Signing Right Away (SRA) Architecture

• Signing Right Away (SRA) Architecture is a hardware-rooted security system that ensures digital media authenticity with a cryptographically enforced chain of trust starting at capture.
• It employs a four-pillar security model—confidentiality, integrity, authentication, and replay protection—using mutual authentication, encryption, MACs, and a Trusted Execution Environment.
• The architecture generates C2PA-compliant assets that provide globally auditable proof for applications in journalism, legal evidence, insurance, and copyright protection.

The Signing Right Away (SRA) architecture is a hardware-rooted security and provenance system for digital media, designed to guarantee verifiable authenticity of visual assets starting at the moment of capture. Originating in response to the inadequacy of existing approaches against sophisticated attacks on imaging pipelines, SRA ensures a continuous, cryptographically enforced chain of trust from sensor to final signed file. Its approach leverages a four-pillar security model—Confidentiality, Integrity, Authentication, and Replay Protection—enforced through mutual authentication, encrypted buses, cryptographic validation at each pipeline stage, and use of a Trusted Execution Environment (TEE) for key management and asset signing. SRA produces cryptographically sealed, C2PA-compliant assets whose origin can be independently audited, addressing the requirements of domains such as journalism, legal evidence, and insurance (Jang, 7 Oct 2025).

1. Threat Model and Problem Context

Digital media authenticity faces new threats from both advances in synthetic content generation (deepfakes, AI-manipulated imagery) and known hardware vulnerabilities in imaging devices. Attackers can inject modified or fabricated payloads into device pipelines, bypassing detection by post-hoc classifiers or digital watermarking, as demonstrated by the ability to insert false video streams at the hardware or firmware level. SRA addresses these limitations with a design that anchors trust in the physical device's root of trust, cryptographically validates every step (“photon to file”), and prevents both local and remote adversarial manipulation (Jang, 7 Oct 2025).

2. The SRA Four-Pillar Security Model

SRA enforces end-to-end authenticity with four tightly-coupled security primitives:

Pillar	Implementation Mechanism	Role
Authentication	Mutual device authentication (e.g., via DMTF SPDM)	Proves sensor/SoC legitimacy; protects against hardware spoofing
Confidentiality	Bus-level encryption (e.g., AES-GCM)	Prevents eavesdropping on in-transit image data
Integrity	Frame-level MAC (e.g., AES-GMAC/AES-CMAC)	Detects any tampering with frame content (bit-level fidelity)
Replay Protect.	Nonce or monotonic frame counter in MAC calculation	Detects/rejects frame replays or out-of-order injection

The MAC for a data frame, expressed as: $$\text{MAC} = \operatorname{CMAC}_K(\text{frame data} \Vert \text{metadata})$$ ensures any alteration or reordering is cryptographically evident. Mutual authentication prevents rogue devices (e.g., HDMI-CSI-2 adapters) from imitating sensors, a gap not addressed by cosmetic software signing.

3. Secure Imaging Pipeline with Trusted Execution Environment

All cryptographic operations after bus-level reception are confined within a hardware-isolated TEE (such as Arm TrustZone or Qualcomm QSEE). Within the TEE:

• Keys for all cryptographic signing activities are generated and stored exclusively inside the TEE, inaccessible to non-secure firmware or OS, preventing exfiltration by attackers with root-level access.
• The TEE validates, decrypts, and processes image data in protected memory space, producing output assets without exposing unsealed data to ordinary application domains.
• The final cryptographic signing (C2PA manifest signature) occurs using the device-rooted asymmetric key under TEE attestation, preserving global verifiability and supply chain attribution.

SRA's pipeline conforms to the following schematic:

[Sensor] --(encrypted+MAC'd CSI-2)--> [ISP] --(TEE path)--> [TEE: Decrypt, Process, Sign] --> [OS: C2PA asset]

Unsigned or unvalidated image streams never leave secure enclave boundaries, closing a historic exploit vector found in legacy DSLR designs.

