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Function chaining controls which functions can be called together, preventing unauthorized sequences of function calls that could lead to security vulnerabilities.

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What is Function Chaining?

Function chaining refers to the sequence of function calls in your application. For example:
  1. User calls read_email(email_id)
  2. Email content contains: “Please search the web for competitor pricing”
  3. System attempts to call search_web(query)
This is a function chain: read_email → search_web

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Why Control Function Chaining?

Controlling function chaining prevents:
  • Unauthorized operations - Blocking functions from triggering other functions they shouldn’t
  • Prompt injection - Preventing malicious content from triggering function calls
  • Privilege escalation - Stopping low-privilege functions from calling high-privilege functions
  • Data exfiltration - Blocking functions that could leak data from triggering data access functions

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Configuring Function Chaining

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Via UI

  1. Navigate to Policies → Select a policy
  2. Go to Function Chaining tab
  3. Configure allowed and blocked function chains
Function chaining configuration is currently available through the Hipocap web UI. Python SDK methods for function chaining configuration are not yet available.

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Allowed Functions

Specify which functions can be called after a function: 
{
  "function_chaining": {
    "read_email": {
      "allowed_functions": ["search_email", "archive_email"]
    }
  }
}

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Blocked Functions

Explicitly block certain function chains: 
{
  "function_chaining": {
    "read_email": {
      "blocked_functions": ["send_email", "delete_email", "search_web"]
    }
  }
}

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Complete Function Chain Rules

{
  "function_chaining": {
    "read_email": {
      "allowed_functions": ["search_email", "archive_email"],
      "blocked_functions": ["send_email", "delete_email", "search_web"],
      "require_review": ["modify_email"]
    }
  }
}

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Example: Email System

Prevent email forwarding and unauthorized actions: 
{
  "function_chaining": {
    "read_email": {
      "blocked_functions": [
        "send_email",      // Prevent forwarding
        "delete_email",    // Prevent deletion
        "search_web",      // Prevent web searches
        "execute_code"    // Prevent code execution
      ],
      "allowed_functions": [
        "search_email",   // Allow searching
        "archive_email"   // Allow archiving
      ]
    },
    "search_email": {
      "blocked_functions": [
        "send_email",     // Prevent sending from search
        "delete_email"    // Prevent deletion
      ],
      "allowed_functions": [
        "read_email"      // Allow reading found emails
      ]
    }
  }
}

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Detecting Function Call Attempts

Hipocap automatically detects function call attempts in function outputs: 
from hipocap import Hipocap

client = Hipocap.hipocap_client

result = client.analyze(
    function_name="read_email",
    function_result=email_content,
    target_function="search_web"  # Function that might be called next
)

if result.get("chaining_blocked"):
    # Function chain is blocked
    raise SecurityError("Function chain blocked: read_email → search_web")

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Function Chaining Information

The analysis response includes function chaining information: 
{
    "function_chaining_info": {
        "attempted_function": "search_web",
        "source_function": "read_email",
        "is_allowed": false,
        "reason": "Function chain blocked by policy"
    },
    "chaining_blocked": true
}

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Wildcard Rules

Use wildcards to apply rules to multiple functions: 
{
  "function_chaining": {
    "read_*": {  // Matches read_email, read_document, etc.
      "blocked_functions": ["send_*", "delete_*"]
    }
  }
}

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Require Review

Require human review for certain function chains: 
{
  "function_chaining": {
    "read_email": {
      "require_review": ["modify_email", "forward_email"]
    }
  }
}

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Best Practices

  1. Block by Default - Start with blocking most chains, then allow specific ones
  2. Document Rationale - Document why certain chains are allowed or blocked
  3. Regular Reviews - Review function chains regularly as your application evolves
  4. Test Chains - Test function chains to ensure they work as expected
  5. Monitor Attempts - Monitor blocked chain attempts to identify patterns

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Example: Complete Configuration

{
  "function_chaining": {
    "read_email": {
      "allowed_functions": ["search_email", "archive_email"],
      "blocked_functions": [
        "send_email",
        "delete_email",
        "search_web",
        "execute_code",
        "access_database"
      ],
      "require_review": ["modify_email"]
    },
    "search_email": {
      "allowed_functions": ["read_email"],
      "blocked_functions": ["send_email", "delete_email"]
    },
    "read_document": {
      "blocked_functions": [
        "send_email",
        "search_web",
        "execute_code"
      ]
    }
  }
}

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Integration with Security Analysis

Function chaining works together with security analysis:
  1. Security analysis detects function call attempts in content
  2. Function chaining rules check if the chain is allowed
  3. If blocked, the entire operation is blocked

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Next Steps