Keychain Core Documentation
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Security Threat Model

This document defines the comprehensive security threat model for the Keychain Core SDK and its distributed PKI system. It establishes the security assumptions, identifies potential adversaries and their capabilities, and outlines the security guarantees provided by the system.

Overview

The Keychain Core security threat model provides a framework for understanding the security boundaries and protections offered by the system. This model helps developers and security architects understand what threats are mitigated, what assumptions must hold, and how to properly deploy and use Keychain Core in security-critical applications.

Security Assumptions

The Keychain Core threat model is built upon several fundamental security assumptions that must be maintained for the system to provide its security guarantees.

Device Security

Local Device Integrity

  • Assumption: User devices (endpoints) running Keychain Core are physically and operationally secure

  • Requirements:

    • Users can securely enter passphrases and submit them to Keychain software

    • No unauthorized parties have access to core system functions (memory bus, process memory, root access)

    • The device’s hardware security features (if available) function correctly

    • The operating system and Keychain software are free from compromise

Passphrase Protection

  • Assumption: Users protect and maintain confidentiality of their Keychain gateway passphrases

  • Requirements:

    • Passphrases are kept secret from unauthorized parties

    • Users follow secure passphrase generation and storage practices

    • Passphrase entry occurs in a secure environment

Network and Infrastructure

Network Connectivity

  • Assumption: Network connectivity is of sufficient quality for reliable data transmission

  • Requirements:

    • Data can be transmitted between parties within reasonable delay tolerances

    • Blockchain operations can complete within acceptable timeframes

    • Network partitions do not persist indefinitely

Blockchain Security

  • Assumption: The underlying blockchain network maintains sufficient decentralization and security

  • Requirements:

    • The cost of censoring Keychain operations is prohibitively high relative to potential value

    • In proof-of-work systems, the network difficulty remains sufficiently high

    • The blockchain network resists 51% attacks and other consensus-level threats

User Behavior and Trust

User Responsibility

  • Assumption: End users are motivated to protect their data and act in their own security interests

  • Requirements:

    • Users implement appropriate operational security practices

    • Users understand the security implications of their actions

    • Users maintain secure environments for sensitive operations

Trust Relationships

  • Assumption: Users can appropriately assess and manage trust relationships

  • Requirements:

    • Users can trust counterparties with data access or accept responsibility for sharing

    • In business contexts, legal frameworks support digital signature validity

    • Users understand the implications of granting data access to others

Adversary Model

The threat model categorizes potential adversaries into three distinct classes based on their capabilities and resources.

Weak Adversary

Weak adversaries represent the most common threat scenario, including passive surveillance and basic network attacks.

Observational Capabilities

Weak adversaries can observe but not significantly alter the communication environment:

  • Blockchain Surveillance: Complete visibility of all public blockchain transactions and metadata

  • Network Traffic Analysis: Observation of encrypted messages, timestamps, routing data, and communication patterns

  • Encrypted Data Access: Ability to observe data after encryption but before decryption by Keychain

  • Limited Device Access: Access to some aspects of users' devices (system logs, general applications) but not Keychain process memory

  • Social Engineering: Standard surveillance techniques (video capture, location tracking, data from other applications)

  • Identity Correlation: May know mappings between real-world identities and their Keychain personas

  • Protocol Participation: Can pair with parties and participate in the Keychain protocol

Limitations

  • Cannot access Keychain process memory or secure storage

  • Cannot intercept passphrases during secure entry

  • Cannot alter data in transit (though may attempt injection attacks)

  • Limited computational resources for cryptographic attacks

Intermediate Adversary

Intermediate adversaries possess additional resources and capabilities beyond weak adversaries.

Enhanced Capabilities

  • Traffic Analysis: Deep analysis of message patterns, timing, and metadata to infer communication content

  • Chosen Ciphertext Attacks: Access to Keychain-compatible software to perform sophisticated cryptographic attacks

  • Identity Mapping: Comprehensive knowledge of real-world participant identities and their corresponding Keychain personas

  • Content Inference: Ability to deduce general message subjects through pattern analysis

Attack Strategies

  • Timing Attacks: Exploitation of timing variations in cryptographic operations

  • Side-Channel Analysis: Use of metadata and behavioral patterns to infer sensitive information

  • Targeted Cryptographic Attacks: Focused attacks on specific encryption instances

Mitigation Requirements

Applications may need to implement additional protections against intermediate adversaries:

  • Padding Strategies: Adding random padding to obscure message sizes

  • Timing Obfuscation: Introducing random delays to prevent timing analysis

  • Traffic Shaping: Normalizing communication patterns to reduce metadata leakage

Strong Adversary

Strong adversaries represent nation-state level threats with significant resources and capabilities.

