How Bitwarden Encrypts and Decrypts Secrets
a day ago
- Bitwarden encrypts all secrets (passwords, usernames, URLs, notes, etc.) on the client before sending to the server.
- The master key is a 64-byte random sequence split into a 32-byte encryption key and a 32-byte MAC key.
- Encrypted secrets are stored in version 2 format: initialization vector (iv), ciphertext, and MAC signature, all base64 encoded.
- Decryption uses AES-256 in CBC mode with PKCS7 padding, and integrity is verified via HMAC-SHA256.
- To decrypt the master key, the client derives keys from the user's email and passphrase using PBKDF2 (600,000 iterations) and HKDF-Expand.
- The author provides complete Python code for both decryption and encryption of secrets.
- The author plans to build a custom client that syncs with a Vaultwarden database but keeps secret management local.