Crypto Ctf

Crypto CTF

Goal: solve cryptography challenge solving tasks with professional offensive methodology, preserved imported technique coverage, and reproducible evidence.

When this skill applies

• ciphertexts, keys, signatures, oracles, transcripts, proofs, PRNG outputs, or mathematical protocol code
• RSA, ECC, DH, DSA/ECDSA, lattice/LWE, PRNG, symmetric-mode, stream-cipher, ZKP, secret-sharing, or exotic algebraic weaknesses

Operating model

1. Classify the dominant artifact, primitive, or objective.
2. Load the closest offensive-techniques methodology before selecting tools.
3. Load references only for deep technique details.
4. Choose the smallest tool chain that can produce a validation signal.
5. Record the exact proof path and stop once the objective is reproducible.

Technique integration

Primary methodology to load:

• crypto-technique
• cracking-technique

Use these as decision engines. This skill adds challenge-oriented triage, time-boxing, and preserved specialized patterns from the imported corpus.

Tool routing

Prefer these tool families when the corresponding signal appears:

• rsactftool
• sagemath
• cyberchef
• hashcat
• john
• coding/python-patterns

Tool syntax belongs in the tool skills. This skill decides when a tool family fits and what output should validate progress.

Category-specific quick pivots

• Extract parameters before choosing attacks: modulus, exponent, curve order, nonce, IV, oracle response, random source, and serialization.
• Rank attacks by structural evidence: factorability, smoothness, nonce reuse, small roots, linear recurrence, or mode misuse.
• Validate recovered material by re-encryption, signature verification, oracle replay, or known plaintext.

Targeted hint research gate

If local triage has already classified the primitive, ranked attacks, and still hit a specific wall, load knowledge/known-problem-hint-research.

Use it only as a post-triage spike to find a paper, blog, article, public analysis, source discussion, or implementation note that maps to the exact problem fingerprint. Do not use it as broad search or before the local pivot ledger has evidence.

Quality gates

• No claim without a validation signal: recovered secret, replayed exploit, decoded artifact, reproduced model behavior, or corroborated evidence.
• Do not brute force before representation, constraints, and success oracle are known.
• Keep a pivot ledger: hypothesis, evidence, result, next shortest path.
• Preserve coverage by keeping every operational topic reachable from the Resources routing below.
• Keep challenge/platform/competition names out of notes and generated reports.

Resources

Modern Cipher Attacks

• references/modern-cipher-modes-and-forgery.md — AES/CFB/CBC/CTR/GCM/OFB mode failures, padding and decode oracles, bit-flip/cut-and-paste forgeries, cookie/session tampering, and practical ciphertext manipulation workflows.
• references/modern-hash-mac-and-collision-attacks.md — Hash/MAC weaknesses: length extension, CRC misuse, chosen-prefix and multi-collision workflows, linear-MAC breaks, and aggregate-hash forgery patterns.
• references/modern-oracles-protocols-and-custom-crypto.md — Protocol and design failures: Bleichenbacher/Rabin/Blum-Goldwasser oracles, SRP and KDF flaws, reduced-round/custom constructions, and algebraic attack pivots.

RSA Attacks

• references/rsa-attacks.md — Small exponent recovery, common modulus attacks, Wiener's attack, Pollard p-1 factorization, Hastad broadcast, Fermat factorization, multi-prime RSA, restricted-digit primes, Coppersmith attacks, Manger's padding oracle, specialized RSA (p=q bypass, gcd(e,phi)>1, phi-multiple factoring, CRT faults, homomorphic bypass, batch GCD, partial key recovery), signature forgery (homomorphic, Bleichenbacher, low-exponent), ROCA attack (CVE-2017-15361), timing attacks, dependent-prime RSA, three-key GCD.

Exotic Cryptography

• references/exotic-crypto.md — Braid group DH (Alexander polynomial multiplicativity), monotone function inversion, tropical semiring residuation, Paillier homomorphic encryption, Hamming codes, ElGamal variants, format-preserving encryption Feistel, icosahedral symmetry group cipher, Goldwasser-Micali ciphertext replication, BB-84 quantum key distribution MITM.

PRNG & Key Recovery

• references/prng.md — Mersenne Twister state recovery (untemper, symbolic solving), MT from random.random() floats via GF(2) matrix (not_random library), time-based seed attacks, C srand/rand via ctypes, layered encryption recovery, LCG parameter recovery, ChaCha20 key recovery, GF(2) matrix PRNG seed recovery, middle-square PRNG brute-force, deterministic RNG from flag bytes (hill climbing), byte-by-byte oracle, RSA key reuse, logistic map/chaotic PRNG seed recovery, V8 XorShift128+ state recovery (Math.random prediction), and CTF-era advanced techniques (MT constraint propagation, Z3 timing oracle, cellular automaton LFSR, Java LCG MITM), EC-LCG state recovery from truncated EC coordinates.

Elliptic Curve Attacks

• references/ecc-attacks.md — Small subgroup attacks, invalid curve attacks, Smart's attack, ECDSA nonce reuse, curve order factorization, twist attacks, anomalous curves, special-form curve weaknesses, BLS aggregate signature rogue-key attacks, proof-of-possession bypass.

Advanced Mathematics

• references/advanced-math.md — Isogenies and CSIDH, Pohlig-Hellman algorithm, LLL lattice reduction, Coppersmith small-roots method, Clock group DLP, Babai nearest-plane algorithm, CVP/SVP solvers, GF(2) linear algebra, generalized birthday attacks, sparse polynomial systems.

Lattice & LWE

• references/lattice-and-lwe.md — Lattice problems (SVP, CVP, HNP), LWE attacks (Gaussian elimination, BKZ reduction), hidden number problem, ECDSA partial-nonce recovery via lattice, LWE parameter tweaking, NTRU attacks.

Classic Ciphers

• references/classic-ciphers.md — Vigenere cipher frequency analysis, Atbash simple substitution, Polybius square attacks, substitution cipher key recovery, XOR-based cipher analysis, pattern matching and constraint solving.

Stream Ciphers

• references/stream-ciphers.md — LFSR feedback polynomial recovery, RC4 state recovery and keystream prediction, XOR-based stream cipher weaknesses, mode misuse (reusing nonces/IVs), correlated keystream analysis.

Historical Ciphers

• references/historical.md — Lorenz SZ40/42 rotor machine analysis, book cipher key recovery, pre-modern cryptanalysis techniques, mechanical cipher exploitation.

ZKP & Advanced Techniques

• references/zkp-and-advanced.md — Zero-knowledge proof attacks, interactive proof verification bypass, Z3 SMT solver application, garbled circuits (generator/evaluator attacks), Shamir secret sharing, race conditions in crypto protocols, Fiat-Shamir heuristic vulnerabilities.