ARM® TrustZone® CryptoCell 310 (CRYPTOCELL) is a security subsystem which provides root of trust (RoT) and cryptographic services for a device.

Figure 1. Block diagram for CRYPTOCELL

Block diagram for CRYPTOCELL

The following cryptographic features are provided:

  • True random number generator (TRNG) compliant with NIST 800-90B, AIS-31, and FIPS 140-2
  • Pseudorandom number generator (PRNG) using underlying AES engine compliant with NIST 800-90A
  • RSA public key cryptography
    • Up to 2048-bit key size
    • PKCS#1 v2.1/v1.5
    • Optional CRT support
  • Elliptic curve cryptography (ECC)
    • NIST FIPS 186-4 recommended curves using pseudorandom parameters, up to 521 bits:
      • Prime field: P-192, P-224, P-256, P-384, P-521
    • SEC 2 recommended curves using pseudorandom parameters, up to 521 bits:
      • Prime field: secp160r1, secp192r1, secp224r1, secp256r1, secp384r1, secp521r1
    • Koblitz curves using fixed parameters, up to 256 bits:
      • Prime field: secp160k1, secp192k1, secp224k1, secp256k1
    • Edwards/Montgomery curves:
      • Ed25519, Curve25519
    • ECDH/ECDSA support
  • Secure remote password protocol (SRP)
    • Up to 3072-bit operations
  • Hashing functions
    • SHA-1, SHA-2 up to 256 bits
    • Keyed-hash message authentication code (HMAC)
  • AES symmetric encryption
    • General purpose AES engine (encrypt/decrypt, sign/verify)
    • 128-bit key size
    • Supported encryption modes: ECB, CBC, CMAC/CBC-MAC, CTR, CCM/CCM* (CCM* is a minor variation of CCM)
  • ChaCha20/Poly1305 symmetric encryption
    • Supported key size: 128 and 256 bits
    • Authenticated encryption with associated data (AEAD) mode

Usage

The CRYPTOCELL state is controlled via a register interface. The cryptographic functions of CRYPTOCELL are accessible by using a software library provided in the device SDK, not directly via a register interface.

To enable CRYPTOCELL, use register ENABLE.

Note: Keeping the CRYPTOCELL subsystem enabled will prevent the device from reaching the System ON, All Idle state.

Always-on (AO) power domain

The CRYPTOCELL subsystem has an internal always-on (AO) power domain for retaining device secrets when CRYPTOCELL is disabled.

The following information is retained by the AO power domain:
  • 4 bits indicating the configured CRYPTOCELL lifecycle state (LCS)
  • 1 bit indicating if the hard-coded RTL key, KPRTL (see RTL key), is available for use
  • 128-bit device root key, KDR (see Device root key)

A reset from any reset source will erase the content in the AO power domain.

Lifecycle state (LCS)

Lifecycle refers to multiple states a device goes through during its lifetime. Two valid lifecycle states are offered for the device - debug and secure.

The CRYPTOCELL subsystem lifecycle state (LCS) is controlled through register HOST_IOT_LCS. A valid LCS is configured by writing either value Debug or Secure into the LCS field of this register. A correctly configured LCS can be validated by reading back the read-only field LCS_IS_VALID from the abovementioned register. The LCS_IS_VALID field value will change from Invalid to Valid once a valid LCS value has been written.

Table 1. Lifecycle states
LCS field value LCS_IS_VALID field value Description
Secure Invalid Default reset value indicating that LCS has not been configured.
Secure Valid LCS set to secure mode, and LCS is valid. Registers HOST_IOT_KDR[0..3] can only be written once per reset cycle. Any additional writes will be ignored.
Debug Valid LCS set to debug mode, and LCS is valid. Registers HOST_IOT_KDR[0..3] can be written multiple times.

Cryptographic key selection

The CRYPTOCELL subsystem can be instructed to operate on different cryptographic keys.

Through register HOST_CRYPTOKEY_SEL, the following key types can be selected for cryptographic operations:
  • RTL key KPRTL
  • Device root key KDR
  • Session key

KPRTL and KDR are configured as part of the CRYPTOCELL initialization process, while session keys are provided by the application through the software library API.

RTL key

The ARM® TrustZone® CryptoCell 310 contains one hard-coded RTL key referred to as KPRTL. This key is set to the same value for all devices with the same part code in the hardware design and cannot be changed.

The KPRTL key can be requested for use in cryptographic operations by the CRYPTOCELL, without revealing the key value itself. Access to use of KPRTL in cryptographic operations can be disabled until next reset by writing to register HOST_IOT_KPRTL_LOCK. If a locked KPRTL key is requested for use, a zero vector key will be routed to the AES engine instead.

Device root key

The device root key KDR is a 128-bit AES key programmed into the CRYPTOCELL subsystem using firmware. It is retained in the AO power domain until the next reset.

