Getting it into your agent
One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.
npx skills add dailyyarn/CTF-agent --skill ctf-cryptogit clone --depth 1 https://github.com/dailyyarn/CTF-agentWrote this? Show the measurements
A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.
[](https://agentmods.dev/skills/dailyyarn/ctf-agent/ctf-crypto)<a href="https://agentmods.dev/skills/dailyyarn/ctf-agent/ctf-crypto"><img src="https://agentmods.dev/badge/skills/dailyyarn/ctf-agent/ctf-crypto.svg" alt="Measured on agentmods" height="20"></a>What it costs to keep this loaded
Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.
| Model | Per session | Once invoked |
|---|---|---|
| Fable 5.1 | $0.00078 | $0.04476 |
| Opus 5 | $0.00039 | $0.02238 |
| Sonnet 5 | $0.00016 | $0.00895 |
| Haiku 4.5 | $0.00008 | $0.00448 |
Grade A, and why
ctf-crypto scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 7d ago.
A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.
Nothing flagged
None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.
How it starts
The opening of the file, as written. The whole thing — 195 lines — stays where its author put it; the contents beside it link to each section on GitHub.
CTF Cryptography
Quick reference for crypto CTF challenges. Each technique has a one-liner here; see supporting files for full details with code.
Additional Resources
- classic-ciphers.md - Classic ciphers: Vigenere (+ Kasiski examination), Atbash, substitution wheels, XOR variants (+ multi-byte frequency analysis), deterministic OTP, cascade XOR, book cipher, OTP key reuse / many-time pad, variable-length homophonic substitution
- modern-ciphers.md - Modern cipher attacks: AES (CFB-8, ECB leakage), CBC-MAC/OFB-MAC, padding oracle, S-box collisions, GF(2) elimination, LCG partial output recovery, CBC padding oracle (full block decryption), Bleichenbacher RSA PKCS#1 v1.5 padding oracle (ROBOT), birthday attack / meet-in-the-middle, LFSR stream cipher attacks (Berlekamp-Massey, correlation attack), CRC32 collision signature forgery, Blum-Goldwasser bit-extension oracle, hash length extension, compression oracle (CRIME-style), RC4 second-byte bias, XOR consecutive byte correlation
- rsa-attacks.md - RSA attacks: small e (cube root), common modulus, Wiener's, Pollard's p-1, Hastad's broadcast, Fermat/consecutive primes, multi-prime, restricted-digit, Coppersmith structured primes, Manger oracle, polynomial hash, RSA p=q validation bypass, cube root CRT gcd(e,phi)>1, factoring from phi(n) multiple, multiplicative homomorphism signature forgery, weak keygen via base representation, RSA with gcd(e,phi)>1 exponent reduction
- ecc-attacks.md - ECC attacks: small subgroup, invalid curve, Smart's attack (anomalous, with Sage code), fault injection, clock group DLP, Pohlig-Hellman, ECDSA nonce reuse, Ed25519 torsion side channel
- zkp-and-advanced.md - ZKP/graph 3-coloring, Z3 solver guide, garbled circuits, Shamir SSS, bigram constraint solving, race conditions, Groth16 broken setup, DV-SNARG forgery, KZG pairing oracle for permutation recovery
- prng.md - PRNG attacks (MT19937, MT float recovery via GF(2) magic matrix for token prediction, LCG, GF(2) matrix PRNG, V8 XorShift128+ Math.random state recovery via Z3, middle-square, deterministic RNG hill climbing, random-mode oracle, time-based seeds, C srand/rand synchronization via ctypes, password cracking, logistic map chaotic PRNG)
- historical.md - Historical ciphers (Lorenz SZ40/42, book cipher implementation)
- advanced-math.md - Advanced mathematical attacks (isogenies, Pohlig-Hellman, LLL, Merkle-Hellman knapsack via LLL, Coppersmith, quaternion RSA, GF(2)[x] CRT, S-box collision code, LWE lattice CVP attack, affine cipher over non-prime modulus)
- exotic-crypto.md - Exotic algebraic structures (braid group DH / Alexander polynomial, monotone function inversion, tropical semiring residuation, Paillier cryptosystem, Hamming code helical interleaving, ElGamal universal re-encryption)
What ships with it
9 files beside SKILL.md in the same directory: the scripts, references and assets a skill reads on demand. Not counted in the per-session cost; read them before you install if any of them is executable.
What this file has done since we first saw it
Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.
- 7d ago First seen · 195 lines · 78 tokens per session scan A da86abb6ca55
ctf-crypto is a skill published in the GitHub repository dailyyarn/CTF-agent (5 stars, last pushed 5mo ago), licensed MIT. It adds 78 tokens to every session and 4,476 once invoked, about $0.0004 per session on Opus 5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-31.
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