Bitwarden Security Context Agent Skill

Bitwarden Security Context

Quick-reference for Bitwarden's foundational security framework. Use this for security context during development, code review, or security analysis without loading the full threat-modeling or architecture-review skills.

Security Principles (P01-P06)

These six principles form the foundation for all security decisions at Bitwarden.

| Principle | Name | Core Guarantee |

| --------- | -------------------------------------------- | ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |

| P01 | Servers are Zero Knowledge | Bitwarden infrastructure cannot access unencrypted user data. The server must not enable weakening of user-chosen protections, masquerade server data as user-encrypted content, or access encrypted data outside the client context. |

| P02 | A Locked Vault is Secure | Highly sensitive vault data cannot be accessed in plaintext once the vault is locked, even if the device is compromised after locking. Platform limitations (e.g., JS memory) are mitigated through buffer clearing and available security features. |

| P03 | Limited Security on Semi-Compromised Devices | For unlocked vaults on devices with userspace malware (but intact OS/kernel), clients maximize kernel/OS-level protections and balance security with usability through controls like biometrics. |

| P04 | No Security on Fully Compromised Systems | Bitwarden cannot guarantee vault protection when hardware or OS-level integrity is fully compromised. This applies to unlocked vaults only — locked vaults are covered by P02. |

| P05 | Controlled Access to Vault Data | Vault data, whether at rest or in use, is accessible only to authorized parties under the user's explicit control. Isolation mechanisms are critical in high-risk environments like web browsers. |

| P06 | Minimized Impact of Security Breaches | Limit breach scope and duration through session invalidation, key rotation (countering "harvest now, decrypt later"), and post-compromise security (new data remains protected after a breach). |

Controlled Exceptions

Principles have documented exceptions. Known examples:

• P01 — Key Connector: Self-hosted SSO without passwords. The server holds encryption keys on behalf of the user.
• P01 — Icons Service: Plaintext domain names are sent to retrieve favicons.

Full documentation: Security Principles

Security Vocabulary

Standard terminology for security discussions at Bitwarden.

| Term | Definition |

| -------------------------------- | ---------------------------------------------------------------------------------------------------------------------------- |

| Vault Data | A user's private information stored in Bitwarden (passwords, usernames, secure notes, credit cards, identities, attachments) |

| Protected Data | Data stored in unreadable format (typically encrypted) with expectations about secure key storage |

| Data at Rest | Stored data not actively used or transmitted (disk storage on devices or servers) |

| Data in Use | Data actively being processed or accessed, held in volatile memory |

| Data in Transit | Data actively transferred between locations, processes, or devices |

| Secure Channel | A communication channel providing confidentiality (unreadable to unauthorized parties) and integrity (tamper-proof) |

| Trusted Channel | A secure channel that also provides authenticity (verified identities of communicating parties) |

| Data Exporting | Controlled process where data leaves Bitwarden unprotected, nullifying security guarantees. Requires informed consent. |

| Data Sharing | Controlled data exchange within the Bitwarden secure environment (security guarantees maintained) |

| Data Leaking | Unintentional departure of data from Bitwarden unprotected |

| Bitwarden Secure Environment | Any process or application adhering to Bitwarden's security standards |

Full documentation: Security Definitions

Security Requirements by Category

| Category | Scope | Key Obligations |

| -------- | --------------------- | --------------------------------------------------------------------------------------------------------------------------------------------------- |

| VD | Vault Data | Protected at rest (encrypted with UserKey), allowed in use (decrypted during unlock), trusted channels in transit, export requires informed consent |

| EK | Encryption Keys | 256-bit security strength, protected at rest and in transit, must never be exported |

| AT | Authentication Tokens | Protected storage at rest, mandatory transit protection |

| SC | Secure Channels | Confidentiality, integrity, replay prevention, forward secrecy for long-lived channels |

| TC | Trusted Channels | Secure channel properties plus receiver identity verification |

Full documentation: Security Requirements

Architecture Decision Records (ADRs)

Bitwarden's accepted architecture decisions are catalogued separately from the security principles above. See ${CLAUDE_PLUGIN_ROOT}/references/adr-alignment.md for how security assessments should check alignment against them.