crypto module

Learn the crypto module and hash functions.

The crypto module

Node.js's built-in crypto module does cryptographic operations: hashing, random byte generation, encryption and decryption. You do not need a separate package; the safest way to import is with the node: prefix: require("node:crypto").

Core concepts: a hash summarizes data into a fixed length; it is one-way and irreversible. HMAC adds a key to a hash; only the key holder can verify. AES is two-way symmetric encryption; it encrypts and decrypts data with a key. randomBytes generates cryptographically secure random bytes; unlike Math.random it is unpredictable. This module underlies password storage, JWT signing and the HTTPS handshake.

Hash properties

A hash function turns data into a fixed-length string. The same input always gives the same output (deterministic). You cannot recover the input from the output (one-way).

Example: crypto.createHash("sha256").update("hello").digest("hex") always gives a 64-character hex string. sha256 is one of the most common algorithms; md5 and sha1 are weak and not used for security. update() feeds data, digest("hex") returns the hash as a string. Hashes are used for password storage (with salt), file integrity checks, and detecting data changes. If two files have the same hash, their content is the same (most likely).

Exercise Import the crypto module and test it

Import with const crypto = require("node:crypto");. Print "Crypto ready" with console.log.

Show example solution

const crypto = require("node:crypto");
console.log("Crypto ready");

Test yourself

What does crypto.createHash do?
```
crypto.createHash("sha256")
```
- Encrypts the data
- Decrypts the data
- Generates random bytes
- Creates a hash generator
Show answer

Creates a hash generator — createHash creates a hash generator.

Complete the import

const crypto = require(____);

Show answer

const crypto = require("node:crypto");

Match each piece to its role

createHash

Creates a hash
randomBytes

Generates random bytes
createHmac

Keyed hash
createCipheriv

Encrypts

Next lesson: createHash

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