1.5. Security

This chapter describes how authentication, rule-based authorization, encryption, and digital signing can be accomplished using Qpid. Authentication is the process of verifying the identity of a user; in Qpid, this is done using the SASL framework. Rule-based authorization is a mechanism for specifying the actions that each user is allowed to perform; in Qpid, this is done using an Access Control List (ACL) that is part of the Qpid broker. Encryption is used to ensure that data is not transferred in a plain-text format that could be intercepted and read. Digital signatures provide proof that a given message was sent by a known sender. Encryption and signing are done using SSL (they can also be done using SASL, but SSL provides stronger encryption).

1.5.1. User Authentication

AMQP uses Simple Authentication and Security Layer (SASL) to authenticate client connections to the broker. SASL is a framework that supports a variety of authentication methods. For secure applications, we suggest CRAM-MD5, DIGEST-MD5, or GSSAPI. The ANONYMOUS method is not secure. The PLAIN method is secure only when used together with SSL.

Both the Qpid broker and Qpid clients use the Cyrus SASL library, a full-featured authentication framework, which offers many configuration options. This section shows how to configure users for authentication with SASL, which is sufficient when using SASL PLAIN. If you are not using SSL, you should configure SASL to use CRAM-MD5, DIGEST-MD5, or GSSAPI (which provides Kerberos authentication). For information on configuring these and other options in SASL, see the Cyrus SASL documentation.

Important

The SASL PLAIN method sends passwords in cleartext, and is vulnerable to man-in-the-middle attacks unless SSL (Secure Socket Layer) is also used (see Section 1.5.3, “Encryption using SSL”).

If you are not using SSL, we recommend that you disable PLAIN authentication in the broker.

The Qpid broker uses the auth yes|no option to determine whether to use SASL authentication. Turn on authentication by setting auth to yes in /etc/qpidd.conf:

# /etc/qpidd.conf
#
# Set auth to 'yes' or 'no'

auth=yes

1.5.1.1. Configuring SASL

On Linux systems, the SASL configuration file is generally found in /etc/sasl2/qpidd.conf or /usr/lib/sasl2/qpidd.conf.

The SASL database contains user names and passwords for SASL. In SASL, a user may be associated with a realm. The Qpid broker authenticates users in the QPID realm by default, but it can be set to a different realm using the realm option:

# /etc/qpidd.conf
#
# Set the SASL realm using 'realm='

auth=yes
realm=QPID

The SASL database is installed at /var/lib/qpidd/qpidd.sasldb; initially, it has one user named guest in the QPID realm, and the password for this user is guest.

Note

The user database is readable only by the qpidd user. When run as a daemon, Qpid always runs as the qpidd user. If you start the broker from a user other than the qpidd user, you will need to either reconfigure SASL or turn authentication off.

Important

The SASL database stores user names and passwords in plain text. If it is compromised so are all of the passwords that it stores. This is the reason that the qpidd user is the only user that can read the database. If you modify permissions, be careful not to expose the SASL database.

Add new users to the database by using the saslpasswd2 command, which specifies a realm and a user ID. A user ID takes the form user-id@domain..

# saslpasswd2 -f /var/lib/qpidd/qpidd.sasldb -u realm new_user_name

To list the users in the SASL database, use sasldblistusers2:

# sasldblistusers2 -f /var/lib/qpidd/qpidd.sasldb

If you are using PLAIN authentication, users who are in the database can now connect with their user name and password. This is secure only if you are using SSL. If you are using a more secure form of authentication, please consult your SASL documentation for information on configuring the options you need.

1.5.1.2. Kerberos

Both the Qpid broker and Qpid users are 'principals' of the Kerberos server, which means that they are both clients of the Kerberos authentication services.

To use Kerberos, both the Qpid broker and each Qpid user must be authenticated on the Kerberos server:

  1. Install the Kerberos workstation software and Cyrus SASL GSSAPI on each machine that runs a qpidd broker or a qpidd messaging client:

    $ sudo yum install cyrus-sasl-gssapi krb5-workstation
  2. Make sure that the Qpid broker is registered in the Kerberos database.

    Traditionally, a Kerberos principal is divided into three parts: the primary, the instance, and the realm. A typical Kerberos V5 has the format primary/instance@REALM. For a Qpid broker, the primary is qpidd, the instance is the fully qualified domain name, which you can obtain using hostname --fqdn, and the REALM is the Kerberos domain realm. By default, this realm is QPID, but a different realm can be specified in qpid.conf, e.g.:

    realm=EXAMPLE.COM

    For instance, if the fully qualified domain name is dublduck.example.com and the Kerberos domain realm is EXAMPLE.COM, then the principal name is qpidd/dublduck.example.com@EXAMPLE.COM.

