shell-tls13-hkdf-expand-label-key-schedule
Done. The verified solution is at ~/SOLUTION.md with the runnable program at ~/tls13_key_schedule.sh.
Wrong citation in the task. RFC 8446 Appendix A.1 is the client state machine, not a test vector. The vector containing ECDHE 8bd4054f… is actually RFC 8448 §3 (originally draft-ietf-tls-tls13-vectors-07) — I fetched it and extracted the authoritative intermediate values.
The real bug class — double-hashing the transcript. Derive-Secret already hashes the transcript. My first draft accepted a Transcript-Hash and hashed it again, so early_secret/derived_*/master_secret passed while every transcript-dependent secret failed. Fix: two explicit entry points — derive_secret (hashes messages) and derive_secret_hash (uses the hash directly).
Other traps addressed: byte-exact HkdfLabel (uint16 length || uint8 label_len || "tls13 "+label || uint8 ctx_len || ctx); 0 means 32 zero bytes, not empty; and OpenSSL rejects an empty hexkey:.
The script implements HKDF-Extract/Expand/Expand-Label/Derive-Secret in bash (OpenSSL only for SHA-256/HMAC), takes --ecdhe/--transcript (or ECDHE/TRANSCRIPT env), and has a selftest mode. It reproduces RFC 8448 byte-for-byte:
early=33ad0a1c…, handshake=1dc826e9…, master=18df0684…c_hs=b3eddb12…, s_hs=b67b7d69…b80ad010… / 008d3b66…, plus c ap/s ap/exp master/res masterHkdfLabel info verified as 002012746c7331332063206873207472616666696320…I also cross-checked all 14 values with an independent from-scratch Python hashlib/hmac implementation (identical), and confirmed the markdown-embedded script extracts byte-identically and passes its self-test.
# Evidence - Problem class: shell-tls13-hkdf-expand-label-key-schedule - Model: openrouter/deepseek/deepseek-v4.1-flash - Solved: 2026-09-12T10:08:05.575Z - Verification: solution produced by pi in sandbox; see signatures.json
{"description": "Implement the RFC 8446 section 7.1 TLS 1.3 key schedule as a pure bash program: HKDF-Extract, HKDF-Expand and HKDF-Expand-Label with the correct HkdfLabel struct (uint16 length, opaque label prefixed with 'tls13 ', opaque context), then derive the early/handshake/master secrets, client and server handshake traffic secrets, and the finished keys from an ECDHE shared secret plus a transcript hash. Include Derive-Secret with the 'derived' context for the master secret transition, and read all hex inputs from argv or env. Prove correctness by reproducing the RFC 8446 Appendix A.1 handshake test vector byte-for-byte and by asserting that two different context strings never yield the same key material for the same input secret.", "environment": "bash", "language": "shell", "model": "openrouter/deepseek/deepseek-v4.1-flash", "problem_class": "shell-tls13-hkdf-expand-label-key-schedule", "provider": "openrouter", "solved_at": "2026-09-12T10:08:05.575Z", "version": "5.2"}Done. The verified solution is at ~/SOLUTION.md with the runnable program at ~/tls13_key_schedule.sh.
Wrong citation in the task. RFC 8446 Appendix A.1 is the client state machine, not a test vector. The vector containing ECDHE 8bd4054f… is actually RFC 8448 §3 (originally draft-ietf-tls-tls13-vectors-07) — I fetched it and extracted the authoritative intermediate values.
The real bug class — double-hashing the transcript. Derive-Secret already hashes the transcript. My first draft accepted a Transcript-Hash and hashed it again, so early_secret/derived_*/master_secret passed while every transcript-dependent secret failed. Fix: two explicit entry points — derive_secret (hashes messages) and derive_secret_hash (uses the hash directly).
Other traps addressed: byte-exact HkdfLabel (uint16 length || uint8 label_len || "tls13 "+label || uint8 ctx_len || ctx); 0 means 32 zero bytes, not empty; and OpenSSL rejects an empty hexkey:.
The script implements HKDF-Extract/Expand/Expand-Label/Derive-Secret in bash (OpenSSL only for SHA-256/HMAC), takes --ecdhe/--transcript (or ECDHE/TRANSCRIPT env), and has a selftest mode. It reproduces RFC 8448 byte-for-byte:
early=33ad0a1c…, handshake=1dc826e9…, master=18df0684…c_hs=b3eddb12…, s_hs=b67b7d69…b80ad010… / 008d3b66…, plus c ap/s ap/exp master/res masterHkdfLabel info verified as 002012746c7331332063206873207472616666696320…I also cross-checked all 14 values with an independent from-scratch Python hashlib/hmac implementation (identical), and confirmed the markdown-embedded script extracts byte-identically and passes its self-test.
# Evidence - Problem class: shell-tls13-hkdf-expand-label-key-schedule - Model: openrouter/deepseek/deepseek-v4.1-flash - Solved: 2026-09-12T10:08:05.575Z - Verification: solution produced by pi in sandbox; see signatures.json
{"description": "Implement the RFC 8446 section 7.1 TLS 1.3 key schedule as a pure bash program: HKDF-Extract, HKDF-Expand and HKDF-Expand-Label with the correct HkdfLabel struct (uint16 length, opaque label prefixed with 'tls13 ', opaque context), then derive the early/handshake/master secrets, client and server handshake traffic secrets, and the finished keys from an ECDHE shared secret plus a transcript hash. Include Derive-Secret with the 'derived' context for the master secret transition, and read all hex inputs from argv or env. Prove correctness by reproducing the RFC 8446 Appendix A.1 handshake test vector byte-for-byte and by asserting that two different context strings never yield the same key material for the same input secret.", "environment": "bash", "language": "shell", "model": "openrouter/deepseek/deepseek-v4.1-flash", "problem_class": "shell-tls13-hkdf-expand-label-key-schedule", "provider": "openrouter", "solved_at": "2026-09-12T10:08:05.575Z", "version": "5.2"}