Baileys/src/Utils/legacy-msgs.ts

import { Boom } from '@hapi/boom'
import { randomBytes } from 'crypto'
import { AuthenticationCreds, Contact, CurveKeyPair, DisconnectReason, LegacyAuthenticationCreds, WATag } from '../Types'
import { decodeBinaryNodeLegacy, jidNormalizedUser } from '../WABinary'
import { aesDecrypt, Curve, hkdf, hmacSign } from './crypto'
import { BufferJSON } from './generics'

export const newLegacyAuthCreds = () => ({
	clientID: randomBytes(16).toString('base64')
}) as LegacyAuthenticationCreds

export const decodeWAMessage = (
	message: Buffer | string,
	auth: { macKey: Buffer, encKey: Buffer },
	fromMe: boolean = false
) => {
	let commaIndex = message.indexOf(',') // all whatsapp messages have a tag and a comma, followed by the actual message
	if(commaIndex < 0) {
		throw new Boom('invalid message', { data: message })
	} // if there was no comma, then this message must be not be valid

	if(message[commaIndex + 1] === ',') {
		commaIndex += 1
	}

	let data = message.slice(commaIndex + 1, message.length)

	// get the message tag.
	// If a query was done, the server will respond with the same message tag we sent the query with
	const messageTag: string = message.slice(0, commaIndex).toString()
	let json: any
	let tags: WATag
	if(data.length) {
		const possiblyEnc = (data.length > 32 && data.length % 16 === 0)
		if(typeof data === 'string' || !possiblyEnc) {
			json = JSON.parse(data.toString()) // parse the JSON
		} else {
			try {
				json = JSON.parse(data.toString())
			} catch{
				const { macKey, encKey } = auth || {}
				if(!macKey || !encKey) {
					throw new Boom('recieved encrypted buffer when auth creds unavailable', { data: message, statusCode: DisconnectReason.badSession })
				}

				/*
                    If the data recieved was not a JSON, then it must be an encrypted message.
                    Such a message can only be decrypted if we're connected successfully to the servers & have encryption keys
                */
				if(fromMe) {
					tags = [data[0], data[1]]
					data = data.slice(2, data.length)
				}

				const checksum = data.slice(0, 32) // the first 32 bytes of the buffer are the HMAC sign of the message
				data = data.slice(32, data.length) // the actual message
				const computedChecksum = hmacSign(data, macKey) // compute the sign of the message we recieved using our macKey

				if(checksum.equals(computedChecksum)) {
					// the checksum the server sent, must match the one we computed for the message to be valid
					const decrypted = aesDecrypt(data, encKey) // decrypt using AES
					json = decodeBinaryNodeLegacy(decrypted, { index: 0 }) // decode the binary message into a JSON array
				} else {
					throw new Boom('Bad checksum', {
						data: {
							received: checksum.toString('hex'),
							computed: computedChecksum.toString('hex'),
							data: data.slice(0, 80).toString(),
							tag: messageTag,
							message: message.slice(0, 80).toString()
						},
						statusCode: DisconnectReason.badSession
					})
				}
			}
		}
	}

	return [messageTag, json, tags] as const
}

/**
* Once the QR code is scanned and we can validate our connection, or we resolved the challenge when logging back in
* @private
* @param json
*/
export const validateNewConnection = (
	json: { [_: string]: any },
	auth: LegacyAuthenticationCreds,
	curveKeys: CurveKeyPair
) => {
	// set metadata: one's WhatsApp ID [cc][number]@s.whatsapp.net, name on WhatsApp, info about the phone
	const onValidationSuccess = () => {
	   const user: Contact = {
			id: jidNormalizedUser(json.wid),
			name: json.pushname
		}
	   return { user, auth, phone: json.phone }
	}

	if(!json.secret) {
	   // if we didn't get a secret, we don't need it, we're validated
	   if(json.clientToken && json.clientToken !== auth.clientToken) {
			auth = { ...auth, clientToken: json.clientToken }
	   }

	   if(json.serverToken && json.serverToken !== auth.serverToken) {
		   auth = { ...auth, serverToken: json.serverToken }
	   }

	   return onValidationSuccess()
	}

	const secret = Buffer.from(json.secret, 'base64')
	if(secret.length !== 144) {
	   throw new Error ('incorrect secret length received: ' + secret.length)
	}

	// generate shared key from our private key & the secret shared by the server
	const sharedKey = Curve.sharedKey(curveKeys.private, secret.slice(0, 32))
	// expand the key to 80 bytes using HKDF
	const expandedKey = hkdf(sharedKey as Buffer, 80, { })

	// perform HMAC validation.
	const hmacValidationKey = expandedKey.slice(32, 64)
	const hmacValidationMessage = Buffer.concat([secret.slice(0, 32), secret.slice(64, secret.length)])

	const hmac = hmacSign(hmacValidationMessage, hmacValidationKey)

	if(!hmac.equals(secret.slice(32, 64))) {
	   // if the checksums didn't match
	   throw new Boom('HMAC validation failed', { statusCode: 400 })
	}

	// computed HMAC should equal secret[32:64]
	// expandedKey[64:] + secret[64:] are the keys, encrypted using AES, that are used to encrypt/decrypt the messages recieved from WhatsApp
	// they are encrypted using key: expandedKey[0:32]
	const encryptedAESKeys = Buffer.concat([
	   expandedKey.slice(64, expandedKey.length),
	   secret.slice(64, secret.length),
	])
	const decryptedKeys = aesDecrypt(encryptedAESKeys, expandedKey.slice(0, 32))
	// set the credentials
	auth = {
	   encKey: decryptedKeys.slice(0, 32), // first 32 bytes form the key to encrypt/decrypt messages
	   macKey: decryptedKeys.slice(32, 64), // last 32 bytes from the key to sign messages
	   clientToken: json.clientToken,
	   serverToken: json.serverToken,
	   clientID: auth.clientID,
	}
	return onValidationSuccess()
}

export const computeChallengeResponse = (challenge: string, auth: LegacyAuthenticationCreds) => {
	const bytes = Buffer.from(challenge, 'base64') // decode the base64 encoded challenge string
	const signed = hmacSign(bytes, auth.macKey).toString('base64') // sign the challenge string with our macKey
	return ['admin', 'challenge', signed, auth.serverToken, auth.clientID] // prepare to send this signed string with the serverToken & clientID
}

export const useSingleFileLegacyAuthState = (file: string) => {
	// require fs here so that in case "fs" is not available -- the app does not crash
	const { readFileSync, writeFileSync, existsSync } = require('fs')
	let state: LegacyAuthenticationCreds

	if(existsSync(file)) {
		state = JSON.parse(
			readFileSync(file, { encoding: 'utf-8' }),
			BufferJSON.reviver
		)
		if(typeof state.encKey === 'string') {
			state.encKey = Buffer.from(state.encKey, 'base64')
		}

		if(typeof state.macKey === 'string') {
			state.macKey = Buffer.from(state.macKey, 'base64')
		}
	} else {
		state = newLegacyAuthCreds()
	}

	return {
		state,
		saveState: () => {
			const str = JSON.stringify(state, BufferJSON.replacer, 2)
			writeFileSync(file, str)
		}
	}
}

export const getAuthenticationCredsType = (creds: LegacyAuthenticationCreds | AuthenticationCreds) => {
	if('clientID' in creds && !!creds.clientID) {
		return 'legacy'
	}

	if('noiseKey' in creds && !!creds.noiseKey) {
		return 'md'
	}
}