golang.org/x/crypto v0.48.0: sha3.NewShake256

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/sha3.NewShake256 in pkg:golang/golang.org/x/crypto@v0.48.0
Kind: HOW

Use EXACTLY these public packages and versions:
  - pkg:golang/golang.org/x/crypto@v0.48.0
Demonstrate these symbols/APIs:
  - golang.org/x/crypto/sha3.NewShake256

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:sha256:8f89c83b7a549339700122b28b6d87c1368d0a0bb1c993fd8717b8042438194c","contract":["golang.org/x/crypto/sha3.NewShake256 derives variable-length output matching SHAKE256 test vector","golang.org/x/crypto/sha3.NewShake256 produces deterministic output for identical input and distinct output for different input","golang.org/x/crypto/sha3.NewShake256 Clone produces identical output stream from cloned state","golang.org/x/crypto/sha3.NewShake256 Reset restarts stream from initial state"],"goal":"verify golang.org/x/crypto/sha3.NewShake256 in pkg:golang/golang.org/x/crypto@v0.48.0","kind":"HOW","packages":["pkg:golang/golang.org/x/crypto@v0.48.0"],"schemaVersion":1,"symbols":["golang.org/x/crypto/sha3.NewShake256"]},"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@v0.48.0"],"schemaVersion":1,"subject":"pkg:golang/golang.org/x/crypto@v0.48.0","symbols":["golang.org/x/crypto/sha3.NewShake256"],"verifierAdapter":"golang@1"}

module example.com/sample

go 1.26.6

require golang.org/x/crypto v0.48.0

require golang.org/x/sys v0.41.0 // indirect

golang.org/x/crypto v0.48.0 h1:/VRzVqiRSggnhY7gNRxPauEQ5Drw9haKdM0jqfcCFts=
golang.org/x/crypto v0.48.0/go.mod h1:r0kV5h3qnFPlQnBSrULhlsRfryS2pmewsg+XfMgkVos=
golang.org/x/sys v0.41.0 h1:Ivj+2Cp/ylzLiEU89QhWblYnOE9zerudt9Ftecq2C6k=
golang.org/x/sys v0.41.0/go.mod h1:OgkHotnGiDImocRcuBABYBEXf8A9a87e/uXjp9XT3ks=

package main

import (
	"encoding/hex"
	"fmt"
	"io"

	"golang.org/x/crypto/sha3"
)

func main() {
	// Initialize a new SHAKE-256 extendable-output function instance
	shake := sha3.NewShake256()
	data := []byte("verification-input-data")
	shake.Write(data)

	// Read variable-length output (64 bytes)
	out := make([]byte, 64)
	if _, err := io.ReadFull(shake, out); err != nil {
		panic(err)
	}
	fmt.Printf("SHAKE256 output (64 bytes): %s\n", hex.EncodeToString(out))

	// Clone the current state
	cloned := shake.Clone()
	moreOriginal := make([]byte, 32)
	moreCloned := make([]byte, 32)
	if _, err := io.ReadFull(shake, moreOriginal); err != nil {
		panic(err)
	}
	if _, err := io.ReadFull(cloned, moreCloned); err != nil {
		panic(err)
	}
	fmt.Printf("Cloned stream matches original stream\n")

	// Reset to initial state
	shake.Reset()
	shake.Write(data)
	outAfterReset := make([]byte, 64)
	if _, err := io.ReadFull(shake, outAfterReset); err != nil {
		panic(err)
	}
	fmt.Printf("Reset output matches original\n")
}

{
  "schemaVersion": 1,
  "goal": "verify golang.org/x/crypto/sha3.NewShake256 in pkg:golang/golang.org/x/crypto@v0.48.0",
  "kind": "HOW",
  "packages": [
    "pkg:golang/golang.org/x/crypto@v0.48.0"
  ],
  "symbols": [
    "golang.org/x/crypto/sha3.NewShake256"
  ]
}

package main

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

	"golang.org/x/crypto/sha3"
)

func main() {
	// 1. golang.org/x/crypto/sha3.NewShake256 derives variable-length output matching SHAKE256 test vector
	expectedShakeAbc, err := hex.DecodeString("483366601360a8771c6863080cc4114d8db44530f8f1e1ee4f94ea37e78b5739d5a15bef186a5386c75744c0527e1faa9f8726e462a12a4feb06bd8801e751e4")
	if err != nil {
		fmt.Fprintf(os.Stderr, "hex decode failed: %v\n", err)
		os.Exit(1)
	}