Advanced Capabilities

Strong adversaries possess one or more of the following capabilities:

  • Infrastructure Control: Control over network channels, hardware manufacturers, or critical infrastructure

  • Device Compromise: Ability to obtain root access to user devices

  • Computational Resources: Extreme computational power sufficient to brute-force private keys within the chosen cryptoperiod

Attack Scenarios

  • Supply Chain Attacks: Compromise of hardware or software during manufacturing or distribution

  • Zero-Day Exploits: Use of unknown vulnerabilities to compromise secure devices

  • Nation-State Resources: Deployment of advanced persistent threats and sophisticated attack campaigns

  • Quantum Computing: Potential future capability to break current cryptographic schemes

Protection Limitations

Against strong adversaries, Keychain Core’s security guarantees may be reduced or eliminated:

  • Device Compromise: If the endpoint is compromised, local security guarantees are void

  • Cryptographic Breaks: Sufficient computational power may overcome cryptographic protections

  • Infrastructure Attacks: Control of critical infrastructure may enable various attack scenarios

Security Guarantees

Keychain Core provides specific security guarantees against the defined adversary classes.

Encryption Security

Semantic Security (IND-CCA2)

Each encrypted message maintains semantic security under adaptive chosen-ciphertext attacks by weak and intermediate adversaries:

  • Confidentiality: Encrypted data remains confidential regardless of storage location or transmission medium

  • Integrity: Tampering with ciphertext or associated authenticated data is detectable

  • Access Control: Only recipients explicitly granted access can decrypt data using their private keys

  • Attack Resistance: Protection against adaptive chosen-ciphertext attacks within the cryptoperiod

Tamper Evidence

The system provides comprehensive tamper detection:

  • Data Integrity: Any modification of encrypted data is detectable by recipients

  • Authentication Data: Associated metadata cannot be altered without detection

  • Decryption Protection: Recipients are prevented from receiving results of tampered ciphertext

Digital Signature Security

Existential Unforgeability (EUF-CMA)

Digital signatures provide protection against existential forgery under adaptive chosen message attacks:

  • Signature Authenticity: Signatures cannot be forged by weak or intermediate adversaries

  • Message Integrity: Any alteration of signed data or signatures is detectable

  • Non-Repudiation: Valid signatures provide cryptographic proof of authorship

  • Identity Verification: Recipients are notified when signatures come from unknown or unpaired entities

Trust Relationship Validation

The signature system includes trust relationship validation:

  • Known Signer Detection: Recipients are alerted when signatures come from unknown entities

  • Pairing Validation: The system verifies whether signers were previously paired with recipients

  • Trust Chain Verification: Signature validation includes verification of trust relationships

Security Considerations for Deployment

Operational Security

Key Management

  • Implement secure key generation, storage, and rotation procedures

  • Use hardware security modules (HSMs) where appropriate

  • Establish clear key recovery and escrow policies

Network Security

  • Deploy network monitoring to detect anomalous traffic patterns

  • Implement defense-in-depth strategies for network protection

  • Use secure communication channels for sensitive operations

Device Security

  • Maintain up-to-date operating systems and security patches

  • Implement device encryption and secure boot processes

  • Use endpoint detection and response (EDR) solutions

Application Integration

Threat Boundary Management

  • Clearly define the security boundaries between Keychain Core and application code

  • Implement appropriate input validation and sanitization

  • Design applications to fail securely when Keychain operations fail

Privacy Protection

  • Implement traffic obfuscation techniques for sensitive applications

  • Consider using mix networks or onion routing for enhanced privacy

  • Design communication patterns to minimize metadata leakage

Regulatory Compliance

  • Ensure digital signature implementation meets relevant legal standards

  • Implement audit logging for compliance requirements

  • Consider data residency and sovereignty requirements

Business Continuity

  • Develop key recovery procedures for business continuity

  • Implement appropriate backup and disaster recovery procedures

  • Plan for cryptographic agility and algorithm migration

Threat Mitigation Strategies

Defense Against Weak Adversaries

  • Encryption: Use strong, validated encryption algorithms with appropriate key sizes

  • Authentication: Implement robust message authentication and digital signatures

  • Key Management: Use secure key generation and distribution mechanisms

  • Protocol Security: Follow established secure communication protocols

Defense Against Intermediate Adversaries

  • Traffic Analysis Resistance: Implement padding, timing obfuscation, and traffic shaping

  • Side-Channel Protection: Use constant-time algorithms and secure implementations

  • Advanced Authentication: Implement multi-factor authentication and enhanced identity verification

  • Metadata Protection: Minimize exposure of communication metadata

Defense Against Strong Adversaries

  • Cryptographic Agility: Design systems to support algorithm upgrades and migration

  • Zero-Trust Architecture: Assume compromise and implement verification at every step

  • Hardware Security: Use trusted execution environments and hardware security modules

  • Operational Resilience: Implement robust incident response and recovery procedures

Conclusion

The Keychain Core security threat model provides a comprehensive framework for understanding and managing security risks in distributed PKI applications. By clearly defining adversary capabilities and security guarantees, this model enables developers and organizations to make informed decisions about deployment and operational security.

Key Takeaways

  • Device Security is Critical: The security assumptions require maintaining device integrity and passphrase confidentiality

  • Adversary Capabilities Vary: Different threat actors require different defensive strategies

  • Layered Defense: Multiple security measures are needed to address various attack scenarios

  • Operational Security Matters: Technical security must be combined with appropriate operational practices

Organizations implementing Keychain Core should use this threat model to inform their security architecture, operational procedures, and risk management strategies.