    The following script creates a principal for qpidd:

    FDQN=`hostname --fqdn`
    REALM="EXAMPLE.COM"
    kadmin -r $REALM  -q "addprinc -randkey -clearpolicy qpidd/$FQDN"
    

    Now create a Kerberos keytab file for the Qpid broker. The Qpid broker must have read access to the keytab file. The following script creates a keytab file and allows the broker read access:

    QPIDD_GROUP="qpidd"
    kadmin -r $REALM  -q "ktadd -k /etc/qpidd.keytab qpidd/$FQDN@$REALM"
    chmod g+r /etc/qpidd.keytab
    chgrp $QPIDD_GROUP /etc/qpidd.keytab
    

    The default location for the keytab file is /etc/krb5.keytab. If a different keytab file is used, the KRB5_KTNAME environment variable must contain the name of the file, e.g.:

    export KRB5_KTNAME=/etc/qpidd.keytab
    

    If this is correctly configured, you can now enable kerberos support on the Qpid broker by setting the auth and realm options in /etc/qpidd.conf:

    # /etc/qpidd.conf
    auth=yes
    realm=EXAMPLE.COM
    

    Restart the broker to activate these settings.

  3. Make sure that each Qpid user is registered in the Kerberos database, and that Kerberos is correctly configured on the client machine. The Qpid user is the account from which a Qpid messaging client is run. If it is correctly configured, the following command should succeed:

    $ kinit user@REALM.COM

Java JMS clients require a few additional steps.

  1. The Java JVM must be run with the following arguments:

    -Djavax.security.auth.useSubjectCredsOnly=false

    Forces the SASL GASSPI client to obtain the kerberos credentials explicitly instead of obtaining from the "subject" that owns the current thread.

    -Djava.security.auth.login.config=myjas.conf

    Specifies the jass configuration file. Here is a sample JASS configuration file:

    com.sun.security.jgss.initiate {
        com.sun.security.auth.module.Krb5LoginModule required useTicketCache=true;
    };
    
    -Dsun.security.krb5.debug=true

    Enables detailed debug info for troubleshooting

  2. The client's Connection URL must specify the following Kerberos-specific broker properties:

    • sasl_mechs must be set to GSSAPI.

    • sasl_protocol must be set to the principal for the qpidd broker, e.g. qpidd/

    • sasl_server must be set to the host for the SASL server, e.g. sasl.com.

    Here is a sample connection URL for a Kerberos connection:

    amqp://guest@clientid/testpath?brokerlist='tcp://localhost:5672?sasl_mechs='GSSAPI'&sasl_protocol='qpidd'&sasl_server='<server-host-name>''

1.5.2. Authorization

In Qpid, Authorization specifies which actions can be performed by each authenticated user using an Access Control List (ACL). Use the --acl-file command to load the access control list. The filename should have a .acl extension:

$ qpidd --acl-file ./aclfilename.acl

Each line in an ACL file grants or denies specific rights to a user. If the last line in an ACL file is acl deny all all, the ACL uses deny mode, and only those rights that are explicitly allowed are granted:

acl allow rajith@QPID all all
acl deny all all

On this server, rajith@QPID can perform any action, but nobody else can. Deny mode is the default, so the previous example is equivalent to the following ACL file:

acl allow rajith@QPID all all

In deny mode, denying rights to an action is redundant and has no effect.

acl allow rajith@QPID all all
acl deny jonathan@QPID all all # This rule is redundant, and has no effect
acl deny all all

If the last line in an ACL file is acl allow all all, ACL uses allow mode, and all rights are granted except those that are explicitly denied. The following ACL file allows everyone else to perform any action, but denies jonathan@QPID all permissions.

acl deny jonathan@QPID all all
acl allow all all

In allow mode, allowing rights to an action is redundant and has no effect.

acl allow rajith@QPID all all # This rule is redundant, and has no effect
acl deny jonathan@QPID all all
acl allow all all

Important

ACL processing ends when one of the following lines is encountered:

acl allow all all
acl deny all all

Any lines that occur after one of these statements will be ignored:

acl allow all all
acl deny jonathan@QPID all all # This line is ignored !!!

ACL syntax allows fine-grained access rights for specific actions:

acl allow carlt@QPID create exchange name=carl.*
acl allow fred@QPID create all
acl allow all consume queue
acl allow all bind exchange
acl deny all all

An ACL file can define user groups, and assign permissions to them:

group admin ted@QPID martin@QPID
acl allow admin create all
acl deny all all

1.5.2.1. ACL Syntax

ACL rules must be on a single line and follow this syntax:

acl permission {<group-name>|<user-name>|"all"} {action|"all"} [object|"all"] [property=<property-value>]

ACL rules can also include a single object name (or the keyword all) and one or more property name value pairs in the form property=value

The following tables show the possible values for permission, action, object, and property in an ACL rules file.

