NexisCore: Zero-Trust Runtime Sandbox & Cryptographic Attestation Engine

Modern AI agentic workflows built on the Model Context Protocol (MCP) enable Large Language Models (LLMs) to execute tools, interact with file systems, query databases, and execute arbitrary code.

Technical Architecture & Enforcement Grid

Core Security Pillars

1. Cryptographic Provenance Attestation & Replay Prevention

Every MCP tool request must include an ECDSA P-256 digital signature, a cryptographic nonce, and a UNIX epoch timestamp within its request manifest:

• ASN.1 Coordinate Decoding: Decodes $(R, S)$ signature parameters and verifies them against the registered agent's public key.
• Epoch Drift Validation: Rejects requests where the timestamp drifts beyond a strict configurable window (within 30 seconds) to defeat delayed playback attacks.
• Sliding-Window Nonce Cache: Maintains a high-speed lock-free ring cache storing active nonces, instantly rejecting duplicate submissions.

2. eBPF-Powered Kernel Isolation & Tracepoint Monitoring

While containers isolate namespaces, NexisCore attaches low-overhead eBPF kprobes and tracepoints directly inside the Linux kernel:

• Network Egress Firewall (sys_enter_connect): If a sandboxed tool attempts to open a socket connection outside pre-approved allowlists, the eBPF program instantly triggers bpf_send_signal(SIGKILL), terminating the process.
• Anti-Tampering Probes (sys_enter_ptrace, sys_enter_mprotect): Blocks debugger attachment or execution of self-modifying code pages within the attestation runtime itself.

Go Attestation Engine Snippet

package gateway

import (
    "crypto/ecdsa"
    "crypto/sha256"
    "errors"
    "math/big"
    "time"
)

type AttestationManifest struct {
    AgentID   string `json:"agent_id"`
    Payload   []byte `json:"payload"`
    Nonce     string `json:"nonce"`
    Timestamp int64  `json:"timestamp"`
    R         *big.Int
    S         *big.Int
}

func (gw *Gateway) ValidateProvenance(m *AttestationManifest, pubKey *ecdsa.PublicKey) error {
    // 1. Check Temporal Freshness
    if time.Now().Unix()-m.Timestamp > 30 {
        return errors.New("attestation token expired (epoch drift)")
    }

    // 2. Check Sliding Window Nonce Cache
    if gw.nonceCache.Has(m.Nonce) {
        return errors.New("replay attack detected: nonce already spent")
    }
    gw.nonceCache.Add(m.Nonce)

    // 3. Compute SHA-256 Payload Hash
    hash := sha256.Sum256(m.Payload)

    // 4. Verify ECDSA P-256 Signature
    if !ecdsa.Verify(pubKey, hash[:], m.R, m.S) {
        return errors.New("invalid signature: payload has been tampered with")
    }

    return nil
}

Summary & Impact

• GitHub Repository: rdxkeerthi/NexisCore
• Primary Stack: Go, eBPF (Cilium/ebpf), gVisor, OCSF
• License: MIT