Decrypt ciphertext using Vigenère cipher with known key.
AI agents call vigenere_decrypt to retrieve information from Crypto Tools MCP Server without modifying anything — typically the context-gathering step in research, monitoring, and reporting workflows, before the agent takes action elsewhere.
Decryption with a known key is a cryptanalytic read operation. It retrieves information from encrypted data but does not modify, delete, execute code, move money, or cause irreversible changes. The fact that this is a classical cipher of minimal practical security does not elevate it beyond Read category.
From the tool's definition Tool name is 'vigenere_decrypt' and description states it 'Decrypt ciphertext using Vigenère cipher with known key.' The tool retrieves/recovers plaintext from ciphertext—a retrieval operation with no side effects.
Attacks that exploit this kind of access
Decrypt ciphertext using Vigenère cipher with known key. It is categorised as a Read tool in the Crypto Tools MCP Server MCP Server, which means it retrieves data without modifying state.
Register the Crypto Tools MCP Server MCP server in PolicyLayer and add a rule for vigenere_decrypt: allow, deny, rate-limit, or require approval. Point your MCP client at the PolicyLayer proxy URL and the rule is enforced on every call, before it reaches Crypto Tools MCP Server. Nothing to install.
vigenere_decrypt is a Read tool with low risk. Read-only tools are generally safe to allow by default.
Yes. Add a rate_limit block to the vigenere_decrypt rule in your PolicyLayer policy. For example, setting max: 10 and window: 60 limits the tool to 10 calls per minute. Rate limits are tracked per agent session and reset automatically.
Set action: deny in the PolicyLayer policy for vigenere_decrypt. The AI agent will receive a policy violation error and cannot call the tool. You can also include a reason field to explain why the tool is blocked.
vigenere_decrypt is provided by the Crypto Tools MCP Server MCP server (marc-shade/crypto-tools-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Every MCP server has a record like this.
Type a name, get the same breakdown: verified identity, auth posture, risk grade, capabilities, recommended policy.
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