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@erickwendel/ciphersuite-mcp

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@erickwendel/ciphersuite-mcp

An MCP (Model Context Protocol) server that provides AES-256-CBC encryption and decryption tools, a resource describing the algorithm, and ready-to-use prompts — all runnable directly inside VS Code Copilot Chat.

What it does

Capability

Name

Description

🔧 Tool

encrypt_message

Encrypts any plain-text message with a passphrase

🔧 Tool

decrypt_message

Decrypts a previously encrypted message with the same passphrase

📄 Resource

encryption://info

Returns details about the algorithm, key derivation, and output format

💬 Prompt

encrypt_message_prompt

Pre-built prompt that asks the agent to encrypt a message

💬 Prompt

decrypt_message_prompt

Pre-built prompt that asks the agent to decrypt a message

How encryption works

  • Algorithm: AES-256-CBC

  • Key derivation: scrypt(passphrase, fixedSalt, 32) — you pass any passphrase string; the server derives a strong 32-byte key automatically

  • Output format: <IV in hex>:<ciphertext in hex> — keep the full string to decrypt later

  • IV: a fresh random 16-byte IV is generated on every encryption call, so the same message encrypted twice produces different output

Related MCP server: Vibe Coder MCP

Prerequisites

  • Node.js v24+ (see engines in package.json)

Installation

npm install

No build step is needed — the server runs TypeScript directly via Node.js native TypeScript support.

Using in VS Code

1. Add the MCP server configuration

Create (or open) .vscode/mcp.json in your workspace and add:

{
  "servers": {
    "ciphersuite-mcp": {
      "command": "node",
      "args": ["--experimental-strip-types", "ABSOLUTE_PATH_TO_PROJECT/src/index.ts"]
    }
  }
}

or via npm

{
  "servers": {
    "ciphersuite-mcp": {
      "command": "npx",
      "args": ["-y", "@erickwendel/ciphersuite-mcp"]
    }
  }
}

Tip: You can also add this server to your user-level MCP config at ~/.vscode/mcp.json to make it available in every workspace.

2. Reload VS Code

Open the Command Palette (Cmd+Shift+P) and run Developer: Reload Window (or just restart VS Code).

3. Use it in Copilot Chat

Open Copilot Chat (Agent mode) and try:

Encrypt the message "Hello, World!" using the passphrase "my-secret-key"
Decrypt this message: a3f1...:<ciphertext> using the passphrase "my-secret-key"
Show me the encryption://info resource

The agent will automatically call the appropriate tool and return the result.

Running the MCP Inspector

The MCP Inspector lets you explore and test all tools, resources, and prompts interactively in a browser UI:

npm run mcp:inspect

This opens the inspector at http://localhost:5173 and connects it to the running server.

Running tests

# Run all tests once
npm test

# Run tests in watch mode (with debugger)
npm run test:dev

The test suite covers:

  • Encrypting a message

  • Decrypting a message with the correct passphrase

  • Listing and reading the encryption://info resource

  • Fetching both prompts

  • Error: decrypting with the wrong passphrase

  • Error: decrypting a malformed ciphertext

Project structure

src/
  index.ts   # Entry point — connects the server to stdio transport
  mcp.ts     # All tools, resources, and prompts are registered here
tests/
  mcp.test.ts

Available scripts

Script

Description

npm start

Start the server (used by MCP clients)

npm run dev

Start with file-watch and Node.js inspector

npm test

Run all tests

npm run test:dev

Run tests in watch mode

npm run mcp:inspect

Open the MCP Inspector UI

serverMCP

Available Tools

2 tools
decrypt_messageA

Decrypt a message that was encrypted with the encrypt_message tool

ParametersJSON Schema
NameRequiredDescriptionDefault
encryptionKeyYesThe same passphrase used during encryption
encryptedMessageYesThe encrypted message (format: iv:ciphertext)

Output Schema

ParametersJSON Schema
NameRequiredDescription
decryptedMessageYesThe decrypted plain-text message

TDQS

A3.8/5.0
Behavior2/5

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

No annotations are provided, so the description must disclose behavioral traits. It does not state whether the operation is read-only, has side effects, or what happens on failure (e.g., wrong key). The only behavioral detail is the requirement for the same passphrase, which partially addresses input constraints but not the tool's overall safety profile. This is a significant gap.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness5/5

Is the description appropriately sized, front-loaded, and free of redundancy?

