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HKDF Extract-Then-Expand Key Derivation (RFC 5869)
x402
HKDF Extract-Then-Expand Key Derivation (RFC 5869) is a paid API for AI agents from agent402.tools, paid per call via x402, $0.001/call, status unknown (last checked 2026-09-14).
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.
Price / call$0.001
Success—
StatusUnknown
How this service works
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.
Output
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.
Example use cases
Example prompt
“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.”
Technical details
Endpoint
POSThttps://agent402.tools/api/hkdf-expandWhen to prefer
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.
Side effects
- 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
Input
Schema · Request body
| Field | Type | Description |
|---|---|---|
| ikm | string | Initial keying material (the shared secret) |
| info | string | Optional context/application info (empty string if omitted) |
| salt | string | Optional salt (empty string if omitted) |
| digest | string | Hash algorithm: sha1, sha256, sha384, sha512 (default sha256) |
| keyLength | integer | Desired output key length in bytes (default 32, max 128) |
Output
Schema · Response
{
"type": "json",
"example": {
"okm": "a1b2c3d4e5f6...",
"digest": "sha256",
"algorithm": "hkdf",
"keyLength": 32
}
}Tags
x402
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