---
layout: "docs"
page_title: "Seal/Unseal"
sidebar_title: "Seal/Unseal"
sidebar_current: "docs-concepts-seal"
description: |-
  A Vault must be unsealed before it can access its data. Likewise, it can be sealed to lock it down.
---

# Seal/Unseal

When a Vault server is started, it starts in a _sealed_ state. In this
state, Vault is configured to know where and how to access the physical
storage, but doesn't know how to decrypt any of it.

_Unsealing_ is the process of constructing the master key necessary to
read the decryption key to decrypt the data, allowing access to the Vault.

Prior to unsealing, almost no operations are possible with Vault. For
example authentication, managing the mount tables, etc. are all not possible.
The only possible operations are to unseal the Vault and check the status
of the unseal.

## Why?

The data stored by Vault is stored encrypted. Vault needs the
_encryption key_ in order to decrypt the data. The encryption key is
also stored with the data, but encrypted with another encryption key
known as the _master key_. The master key isn't stored anywhere.

Therefore, to decrypt the data, Vault must decrypt the encryption key
which requires the master key. Unsealing is the process of reconstructing
this master key.

Instead of distributing this master key as a single key to an operator,
Vault uses an algorithm known as
[Shamir's Secret Sharing](https://en.wikipedia.org/wiki/Shamir%27s_Secret_Sharing)
to split the key into shards. A certain threshold of shards is required to
reconstruct the master key.

This is the _unseal_ process: the shards are added one at a time (in any
order) until enough shards are present to reconstruct the key and
decrypt the data.

## Unsealing

The unseal process is done by running `vault operator unseal` or via the API.
This process is stateful: each key can be entered via multiple mechanisms
on multiple computers and it will work. This allows each shard of the master
key to be on a distinct machine for better security.

Once a Vault is unsealed, it remains unsealed until one of two things happens:

  1. It is resealed via the API (see below).

  2. The server is restarted.

-> **Note:** Unsealing makes the process of automating a Vault install
difficult. Automated tools can easily install, configure, and start Vault,
but unsealing it is a very manual process. We have plans in the future to
make it easier. For the time being, the best method is to manually unseal
multiple Vault servers in [HA mode](/docs/concepts/ha.html). Use a tool such
as Consul to make sure you only query Vault servers that are unsealed.

## Sealing

There is also an API to seal the Vault. This will throw away the master
key and require another unseal process to restore it. Sealing only requires
a single operator with root privileges.

This way, if there is a detected intrusion, the Vault data can be locked
quickly to try to minimize damages. It can't be accessed again without
access to the master key shards.

## Auto Unseal

Auto Unseal was developed to aid in reducing the operational complexity of 
keeping the master key secure.  This feature delegates the responsibility of 
securing the master key from users to a trusted device or service.  Instead of 
only constructing the key in memory, the master key is encrypted with one of 
these services or devices and then stored in the storage backend allowing Vault 
to decrypt the master key at startup and unseal automatically. 

When using a Auto Unseal, there are certain operations in Vault that still
require a quorum of users to perform an operation such as generating a root token. 
During the initialization process, a set of Shamir keys are generated that are called 
Recovery Keys and are used for these operations.

For a list of examples and supported providers, please see the
[seal documentation](/docs/configuration/seal/index.html).

## Seal Migration

The seal can be migrated between Shamir keys and automatic migration and vice versa.

  ~> **NOTE**: This is not currently supported when using replication. While
  the primary can be migrated without issue, the secondaries, depending on
  which type of seal is being migrated from/to, may not work correctly. We plan
  to support this officially in Vault 1.1.

To migrate from Shamir keys to Auto Unseal, take your server cluster offline and update
the [seal configuration](/docs/configuration/seal/index.html) with the appropriate seal
configuration.  When you bring up your server back up, run the unseal process with the
`-migrate` flag.  All unseal commands must specify the `-migrate` flag.  Once the
required threshold of unseal keys are entered, the unseal keys will be migrated to 
recovery keys.

```
$ vault operator unseal -migrate
```

To migrate from Auto Unseal to Shamir keys, take your server cluster offline and update
the [seal configuration](/docs/configuration/seal/index.html) and add `disabled = "true"`
to the seal block.  This allows the migration to use this information to decrypt the key
but will not unseal Vault.  When you bring up your server back up, run the unseal process 
with the `-migrate` flag and use the Recovery Keys to perform the migration.  All unseal 
commands must specify the `-migrate` flag.  Once the required threshold of recovery keys
are entered, the recovery keys will be migrated to be used as unseal keys.