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Security Guide

CrossTerm is designed with security as a core principle. This guide covers the encryption model, credential storage, SSH security, and best practices for keeping your connections safe.

Credential Vault Encryption

Encryption Algorithm

All credentials stored in the vault are encrypted using AES-256-GCM (Advanced Encryption Standard with 256-bit keys in Galois/Counter Mode). This provides both confidentiality and authenticity — any tampering with encrypted data is detected.

  • Algorithm: AES-256-GCM
  • Key Size: 256 bits
  • Nonce: 96-bit random nonce per encryption operation
  • Tag Size: 128-bit authentication tag

Key Derivation

The encryption key is derived from your master password using Argon2id, the winner of the Password Hashing Competition. Argon2id combines:

  • Memory-hardness — Requires significant RAM, making GPU/ASIC attacks expensive
  • Time-hardness — Multiple iterations increase computation cost
  • Side-channel resistance — The "id" variant resists timing attacks

Default parameters: - Memory: 64 MiB - Iterations: 3 - Parallelism: 4 - Salt: 16 bytes (randomly generated per vault) - Output: 32 bytes (256-bit key)

Memory Protection

Key material is held in Rust's Zeroizing<Vec<u8>> wrapper, which guarantees the key is overwritten with zeros when it goes out of scope. This prevents key material from lingering in memory after the vault is locked.

No Backdoor

There is no password recovery mechanism. If you forget your master password, the vault contents cannot be recovered. This is by design — it ensures that even the application developers cannot access your credentials.

Master Password Best Practices

Choose a strong master password:

  1. Length — Use at least 12 characters. Longer is better.
  2. Complexity — Mix uppercase, lowercase, numbers, and symbols.
  3. Uniqueness — Never reuse your master password elsewhere.
  4. Passphrase — Consider a random multi-word passphrase (e.g., "correct-horse-battery-staple").
  5. Password Manager — Store your master password in a separate password manager as a backup.

Auto-Lock

Configure automatic vault locking from Settings → Security → Vault Auto-Lock. Set the idle timeout in minutes (0 = never auto-lock). The default is 15 minutes of inactivity.

Clipboard Auto-Clear

When you copy a password from the vault, CrossTerm can automatically clear your clipboard after a configurable delay. Set this from Settings → Security → Clipboard Auto-Clear (seconds, 0 = never).

SSH Security

Known Hosts Verification

CrossTerm verifies SSH server fingerprints against a known hosts database:

  1. First Connection — You are prompted to accept or reject the server's host key fingerprint.
  2. Subsequent Connections — The fingerprint is compared against the stored value. If it changes, CrossTerm warns you of a potential man-in-the-middle attack.
  3. Storage — Known hosts are stored locally per profile, isolated from other profiles.

Cipher Policy

CrossTerm supports modern SSH ciphers and key exchange algorithms:

Ciphers (in order of preference): - chacha20-poly1305@openssh.com - aes256-gcm@openssh.com - aes128-gcm@openssh.com - aes256-ctr - aes192-ctr - aes128-ctr

Key Exchange: - curve25519-sha256 - curve25519-sha256@libssh.org - ecdh-sha2-nistp256 - ecdh-sha2-nistp384 - diffie-hellman-group16-sha512 - diffie-hellman-group14-sha256

Host Key Algorithms: - ssh-ed25519 - ecdsa-sha2-nistp256 - ecdsa-sha2-nistp384 - rsa-sha2-512 - rsa-sha2-256

Legacy algorithms (e.g., arcfour, blowfish-cbc, diffie-hellman-group1-sha1) are not supported.

SSH Key Types

CrossTerm supports the following SSH key types for authentication:

  • Ed25519 (recommended) — Fast, secure, compact keys
  • ECDSA (P-256, P-384, P-521) — Elliptic curve keys
  • RSA (2048-bit minimum) — Legacy compatibility; 4096-bit recommended

Agent Forwarding

SSH agent forwarding allows you to use your local SSH keys on remote servers without copying the keys. Enable it per-session in the connection settings. Caution: Only enable agent forwarding on trusted servers, as a compromised server could use your forwarded agent.

Credential Storage

Supported Credential Types

The vault stores six types of credentials:

Type Use Case
Password Username/password authentication
SSH Key Key-based SSH authentication
Certificate X.509 certificate authentication
API Token Service tokens (GitHub, AWS, etc.)
Cloud Credential AWS/Azure/GCP access keys
TOTP Seed Time-based one-time passwords

Sensitive Field Handling

  • Sensitive fields (passwords, private keys, tokens) are marked with #[serde(skip_serializing)] and never written to logs or exported.
  • All identifiers use UUID v4 for unpredictability.
  • Credentials are encrypted individually — compromising one does not expose others.

Audit Trail

CrossTerm logs security-relevant events to the Audit Log:

  • Vault unlock / lock events
  • Credential access (read, create, update, delete)
  • SSH connection attempts and authentication results
  • Port forwarding setup and teardown
  • Profile switches

View the audit log from the Bottom Panel → Audit Log tab. Logs are stored locally and scoped per profile.

Security Checklist

  • [ ] Use a strong, unique master password (12+ characters)
  • [ ] Enable vault auto-lock (15 minutes or less)
  • [ ] Enable clipboard auto-clear for copied passwords
  • [ ] Use Ed25519 SSH keys where possible
  • [ ] Verify SSH host key fingerprints on first connection
  • [ ] Only enable SSH agent forwarding on trusted hosts
  • [ ] Run cargo audit and npm audit regularly
  • [ ] Keep CrossTerm updated for security patches