Membership Service Providers (MSP)

The document serves to provide details on the setup and best practices for MSPs.

Membership Service Provider (MSP) is a component that aims to offer an abstraction of a membership operation architecture.

In particular, MSP abstracts away all cryptographic mechanisms and protocols behind issuing and validating certificates, and user authentication. An MSP may define their own notion of identity, and the rules by which those identities are governed (identity validation) and authenticated (signature generation and verification).

A Hyperledger Fabric blockchain network can be governed by one or more MSPs. This provides modularity of membership operations, and interoperability across different membership standards and architectures.

In the rest of this document we elaborate on the setup of the MSP implementation supported by Hyperledger Fabric, and discuss best practices concerning its use.

MSP Configuration

To setup an instance of the MSP, its configuration needs to be specified locally at each peer and orderer (to enable peer, and orderer signing), and on the channels to enable peer, orderer, client identity validation, and respective signature verification (authentication) by and for all channel members.

Firstly, for each MSP a name needs to be specified in order to reference that MSP in the network (e.g. msp1, org2, and org3.divA). This is the name under which membership rules of an MSP representing a consortium, organization or organization division is to be referenced in a channel. This is also referred to as the MSP Identifier or MSP ID. MSP Identifiers are required to be unique per MSP instance. For example, shall two MSP instances with the same identifier be detected at the system channel genesis, orderer setup will fail.

In the case of default implementation of MSP, a set of parameters need to be specified to allow for identity (certificate) validation and signature verification. These parameters are deduced by RFC5280, and include:

  • A list of self-signed (X.509) certificates to constitute the root of trust
  • A list of X.509 certificates to represent intermediate CAs this provider considers for certificate validation; these certificates ought to be certified by exactly one of the certificates in the root of trust; intermediate CAs are optional parameters
  • A list of X.509 certificates with a verifiable certificate path to exactly one of the certificates of the root of trust to represent the administrators of this MSP; owners of these certificates are authorized to request changes to this MSP configuration (e.g. root CAs, intermediate CAs)
  • A list of Organizational Units that valid members of this MSP should include in their X.509 certificate; this is an optional configuration parameter, used when, e.g., multiple organizations leverage the same root of trust, and intermediate CAs, and have reserved an OU field for their members
  • A list of certificate revocation lists (CRLs) each corresponding to exactly one of the listed (intermediate or root) MSP Certificate Authorities; this is an optional parameter
  • A list of self-signed (X.509) certificates to constitute the TLS root of trust for TLS certificate.
  • A list of X.509 certificates to represent intermediate TLS CAs this provider considers; these certificates ought to be certified by exactly one of the certificates in the TLS root of trust; intermediate CAs are optional parameters.

Valid identities for this MSP instance are required to satisfy the following conditions:

  • They are in the form of X.509 certificates with a verifiable certificate path to exactly one of the root of trust certificates;
  • They are not included in any CRL;
  • And they list one or more of the Organizational Units of the MSP configuration in the OU field of their X.509 certificate structure.

For more information on the validity of identities in the current MSP implementation, we refer the reader to MSP Identity Validity Rules.

In addition to verification related parameters, for the MSP to enable the node on which it is instantiated to sign or authenticate, one needs to specify:

  • The signing key used for signing by the node (currently only ECDSA keys are supported), and
  • The node’s X.509 certificate, that is a valid identity under the verification parameters of this MSP.

It is important to note that MSP identities never expire; they can only be revoked by adding them to the appropriate CRLs. Additionally, there is currently no support for enforcing revocation of TLS certificates.

How to generate MSP certificates and their signing keys?

To generate X.509 certificates to feed its MSP configuration, the application can use Openssl. We emphasize that in Hyperledger Fabric there is no support for certificates including RSA keys.

Alternatively one can use cryptogen tool, whose operation is explained in Getting Started.

Hyperledger Fabric CA can also be used to generate the keys and certificates needed to configure an MSP.

MSP setup on the peer & orderer side

To set up a local MSP (for either a peer or an orderer), the administrator should create a folder (e.g. $MY_PATH/mspconfig) that contains six subfolders and a file:

  1. a folder admincerts to include PEM files each corresponding to an administrator certificate
  2. a folder cacerts to include PEM files each corresponding to a root CA’s certificate
  3. (optional) a folder intermediatecerts to include PEM files each corresponding to an intermediate CA’s certificate
  4. (optional) a file config.yaml to configure the supported Organizational Units and identity classifications (see respective sections below).
  5. (optional) a folder crls to include the considered CRLs
  6. a folder keystore to include a PEM file with the node’s signing key; we emphasise that currently RSA keys are not supported
  7. a folder signcerts to include a PEM file with the node’s X.509 certificate
  8. (optional) a folder tlscacerts to include PEM files each corresponding to a TLS root CA’s certificate
  9. (optional) a folder tlsintermediatecerts to include PEM files each corresponding to an intermediate TLS CA’s certificate

