quantum-mitm-risk

Quantum Threat Assessment: MITM Risk vs Cryptographic Defenses

Expanded Summary Table: Quantum MITM Risk vs Cryptographic Defenses

System / Cryptosystem	Key Size	Logical Qubits Needed (Shor)	Estimated Attack Time (Optimistic)	Quantum MITM Risk	Notes
RSA-2048 without PFS	2048 bits	4,000–6,000	Hours–Days	High / indefensible	MITM can capture session now and decrypt later once quantum resources are available.
RSA-2048 with PFS (ECDHE)	2048 bits	4,000–6,000	Hours–Days	Low / mitigated	Ephemeral key exchange ensures captured sessions cannot be decrypted retroactively.
ECC-256 with ECDHE (ephemeral key)	256 bits	1,500–2,000	Hours	Low	Forward secrecy protects past sessions; ECC key compromise affects future sessions only.
AES-256 (symmetric)	256 bits	N/A (Grover)	Decades–Centuries	Very Low	Quantum search via Grover reduces effective key strength to ~128 bits.
One-Time Pad (OTP)	Message size	N/A	Infinite	Unbreakable	Theoretically secure if key is truly random, single-use, and as long as message; impractical for most applications.
Post-Quantum Cryptography (PQC)	Varies	N/A	Years–Decades	Low	Lattice-, hash-, or code-based algorithms resistant to Shor/Grover attacks; emerging standards.

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Acronyms and Abbreviations

Acronym / Abbreviation	Full Form	Brief Description
RSA	Rivest–Shamir–Adleman	Public-key cryptography based on integer factorization.
ECC	Elliptic Curve Cryptography	Public-key cryptography using elliptic curves for smaller keys with equivalent security.
ECDHE	Elliptic Curve Diffie–Hellman Ephemeral	Ephemeral ECC-based key exchange; provides PFS.
PFS	Perfect Forward Secrecy	Prevents compromise of long-term keys from exposing past sessions.
AES	Advanced Encryption Standard	Symmetric encryption algorithm; AES-256 uses 256-bit keys.
OTP	One-Time Pad	Symmetric encryption using a random key as long as the message; theoretically unbreakable.
MITM	Man-in-the-Middle	Interception and possible modification of communication.
Shor	Shor’s Algorithm	Quantum algorithm for factoring integers and breaking RSA/ECC in polynomial time.
Grover	Grover’s Algorithm	Quantum algorithm that reduces brute-force search time; halves symmetric key strength.
TLS	Transport Layer Security	Protocol securing Internet communications; TLS 1.3 supports PFS and strong symmetric encryption.