Table 1.4. ACL Rules: permission

allow

Allow the action

allow-log

Allow the action and log the action in the event log

deny

Deny the action

deny-log

Deny the action and log the action in the event log


Table 1.5. ACL Rules:action

consume

Applied when subscriptions are created

publish

Applied on a per message basis on publish message transfers, this rule consumes the most resources

create

Applied when an object is created, such as bindings, queues, exchanges, links

access

Applied when an object is read or accessed

bind

Applied when objects are bound together

unbind

Applied when objects are unbound

delete

Applied when objects are deleted

purge

Similar to delete but the action is performed on more than one object

update

Applied when an object is updated


Table 1.6. ACL Rules:object

queue

A queue

exchange

An exchange

broker

The broker

link

A federation or inter-broker link

method

Management or agent or broker method


Table 1.7. ACL Rules:property

name

String. Object name, such as a queue name or exchange name.

durable

Boolean. Indicates the object is durable

routingkey

Sring. Specifies routing key

passive

Boolean. Indicates the presence of a passive flag

autodelete

Boolean. Indicates whether or not the object gets deleted when the connection is closed

exclusive

Boolean. Indicates the presence of an exclusive flag

type

String. Type of object, such as topic, fanout, or xml

alternate

String. Name of the alternate exchange

queuename

String. Name of the queue (used only when the object is something other than queue

schemapackage

String. QMF schema package name

schemaclass

String. QMF schema class name


1.5.2.2. ACL Syntactic Conventions

In ACL files, the following syntactic conventions apply:

  • A line starting with the # character is considered a comment and is ignored.

  • Empty lines and lines that contain only whitespace are ignored

  • All tokens are case sensitive. name1 is not the same as Name1 and create is not the same as CREATE

  • Group lists can be extended to the following line by terminating the line with the \ character

  • Additional whitespace - that is, where there is more than one whitespace character - between and after tokens is ignored. Group and ACL definitions must start with either group or acl and with no preceding whitespace.

  • All ACL rules are limited to a single line

  • Rules are interpreted from the top of the file down until the name match is obtained; at which point processing stops.

  • The keyword all matches all individuals, groups and actions

  • The last line of the file - whether present or not - will be assumed to be acl deny all all. If present in the file, all lines below it are ignored.

  • Names and group names may contain only a-z, A-Z, 0-9, - and _

  • Rules must be preceded by any group definitions they can use. Any name not defined as a group will be assumed to be that of an individual.

1.5.2.3. Specifying ACL Permissions

Now that we have seen the ACL syntax, we will provide representative examples and guidelines for ACL files.

Most ACL files begin by defining groups:

group admin ted@QPID martin@QPID
group user-consume martin@QPID ted@QPID
group group2 kim@QPID user-consume rob@QPID
group publisher group2 \
tom@QPID andrew@QPID debbie@QPID

Rules in an ACL file grant or deny specific permissions to users or groups:

acl allow carlt@QPID create exchange name=carl.*
acl allow rob@QPID create queue
acl allow guest@QPID bind exchange name=amq.topic routingkey=stocks.rht.#
acl allow user-consume create queue name=tmp.*

acl allow publisher publish all durable=false
acl allow publisher create queue name=RequestQueue
acl allow consumer consume queue durable=true
acl allow fred@QPID create all
acl allow bob@QPID all queue
acl allow admin all
acl allow all consume queue
acl allow all bind exchange
acl deny all all

In the previous example, the last line, acl deny all all, denies all authorizations that have not been specifically granted. This is the default, but it is useful to include it explicitly on the last line for the sake of clarity. If you want to grant all rights by default, you can specify acl allow all all in the last line.

Do not allow guest to access and log QMF management methods that could cause security breaches:

group allUsers guest@QPID
....
acl deny-log allUsers create link
acl deny-log allUsers access method name=connect
acl deny-log allUsers access method name=echo
acl allow all all

1.5.3. Encryption using SSL

Encryption and certificate management for qpidd is provided by Mozilla's Network Security Services Library (NSS).

Enabling SSL for the Qpid broker

  1. You will need a certificate that has been signed by a Certification Authority (CA). This certificate will also need to be trusted by your client. If you require client authentication in addition to server authentication, the client's certificate will also need to be signed by a CA and trusted by the broker.

    In the broker, SSL is provided through the ssl.so module. This module is installed and loaded by default in Qpid. To enable the module, you need to specify the location of the database containing the certificate and key to use. This is done using the ssl-cert-db option.

