We’ve come a long way in usability of these tools since my first exposure using Password Safe. Services such as Bitwarden, LastPass, 1Password, and so on have made it extremely easy to get on board with using a single master password to decrypt a database of passwords (that are ideally random, long and unique), clients working across multiple devices and OS, vault storage in the cloud. They also generally come with 2FA options, sounds super secure.

I’ve been using these types of services for a while (LastPass originally then migrating to Bitwarden a few years ago, Bitwarden is great), they really do make life easier and solve the password re-use problem. But I got curious recently as to how these services are supposedly secure, after researching how my current provider (Bitwarden) works I thought it useful to document here in simple language what’s going on.

I’ll assume these providers all use a similar scheme, they tend to use flashy marketing saying it’s all awesome, listing accreditations and then direct you to white-papers for the details. I read through the paper for Bitwarden and I can see why it’s probably not shouted far and wide because it appears not particularly secure at a glance, but it is pretty good, though it does have pitfalls that should be made clearer.

Encryption keys

Master Password ($MASTER_PW)

This is your (changeable) password to login to the cloud service and decrypt the vault to retrieve your passwords. This theoretically never leaves your local machine.

The Vault ($VAULT_KEY)

When your account is created a symmetric key is generated locally, generally in your browser. This key will then be used to encrypt and decrypt all the data stored in your vault.



The symmetric vault key is encrypted and stored using symmetric encryption keyed with $MASTER_PW.


The vault is stored in the “cloud” encrypted with $VAULT_KEY.


When you log in to a service you send a hash of $LOGIN+$MASTER_PW to the remote service, if you have enabled 2FA the service may require this to authenticate you (note: this 2FA has nothing to do with your vault), if you have successfully authenticated you will receive back a copy of the encrypted vault and $ENC_VAULTKEY.

The local client will then decrypt $ENC_VAULTKEY to further decrypt the vault itself.

Master Password Change

When you change your master password $MASTER_PW and $ENC_VAULTKEY will change, however $VAULT_KEY will not.

The One Ring

In general there is one original key, the $VAULT_KEY that if compromised is not good. If the $VAULT_KEY is compromised the vault can be decrypted, even after a $MASTER_PW change. So in summary the service stores your vault and $ENC_VAULTKEY, theoretically locking access to both of those behind potential 2FA and $MASTER_PW.

It still is a pretty good system but pitfalls should be obvious after reading this, be careful where you unlock the vault.