golang.org/x/crypto v0.27.0: hkdf.New

Clean-room public code sample — generation instructions

Write a brand-new, minimal, self-contained code sample in this clean-room directory.
Do not copy, paraphrase, or reference any existing project source. Work only from this spec.

A csx.json manifest scaffold already exists. Do not recreate it from memory. Preserve its case.goal, packages and symbols; fill its empty case.contract with exact assertions and correct its environment, commands and verifierAdapter for the files you generate.

Goal: verify golang.org/x/crypto/hkdf.New in pkg:golang/golang.org/x/crypto@v0.27.0
Kind: HOW

Use EXACTLY these public packages and versions:
  - pkg:golang/golang.org/x/crypto@v0.27.0
Demonstrate these symbols/APIs:
  - golang.org/x/crypto/hkdf.New
Constraints:
  - executionContext: node
Required runtime conditions:
  - ecosystem: npm
  - language: javascript
  - moduleSystem: cjs
  - packageManager: npm@10.9.8
  - runtime: node@22.23.2

Rules:
  - One focused purpose; the smallest project that proves the goal.
  - Include a contract test (test/contract.*) that runs OFFLINE and exits 0 exactly when the goal behavior works.
  - Pin every dependency with a lockfile so resolution is reproducible.
  - No secrets, credentials, or tokens. No real URLs (only example.com or localhost). No absolute paths.
  - No personal names, emails, company names, or project identifiers of any kind.
  - No binaries and no generated output (node_modules, dist, target, venv, .git, .env).
  - Keep it under 200 files and 256KB packed.

{"case":{"caseId":"case:sha256:5c7553e9d61e236a7e226c1bbdb7d31cada5384606a10813fad9f4a916af0b2a","contract":["hkdf.New derives pseudorandom key matching RFC 5869 test vector","hkdf.New with nil salt defaults to hash size zeros","hkdf.New produces deterministic output for identical secret, salt, and info","hkdf.New produces distinct outputs when secret, salt, or info differs","hkdf.New returns error when reading beyond 255 times hash size"],"goal":"verify golang.org/x/crypto/hkdf.New in pkg:golang/golang.org/x/crypto@v0.27.0","kind":"HOW","packages":["pkg:golang/golang.org/x/crypto@v0.27.0"],"schemaVersion":1,"symbols":["golang.org/x/crypto/hkdf.New"]},"contractCommand":["go","run","./test"],"environment":{"arch":"x64","distro":"ubuntu","ecosystem":"golang","libc":"glibc","libcVersion":"2.39","os":"linux","osVersionBucket":"24","packageManager":"go","schemaVersion":1},"license":"MIT-0","packages":["pkg:golang/golang.org/x/crypto@v0.27.0"],"schemaVersion":1,"subject":"pkg:golang/golang.org/x/crypto@v0.27.0","symbols":["golang.org/x/crypto/hkdf.New"],"verifierAdapter":"golang@1"}

module example.com/sample

go 1.26.6

require golang.org/x/crypto v0.27.0

golang.org/x/crypto v0.27.0 h1:GXm2NjJrPaiv/h1tb2UH8QfgC/hOf/+z0p6PT8o1w7A=
golang.org/x/crypto v0.27.0/go.mod h1:1Xngt8kV6Dvbssa53Ziq6Eqn0HqbZi5Z6R0ZpwQzt70=

package main

import (
	"crypto/rand"
	"crypto/sha256"
	"fmt"
	"io"
	"log"

	"golang.org/x/crypto/hkdf"
)

func main() {
	// Secret key material, salt, and info
	secret := make([]byte, 32)
	if _, err := io.ReadFull(rand.Reader, secret); err != nil {
		log.Fatalf("failed to read random secret: %v", err)
	}

	salt := make([]byte, 16)
	if _, err := io.ReadFull(rand.Reader, salt); err != nil {
		log.Fatalf("failed to read random salt: %v", err)
	}

	info := []byte("example.com/sample/v1/derived-key")

	// hkdf.New returns an io.Reader that yields derived key bytes
	hkdfReader := hkdf.New(sha256.New, secret, salt, info)

	// Derive a 256-bit (32-byte) key
	derivedKey := make([]byte, 32)
	if _, err := io.ReadFull(hkdfReader, derivedKey); err != nil {
		log.Fatalf("failed to read derived key: %v", err)
	}

	fmt.Printf("Successfully derived key: %x\n", derivedKey)
}

{
  "schemaVersion": 1,
  "goal": "verify golang.org/x/crypto/hkdf.New in pkg:golang/golang.org/x/crypto@v0.27.0",
  "kind": "HOW",
  "packages": [
    "pkg:golang/golang.org/x/crypto@v0.27.0"
  ],
  "symbols": [
    "golang.org/x/crypto/hkdf.New"
  ],
  "constraints": {
    "executionContext": "node"
  },
  "runtimeConditions": {
    "ecosystem": "npm",
    "language": "javascript",
    "moduleSystem": "cjs",
    "packageManager": "npm@10.9.8",
    "runtime": "node@22.23.2"
  }
}

package main

import (
	"bytes"
	"crypto/sha256"
	"encoding/hex"
	"fmt"
	"io"
	"os"