Once configured, it is possible to perform cryptographic operations using the CRYPTOCELL subsystem where KDR is selected as key input without having access to the key value itself. The KDR key value must be written to registers HOST_IOT_KDR[0..3]. These 4 registers are write-only if LCS is set to debug mode, and write-once if LCS is set to secure mode. The KDR key value is successfully retained when the read-back value of register HOST_IOT_KDR0 changes to 1.

Direct memory access (DMA)

The CRYPTOCELL subsystem implements direct memory access (DMA) for accessing memory without CPU intervention.

Any data stored in memory type(s) not accessible by the DMA engine must be copied to SRAM before it can be processed by the CRYPTOCELL subsystem. Maximum DMA transaction size is limited to 216-1 bytes.

Standards

ARM® TrustZone® CryptoCell 310 (CRYPTOCELL) supports a number of cryptography standards.

Table 2. CRYPTOCELL cryptography standards
Algorithm family Identification code Document title
TRNG NIST SP 800-90B Recommendation for the Entropy Sources Used for Random Bit Generation
AIS-31 A proposal for: Functionality classes and evaluation methodology for physical random number generators
FIPS 140-2 Security Requirements for Cryptographic Modules
PRNG NIST SP 800-90A Recommendation for Random Number Generation Using Deterministic Random Bit Generators
Stream cipher Chacha ChaCha, a variant of Salsa20, Daniel J. Bernstein, January 28th 2008
MAC Poly1305

The Poly1305-AES message-authentication code, Daniel J. Bernstein

Cryptography in NaCl, Daniel J. Bernstein
Key agreement SRP The Secure Remote Password Protocol, Thomas Wu, November 11th 1997
AES FIPS-197 Advanced Encryption Standard (AES)
NIST SP 800-38A Recommendation for Block Cipher Modes of Operation - Methods and Techniques
NIST SP 800-38B Recommendation for Block Cipher Modes of Operation: The CMAC Mode for Authentication
NIST SP 800-38C Recommendation for Block Cipher Modes of Operation: The CCM Mode for Authentication and Confidentiality
ISO/IEC 9797-1 AES CBC-MAC per ISO/IEC 9797-1 MAC algorithm 1
IEEE 802.15.4-2011 IEEE Standard for Local and metropolitan area networks - Part 15.4: Low-Rate Wireless Personal Area Networks (LR-WPANs), Annex B.4: Specification of generic CCM* mode of operation
Hash FIPS 180-3 Secure Hash Standard (SHA1, SHA-224, SHA-256)
RFC2104 HMAC: Keyed-Hashing for Message Authentication
RSA PKCS#1 Public-Key Cryptography Standards (PKCS) #1: RSA Cryptography Specifications v1.5/2.1
Diffie-Hellman ANSI X9.42 Public Key Cryptography for the Financial Services Industry: Agreement of Symmetric Keys Using Discrete Logarithm Cryptography
PKCS#3 Diffie-Hellman Key-Agreement Standard
ECC ANSI X9.63 Public Key Cryptography for the Financial Services Industry - Key Agreement and Key Transport Using Elliptic Curve Cryptography
IEEE 1363 Standard Specifications for Public-Key Cryptography
ANSI X9.62 Public Key Cryptography For The Financial Services Industry: The Elliptic Curve Digital Signature Algorithm (ECDSA)
Ed25519 Edwards-curve, Ed25519: high-speed high-security signatures, Daniel J. Bernstein, Niels Duif, Tanja Lange, Peter Schwabe, and Bo-Yin Yang
Curve25519 Montgomery curve, Curve25519: new Diffie-Hellman speed records, Daniel J. Bernstein
FIPS 186-4 Digital Signature Standard (DSS)
SEC 2 Recommended Elliptic Curve Domain Parameters, Certicom Research
NIST SP 800-56A rev. 2 Recommendation for Pair-Wise Key Establishment Schemes Using Discrete Logarithm Cryptography

Registers

Instances

Instance Base address TrustZone Split access Description
Map Att DMA
CRYPTOCELL 0x50840000 HF S NSA No

CryptoCell sub-system control interface

Register overview

Register Offset TZ Description
ENABLE 0x500

Enable CRYPTOCELL subsystem

ENABLE

Address offset: 0x500

Enable CRYPTOCELL subsystem

Bit number 31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
ID A
Reset 0x00000000 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
ID R/W Field Value ID Value Description
A

RW

ENABLE

Enable or disable the CRYPTOCELL subsystem

Disabled

0

CRYPTOCELL subsystem disabled

Enabled

1

CRYPTOCELL subsystem enabled.

When enabled the CRYPTOCELL subsystem can be initialized and controlled through the CryptoCell firmware API.

Host interface

This chapter describes host registers used to control the CRYPTOCELL subsystem behavior.

HOST_RGF block

The HOST_RGF block contains registers for configuring LCS and device root key KDR, in addition to selecting which cryptographic key is connected to the AES engine.

