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V4/Password Vault/Design

Name: V4/Password Vault/Design
Ticket: #3872
Target version: 4.2.0
Author: Nkinder, Endi Sukma Dewata
Incomplete.png Pending review
Last updated: 2015-10-13 by Alich

Overview

Users often want a way to securely store passwords so they don't have to remember them. This is often handled by a password keyring type functionality on a client system. This works fine from a single client system, but it doesn't work well if a user wants to access their passwords from multiple systems. A network-based approach allows an authenticated user to retrieve passwords from multiple client systems.

It is also common for services to require knowledge of passwords or keys, which is typically handled by storing those secrets locally on the system where the service is installed. Storing these secrets locally is inconvenient and has security risk. This inconvenience and risk is also compounded when multiple instances of the same service require knowledge of the same secrets. Storing these secrets centrally makes authorization, distribution and rollover of secrets for services much easier to maintain.

Use Cases

  1. A service wants to securely store passwords in a centralized location and have the ability to easily retrieve them programatically when the password needs to be used. Nobody other than the service and the service administrator should be able to access the password.
  1. A user wants to securely store passwords in a centralized location and have the ability to easily retrieve them manually when the password is forgotten. An escrow key will optionally be available to authorized administrators to prevent loss of the passwords.

Design

A user or service who archives secrets in the password vault will encrypt their secrets on the client side prior to sending them to IPA. This encryption will use a symmetric key that is generated from a vault password that is only known by the user or service. This approach ensures that IPA never has direct knowledge of one of the clear-text secrets that a user or service is storing.

If escrow functionality is desired, an escrow officer will need to be created. This entails generating an escrow officer keypair that will be used to encrypt/decrypt the vault encryption key associated with a user or service. The ability to have multiple escrow officers is possible. This would allow different groups of users to be assigned to different escrow officers, which could be used to have different levels of security with regards to escrowed key access. The escrow officer public keys must be available to IPA clients. The escrow officer private keys can be stored on an IPA server, or offline (preferred for security paranoid situations).

Definitions

  • Secret - A Secret is a password or key that a user or service wants to securely archive in the Password Vault.
  • Vault Password - A password that is used by a user or a service when archiving or retrieving secrets from the Password Vault. A Vault Password is used to derive a Vault Encryption Key for a user or service. The Vault Password is only known by the user or service who owns it.
  • Vault Encryption Key - A symmetric key that is used to encrypt secrets that a user or a service stores in the Password Vault. Each user or service usually has their own encryption key, though an encryption key might be shared among multiple instances of a service if desired.
  • Data Recovery Manager (DRM) - A Dogtag subsystem that is designed for secure archival and retrieval of keys. A DRM subsystem will be created when the Password Vault feature is enabled.
  • Secret ID - An identifier that the user or service uses to identify a Secret. This identifier is a simple name that is unique per user or service. The user or service will use this identifier directly when performing archival and retrieval operations.
  • Client ID - An identifier that the DRM uses as a convenience label for an archived key. This identifier is a simple name. The DRM does not enforce the uniqueness of this identifier, though IPA should. This identifier is not exposed to the user or service.
  • Key ID - An identifier that the DRM uses to identify an archived key. This is a unique hexadecimal identifer that the DRM generates when a key is archived. This identifier is later used during key retrieval. This identifier is not exposed to the user or service.

Authentication and Authorization

For simplicity, the workflow diagrams in this document do not show details about authentication or authorization. This section describes how authentication and authorization are handed.

A user or service authenticates to the IPA Server using Kerberos/GSSAPI just as they do when running any of the IPA client commands. The IPA Server is responsible for authorizing a user or service to retrieve or store a secret.

The IPA Server authenticates to the DRM as a special Agent user using an x.509 certificate. This Agent is allowed to archive or retrieve any secret that is stored in the DRM, though it is important to note that the secrets are encrypted such that the IPA Server is unable to decrypt them.

Common Workflows

The following workflows apply to the common use-cases of archiving and retrieving secrets from the Password Vault.

