"Unsupported state or unable to authenticate data" with aes-128-gcm in Node - node.js

Question

I'm trying to implement encrypt/decrypt functions using aes-128-gcm as provided by node crypto. From my understanding, gcm encrypts the ciphertext but also hashes it and provides this as an 'authentication tag'. However, I keep getting the error: "Unsupported state or unable to authenticate data".
I'm not sure if this is an error in my code - looking at the encrypted ciphertext and auth tag, the one being fetched by the decrypt function is the same as the one produced by the encrypt function.
function encrypt(plaintext) {
// IV is being generated for each encryption
var iv = crypto.randomBytes(12),
cipher = crypto.createCipheriv(aes,key,iv),
encryptedData = cipher.update(plaintext),
tag;
// Cipher.final has been called, so no more encryption/updates can take place
encryptedData += cipher.final();
// Auth tag must be generated after cipher.final()
tag = cipher.getAuthTag();
return encryptedData + "$$" + tag.toString('hex') + "$$" + iv.toString('hex');
}
function decrypt(ciphertext) {
var cipherSplit = ciphertext.split("$$"),
text = cipherSplit[0],
tag = Buffer.from(cipherSplit[1], 'hex'),
iv = Buffer.from(cipherSplit[2], 'hex'),
decipher = crypto.createDecipheriv(aes,key,iv);
decipher.setAuthTag(tag);
var decryptedData = decipher.update(text);
decryptedData += decipher.final();
}
The error is being thrown by decipher.final().

Answer 1

In case if someone still tries to get a working example of encryption and decryption process.
I've left some comments that should be taken into consideration.
import * as crypto from 'crypto';
const textToEncode = 'some secret text'; // utf-8
const algo = 'aes-128-gcm';
// Key bytes length depends on algorithm being used:
// 'aes-128-gcm' = 16 bytes
// 'aes-192-gcm' = 24 bytes
// 'aes-256-gcm' = 32 bytes
const key = crypto.randomBytes(16);
const iv = crypto.randomBytes(16);
const cipher = crypto.createCipheriv(algo, key, iv);
const encrypted = Buffer.concat([
cipher.update(Buffer.from(textToEncode, 'utf-8')),
cipher.final(),
]);
const authTag = cipher.getAuthTag();
console.info('Value encrypted', {
valueToEncrypt: textToEncode,
encryptedValue: encrypted.toString('hex'),
authTag: authTag.toString('hex'),
});
// It's important to use the same authTag and IV that were used during encoding
const decipher = crypto.createDecipheriv(algo, key, iv);
decipher.setAuthTag(authTag);
const decrypted = Buffer.concat([
decipher.update(encrypted),
decipher.final(),
]);
console.info('Value decrypted', {
valueToDecrypt: encrypted.toString('hex'),
decryptedValue: decrypted.toString('utf-8'),
});

Answer 2

I managed to fix this: the issue was that I wasn't specifying an encoding type for cipher.final() and I was returning it within a String, so it wasn't returning a Buffer object, which decipher.final() was expecting.
To fix, I add 'utf-8' to 'hex' encoding parameters within my cipher.update and cipher.final, and vice versa in decipher.
Edited to add code example - note this is from 2018, so may be outdated now.
function encrypt(plaintext) {
// IV is being generated for each encryption
var iv = crypto.randomBytes(12),
cipher = crypto.createCipheriv(aes,key,iv),
encryptedData = cipher.update(plaintext, 'utf-8', 'hex'),
tag;
// Cipher.final has been called, so no more encryption/updates can take place
encryptedData += cipher.final('hex');
// Auth tag must be generated after cipher.final()
tag = cipher.getAuthTag();
return encryptedData + "$$" + tag.toString('hex') + "$$" + iv.toString('hex');
}
function decrypt(ciphertext) {
var cipherSplit = ciphertext.split("$$"),
text = cipherSplit[0],
tag = Buffer.from(cipherSplit[1], 'hex'),
iv = Buffer.from(cipherSplit[2], 'hex'),
decipher = crypto.createDecipheriv(aes, key, iv);
decipher.setAuthTag(tag);
var decryptedData = decipher.update(text, 'hex', 'utf-8');
decryptedData += decipher.final('utf-8');
}