qortal-ui/qortal-ui-crypto/api/transactions/chat/decryptChatMessage.js

import nacl from '../../deps/nacl-fast.js'
import Base58 from '../../deps/Base58.js'
import ed2curve from '../../deps/ed2curve.js'
import { Sha256 } from 'asmcrypto.js'


export const decryptChatMessage = (encryptedMessage, privateKey, recipientPublicKey, lastReference) => {
    let _encryptedMessage = Base58.decode(encryptedMessage)

    const _base58RecipientPublicKey = recipientPublicKey instanceof Uint8Array ? Base58.encode(recipientPublicKey) : recipientPublicKey
    const _recipientPublicKey = Base58.decode(_base58RecipientPublicKey)

    const _lastReference = lastReference instanceof Uint8Array ? lastReference : Base58.decode(lastReference)

    const convertedPrivateKey = ed2curve.convertSecretKey(privateKey)
    const convertedPublicKey = ed2curve.convertPublicKey(_recipientPublicKey)
    const sharedSecret = new Uint8Array(32);
    nacl.lowlevel.crypto_scalarmult(sharedSecret, convertedPrivateKey, convertedPublicKey);

    const _chatEncryptionSeed = new Sha256().process(sharedSecret).finish().result
    const _decryptedMessage = nacl.secretbox.open(_encryptedMessage, _lastReference.slice(0, 24), _chatEncryptionSeed)

    let decryptedMessage = ''

    _decryptedMessage === false ? decryptedMessage : decryptedMessage = new TextDecoder('utf-8').decode(_decryptedMessage);
    return decryptedMessage
}