Archival

The following diagram illustrates the workflow that is used when a user or service wants to archive a secret in the Password Vault. From the user or service's point of view, they simply supply their Vault Password, the Secret that they want to store, and the Secret ID that they want to use to identify the Secret for future retrieval.

Password Vault Archival.png

Retrieval

The following diagram illustrates the workflow that is used when a user or service wants to retrieve a secret from the Password Vault. From the user or service's point of view, they simply supply their Vault Password and the Secret ID that identifies the Secret that they want to retrieve. They will be given the clear-text Secret in response.

Password Vault Retrieval.png

Vault Password Reset

  • User uses IPA CLI reset their vault password.
  • User supplies old vault password, which derives the current symmetric encryption key on the client side.
  • User supplies a new vault password, which derives a new symmetric encryption key on the client side.
  • Client CLI contacts IPA to retrieve all stored secrets.
  • Retrieved secrets are decrypted using the current encryption key, then re-encrypted using the new encryption key.
  • Newly encrypted secrets are sent to IPA as archival requests.

Service Workflows

The following workflows apply to the use case where a service is storing secrets in the Password Vault. These workflows assume that the process of a service retrieving and decrypting secrets is handled in an automated fashion. In particular, this changes things with respect to the use of a vault password, as there is no way for the service to interactively provide this password to encrypt/decrypt secrets.

Instead of simply storing the service's vault password (that might be shared by multiple instances of a service) in a file on the system where the service is installed, public key cryptography is used to allow the service to securely retrieve it's vault password from the password vault. This requires each instance of a service to have it's own public/private key pair that a service administrator sets up on the system where the service runs. The private key could be protected by file system permissions to allow it to be used in a completely automated fashion, or it could be password protected (requiring it to be manually unlocked each time the service is started).

A vault password for a service (or a group of services that need to access the same archived secrets) is stored in the password vault using a service administrator vault password. This is done using the user use case workflow described above. This allows the service administrator to retrieve the service vault password when they set up a new instance of the service. The service administrator can then archive a copy of the service vault password that is encrypted using the service instance's public key so it can only be decrypted by that single instance of the installed service. This approach allows an administrator to add or remove instances of a service without affecting other instances of the same service. It also allows an admin to change the service vault password for all instances of a service by archiving encrypted copies the new vault password with the public keys of the service instances.

Archival of a service vault password (at service set up time)

The following diagram illustrates the workflow that is used when a service administrator is setting up a new instance of a service. This workflow assumes that a few prerequisite tasks have been completed:

  • The service administrator has the desired Service Vault Password archived as one of their personal secrets. This can be completed using the normal archival workflow.
  • The new service instance has been defined in IPA.
  • IPA has issued a certificate for the new service instance.

From the service administrator's point of view, they simply supply their Vault Password, the Secret ID that identifies the Service Vault Password that is shared by all instances of the service, and the Service Principal that identifies the instance of the service that they are setting up. The result is that a copy of the Service Vault Password is archived that can only be retrieved and decrypted by the new service instance.

Password Vault Service Password Archival.png

Retrieval of service vault password (automated)

  • The service retrieves it's copy of the encrypted service vault password from the password vault.
  • The service decrypts the service vault password using it's private key. This decrypted vault password can be used to decrypt retrieved secrets that the service is allowed to access.

Escrow Workflows

Archival

  • If escrow functionality is desired, the IPA client framework retrieves escrow officer public key from LDAP and uses it to encrypt the new encryption key. This encrypted encryption key is sent to IPA over a GSSAPI protected connection and is stored in the DRM.

Retrieval (escrow officer initiated)

  • Authenticated escrow officer requests administrative retrieval of a user's secret from IPA CLI.
  • IPA receives the administrative retrieval request and requests retrieval from the DRM using the agent certificate to authenticate.
  • IPA receives the encrypted secret from the DRM and sends it back to the escrow officer.
  • IPA retrieves the user's encrypted escrowed encryption key and sends it back to the escrow officer.
  • IPA client framework decrypts the encrypted encryption key using the escrow officer's private key on the escrow officer's workstation.
  • IPA client framework uses the encryption key to decrypt the secret and presents it to the escrow officer.