A single, front-loaded sentence with zero filler. It states the verb, object, and connection to the sibling tool efficiently, making it easy to scan and understand quickly.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness4/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

Given the tool's simplicity, full parameter coverage, and presence of an output schema, the description is mostly complete. It correctly identifies the key requirement and relationship to encrypt_message. However, lacking behavioral disclosure (e.g., error handling, purity) means it is not fully complete for an agent deciding to invoke it safely.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters3/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema coverage is 100%, so each parameter already has a description. The tool description adds minimal semantic value beyond mentioning the key matches encrypt_message, which mirrors what the schema already states. This meets the baseline for full schema coverage but does not provide additional meaning.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

States a specific verb ('Decrypt') and resource ('a message'), and explicitly ties it to the encrypt_message tool, which differentiates it from the sibling. It is not a tautology; it names the exact operation and its counterpart.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines4/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

Clearly implies usage context by referencing encrypt_message, indicating it is the decryption counterpart. However, it does not explicitly state when not to use it or name alternative tools beyond the implicit sibling relationship. This is clear context but lacks explicit exclusions.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.

encrypt_messageC

Encrypt a message

ParametersJSON Schema
NameRequiredDescriptionDefault
messageYesThe message to encrypt
encryptionKeyYesAny passphrase to use for encryption — the server derives a strong key from it automatically

Output Schema

ParametersJSON Schema
NameRequiredDescription
encryptedMessageYesThe encrypted message (format: iv:ciphertext)

TDQS

C2.8/5.0
Behavior2/5

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

With no annotations provided, the description carries the full burden for behavioral disclosure, but it only states the action. It does not mention that encryption is irreversible (without the key), the output format, or any side effects. The schema hints at key derivation, but the description itself adds no behavioral context.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness3/5

Is the description appropriately sized, front-loaded, and free of redundancy?

The description is concise and front-loaded, but it essentially restates the tool name without adding operational detail. While not verbose, it doesn't earn its place beyond the name—acceptable but minimal.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness2/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

Despite an output schema existing, the description is too sparse for an encryption operation. It lacks information about when encryption is appropriate, the nature of the output, or any warnings. The agent is left to infer everything from the schema and sibling naming, which is insufficient for correct invocation in varied contexts.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters3/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema description coverage is 100% for both parameters, so the schema already documents 'message' and 'encryptionKey' with meaningful descriptions. The tool description adds no extra parameter information, but the baseline is 3 given high schema coverage.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose4/5

Does the description clearly state what the tool does and how it differs from similar tools?

The description clearly states the action ('Encrypt a message') with a specific verb and resource. It implicitly distinguishes from the sibling tool 'decrypt_message' by focusing on encryption, though it doesn't explicitly name the alternative.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines2/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

No guidance on when to use this tool versus decrypt_message or any other context. There is no mention of prerequisites, security considerations, or typical use cases.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.

Tool Schema Changelog

Recent tool additions, removals, and schema changes observed during successful MCP inspections.

  1. 2 tool updatesv0.0.1
    • First observeddecrypt_message
    • First observedencrypt_message
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TDQS

B3.4/5.0

Scored across 2 tools

Disambiguation5/5

The two tools, encrypt_message and decrypt_message, have clearly distinct and mutually exclusive purposes with no overlap. An agent can easily distinguish between encryption and decryption operations.

Naming Consistency5/5

Both tool names follow a consistent verb_noun pattern (encrypt_message, decrypt_message), using the same noun 'message' and complementary verbs. The naming is uniform and predictable.

Tool Count3/5

With only 2 tools, the server is minimal but appropriate for a focused encryption/decryption purpose. However, the count feels slightly thin as additional tools like key management or algorithm selection might be expected in a complete ciphersuite.

Completeness3/5

The tool set covers the core encryption and decryption operations, but lacks supporting functionality such as key generation, algorithm selection, or message signing. This limits the server's utility for more complex workflows.

Maintenance

ActivityInactive
ResponsivenessNo issues

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