OASIS Advanced Message Queuing Protocol (AMQP) Version 1.0, Part 5: Security

The Advanced Message Queuing Protocol (AMQP) is an open internet protocol for business messaging. It defines a binary wire-level protocol that allows for the reliable exchange of business messages between two parties. AMQP has a layered architecture and the specification is organized as a set of parts that reflects that architecture. Part 1 defines the AMQP type system and encoding. Part 2 defines the AMQP transport layer, an efficient, binary, peer-to-peer protocol for transporting messages between two processes over a network. Part 3 defines the AMQP message format, with a concrete encoding. Part 4 defines how interactions can be grouped within atomic transactions. Part 5 defines the AMQP security layers.

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←5.1 Security Layers

Security layers are used to establish an authenticated and/or encrypted transport over which regular AMQP traffic can be tunneled. Security layers can be tunneled through one another (for instance a security layer used by the peers to do authentication might be tunneled through a security layer established for encryption purposes).

The framing and protocol definitions for security layers are expected to be defined externally to the AMQP specification as in the case of TLS [RFC5246]. An exception to this is the SASL [RFC4422] security layer which depends on its host protocol to provide framing. Therefore section 5.3 defines the frames necessary for SASL to function. When a security layer terminates (either before or after a secure tunnel is established), the TCP connection MUST be closed by first shutting down the outgoing stream and then reading the incoming stream until it is terminated.

←5.2 TLS

To establish a TLS session, each peer MUST start by sending a protocol header before commencing with TLS negotiation. The protocol header consists of the upper case ASCII letters "AMQP" followed by a protocol id of two, followed by three unsigned bytes representing the major, minor, and revision of the specification version (currently 1 (TLS-MAJOR), 0 (TLS-MINOR), 0 (TLS-REVISION)). In total this is an 8-octet sequence:

Figure 5.1: Protocol Header for TLS Security Layer
4 OCTETS 1 OCTET 1 OCTET 1 OCTET 1 OCTET +----------+---------+---------+---------+----------+ \| "AMQP" \| %d2 \| major \| minor \| revision \| +----------+---------+---------+---------+----------+

Other than using a protocol id of two, the exchange of TLS protocol headers follows the same rules specified in the version negotiation section of the transport specification (See section 2.2).

The following diagram illustrates the interaction involved in creating a TLS security layer:

Figure 5.2: Establishing a TLS Security Layer
TCP Client TCP Server ========================================= AMQP%d2.1.0.0 ---------> <--------- AMQP%d2.1.0.0 : : <TLS negotiation> : : AMQP%d0.1.0.0 ---------> (over TLS secured connection) <--------- AMQP%d0.1.0.0 open ---------> <--------- open

When the use of the TLS security layer is negotiated, the following rules apply:

The TLS client peer and TLS server peer are determined by the TCP client peer and TCP server peer respectively.
The TLS client peer SHOULD use the server name indication extension as described in RFC-4366 [RFC4366]. If it does so, then it is undefined what happens if this differs from hostname in the sasl-init and open frame frames.

This field can be used by AMQP proxies to determine the correct back-end service to connect the client to, and to determine the domain to validate the client's credentials against if TLS client certificates are being used.
The TLS client MUST validate the certificate presented by the TLS server.
Implementations MAY choose to use TLS with unidirectional shutdown, i.e., an application initiating shutdown using close_notify is not obliged to wait for the peer to respond, and MAY close the write half of the TCP socket.

←5.2.1 Alternative Establishment

In certain situations, such as connecting through firewalls, it might not be possible to establish a TLS security layer using the above procedure (for example, because a deep packet inspecting firewall sees the first few bytes of the connection 'as not being TLS').

As an alternative, implementations MAY run a pure TLS server, i.e., one that does not expect the initial TLS-invoking handshake. The IANA service name for this is amqps and the port is SECURE-PORT (5671). Implementations MAY also choose to run this pure TLS server on other ports, if this is operationally necessary (e.g., to tunnel through a legacy firewall that only expects TLS traffic on port 443).

←5.2.2 Constant Definitions

TLS-MAJOR	1	major protocol version.
TLS-MINOR	0	minor protocol version.
TLS-REVISION	0	protocol revision.

←5.3 SASL

To establish a SASL layer, each peer MUST start by sending a protocol header. The protocol header consists of the upper case ASCII letters "AMQP" followed by a protocol id of three, followed by three unsigned bytes representing the major, minor, and revision of the specification version (currently 1 (SASL-MAJOR), 0 (SASL-MINOR), 0 (SASL-REVISION)). In total this is an 8-octet sequence:

Figure 5.3: Protocol Header for SASL Security Layer
4 OCTETS 1 OCTET 1 OCTET 1 OCTET 1 OCTET +----------+---------+---------+---------+----------+ \| "AMQP" \| %d3 \| major \| minor \| revision \| +----------+---------+---------+---------+----------+

Other than using a protocol id of three, the exchange of SASL layer headers follows the same rules specified in the version negotiation section of the transport specification (See section 2.2).

The following diagram illustrates the interaction involved in creating a SASL security layer:

Figure 5.4: Establishing a SASL Security Layer
TCP Client TCP Server ========================================= AMQP%d3.1.0.0 ---------> <--------- AMQP%d3.1.0.0 : : <SASL negotiation> : : AMQP%d0.1.0.0 ---------> (over SASL secured connection) <--------- AMQP%d0.1.0.0 open ---------> <--------- open

←5.3.1 SASL Frames

SASL performatives are framed as per section 2.3. A SASL frame has a type code of 0x01. Bytes 6 and 7 of the header are ignored. Implementations SHOULD set these to 0x00. The extended header is ignored. Implementations SHOULD therefore set DOFF to 0x02.