Vault Password Reset (with escrowed encryption key)

  • User forgets their vault password.
  • User requests to reset their vault password from CLI.
  • User supplies a new vault password, which derives a new symmetric encryption key on the client side.
  • IPA client framework retrieves escrow officer public key from LDAP and uses it to encrypt the new encryption key.
  • Encrypted new encryption key is sent to IPA over a GSSAPI protected connection.
  • IPA accesses the online private escrow officer key that is associated with this user.
    • For the offline private key case, admin intervention is required here to perform the stored secret rewrapping. This will require a two-step process or an admin initiated password reset.
  • Escrowed user encryption key is fetched and decrypted using the private escrow officer key on the IPA server.
    • This would happen on the escrow officer workstation for the offline private key case.
  • New user encryption key is decrypted using the private escrow officer key on the IPA server.
    • This would happen on the escrow officer workstation for the offline private key case.
  • User's stored secrets are extracted from the DRM, decrypted using the escrowed user encryption key, and re-encrypted using the new user encryption key. The re-encrypted secrets are stored in the DRM, replacing the old secrets. This all takes place on the IPA server.
    • This decryption/encryption would happen on the escrow officer workstation for the offline private key case. The escrow officer would need to be allowed to retrieve and store secrets for users they are assigned to.
  • New encryption key (encrypted with the escrow officer's public key) is stored, replacing the old escrowed encryption key.

Implementation

The implementation details still need to be defined. Consider this section as a work in progress.

DRM Namespace

The namespace used to store secrets in the DRM needs to be defined. We likely want a naming scheme that gives each user a namespace. One possible naming scheme is:

<uid>-<secret name>

LDAP Implementation Details

Escrow Officer Assignment

The LDAP schema used to assign an escrow officer to users and groups needs to be defined.

Stored Secret Tracking

We will need to track the secrets that are stored for users in LDAP. The main reason for this is to keep track of the names of secrets that a user has stored in the DRM. This will allow IPA to perform some basic access control checks, such as rejecting attempts to retrieve a secret that IPA is not aware of.

Having entries that track the stored secrets will also allow us to have some more advanced access control, such as host-based restrictions. An LDAP entry that represents a stored secret could hold attributes that list hosts or hostgroups that are allowed to retrieve a stored secret.

The LDAP schema and entry location for this needs to be defined.

Feature Management

UI

TBD

CLI

TBD

Major configuration options and enablement

The password vault should be an optional feature that is enabled at install time, or afterwards. This will require changes to ipa-server-install as well as a new command such as ipa-enable-vault. When a vault is desired, a new DRM instance will need to be created and configured using pkispawn.

Replication

The password vault should be replicated for redundancy. This would leverage the existing Dogtag cloning functionality for the DRM subsystem. This would require separate replication agreements since the DRM internal database would be stored in a separate suffix in 389 DS. This would allow some FreeIPA replicas to have a password vault while other do not.

Updates and Upgrades

The password vault requires that a DRM instance is created on each FreeIPA replica. If an existing IPA replica does not have a DRM created, the new functionality will not be available. We should not create a DRM at upgrade time. Instead, one would have to manually enable the password vault feature on existing FreeIPA replicas, which would trigger DRM creation.

Currently, the Dogtag DRM subsystem requires a CA subsystem. This means we will not be able to offer password vault functionality in a CA-less installation. There are plans for Dogtag to support a standalone DRM, which will allow FreeIPA to have a password vault without a CA.

Dependencies

The password vault would use the Dogtag DRM subsystem. FreeIPA already relies on Dogtag for it's CA subsystem, but the DRM subsystem is contained in an additional package. This dependency should be optional since not everyone would have the password vault functionality enabled.

External Impact

Development of this functionality will require working closely with the Dogtag development team. There might be new DRM interfaces that are required by this feature that will require RFEs for Dogtag. One such RFE that is known is support for a standalone DRM subsystem to allow it to work in a CA-less FreeIPA installation.

Backup and Restore

The password vault will need to be backed up. This will require backing up the DRM data from LDAP, DRM certificate databases, and DRM configuration files.

Test Plan

References