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wolfBoot/docs/PQ.md

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Post-Quantum Signatures in wolfBoot

wolfBoot provides support for NIST-approved post-quantum (PQ) signature algorithms to ensure future-proof secure boot capabilities.

Supported Algorithms

1. ML-DSA (Lattice-Based)

  • FIPS 204 standardized algorithm
  • Derived from CRYSTALS-DILITHIUM
  • Reference: FIPS 204 Final

2. LMS/HSS (Hash-Based)

  • Stateful hash-based signature scheme
  • NIST SP 800-208 recommended
  • Reference: NIST Stateful HBS

3. XMSS/XMSS^MT (Hash-Based)

  • Stateful hash-based signature scheme
  • NIST SP 800-208 recommended
  • Reference: NIST Stateful HBS

Algorithm Comparison

Feature ML-DSA LMS/HSS & XMSS/XMSS^MT
Verification Speed Fast Fast
Signature Size Variable Variable
Key Generation Fast Slower
Public Key Size Larger, Variable Smaller
Private Key Stateless Stateful*

*Stateful private keys require careful management during key generation and signing.

Example Configurations

Find example configurations in:

config/examples/sim-ml-dsa.config  # ML-DSA example
config/examples/sim-lms.config     # LMS/HSS example
config/examples/sim-xmss.config    # XMSS/XMSS^MT example

ML-DSA Implementation

Overview

ML-DSA (Module-Lattice Digital Signature Algorithm) is a FIPS 204 standardized algorithm based on lattice cryptography, derived from CRYSTALS-DILITHIUM.

Parameter Sets

ML-DSA offers three security levels, with numerical suffixes indicating matrix dimensions:

Parameter Set Security Category Description
ML-DSA-44 Category 2 Lower security, smaller sizes
ML-DSA-65 Category 3 Medium security, balanced
ML-DSA-87 Category 5 Highest security, larger sizes

Key and Signature Sizes

Parameter Set Private Key (bytes) Public Key (bytes) Signature (bytes) Security Category
ML-DSA-44 2,560 1,312 2,420 Category 2
ML-DSA-65 4,032 1,952 3,309 Category 3
ML-DSA-87 4,896 2,592 4,627 Category 5

Configuration

Basic Setup

# In config file (e.g., config/examples/sim-ml-dsa.config)
ML_DSA_LEVEL=2                # Security category (2, 3, or 5)
IMAGE_SIGNATURE_SIZE=2420     # Must match parameter set
IMAGE_HEADER_SIZE?=4840       # Typically 2x signature size

Standards Compliance

  • Default: FIPS 204 Final Standard
  • Legacy Support: Use WOLFSSL_DILITHIUM_FIPS204_DRAFT for draft standard

Stateful Hash-Based Signatures (HBS)

Overview

LMS/HSS and XMSS/XMSS^MT are quantum-resistant signature schemes based on hash functions and Merkle trees.

Key Features:

  • Small public key sizes
  • Fast signature operations
  • Configurable signature sizes
  • Strong security foundations
    • Based on hash function security
    • Quantum-resistant by design
    • Recommended by NIST SP 800-208
    • Included in NSA's CNSA 2.0 suite

Implementation Details:

  • LMS/HSS Implementation:

    • Core files: wc_lms.c, wc_lms_impl.c
    • Provides HSS (Hierarchical Signature System)

  • XMSS/XMSS^MT Implementation:

    • Core files: wc_xmss.c, wc_xmss_impl.c
    • Supports both single-tree and multi-tree variants

Additional Resources:

LMS/HSS Configuration

Basic Setup

# In config/examples/sim-lms.config
SIGN?=LMS
LMS_LEVELS=2                  # Number of HSS levels
LMS_HEIGHT=5                  # Tree height
LMS_WINTERNITZ=8             # Winternitz parameter
IMAGE_SIGNATURE_SIZE=2644     # From lms_siglen.sh
IMAGE_HEADER_SIZE?=5288       # Typically 2x signature size

Signature Size Calculator

Use the provided helper script to calculate required signature size:

$ ./tools/lms/lms_siglen.sh 2 5 8
levels:     2
height:     5
winternitz: 8
signature length: 2644

XMSS/XMSS^MT Configuration

Basic Setup

# In config/examples/sim-xmss.config
SIGN?=XMSS
XMSS_PARAMS='XMSS-SHA2_10_256'    # From NIST SP 800-208
IMAGE_SIGNATURE_SIZE=2500          # From xmss_siglen.sh
IMAGE_HEADER_SIZE?=5000            # Typically 2x signature size

Parameter Sets

Supports all SHA256 parameter sets from NIST SP 800-208 Tables 10 and 11.

Signature Size Calculator

# Single-tree XMSS
$ ./tools/xmss/xmss_siglen.sh XMSS-SHA2_10_256
parameter set:    XMSS-SHA2_10_256
signature length: 2500

# Multi-tree XMSS^MT
$ ./tools/xmss/xmss_siglen.sh XMSSMT-SHA2_20/2_256
parameter set:    XMSSMT-SHA2_20/2_256
signature length: 4963

Hybrid Mode (Classic + Post-Quantum)

Overview

wolfBoot supports hybrid signatures combining classic and post-quantum algorithms for:

  • Gradual transition to post-quantum security
  • Protection against vulnerabilities in either algorithm
  • Maintaining backwards compatibility

Configuration

Required Settings

SECONDARY_SIGN=<algorithm>           # Enable hybrid mode
WOLFBOOT_UNIVERSAL_KEYSTORE=1        # Required for hybrid keys

Example Configuration

See config/examples/sim-ml-dsa-ecc-hybrid.config for ML-DSA-65 + ECC-384 hybrid setup.

Hybrid Signature Support

Key Generation Options

  1. Simultaneous Key Generation (Recommended)

    • Generates both keys at once
    • Automatically adds both to keystore
    • Ensures proper key compatibility

  2. Sequential Key Generation

    • Allows adding PQ keys to existing classic setup
    • Requires manual keystore management
    • Must follow specific import procedure

Key Generation Procedures

Method 1: Single Command Generation

# Generate both ML-DSA and ECC384 keys
./tools/keytools/keygen --ml_dsa -g wolfboot_signing_private_key.der \
                       --ecc384 -g wolfboot_signing_second_private_key.der

Result: Both keys are automatically added to keystore

Method 2: Sequential Generation

  1. Generate First Key:

    # Generate ML-DSA key
./tools/keytools/keygen --ml_dsa -g wolfboot_signing_private_key.der

  2. Extract Public Key:

    # Skip 16-byte keystore header
dd if=keystore.der of=ml_dsa-pubkey.der bs=1 skip=16

  3. Generate Second Key with Import:

    # Generate ECC384 key while importing ML-DSA key
./tools/keytools/keygen --ml_dsa -i ml_dsa-pubkey.der \
                       --ecc384 -g wolfboot_signing_second_private_key.der

Result: Complete keystore with both keys ready for hybrid verification

Firmware Signing with Hybrid Keys

Signing Command

./tools/sign/sign --ml_dsa --ecc384 --sha256 test-app/image.elf \
    wolfboot_signing_private_key.der \
    wolfboot_signing_second_private_key.der 1

Command Parameters

  • --ml_dsa --ecc384: Specify both signature algorithms
  • --sha256: Hash algorithm
  • test-app/image.elf: Input firmware image
  • wolfboot_signing_private_key.der: Primary key (ML-DSA)
  • wolfboot_signing_second_private_key.der: Secondary key (ECC384)
  • 1: Target partition ID

Expected Output

wolfBoot KeyTools (Compiled C version)
wolfBoot version 2020000
Parsing arguments in hybrid mode
...
Creating hybrid signature

Results

  • Output file: test-app/image_v1_signed.bin
  • Contains both ML-DSA and ECC384 signatures
  • Compatible with hybrid-enabled wolfBoot
  • Verifiable using both algorithms during boot

Note: Ensure wolfBoot is compiled with hybrid signature support to verify these images.