Android Remote Key Provisioning (Software)

Software implementation of the Android RKP protocol that generates AuthenticatedRequest CSRs, communicates with Google's production RKP server, and exports keybox.xml for key attestation.

Overview

Android devices with KeyMint 2.0+ use Remote Key Provisioning to obtain attestation certificates from Google. The on-device flow requires a Trusted Execution Environment (TEE) to derive cryptographic keys and sign provisioning requests.

This tool replicates that flow entirely in software, given a device's 32-byte CDI_Leaf seed.

Architecture

                        +-----------+
                        | RKP Server|  (Google production)
                        +-----+-----+
                              |
                 fetchEekChain / signCertificates
                              |
+-----------------------------+-----------------------------+
|                        rkp_sw.py                          |
|                                                           |
|  CDI_Leaf Seed ─── Signing Key ─── DICE Chain             |
|       |          (Ed25519 or P-256)     |                 |
|       |           ECDH-ES + HKDF ─── AES-256-GCM         |
|       |                |                                  |
|       v                v                                  |
|  COSE_Sign1     COSE_Encrypt0 (ProtectedData)            |
|       |                |                                  |
|       +-------+--------+                                  |
|               |                                           |
|     AuthenticatedRequest (CBOR)                           |
+-----------------------------------------------------------+

Requirements

Python 3.10+
cbor2
cryptography >= 41.0

pip install cbor2 cryptography

Configuration

Copy template.conf to a private config file and fill in device-specific values:

cp template.conf device_prop.conf

The config uses INI format with [device] and [fingerprint] sections. See template.conf for all supported fields. Private config files (device_prop.conf) are excluded from version control via .gitignore.

Usage

Show device and key information

python3 rkp_sw.py info --seed <64-hex> --config device_prop.conf
python3 rkp_sw.py info --seed <64-hex> --curve p256 --config device_prop.conf

Provision attestation keys

Generate EC P-256 keypairs, build a CSR, and submit to Google's RKP server:

python3 rkp_sw.py provision --seed <64-hex> --config device_prop.conf
python3 rkp_sw.py provision --seed <64-hex> --curve p256 --config device_prop.conf -n 2

The --curve flag selects the DICE chain signing key type: ed25519 (default) or p256.

Export keybox.xml

Provision a key and export the result as an Android keybox.xml:

python3 rkp_sw.py keybox --seed <64-hex> --config device_prop.conf -o keybox.xml

Verify a CSR

python3 rkp_sw.py verify csr_output.cbor

Protocol

The tool implements the full generateCertificateRequestV2 protocol:

EEK fetch — POST :fetchEekChain returns the server's Endpoint Encryption Key chain and a challenge nonce.
CSR build — Constructs an AuthenticatedRequest containing:
- DeviceInfo (CBOR map from config)
- DiceCertChain (Degenerate DICE: UDS = CDI_Leaf, self-signed)
- ProtectedData (COSE_Encrypt0 with ECDH-ES + AES-256-GCM)
- SignedData (COSE_Sign1 over challenge + payload)
CSR submit — POST :signCertificates returns X.509 certificate chains signed by Google's attestation root.

References

Specification	Use
RFC 9052	COSE_Sign1, COSE_Encrypt0 structures
RFC 9053	EdDSA, ES256, ECDH-ES, AES-256-GCM algorithm identifiers
RFC 8392	CWT claims (issuer, subject)
Open DICE	DICE certificate chain profile
Android RKP AIDL	AuthenticatedRequest CDDL schema

License

Copyright 2025 mhmrdd <1@mhmrdd.me>

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

    http://www.apache.org/licenses/LICENSE-2.0