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attack-surface.md

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Attack Surface Analysis for google/tink

Attack Surface: Keyset Leakage from Insecure Storage

  • Description: Keysets, containing sensitive cryptographic keys managed by Tink, are stored insecurely, leading to unauthorized access and compromise.
  • Tink Contribution: Tink requires keysets to be stored persistently. While Tink provides APIs for serialization and deserialization of keysets, it delegates the responsibility of secure storage entirely to the application developer. This design choice makes insecure storage a direct attack surface when using Tink.
  • Example: A developer stores serialized Tink keysets as plaintext files on a web server without proper access controls. An attacker gains access to the server and retrieves the keyset files, compromising all cryptographic operations using those keys.
  • Impact: Complete compromise of cryptographic operations protected by the leaked keyset. Attackers can decrypt data, forge signatures, and impersonate legitimate entities.
  • Risk Severity: Critical
  • Mitigation Strategies:
    • Utilize dedicated Key Management Systems (KMS) or Hardware Security Modules (HSM): Integrate Tink with KMS or HSM for secure keyset storage and management. Tink provides interfaces for KMS integration.
    • Encrypt keysets at rest: If file-based storage is necessary, encrypt the serialized keyset files using strong encryption before storing them. Manage the encryption key separately and securely, ideally outside of the application's storage.
    • Implement robust access control: Restrict file system permissions or database access to keyset storage, ensuring only authorized processes and users can access them.
    • Regular security audits of keyset storage: Periodically review and test the security of the chosen keyset storage mechanism.

Attack Surface: Keyset Exposure in Memory

  • Description: Tink keysets are loaded into application memory to perform cryptographic operations. If application memory is compromised, the active keyset can be extracted.
  • Tink Contribution: Tink's design necessitates loading keysets into memory to perform cryptographic operations. This inherent requirement creates a window of vulnerability where keys are exposed in memory while in use by Tink.
  • Example: An attacker exploits a memory corruption vulnerability (e.g., buffer overflow) in the application or a library it depends on. They then perform a memory dump of the application process. This memory dump contains the Tink keyset currently loaded and used by the application.
  • Impact: Compromise of active cryptographic operations. Attackers can potentially intercept and decrypt data being processed or forge signatures in real-time if they can extract the keyset from memory.
  • Risk Severity: High
  • Mitigation Strategies:
    • Minimize keyset lifetime in memory: Load keysets only when actively needed for cryptographic operations and unload them from memory as soon as possible after use.
    • Harden application against memory exploits: Employ memory-safe programming practices, robust input validation, and regularly patch application dependencies to reduce the risk of memory corruption vulnerabilities that could lead to memory dumps.
    • Consider using secure enclaves or Trusted Execution Environments (TEEs): If highly sensitive operations are involved, explore using TEEs to isolate Tink and keysets in a protected memory region, reducing the attack surface for memory-based attacks.

Attack Surface: Deserialization of Malicious Keyset

  • Description: An application using Tink deserializes a keyset from an untrusted or compromised source. Vulnerabilities in Tink's keyset deserialization process can be exploited.
  • Tink Contribution: Tink provides APIs for deserializing keysets from various formats (e.g., binary, JSON, protobuf). If vulnerabilities exist within Tink's deserialization implementations, they can be triggered by malicious keyset data.
  • Example: An attacker intercepts the keyset retrieval process and replaces a legitimate keyset with a crafted malicious keyset. When the application deserializes this malicious keyset using Tink's API, a buffer overflow or other vulnerability in Tink's deserialization code is triggered, leading to remote code execution on the application server.
  • Impact: Remote code execution, denial of service, or data corruption, depending on the specific vulnerability in Tink's deserialization process.
  • Risk Severity: High to Critical (depending on the vulnerability type)
  • Mitigation Strategies:
    • Strictly validate keyset source: Only deserialize keysets from highly trusted and authenticated sources. Implement strong integrity checks to ensure keysets haven't been tampered with during transit or storage.
    • Keep Tink and dependencies updated: Regularly update Tink and its dependencies (especially protobuf if used for keyset serialization) to patch known deserialization vulnerabilities.
    • Input validation (limited for binary formats): While challenging for binary formats like protobuf, perform as much validation as possible on the structure and metadata of the keyset data before invoking Tink's deserialization API.

Attack Surface: Vulnerabilities in Tink Library Itself

  • Description: Bugs, security flaws, or implementation vulnerabilities exist within the Tink library's codebase itself.
  • Tink Contribution: As with any software library, Tink is susceptible to containing vulnerabilities in its code, including cryptographic primitive implementations, key management logic, or supporting functionalities.
  • Example: A vulnerability is discovered in Tink's implementation of a specific cryptographic algorithm (e.g., a side-channel timing attack in AES implementation, or a buffer overflow in RSA padding). An attacker can exploit this vulnerability by crafting specific inputs or triggering certain operations through Tink's API, leading to information leakage or potentially remote code execution.
  • Impact: Wide range of impacts, from information disclosure (key leakage, plaintext recovery) to denial of service or remote code execution, depending on the nature and location of the vulnerability within Tink.
  • Risk Severity: Medium to Critical (depending on the vulnerability type and exploitability)
  • Mitigation Strategies:
    • Maintain up-to-date Tink library: Always use the latest stable version of Tink to benefit from bug fixes and security patches released by the Tink development team.
    • Monitor Tink security advisories and release notes: Subscribe to Tink's security mailing lists or regularly check release notes and security advisories to stay informed about known vulnerabilities and recommended updates.
    • Security scanning of Tink dependencies: Regularly scan Tink's dependencies (e.g., BoringSSL, protobuf) for known vulnerabilities and update them promptly.
    • Participate in security community and reporting: If you discover a potential vulnerability in Tink, responsibly report it to the Tink security team to contribute to the library's overall security.