In the configuration file of the node (core.yaml file for the peer, and orderer.yaml for the orderer), one needs to specify the path to the mspconfig folder, and the MSP Identifier of the node’s MSP. The path to the mspconfig folder is expected to be relative to FABRIC_CFG_PATH and is provided as the value of parameter mspConfigPath for the peer, and LocalMSPDir for the orderer. The identifier of the node’s MSP is provided as a value of parameter localMspId for the peer and LocalMSPID for the orderer. These variables can be overridden via the environment using the CORE prefix for peer (e.g. CORE_PEER_LOCALMSPID) and the ORDERER prefix for the orderer (e.g. ORDERER_GENERAL_LOCALMSPID). Notice that for the orderer setup, one needs to generate, and provide to the orderer the genesis block of the system channel. The MSP configuration needs of this block are detailed in the next section.

Reconfiguration of a “local” MSP is only possible manually, and requires that the peer or orderer process is restarted. In subsequent releases we aim to offer online/dynamic reconfiguration (i.e. without requiring to stop the node by using a node managed system chaincode).

Organizational Units

In order to configure the list of Organizational Units that valid members of this MSP should include in their X.509 certificate, the config.yaml file needs to specify the organizational unit identifiers. Here is an example:

OrganizationalUnitIdentifiers:
  - Certificate: "cacerts/cacert1.pem"
    OrganizationalUnitIdentifier: "commercial"
  - Certificate: "cacerts/cacert2.pem"
    OrganizationalUnitIdentifier: "administrators"

The above example declares two organizational unit identifiers: commercial and administrators. An MSP identity is valid if it carries at least one of these organizational unit identifiers. The Certificate field refers to the CA or intermediate CA certificate path under which identities, having that specific OU, should be validated. The path is relative to the MSP root folder and cannot be empty.

Identity Classification

The default MSP implementation allows to further classify identities into clients and peers, based on the OUs of their x509 certificates. An identity should be classified as a client if it submits transactions, queries peers, etc. An identity should be classified as a peer if it endorses or commits transactions. In order to define clients and peers of a given MSP, the config.yaml file needs to be set appropriately. Here is an example:

NodeOUs:
  Enable: true
  ClientOUIdentifier:
    Certificate: "cacerts/cacert.pem"
    OrganizationalUnitIdentifier: "client"
  PeerOUIdentifier:
    Certificate: "cacerts/cacert.pem"
    OrganizationalUnitIdentifier: "peer"

As shown above, the NodeOUs.Enable is set to true, this enables the identify classification. Then, client (peer) identifiers are defined by setting the following properties for the NodeOUs.ClientOUIdentifier (NodeOUs.PeerOUIdentifier) key:

  1. OrganizationalUnitIdentifier: Set this to the value that matches the OU that the x509 certificate of a client (peer) should contain.
  2. Certificate: Set this to the CA or intermediate CA under which client (peer) identities should be validated. The field is relative to the MSP root folder. It can be empty, meaning that the identity’s x509 certificate can be validated under any CA defined in the MSP configuration.

When the classification is enabled, MSP administrators need to be clients of that MSP, meaning that their x509 certificates need to carry the OU that identifies the clients. Notice also that, an identity can be either a client or a peer. The two classifications are mutually exclusive. If an identity is neither a client nor a peer, the validation will fail.

Finally, notice that for upgraded environments the 1.1 channel capability needs to be enabled before identify classification can be used.

Channel MSP setup

At the genesis of the system, verification parameters of all the MSPs that appear in the network need to be specified, and included in the system channel’s genesis block. Recall that MSP verification parameters consist of the MSP identifier, the root of trust certificates, intermediate CA and admin certificates, as well as OU specifications and CRLs. The system genesis block is provided to the orderers at their setup phase, and allows them to authenticate channel creation requests. Orderers would reject the system genesis block, if the latter includes two MSPs with the same identifier, and consequently the bootstrapping of the network would fail.

For application channels, the verification components of only the MSPs that govern a channel need to reside in the channel’s genesis block. We emphasize that it is the responsibility of the application to ensure that correct MSP configuration information is included in the genesis blocks (or the most recent configuration block) of a channel prior to instructing one or more of their peers to join the channel.

When bootstrapping a channel with the help of the configtxgen tool, one can configure the channel MSPs by including the verification parameters of MSP in the mspconfig folder, and setting that path in the relevant section in configtx.yaml.

Reconfiguration of an MSP on the channel, including announcements of the certificate revocation lists associated to the CAs of that MSP is achieved through the creation of a config_update object by the owner of one of the administrator certificates of the MSP. The client application managed by the admin would then announce this update to the channels in which this MSP appears.