Figure 5.5: SASL Frame
type: 0x01 - SASL frame +0 +1 +2 +3 +-----------------------------------+ -. 0 \| SIZE \| \| +-----------------------------------+ \|---> Frame Header 4 \| DOFF \| TYPE \| <IGNORED>1 \| \| (8 bytes) +-----------------------------------+ -' +-----------------------------------+ -. 8 \| ... \| \| . . \|---> Extended Header . <IGNORED>2 . \| (DOFF * 4 - 8) bytes \| ... \| \| +-----------------------------------+ -' +-----------------------------------+ -. 4DOFF \| \| \| . . \| . . \| . Sasl Mechanisms / Sasl Init . \| . Sasl Challenge / Sasl Response . \|---> Frame Body . Sasl Outcome . \| (SIZE - DOFF 4) bytes . . \| . . \| . ________\| \| \| ... \| \| +--------------------------+ -' 1 SHOULD be set to 0x0000 2 Ignored, so DOFF SHOULD be set to 0x02

The maximum size of a SASL frame is defined by MIN-MAX-FRAME-SIZE. There is no mechanism within the SASL negotiation to negotiate a different size. The frame body of a SASL frame MUST contain exactly one AMQP type, whose type encoding MUST have provides="sasl-frame" . Receipt of an empty frame is an irrecoverable error.

←5.3.2 SASL Negotiation

The peer acting as the SASL server MUST announce supported authentication mechanisms using the sasl-mechanisms frame. The partner MUST then choose one of the supported mechanisms and initiate a sasl exchange.

Figure 5.6: SASL Exchange
SASL Client SASL Server ================================ <-- SASL-MECHANISMS SASL-INIT --> ... <-- SASL-CHALLENGE * SASL-RESPONSE --> ... <-- SASL-OUTCOME -------------------------------- * Note that the SASL challenge/response step can occur zero or more times depending on the details of the SASL mechanism chosen.

The peer playing the role of the SASL client and the peer playing the role of the SASL server MUST correspond to the TCP client and server respectively.

←5.3.3 Security Frame Bodies

←5.3.3.1 Sasl Mechanisms

Advertise available sasl mechanisms.

Advertises the available SASL mechanisms that can be used for authentication.

sasl-server-mechanisms	supported sasl mechanisms	mandatory symbol[]
A list of the sasl security mechanisms supported by the sending peer. It is invalid for this list to be null or empty. If the sending peer does not require its partner to authenticate with it, then it SHOULD send a list of one element with its value as the SASL mechanism ANONYMOUS. The server mechanisms are ordered in decreasing level of preference.

←5.3.3.2 Sasl Init

Initiate sasl exchange.

Selects the sasl mechanism and provides the initial response if needed.

mechanism	selected security mechanism	mandatory symbol
The name of the SASL mechanism used for the SASL exchange. If the selected mechanism is not supported by the receiving peer, it MUST close the connection with the authentication-failure close-code. Each peer MUST authenticate using the highest-level security profile it can handle from the list provided by the partner.
initial-response	security response data	optional binary
A block of opaque data passed to the security mechanism. The contents of this data are defined by the SASL security mechanism.
hostname	the name of the target host	optional string
The DNS name of the host (either fully qualified or relative) to which the sending peer is connecting. It is not mandatory to provide the hostname. If no hostname is provided the receiving peer SHOULD select a default based on its own configuration. This field can be used by AMQP proxies to determine the correct back-end service to connect the client to, and to determine the domain to validate the client's credentials against. This field might already have been specified by the server name indication extension as described in RFC-4366 [RFC4366], if a TLS layer is used, in which case this field SHOULD either be null or contain the same value. It is undefined what a different value to those already specified means.

←5.3.3.3 Sasl Challenge

Security mechanism challenge.

Send the SASL challenge data as defined by the SASL specification.

challenge	security challenge data	mandatory binary
Challenge information, a block of opaque binary data passed to the security mechanism.

←5.3.3.4 Sasl Response

Security mechanism response.

Send the SASL response data as defined by the SASL specification.

response	security response data	mandatory binary
A block of opaque data passed to the security mechanism. The contents of this data are defined by the SASL security mechanism.

←5.3.3.5 Sasl Outcome

Indicates the outcome of the sasl dialog.

This frame indicates the outcome of the SASL dialog. Upon successful completion of the SASL dialog the security layer has been established, and the peers MUST exchange protocol headers to either start a nested security layer, or to establish the AMQP connection.

code	indicates the outcome of the sasl dialog	mandatory sasl-code
A reply-code indicating the outcome of the SASL dialog.
additional-data	additional data as specified in RFC-4422	optional binary
The additional-data field carries additional data on successful authentication outcome as specified by the SASL specification [RFC4422]. If the authentication is unsuccessful, this field is not set.

←5.3.3.6 Sasl Code

Codes to indicate the outcome of the sasl dialog.

ok		0
Connection authentication succeeded.
auth		1
Connection authentication failed due to an unspecified problem with the supplied credentials.
sys		2
Connection authentication failed due to a system error.
sys-perm		3
Connection authentication failed due to a system error that is unlikely to be corrected without intervention.
sys-temp		4
Connection authentication failed due to a transient system error.

←5.3.4 Constant Definitions

SASL-MAJOR	1	major protocol version.
SASL-MINOR	0	minor protocol version.
SASL-REVISION	0	protocol revision.

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