    The certificate database is created and managed by the Mozilla Network Security Services (NSS) certutil tool. Information on this utility can be found on the Mozilla website, including tutorials on setting up and testing SSL connections. The certificate database will generally be password protected. The safest way to specify the password is to place it in a protected file, use the password file when creating the database, and specify the password file with the ssl-cert-password-file option when starting the broker.

    The following script shows how to create a certificate database using certutil:

    mkdir ${CERT_DIR}
    certutil -N -d ${CERT_DIR} -f ${CERT_PW_FILE}
    certutil -S -d ${CERT_DIR} -n ${NICKNAME} -s "CN=${NICKNAME}" -t "CT,," -x -f ${CERT_PW_FILE} -z /usr/bin/certutil
    

    When starting the broker, set ssl-cert-password-file to the value of ${CERT_PW_FILE}, set ssl-cert-db to the value of ${CERT_DIR}, and set ssl-cert-name to the value of ${NICKNAME}.

  2. The following SSL options can be used when starting the broker:

    --ssl-use-export-policy

    Use NSS export policy

    --ssl-cert-password-file PATH

    Required. Plain-text file containing password to use for accessing certificate database.

    --ssl-cert-db PATH

    Required. Path to directory containing certificate database.

    --ssl-cert-name NAME

    Name of the certificate to use. Default is localhost.localdomain.

    --ssl-port NUMBER

    Port on which to listen for SSL connections. If no port is specified, port 5671 is used.

    --ssl-require-client-authentication

    Require SSL client authentication (i.e. verification of a client certificate) during the SSL handshake. This occurs before SASL authentication, and is independent of SASL.

    This option enables the EXTERNAL SASL mechanism for SSL connections. If the client chooses the EXTERNAL mechanism, the client's identity is taken from the validated SSL certificate, using the CNliteral>, and appending any DCliteral>s to create the domain. For instance, if the certificate contains the properties CN=bob, DC=acme, DC=com, the client's identity is bob@acme.com.

    If the client chooses a different SASL mechanism, the identity take from the client certificate will be replaced by that negotiated during the SASL handshake.

    --ssl-sasl-no-dict

    Do not accept SASL mechanisms that can be compromised by dictionary attacks. This prevents a weaker mechanism being selected instead of EXTERNAL, which is not vulnerable to dictionary attacks.

    Also relevant is the --require-encryption broker option. This will cause qpidd to only accept encrypted connections.

Enabling SSL in Clients

C++ clients:

  1. In C++ clients, SSL is implemented in the sslconnector.so module. This module is installed and loaded by default in Qpid.

    The following options can be specified for C++ clients using environment variables:

    Table 1.8. SSL Client Environment Variables for C++ clients

    SSL Client Options for C++ clients
    QPID_SSL_USE_EXPORT_POLICY Use NSS export policy
    QPID_SSL_CERT_PASSWORD_FILE PATH File containing password to use for accessing certificate database
    QPID_SSL_CERT_DB PATH Path to directory containing certificate database
    QPID_SSL_CERT_NAME NAME Name of the certificate to use. When SSL client authentication is enabled, a certificate name should normally be provided.

  2. When using SSL connections, clients must specify the location of the certificate database, a directory that contains the client's certificate and the public key of the Certificate Authority. This can be done by setting the environment variable QPID_SSL_CERT_DB to the full pathname of the directory. If a connection uses SSL client authentication, the client's password is also needed—the password should be placed in a protected file, and the QPID_SSL_CERT_PASSWORD_FILE variable should be set to the location of the file containing this password.

  3. To open an SSL enabled connection in the Qpid Messaging API, set the protocol connection option to ssl.

Java clients:

  1. For both server and client authentication, import the trusted CA to your trust store and keystore and generate keys for them. Create a certificate request using the generated keys and then create a certificate using the request. You can then import the signed certificate into your keystore. Pass the following arguments to the Java JVM when starting your client:

    -Djavax.net.ssl.keyStore=/home/bob/ssl_test/keystore.jks
    -Djavax.net.ssl.keyStorePassword=password
    -Djavax.net.ssl.trustStore=/home/bob/ssl_test/certstore.jks
    -Djavax.net.ssl.trustStorePassword=password
    

  2. For server side authentication only, import the trusted CA to your trust store and pass the following arguments to the Java JVM when starting your client:

    -Djavax.net.ssl.trustStore=/home/bob/ssl_test/certstore.jks
    -Djavax.net.ssl.trustStorePassword=password
    

  3. Java clients must use the SSL option in the connection URL to enable SSL encryption, e.g.

    amqp://username:password@clientid/test?brokerlist='tcp://localhost:5672?ssl='true''
    
  4. If you need to debug problems in an SSL connection, enable Java's SSL debugging by passing the argument -Djavax.net.debug=ssl to the Java JVM when starting your client.