{"uid":"cap_KZXELTgdh2tymYcuqIF_S","slug":"hkdf-extract-then-expand-key-derivation-rfc-5869-7cdc057c","name":"HKDF Extract-Then-Expand Key Derivation (RFC 5869)","description":"HKDF extract-then-expand (RFC 5869) — derive output keying material from initial keying material, an optional salt, and an optional info/context string. Useful for deriving multiple keys from a single shared secret. Returns hex-encoded OKM.","url":"https://agent402.tools/api/hkdf-expand","method":"POST","headers":{},"bodySchema":{"type":"object","properties":{"ikm":{"type":"string","description":"Initial keying material (the shared secret)"},"info":{"type":"string","description":"Optional context/application info (empty string if omitted)"},"salt":{"type":"string","description":"Optional salt (empty string if omitted)"},"digest":{"type":"string","description":"Hash algorithm: sha1, sha256, sha384, sha512 (default sha256)"},"keyLength":{"type":"integer","description":"Desired output key length in bytes (default 32, max 128)"}}},"responseSchema":{"type":"json","example":{"okm":"a1b2c3d4e5f6...","digest":"sha256","algorithm":"hkdf","keyLength":32}},"example":null,"exampleRequest":null,"tags":["x402"],"displayCostAmount":"0.001","displayCostAsset":"USDC","priceDynamic":false,"priceHint":null,"priceStatus":"priced","priceSource":"probe","requiresHandshake":false,"reviewCount":0,"rating":{"score":"0.00","successRate":"0.00","reviews":0,"stars":null,"state":"unrated"},"availabilityStatus":"unknown","priceObserved":null,"sessionDeposit":null,"pricing":{"kind":"static","summary":"$0.001/call","primary":{"kind":"static","protocol":"x402","network":"base","amountUsd":"0.001","per":"call","confidence":"exact"},"accepted":[{"kind":"static","protocol":"x402","network":"base","amountUsd":"0.001","per":"call","confidence":"exact"}]},"paymentMethods":[{"uid":"pm_Gl3M9gm8RTEdo6Q31bs4p","protocol":"x402","methodType":"crypto","chain":"base","mode":"charge","costAmount":"0.001","costPer":"request","priority":0,"asset":"0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913","unit":"request","depositMicros":null,"planRef":null}],"brandName":null,"brandSlug":null,"brandBaseUrl":null,"brandDocsUrl":null,"whatItDoes":"Derives cryptographic output keying material (OKM) from initial keying material, an optional salt, and an optional info/context string using HKDF (RFC 5869), returning hex-encoded bytes.","exampleAgentPrompt":"Derive 64 bytes of keying material from my shared secret '3a9f...b2c1' using HKDF with SHA-256, the salt 'mysalt', and context info 'session-encryption-v1', and give me the result as hex.","exampleUseCases":null,"resultDescription":"A hex-encoded string of output keying material (OKM) of the requested byte length (default 32 bytes, up to 128 bytes), derived deterministically from the provided IKM, salt, info, and digest algorithm.","failureModes":["Invalid or unsupported digest algorithm returns an error (only sha1, sha256, sha384, sha512 accepted)","keyLength exceeding 128 bytes returns an error or truncated result","Missing or empty IKM may cause a derivation error or produce degenerate output","Malformed input (non-string IKM/salt/info) returns a 400-level error","Payment failure or insufficient USDC balance returns a 402 Payment Required response"],"whenToPreferThis":"Choose this endpoint when you need to deterministically derive one or more cryptographic keys from a shared secret (e.g., a Diffie-Hellman output) with a specific context binding — especially when following RFC 5869 HKDF. Prefer it over PBKDF2 when the input material is already high-entropy (not a user password) and you need fast key expansion rather than password stretching.","instructions":null,"reviewSummary":null,"reviewSummaryHighlights":null,"reviewSummaryConcerns":null,"reviewSummaryGeneratedAt":null,"activationCount":0,"lastUsedAt":null,"lastSuccessfullyRanAt":null,"lastHealthCheckAt":"2026-09-14T19:14:03.629Z","isFirstParty":false}