Bytes and Hex Text

Part of the Auth and Security section of Coddy's Node.js journey. Lesson 1 of 24.

Cryptographic functions work with bytes. A byte is a number from 0 to 255. UTF-8 encodes text as bytes, and a Buffer holds those bytes in Node. Hexadecimal, or hex, writes each byte as two characters using digits 0 to 9 and letters a to f. This makes bytes convenient to store as text.

const bytes = Buffer.from('Ok', 'utf8');
bytes.toString('hex'); // '4f6b'
Buffer.from('4f6b', 'hex').toString('utf8'); // 'Ok'

The byte for the letter O is 79 in decimal, written 4f in hex.

This conversion is reversible: it changes the representation, not the information. Encoding a password as hex does not protect it. A password hash is checked by recomputing a derived value instead of decoding it. Here the inputs are ordinary text, and the exercise returns their hex representation so you can compare both forms.

Challenge

Easy

This is a small practice project. Its setup is provided; edit only exercise.js.

Return a hex field containing the supplied text encoded as UTF-8 bytes and then hex. POST {"text":"Hi"} to /result returns {"hex":"4869"}. Text Ada returns 416461.

Try it yourself

export function exercise({ text }) {
    return { hex: text };
}

All lessons in Auth and Security

1Passwords

Bytes and Hex TextDeriving a Password Key A Fresh Salt Never Store Passwords Comparing Key Bytes Checking a Password Signup Rules

4Owners and Safety

Only Your Notes Admin Roles

Security Headers

Counting Failed Attempts An Expiring Counter Rate Limiting Logins Input Is Hostile

2Sessions and Cookies

Remembering with Cookies A Session Lookup Login Sessions Routes Behind a Login

Logging Out

Cookie Flags

3Tokens

What a JWT Is Signing Tokens

Verifying Tokens

Token Expiry

Practice on your own: Express playground