AMA Kit Implementation Requirements

Introduction

This page lists the requirements that OEM accessory devices must meet in order to implement the Alexa Mobile Accessory (AMA) Kit:

Bluetooth and Bluetooth Low Energy (BLE) Requirements for AMA

Your accessory's Bluetooth set must meet the following requirements to support AMA:

  • Bluetooth v4.2 dual mode + LE compliance (with DLE support)
  • Standard pairing, authentication, link key, and encryption operation
  • BT Protocols support for SPP/A2DP/HFP /SDP/RFCOMM/SCO
  • Accessories that implement mSBC must be MFi Certified

Codec Requirements for AMA

AMA supports following codecs:

  • Opus
  • mSBC

The recommended parameter settings for these codecs are shown the following table. An AMA enabled device SHALL support at least one of these codecs with the corresponding parameter settings.

CODEC Version Parameter Settings Comments
mSBC   Encoding - MSBC_WITH_PREAMBLE
Sample Frequency - 16000
Sample size in bits - 16
Frame rate = (1000/7.5) // 7.5ms per frame
Frame size = 60 bytes
[x >= 0 && x%8=0] preamble size
Big endian – false
mSBC header size = 64 (used in SBC codec initialization)
Opus CBR 1.2.1 BT
Sample Frequency - 16000
Sample size in bits - 16
Channels – Mono
Encoding format: hard constant encoding
Bit-rate: 64 kbps
Complexity: 4
Frame size: 20 ms

BLE
Sample Frequency - 16000
Sample size in bits - 16
Channels – Mono
Encoding format: hard constant encoding
Bit-rate: 32 kbps
Complexity: 4
Frame size: 20 ms
 

AMA Hardware Requirements

This section provides the AMA hardware requirements for a Push To Talk (PTT) device with a custom implementation and OPUS codec support (v1.1.4). These specifications can vary from device to device depending on the chipset, codec support, and implementation. Moreover, device-specific custom algorithms impact these specifications.

Wake word, AFE, and other front end algorithms impact additional hardware requirements on the DSP depending on the size and implementation.

  Push to Talk Wake Word
BT version 4.2 or higher 4.2 or higher
BT/BLE audio data minimum throughput 64kpbs 64kpbs
SoC/DSP No specific requirements. Extra MIPS needed depending on choice of audio CODEC, whether to support Alexa COMMS. Extra MIPS needed for Wake Word Engine
RAM No specific requirements Extra memory needed for Wake Word Engine, Pre-roll and Wake Word buffering
NVM Need space for OTA update Need space for OTA update
BT to SoC data Interface Can be I2S, UART, SPI or other Recommend to use minimum 1Mbps or faster interface for pre-roll and wake word buffer catch up. I2S interface is not recommended as it may lead to long UPL
BT and SoC security Please see AMA Security Requirements section Please see AMA Security Requirements section

AMA Software Requirements

Your Bluetooth-enabled accessory must support AMA transport and control protocols, including the following requirements:

  • The accessory must encode the user’s utterances using encoding technologies described in the Codec Requirements for AMA and send the encoded utterances to the Alexa app on a phone using the AMA Kit Protocol Specification.
  • The accessory must implement functionality to receive Alexa responses from a mobile phone using the AMA Kit Protocol Specification.
  • The accessory must implement Over-the-Air (OTA) updates through the accessory's companion app, and not through the Alexa app.
  • The accessory must provide device information, such as serial number, name, supported transport, and device type to the AMA protocol stack.

AMA Security Requirements

The Alexa Developer Services Agreement requires that developers implement all reasonable security measures when developing AVS-enabled devices. Your device must meet the following minimum requirements for AMA integration.

Security Feature Requirement Typical response
Secure Simple Pairing - Must support non-zero STK based Just Works if display not available (Caution: Does not provide protection against passive eavesdropping and MITM)
OR
Secure Simple Pairing - Must support Numeric Comparison if display available (Caution: Does not provide protection against passive eavesdropping and MITM)
Mandatory Supports Just Works
OR
Supports Numeric Comparison
Bluetooth 4.2 devices and services should support Security Mode 4 Level 4 whenever possible. If security mode 4 level 4 is not available, the device must use Security Mode 4 level 3. Mandatory Yes, supports security mode 4 level 4
BLE devices and services using Low Energy should implement Secure Connections model using Security Mode 1 Level 4. If security mode 1 level 4 is not available, device must use Security mode 1 level 3. Mandatory Yes, supports security mode 1 level 4
BLE devices should use Privacy feature such as Random Resolvable address (RRA) Optional Yes

In addition to the above requirements, device manufacturers must have the following infrastructure in place:

  • Software maintenance updates: Have a software maintenance update strategy in place that specifically defines how software updates will be created and distributed within a reasonable period of discovery when vulnerabilities are identified.
  • Contact information: Publish information on publicly available websites on how researchers can notify your company of security vulnerabilities in your devices.
  • Security response plan: Implement and share with Amazon a security response plan that describes how your company will proceed if a security incident arises, when your company will communicate with Amazon on an incident, and the estimated timelines for remediation of an incident.
  • Vulnerabilities report: Submit reports of known exploitable security vulnerabilities that exist on the device along with a plan to fix the vulnerabilities.
  • Independent in-depth security review: Provide a report from an independent security expert who has conducted an in-depth security review of the device.

If a developer is engaging with SoC vendor to define or select a new chipset for an AMA device, Amazon highly recommends that developer choose an SoC for designs that are targeting late 2019 with the following capabilities. If you have any concerns or questions, reach out to your business or tech contact at Amazon.

Security Feature Typical response
Verification and integrity of Firmware and Initial Boot Block (Secure Boot) Yes, up to Kernel
Immutable Root of Trust Lockable and access protected storage for secrets with ROM-based secure boot
Anti-rollback Yes; Bootrom supports anti-rollback
Transition from/to low power mode: as secure as cold boot Yes
Hardware-based Cryptographic engines Yes
Support for Amazon approved crypto ciphers in SoC:
Authentication (HMAC-SHA256)
Symmetric (AES128)
Asymmetric (RSA2048/ECC256)

HMAC-SHA256
AES128/192/256
RSA2048/ECC256
Disable debug ports (OTP or protected with lock, password, or certificate) Yes, password protected
No access to internal registers/memories through standard interfaces on a production version Yes, access disabled by OTP
Secure Key Storage Yes, 1key, 512 bits
Secure OTA using asymmetric key exchange Yes, RSA2048