io.github.daedalus/mcp-cryptography

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rsa_decrypt

Decrypt RSA ciphertext with your private key. Provide a PEM private key and base64-encoded ciphertext to retrieve the original data.

Instructions

Decrypt RSA ciphertext using private key.

Args: private_key_pem: RSA private key in PEM format. ciphertext: Base64-encoded ciphertext.

Returns: Decrypted string.

Tool call template

Replace each placeholder with a value matching the input schema. Only required parameters are included; add optional parameters as needed.

{
  "id": 1,
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "arguments": {
      "private_key_pem": "<private_key_pem>",
      "ciphertext": "<ciphertext>"
    },
    "name": "rsa_decrypt"
  }
}

Input Schema

Name	Required	Description	Default
`ciphertext`	Yes
`private_key_pem`	Yes

Output Schema

Name	Required	Description	Default
`result`	Yes

Schema Changelog

Changes observed during successful MCP inspections.

First observedv0.1.1Jul 30, 2026

TDQS

B3.2/5.0

Behavior2/5

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

No annotations are provided, so the description bears full responsibility. It discloses the basic operation (decrypt with private key) but does not mention potential side effects like padding scheme requirements, error behavior on invalid keys or ciphertext, or whether the operation is idempotent.

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

Conciseness4/5

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

The description is concise, using a clear one-line summary followed by Args and Returns sections. Every sentence adds value, with no redundant information.

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

Completeness3/5

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

Given the tool's simplicity (2 parameters, output schema exists), the description is adequate but not thorough. It explains the return value as 'Decrypted string' but omits details about the output encoding or potential failures. For a cryptographic tool, more safety context would be beneficial.

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?

The input schema has 0% description coverage. The description adds meaning by clarifying that private_key_pem must be in PEM format and ciphertext is Base64-encoded. This compensates partially but remains minimal (no format details for PEM, no specification of key length).

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?

The description clearly states 'Decrypt RSA ciphertext using private key,' specifying a precise action and resource. Among sibling tools like rsa_encrypt, rsa_sign, and rsa_verify, this distinguishes itself by focusing on decryption only.

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?

The description provides no guidance on when to use this tool versus alternatives (e.g., fernet_decrypt, aes_decrypt). It does not mention prerequisites, such as the need for a prior encryption step, or any exclusions.

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