Unraveling the Mystery: Why the SHA-256 Hash Computed by CryptoJS is Different

Are you struggling to understand why the SHA-256 hash computed by CryptoJS is different from what you expected? You’re not alone! Many developers have encountered this issue, and it’s not because CryptoJS is faulty, but rather due to some crucial nuances in how the library handles hashing. In this article, we’ll delve into the reasons behind this discrepancy and provide you with clear instructions on how to get the correct hash value.

What is SHA-256 and Why is it Important?

SHA-256 (Secure Hash Algorithm 256) is a widely used cryptographic hash function that produces a 256-bit (32-byte) hash value from input data of any size. This one-way function is designed to be collision-resistant, meaning it’s computationally infeasible to find two different input strings with the same output hash.

SHA-256 is crucial in various cryptographic applications, such as:

• Data integrity: Hashing data to ensure its integrity and detect any tampering.
• Password storage: Storing passwords securely using salted and hashed values.
• Digital signatures: Creating digital signatures to verify the authenticity of messages.

The CryptoJS Library and SHA-256

CryptoJS is a popular JavaScript library for cryptographic functions, including SHA-256. It provides an easy-to-use interface for hashing data, but, as we’ll see, there are some gotchas to be aware of.

const CryptoJS = require('crypto-js');

const data = 'Hello, World!';
const hash = CryptoJS.SHA256(data);
console.log(hash.toString());

This code snippet should give you a SHA-256 hash value, but is it the correct one?

The Problem: Character Encoding and Padding

The issue lies in how CryptoJS handles character encoding and padding. By default, CryptoJS assumes the input data is a string and encodes it as UTF-16 (a 16-bit Unicode encoding scheme). This can lead to different hash values depending on the encoding used.

To further complicate matters, CryptoJS pads the input data with null bytes (‘\x00’) to ensure the data length is a multiple of the block size (64 bytes for SHA-256). This padding can also affect the final hash value.

Solution 1: Using UTF-8 Encoding

const textEncoder = new TextEncoder('utf-8');
const data = 'Hello, World!';
const encodedData = textEncoder.encode(data);
const hash = CryptoJS.SHA256(encodedData);
console.log(hash.toString());

const data = 'Hello, World!';
const hash = CryptoJS.SHA256(data, { 'padding': CryptoJS.pad.NoPadding });
console.log(hash.toString());

const binaryData = new Uint8Array([0x01, 0x02, 0x03, 0x04]);
const hash = CryptoJS.SHA256(binaryData);
console.log(hash.toString());