nobody can rebuild someone from their fingerprint.

In practice

A Danish web shop stores only a slow, deliberately costly hash of each customer's password. When its database is stolen, the attackers get hashes they must guess their way through one by one, not passwords.

Why it matters

It is how systems spot tampering with files and messages, and how they check passwords without having to keep them.

Shared connections

TLS