createHash

Learn to create hashes with crypto.createHash.

createHash

crypto.createHash(algorithm) creates a hash generator. You feed data with update(data) and take the hash with digest(format). Chaining is common.

Example: crypto.createHash("sha256").update("hello").digest("hex"). "sha256" is the algorithm; "hex" is the output format (hexadecimal). Other formats: "base64" gives a shorter string; "latin1" is rarer. update() can be called multiple times; data is concatenated. After digest() the generator cannot be reused. SHA-256 output is always 64 hex characters (256 bits = 32 bytes). For password storage sha256 alone is not enough; salt and slow algorithms are needed.

update and digest

update() can feed data piece by piece. For large files you stream data in; you use less memory. digest() finalizes and returns the hash.

Example: const h = crypto.createHash("sha256"); h.update("part1"); h.update("part2"); h.digest("hex");. This gives the same hash as update("part1part2") because data is concatenated. digest("hex") returns a hex string; digest("base64") a shorter string. After calling digest() calling update() throws; the generator is single-use. To hash the same data again you need a new createHash call. This is why chaining is practical: it finishes all steps in one line.

Exercise Hash a string with SHA-256

Import with const crypto = require("node:crypto");. Get a hash with const hash = crypto.createHash("sha256").update("merhaba").digest("hex");. Print the first 16 characters with console.log(hash.slice(0, 16)).

Show example solution

const crypto = require("node:crypto");
const hash = crypto.createHash("sha256").update("merhaba").digest("hex");
console.log(hash.slice(0, 16));

Test yourself

Complete the createHash call

const hash = crypto.____("sha256").update("merhaba").digest("hex");

Show answer

const hash = crypto.createHash("sha256").update("merhaba").digest("hex");

Match each step to its function

createHash

Creates generator
update

Feeds data
digest

Finalizes hash
"hex"

Hexadecimal format
What kind of value does digest("hex") return?
```
crypto.createHash("sha256").update("x").digest("hex")
```
- A hexadecimal string
- A binary buffer
- A number
- Date nesnesi
Show answer

A hexadecimal string — The hex format gives a hex string.

Next lesson: randomBytes

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