Instances of the Decipher class are used to decrypt data. The class can be used in one of two ways:
- As a
streamthat is both readable and writable, where plain encrypted data is written to produce unencrypted data on the readable side, or - Using the
decipher.update()anddecipher.final()methods to produce the unencrypted data.
The createDecipheriv method is used to create Decipher instances. Decipher objects are not to be created directly using the new keyword.
Example: Using Decipher objects as streams:
import { Buffer } from 'node:buffer';
const {
scryptSync,
createDecipheriv,
} = await import('node:crypto');
const algorithm = 'aes-192-cbc';
const password = 'Password used to generate key';
// Key length is dependent on the algorithm. In this case for aes192, it is
// 24 bytes (192 bits).
// Use the async `crypto.scrypt()` instead.
const key = scryptSync(password, 'salt', 24);
// The IV is usually passed along with the ciphertext.
const iv = Buffer.alloc(16, 0); // Initialization vector.
const decipher = createDecipheriv(algorithm, key, iv);
let decrypted = '';
decipher.on('readable', () => {
let chunk;
while (null !== (chunk = decipher.read())) {
decrypted += chunk.toString('utf8');
}
});
decipher.on('end', () => {
console.log(decrypted);
// Prints: some clear text data
});
// Encrypted with same algorithm, key and iv.
const encrypted =
'e5f79c5915c02171eec6b212d5520d44480993d7d622a7c4c2da32f6efda0ffa';
decipher.write(encrypted, 'hex');
decipher.end();
Example: Using Decipher and piped streams:
import {
createReadStream,
createWriteStream,
} from 'node:fs';
import { Buffer } from 'node:buffer';
const {
scryptSync,
createDecipheriv,
} = await import('node:crypto');
const algorithm = 'aes-192-cbc';
const password = 'Password used to generate key';
// Use the async `crypto.scrypt()` instead.
const key = scryptSync(password, 'salt', 24);
// The IV is usually passed along with the ciphertext.
const iv = Buffer.alloc(16, 0); // Initialization vector.
const decipher = createDecipheriv(algorithm, key, iv);
const input = createReadStream('test.enc');
const output = createWriteStream('test.js');
input.pipe(decipher).pipe(output);
Example: Using the decipher.update() and decipher.final() methods:
import { Buffer } from 'node:buffer';
const {
scryptSync,
createDecipheriv,
} = await import('node:crypto');
const algorithm = 'aes-192-cbc';
const password = 'Password used to generate key';
// Use the async `crypto.scrypt()` instead.
const key = scryptSync(password, 'salt', 24);
// The IV is usually passed along with the ciphertext.
const iv = Buffer.alloc(16, 0); // Initialization vector.
const decipher = createDecipheriv(algorithm, key, iv);
// Encrypted using same algorithm, key and iv.
const encrypted =
'e5f79c5915c02171eec6b212d5520d44480993d7d622a7c4c2da32f6efda0ffa';
let decrypted = decipher.update(encrypted, 'hex', 'utf8');
decrypted += decipher.final('utf8');
console.log(decrypted);
// Prints: some clear text data