Encrypted Backups

ZestSSH backup files use the .zest format. All backups are encrypted — there is no option to export an unencrypted dump. Storing plaintext SSH credentials, private keys, and known hosts in user-accessible storage would be a serious security risk if the device is shared, lost, or scanned by another app.

This is a free feature — not paywalled.

File Format

Every .zest file has the following binary structure:

Offset	Size	Content
0	4 bytes	Magic bytes: ZEST (ASCII)
4	1 byte	Version byte
5	Variable	Encrypted payload

Version Byte

Version	Meaning
1	Encrypted (current) — AES-256-GCM with Argon2id-derived key
2	Legacy unencrypted JSON (import-only, never generated by current builds)

Encrypted Payload (Version 1)

The encrypted payload is structured as:

salt(32 bytes) + IV(12 bytes) + GCM tag(16 bytes) + ciphertext

• Salt: 32 random bytes used for Argon2id key derivation.
• IV: 12-byte AES-GCM initialization vector.
• GCM tag: 16-byte authentication tag for integrity verification.
• Ciphertext: zlib-compressed JSON, encrypted with AES-256-GCM.

Encryption Process

1. All app data is gathered via SyncDataService.gatherAll() into a JSON map.
2. A 32-byte random salt is generated.
3. The user’s backup password is run through Argon2id with the salt to derive a 256-bit key (same parameters as Cloud Sync: 64 MB memory, 3 iterations, 4 parallelism).
4. The JSON is zlib-compressed and encrypted with AES-256-GCM using the derived key.
5. The output is prefixed with the ZEST magic bytes and version 1.

Password Requirements

• Minimum length: 12 characters
• Empty or short passwords are rejected before any encryption occurs.
• The 12-character minimum is enforced because backups land in user-accessible storage (Downloads folder, Files app), where the password is the only barrier against an offline attacker.

What’s Included

A backup contains everything needed to fully restore your ZestSSH configuration:

Data	Included
Connections (host, port, settings, groups)	Yes
Identities (usernames, auth methods)	Yes
Identity secrets (passwords, private keys)	Yes (encrypted)
Connection groups	Yes
Known hosts (fingerprints)	Yes
Snippets	Yes
Port forward rules	Yes

Data that is not included:

• Terminal transcripts / session recordings
• Automation history / audit logs
• App settings and preferences
• Theme customizations

Export Flow

1. Go to Settings > Backup & Restore > Export Backup.
2. Enter a backup password (minimum 12 characters).
3. ZestSSH encrypts all data and writes the .zest file.

File Location by Platform

Platform	Location
Android	/storage/emulated/0/Download/
iOS	Application Documents (accessible via the Files app)
Desktop (Windows/macOS/Linux)	Documents/ZestSSH/backups/

Filename Format

• Manual backups: zestssh_backup_YYYY-MM-DDTHH-MM-SS.zest
• Auto-backups: zestssh_auto_YYYY-MM-DDTHH-MM-SS.zest

Import Flow

1. Go to Settings > Backup & Restore > Import Backup.
2. Select a .zest file.
3. Enter the backup password.
4. ZestSSH decrypts and restores the data.

Import Behavior

• Additive merge: Local data is NOT deleted. Existing records are updated, new records are inserted. This is an upsert, not a replace.
• Identity secrets are restored to Flutter Secure Storage after the database transaction succeeds, preventing orphaned secrets if the transaction rolls back.
• Legacy v2 backups (unencrypted) are accepted for backward compatibility but trigger a UI warning urging the user to re-export with a password.

Import Size Limit

Files larger than 50 MB are rejected before loading into memory to prevent out-of-memory crashes from malicious or corrupted files.

Error Handling

Error	Cause
”Invalid backup file format”	Missing or incorrect ZEST magic bytes
”This backup is password-protected”	Version 1 file but no password entered
”Wrong password or corrupted backup”	AES-GCM decryption failed (wrong key or tampered data)
“Unsupported backup version”	Unknown version byte
”Backup file is too large (max 50 MB)“	File exceeds the safety limit
”Backup file not found”	File path does not exist