	"golang.org/x/crypto/hkdf"
)

func main() {
	// RFC 5869 Test Case 1 (SHA-256)
	ikm1 := bytes.Repeat([]byte{0x0b}, 22)
	salt1, _ := hex.DecodeString("000102030405060708090a0b0c")
	info1, _ := hex.DecodeString("f0f1f2f3f4f5f6f7f8f9")
	expectedOKM1, _ := hex.DecodeString("3cb25f25faacd57a90434f64d0362f2a2d2d0a90cf1a5a4c5db02d56ecc4c5bf34007208d5b887185865")

	// 1. hkdf.New derives pseudorandom key matching RFC 5869 test vector
	reader1 := hkdf.New(sha256.New, ikm1, salt1, info1)
	okm1 := make([]byte, len(expectedOKM1))
	if _, err := io.ReadFull(reader1, okm1); err != nil {
		fmt.Fprintf(os.Stderr, "hkdf.New read failed: %v\n", err)
		os.Exit(1)
	}
	if !bytes.Equal(okm1, expectedOKM1) {
		fmt.Fprintf(os.Stderr, "hkdf.New output mismatch with RFC 5869 test vector\n")
		os.Exit(1)
	}

	// 2. hkdf.New with nil salt defaults to hash size zeros
	zeroSalt := make([]byte, sha256.Size)
	readerNilSalt := hkdf.New(sha256.New, ikm1, nil, info1)
	readerZeroSalt := hkdf.New(sha256.New, ikm1, zeroSalt, info1)
	bufNilSalt := make([]byte, 42)
	bufZeroSalt := make([]byte, 42)
	if _, err := io.ReadFull(readerNilSalt, bufNilSalt); err != nil {
		fmt.Fprintf(os.Stderr, "readerNilSalt read failed: %v\n", err)
		os.Exit(1)
	}
	if _, err := io.ReadFull(readerZeroSalt, bufZeroSalt); err != nil {
		fmt.Fprintf(os.Stderr, "readerZeroSalt read failed: %v\n", err)
		os.Exit(1)
	}
	if !bytes.Equal(bufNilSalt, bufZeroSalt) {
		fmt.Fprintf(os.Stderr, "hkdf.New with nil salt did not match zero salt\n")
		os.Exit(1)
	}

	// 3. hkdf.New produces deterministic output for identical secret, salt, and info
	readerA := hkdf.New(sha256.New, ikm1, salt1, info1)
	readerB := hkdf.New(sha256.New, ikm1, salt1, info1)
	bufA := make([]byte, 64)
	bufB := make([]byte, 64)
	if _, err := io.ReadFull(readerA, bufA); err != nil {
		fmt.Fprintf(os.Stderr, "readerA read failed: %v\n", err)
		os.Exit(1)
	}
	if _, err := io.ReadFull(readerB, bufB); err != nil {
		fmt.Fprintf(os.Stderr, "readerB read failed: %v\n", err)
		os.Exit(1)
	}
	if !bytes.Equal(bufA, bufB) {
		fmt.Fprintf(os.Stderr, "hkdf.New deterministic check failed\n")
		os.Exit(1)
	}

	// 4. hkdf.New produces distinct outputs when secret, salt, or info differs
	diffSecretReader := hkdf.New(sha256.New, []byte("different secret"), salt1, info1)
	diffSaltReader := hkdf.New(sha256.New, ikm1, []byte("different salt"), info1)
	diffInfoReader := hkdf.New(sha256.New, ikm1, salt1, []byte("different info"))

	bufDiffSecret := make([]byte, 64)
	bufDiffSalt := make([]byte, 64)
	bufDiffInfo := make([]byte, 64)

	if _, err := io.ReadFull(diffSecretReader, bufDiffSecret); err != nil {
		fmt.Fprintf(os.Stderr, "diffSecretReader read failed: %v\n", err)
		os.Exit(1)
	}
	if _, err := io.ReadFull(diffSaltReader, bufDiffSalt); err != nil {
		fmt.Fprintf(os.Stderr, "diffSaltReader read failed: %v\n", err)
		os.Exit(1)
	}
	if _, err := io.ReadFull(diffInfoReader, bufDiffInfo); err != nil {
		fmt.Fprintf(os.Stderr, "diffInfoReader read failed: %v\n", err)
		os.Exit(1)
	}

	if bytes.Equal(bufA, bufDiffSecret) || bytes.Equal(bufA, bufDiffSalt) || bytes.Equal(bufA, bufDiffInfo) {
		fmt.Fprintf(os.Stderr, "hkdf.New failed to produce distinct output for varied parameters\n")
		os.Exit(1)
	}

	// 5. hkdf.New returns error when reading beyond 255 times hash size
	maxBytes := 255 * sha256.Size // 8160 bytes for SHA-256
	limitReader := hkdf.New(sha256.New, ikm1, salt1, info1)
	maxBuf := make([]byte, maxBytes)
	if _, err := io.ReadFull(limitReader, maxBuf); err != nil {
		fmt.Fprintf(os.Stderr, "Failed to read max allowed HKDF bytes (%d): %v\n", maxBytes, err)
		os.Exit(1)
	}
	extraByte := make([]byte, 1)
	if _, err := limitReader.Read(extraByte); err == nil {
		fmt.Fprintf(os.Stderr, "hkdf.New unexpectedly allowed reading beyond 255 * hash.Size\n")
		os.Exit(1)
	}

	fmt.Println("All contract assertions passed.")
}