Best Practices

In this section we elaborate on best practices for MSP configuration in commonly met scenarios.

1) Mapping between organizations/corporations and MSPs

We recommend that there is a one-to-one mapping between organizations and MSPs. If a different mapping type of mapping is chosen, the following needs to be to considered:

  • One organization employing various MSPs. This corresponds to the case of an organization including a variety of divisions each represented by its MSP, either for management independence reasons, or for privacy reasons. In this case a peer can only be owned by a single MSP, and will not recognize peers with identities from other MSPs as peers of the same organization. The implication of this is that peers may share through gossip organization-scoped data with a set of peers that are members of the same subdivision, and NOT with the full set of providers constituting the actual organization.
  • Multiple organizations using a single MSP. This corresponds to a case of a consortium of organizations that are governed by similar membership architecture. One needs to know here that peers would propagate organization-scoped messages to the peers that have an identity under the same MSP regardless of whether they belong to the same actual organization. This is a limitation of the granularity of MSP definition, and/or of the peer’s configuration.

2) One organization has different divisions (say organizational units), to which it wants to grant access to different channels.

Two ways to handle this:

  • Define one MSP to accommodate membership for all organization’s members. Configuration of that MSP would consist of a list of root CAs, intermediate CAs and admin certificates; and membership identities would include the organizational unit (OU) a member belongs to. Policies can then be defined to capture members of a specific OU, and these policies may constitute the read/write policies of a channel or endorsement policies of a chaincode. A limitation of this approach is that gossip peers would consider peers with membership identities under their local MSP as members of the same organization, and would consequently gossip with them organization-scoped data (e.g. their status).
  • Defining one MSP to represent each division. This would involve specifying for each division, a set of certificates for root CAs, intermediate CAs, and admin Certs, such that there is no overlapping certification path across MSPs. This would mean that, for example, a different intermediate CA per subdivision is employed. Here the disadvantage is the management of more than one MSPs instead of one, but this circumvents the issue present in the previous approach. One could also define one MSP for each division by leveraging an OU extension of the MSP configuration.

3) Separating clients from peers of the same organization.

In many cases it is required that the “type” of an identity is retrievable from the identity itself (e.g. it may be needed that endorsements are guaranteed to have derived by peers, and not clients or nodes acting solely as orderers).

There is limited support for such requirements.

One way to allow for this separation is to create a separate intermediate CA for each node type - one for clients and one for peers/orderers; and configure two different MSPs - one for clients and one for peers/orderers. Channels this organization should be accessing would need to include both MSPs, while endorsement policies will leverage only the MSP that refers to the peers. This would ultimately result in the organization being mapped to two MSP instances, and would have certain consequences on the way peers and clients interact.

Gossip would not be drastically impacted as all peers of the same organization would still belong to one MSP. Peers can restrict the execution of certain system chaincodes to local MSP based policies. For example, peers would only execute “joinChannel” request if the request is signed by the admin of their local MSP who can only be a client (end-user should be sitting at the origin of that request). We can go around this inconsistency if we accept that the only clients to be members of a peer/orderer MSP would be the administrators of that MSP.

Another point to be considered with this approach is that peers authorize event registration requests based on membership of request originator within their local MSP. Clearly, since the originator of the request is a client, the request originator is always doomed to belong to a different MSP than the requested peer and the peer would reject the request.

4) Admin and CA certificates.

It is important to set MSP admin certificates to be different than any of the certificates considered by the MSP for root of trust, or intermediate CAs. This is a common (security) practice to separate the duties of management of membership components from the issuing of new certificates, and/or validation of existing ones.

5) Blacklisting an intermediate CA.

As mentioned in previous sections, reconfiguration of an MSP is achieved by reconfiguration mechanisms (manual reconfiguration for the local MSP instances, and via properly constructed config_update messages for MSP instances of a channel). Clearly, there are two ways to ensure an intermediate CA considered in an MSP is no longer considered for that MSP’s identity validation:

  1. Reconfigure the MSP to no longer include the certificate of that intermediate CA in the list of trusted intermediate CA certs. For the locally configured MSP, this would mean that the certificate of this CA is removed from the intermediatecerts folder.
  2. Reconfigure the MSP to include a CRL produced by the root of trust which denounces the mentioned intermediate CA’s certificate.

In the current MSP implementation we only support method (1) as it is simpler and does not require blacklisting the no longer considered intermediate CA.

6) CAs and TLS CAs

MSP identities’ root CAs and MSP TLS certificates’ root CAs (and relative intermediate CAs) need to be declared in different folders. This is to avoid confusion between different classes of certificates. It is not forbidden to reuse the same CAs for both MSP identities and TLS certificates but best practices suggest to avoid this in production.