Secret Sharing with zKettle

Share passwords, API keys, tokens, certificates, and other sensitive data via self-destructing, one-time URLs. All encryption happens client-side — the server stores only ciphertext.

Prerequisites

This skill requires a running zKettle MCP server. If zKettle is not installed or configured, see the zKettle README for installation and MCP setup instructions. zKettle also offers a CLI, HTTP API, and Web UI — refer to the README if the MCP tools are insufficient for a particular workflow.

How It Works

• Secrets are encrypted with AES-256-GCM on the client
• The decryption key lives in the URL fragment (#key) — never sent to the server
• Secrets auto-delete after a configurable view count or time limit
• The server is zero-knowledge: it stores only ciphertext and metadata

Tools

create_secret

Encrypt and store a secret, returning an expiring URL.

Provide exactly one of content or file. Returns url (with decryption key in fragment) and delete_token.

read_secret

Decrypt a secret from a zKettle URL. Consumes one view.

Returns decrypted plaintext by default, or a confirmation message when file or clipboard is used.

revoke_secret

Permanently delete a secret before it expires.

list_secrets

List all active secrets (metadata only — no content or keys). Returns IDs, creation time, expiry, and remaining views.

generate_secret

Generate a cryptographically random secret. Optionally encrypt and store it in one step.

Returns raw generated text, or url + delete_token when create=true.

Defaults

• 1 view if views is omitted (single-use)
• 1440 minutes (24 hours) if minutes is omitted

Limits

• 500KB max plaintext per secret
• 100 views max per secret
• 43200 minutes (30 days) max TTL

Secure Patterns

Plaintext secrets can appear in conversation context (tool inputs/outputs). Use these patterns to minimize exposure.

Creating secrets — keep plaintext out of context

• create_secret(file="/path/to/secret.txt") — reads from file, plaintext never in tool call. Ask the user before deleting the source file afterward.
• generate_secret(create=true) — generates + encrypts in one step, plaintext never in response
• Prefer these over create_secret(content="...") which puts the raw value in conversation context

Reading secrets — keep plaintext out of context

• read_secret(url="...", file="/tmp/secret.txt") — writes to file, returns confirmation only
• read_secret(url="...", clipboard=true) — copies to user's clipboard, returns confirmation only
• Subagents can read the file at the written path without the secret entering conversation context
• Default read_secret(url="...") returns plaintext directly into conversation — warn the user before using this form
• File cleanup: Files written by file do NOT self-destruct. After the secret has been used, ask the user for permission to delete the file, then remove it. Do not leave secret files on disk.

Common Workflows

Share a credential with someone

1. create_secret(file="/path/to/credential.txt", views=1, minutes=60)
   — or create_secret(content="the-password", views=1, minutes=60) if plaintext exposure is acceptable
2. Share the returned URL with the recipient

The secret vanishes after one view or 60 minutes, whichever comes first.

Rotate an API key

1. generate_secret(create=true, length=48, charset="alphanumeric", views=2, minutes=240)
2. Share the URL with the team member who needs it
3. revoke_secret(id="old-secret-id", delete_token="old-token") to kill the old one

Temporary access grant

1. create_secret(content="temp-token", views=1, minutes=30)
2. Send the one-time link — expires after a single view or 30 minutes

Audit active secrets

1. list_secrets() — review what's still live
2. revoke_secret() on any that are no longer needed

Read a shared secret

1. Receive a zKettle URL from a human or another agent
2. read_secret(url="https://example.com/s/abc123#key", file="/tmp/secret.txt")
   — or read_secret(url="...", clipboard=true) to copy to clipboard
   — or read_secret(url="...") to return plaintext directly (enters conversation context)
3. Use the decrypted content

Agent-to-Agent Secret Sharing

zKettle is well-suited for secure coordination between agents — subagents, teammates, or any multi-agent workflow where credentials need to move between contexts without leaking into conversation logs.

When to use

• A subagent needs a credential to complete its task (e.g., an engineer agent needs a deploy token)
• Agents on a team need to pass secrets to each other without the lead's context window seeing the plaintext
• A workflow generates a credential in one agent and consumes it in another

Pattern: file-based handoff (recommended)

The creating agent writes the secret to zKettle, passes only the URL to the receiving agent. The receiving agent reads it to a file, uses it, then cleans up.

Agent A (creator):
1. create_secret(content="deploy-token-xyz", views=1, minutes=30)
2. Send the URL to Agent B via message

Agent B (consumer):
1. read_secret(url="...", file="/tmp/deploy-token.txt")
2. Use the file contents for the task
3. Delete /tmp/deploy-token.txt when done

The plaintext never enters either agent's conversation context — Agent A sees only the URL and delete token, Agent B sees only a confirmation message.

Pattern: generated credential handoff

When the secret doesn't need to be a specific value (e.g., a new API key, a temporary password):

Agent A:
1. generate_secret(create=true, length=48, views=2, minutes=60)
2. Send the URL to Agent B and keep the delete_token
3. After Agent B confirms usage, revoke_secret() to clean up

Guidelines

• Set views to the exact number of agents that need to read the secret — no more
• Use short TTLs (minutes) appropriate to the workflow duration
• The creating agent should retain the delete_token and revoke after the workflow completes
• Prefer file on the read side so plaintext stays out of all conversation contexts
• The receiving agent is responsible for deleting the local file after use

Gotchas

• URL fragments matter: The #key portion contains the decryption key. Some tools strip URL fragments — always ensure the full URL (including #key) is passed to read_secret.
• Reading consumes a view: If the secret has only 1 view remaining, read_secret permanently destroys it. Warn the user before reading single-view secrets.
• `list_secrets` is metadata only: It returns IDs, creation time, expiry, and remaining views — never content or decryption keys.
• Conversation exposure: Using create_secret(content="...") puts the plaintext in the conversation context. Use generate_secret(create=true) when the user doesn't need a specific value.