Registers

Instances
Instance Base address TrustZone Split access Description
Map Att DMA
CC_HOST_RGF 0x50840000 HF S NSA No

Host platform interface
Register overview
Register Offset TZ Description
HOST_CRYPTOKEY_SEL 0x1A38

AES hardware key select
HOST_IOT_KPRTL_LOCK 0x1A4C

This write-once register is the K_PRTL lock register. When this register is set, K_PRTL cannot be used and a zeroed key will be used instead. The value of this register is saved in the CRYPTOCELL AO power domain.
HOST_IOT_KDR0 0x1A50

This register holds bits 31:0 of K_DR. The value of this register is saved in the CRYPTOCELL AO power domain. Reading from this address returns the K_DR valid status indicating if K_DR is successfully retained.
HOST_IOT_KDR1 0x1A54

This register holds bits 63:32 of K_DR. The value of this register is saved in the CRYPTOCELL AO power domain.
HOST_IOT_KDR2 0x1A58

This register holds bits 95:64 of K_DR. The value of this register is saved in the CRYPTOCELL AO power domain.
HOST_IOT_KDR3 0x1A5C

This register holds bits 127:96 of K_DR. The value of this register is saved in the CRYPTOCELL AO power domain.
HOST_IOT_LCS 0x1A60

Controls lifecycle state (LCS) for CRYPTOCELL subsystem
HOST_CRYPTOKEY_SEL

Address offset: 0x1A38

AES hardware key select

Note: If the HOST_IOT_KPRTL_LOCK register is set, and the HOST_CRYPTOKEY_SEL register set to 1, then the HW key that is connected to the AES engine is zero
Bit number 31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
ID A A
Reset 0x00000000 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
ID R/W Field Value ID Value Description
A

RW

HOST_CRYPTOKEY_SEL

Select the source of the HW key that is used by the AES engine

K_DR

0

Use device root key K_DR from CRYPTOCELL AO power domain

K_PRTL

1

Use hard-coded RTL key K_PRTL

Session

2

Use provided session key
HOST_IOT_KPRTL_LOCK

Address offset: 0x1A4C

This write-once register is the K_PRTL lock register. When this register is set, K_PRTL cannot be used and a zeroed key will be used instead. The value of this register is saved in the CRYPTOCELL AO power domain.

Bit number 31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
ID A
Reset 0x00000000 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
ID R/W Field Value ID Value Description
A

RW

HOST_IOT_KPRTL_LOCK

This register is the K_PRTL lock register. When this register is set, K_PRTL cannot be used and a zeroed key will be used instead. The value of this register is saved in the CRYPTOCELL AO power domain.

Disabled

0

K_PRTL can be selected for use from register HOST_CRYPTOKEY_SEL

Enabled

1

K_PRTL has been locked until next power-on reset (POR). If K_PRTL is selected anyway, a zeroed key will be used instead.
HOST_IOT_KDR0

Address offset: 0x1A50

This register holds bits 31:0 of K_DR. The value of this register is saved in the CRYPTOCELL AO power domain. Reading from this address returns the K_DR valid status indicating if K_DR is successfully retained.

Bit number 31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
ID A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A
Reset 0x00000000 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
ID R/W Field Value ID Value Description
A

RW

HOST_IOT_KDR0

Write: K_DR bits 31:0.

Read: 0x00000000 when 128-bit K_DR key value is not yet retained in the CRYPTOCELL AO power domain.

Read: 0x00000001 when 128-bit K_DR key value is successfully retained in the CRYPTOCELL AO power domain.
HOST_IOT_KDR1

Address offset: 0x1A54

This register holds bits 63:32 of K_DR. The value of this register is saved in the CRYPTOCELL AO power domain.

Bit number 31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
ID A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A
Reset 0x00000000 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
ID R/W Field Value ID Value Description
A

W

HOST_IOT_KDR1

K_DR bits 63:32
HOST_IOT_KDR2

Address offset: 0x1A58

This register holds bits 95:64 of K_DR. The value of this register is saved in the CRYPTOCELL AO power domain.

Bit number 31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
ID A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A
Reset 0x00000000 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
ID R/W Field Value ID Value Description
A

W

HOST_IOT_KDR2

K_DR bits 95:64
HOST_IOT_KDR3

Address offset: 0x1A5C

This register holds bits 127:96 of K_DR. The value of this register is saved in the CRYPTOCELL AO power domain.

Bit number 31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
ID A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A
Reset 0x00000000 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
ID R/W Field Value ID Value Description
A

W

HOST_IOT_KDR3

K_DR bits 127:96
HOST_IOT_LCS

Address offset: 0x1A60

Controls lifecycle state (LCS) for CRYPTOCELL subsystem

Bit number 31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
ID B A A A
Reset 0x00000002 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0
ID R/W Field Value ID Value Description
A

RW

LCS

Lifecycle state value. This field is write-once per reset.

Debug

0

CC310 operates in debug mode

Secure

2

CC310 operates in secure mode
B

RW

LCS_IS_VALID

Read-only field. Indicates if CRYPTOCELL LCS has been successfully configured since last reset.

Invalid

0

Valid LCS not yet retained in the CRYPTOCELL AO power domain

Valid

1

Valid LCS successfully retained in the CRYPTOCELL AO power domain