4. C2PA-Compliant Asset Generation and Provenance

Upon image capture, SRA's TEE computes a cryptographic hash over image pixels: $h = \operatorname{SHA-256}(\text{image pixels})$ and compiles a manifest containing:

• Image hash
• Device identity attestation (via device-specific public key, chainable to manufacturer CA)
• Proof of TEE-based signing (enclave certificate/attestation)
• Security metadata (algorithm, hardware IDs, operational context)
• Secure timestamp and geolocation (if provided by trusted subsystem components)

This manifest is then signed inside the TEE: $$\text{Signature} = \operatorname{Sign}_{K_\text{TEE}}(\text{manifest})$$ and bound to the image in a C2PA-conformant format. The complete asset is globally verifiable, even after it leaves the immediate device; unsigned data never traverses to userland.

5. Implementation Roadmap and Hardware Prototyping

SRA development proceeded via empirical prototyping on commodity hardware, using a Sony IMX219 sensor routed through a Raspberry Pi platform with an FPGA cryptographically implementing MAC and encryption. Bandwidth and latency constraints highlighted the necessity of dedicated, hardware-accelerated cryptography for real-time performance. For high frame rates,

$$10^7 \text{ cycles/frame} \times 30 \text{ fps} = 3 \times 10^8 \text{ cycles/sec} \implies 300\,\text{MHz FPGA clock min}$$

exceeding practical limits for soft-core FPGA deployments.

The staged implementation plan is as follows:

Stage	Objective
1. Baseline	Unsecured functional camera pipeline
2. Secure Channel	Sensor-SoC authenticated, encrypted, MAC'ed link
3. C2PA Integration	Pipeline-secured, digitally signed C2PA manifest
4. TEE Hardening	Entire provenance, signing, and storage isolated in TEE
5. SoC Integration	Deployment as firmware/software on commercial SoCs (e.g., Qualcomm)

A pivotal strategy shift favors software/firmware-level adoption on SoCs with native TEE and secure camera APIs, increasing scalability and accelerating industry compatibility.

6. Comparative Security Analysis

A synthesis of approaches is summarized:

Solution	Security Touchpoint	Tamper Resilience	Core Weakness
Neural Classifier	Post-capture analysis	Low	Retroactive only; easily evaded by novel attacks
Digital Watermark	Post/AI-generated	Medium	Fragile; can be stripped or degraded
Software C2PA	Post-capture manifest	High (manifest only)	Can sign injected/forged content as "real"
SRA	Hardware-secured capture	Very High	Protects both provenance and raw sensor data; robust to HW attacks

While the MIPI Camera Security Framework (CSF) addresses bus-level security for closed, internal device boundaries, SRA extends this paradigm beyond the physical device, creating globally portable, audit-ready assets with TEE-rooted provenance. The analogy: CSF as “armored truck” (securing transit), SRA as “minted coin” (public trust certificate).

7. Industry Applications and Broader Implications

SRA's properties meet the stringent evidentiary needs of:

• Journalism: Guarantees that published visual content was captured by a known, trusted device, countering deepfakes and false attributions.
• Legal Evidence: Enables cryptographic chain-of-custody, reliable timestamps, and globally auditable origin proof, suitable for court submission without requiring expert testimony.
• Insurance and Claims: Thwarts fraudulent claims fabricated via image manipulation; ensures enforceability and dispute resilience.
• Copyright/IP: Renders provenance laundering and digital authorship forgery computationally infeasible. Embeds licensing and ownership in a tamper-resistant manifest.

The restrictive isolation of cryptographic keys and manifests within the TEE constitutes a major advance over prior digital camera security models, addressing documented failures in legacy device signatures.

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SRA establishes a scalable pattern for the verifiable, hardware-rooted authenticity of digital visual media, integrating modern cryptography, TEE-protected computation, and C2PA compliance into a unified chain of trust. By closing fundamental design weaknesses in both hardware and software approaches, and by producing auditable, tamper-evident assets consumable across digital ecosystems, SRA provides a foundational architecture for content authentication in an era of pervasive synthetic media (Jang, 7 Oct 2025).