MCP deployments face a 'Store Now, Decrypt Later' (SNDL) threat from quantum adversaries who intercept encrypted traffic today to decrypt it once cryptographically relevant quantum computers exist. The recommended defense is hybrid cryptography — combining classical X25519 with NIST-standardized ML-KEM-768 — so both layers must be broken simultaneously. A step-by-step implementation guide covers auditing MCP traffic, upgrading TLS stacks using the Open Quantum Safe (liboqs) library, and managing larger PQC key sizes. Performance benchmarks show hybrid handshakes add only ~7ms over standard ECC when hardware acceleration (AVX-512) is used. Beyond transport, ML-DSA (Dilithium) signatures are recommended for agent-to-tool communications to prevent prompt injection. NIST FIPS 203/204/205 standards and Cloud Security Alliance guidance are cited as compliance anchors for 2026.