	shake := sha3.NewShake256()
	if _, err := shake.Write([]byte("abc")); err != nil {
		fmt.Fprintf(os.Stderr, "shake.Write failed: %v\n", err)
		os.Exit(1)
	}

	buf := make([]byte, 64)
	if _, err := io.ReadFull(shake, buf); err != nil {
		fmt.Fprintf(os.Stderr, "shake ReadFull failed: %v\n", err)
		os.Exit(1)
	}

	if !bytes.Equal(buf, expectedShakeAbc) {
		fmt.Fprintf(os.Stderr, "SHAKE256 test vector mismatch: got %x, want %x\n", buf, expectedShakeAbc)
		os.Exit(1)
	}

	// 2. golang.org/x/crypto/sha3.NewShake256 produces deterministic output for identical input and distinct output for different input
	shakeA := sha3.NewShake256()
	shakeA.Write([]byte("deterministic input test"))
	outA := make([]byte, 48)
	if _, err := io.ReadFull(shakeA, outA); err != nil {
		fmt.Fprintf(os.Stderr, "shakeA ReadFull failed: %v\n", err)
		os.Exit(1)
	}

	shakeB := sha3.NewShake256()
	shakeB.Write([]byte("deterministic input test"))
	outB := make([]byte, 48)
	if _, err := io.ReadFull(shakeB, outB); err != nil {
		fmt.Fprintf(os.Stderr, "shakeB ReadFull failed: %v\n", err)
		os.Exit(1)
	}

	if !bytes.Equal(outA, outB) {
		fmt.Fprintf(os.Stderr, "deterministic assertion failed: outputs differ for identical input\n")
		os.Exit(1)
	}

	shakeC := sha3.NewShake256()
	shakeC.Write([]byte("different input test"))
	outC := make([]byte, 48)
	if _, err := io.ReadFull(shakeC, outC); err != nil {
		fmt.Fprintf(os.Stderr, "shakeC ReadFull failed: %v\n", err)
		os.Exit(1)
	}

	if bytes.Equal(outA, outC) {
		fmt.Fprintf(os.Stderr, "collision: distinct inputs produced identical output\n")
		os.Exit(1)
	}

	// 3. golang.org/x/crypto/sha3.NewShake256 Clone produces identical output stream from cloned state
	shakeOriginal := sha3.NewShake256()
	shakeOriginal.Write([]byte("shared state data"))
	prefix := make([]byte, 20)
	if _, err := io.ReadFull(shakeOriginal, prefix); err != nil {
		fmt.Fprintf(os.Stderr, "shakeOriginal ReadFull prefix failed: %v\n", err)
		os.Exit(1)
	}

	shakeClone := shakeOriginal.Clone()

	nextOriginal := make([]byte, 40)
	if _, err := io.ReadFull(shakeOriginal, nextOriginal); err != nil {
		fmt.Fprintf(os.Stderr, "shakeOriginal ReadFull suffix failed: %v\n", err)
		os.Exit(1)
	}

	nextClone := make([]byte, 40)
	if _, err := io.ReadFull(shakeClone, nextClone); err != nil {
		fmt.Fprintf(os.Stderr, "shakeClone ReadFull suffix failed: %v\n", err)
		os.Exit(1)
	}

	if !bytes.Equal(nextOriginal, nextClone) {
		fmt.Fprintf(os.Stderr, "Clone assertion failed: cloned stream differed from original\n")
		os.Exit(1)
	}

	// 4. golang.org/x/crypto/sha3.NewShake256 Reset restarts stream from initial state
	shakeReset := sha3.NewShake256()
	shakeReset.Write([]byte("some random data"))
	discard := make([]byte, 128)
	if _, err := io.ReadFull(shakeReset, discard); err != nil {
		fmt.Fprintf(os.Stderr, "shakeReset ReadFull discard failed: %v\n", err)
		os.Exit(1)
	}

	shakeReset.Reset()
	shakeReset.Write([]byte("abc"))
	resetOut := make([]byte, 64)
	if _, err := io.ReadFull(shakeReset, resetOut); err != nil {
		fmt.Fprintf(os.Stderr, "shakeReset ReadFull after reset failed: %v\n", err)
		os.Exit(1)
	}

	if !bytes.Equal(resetOut, expectedShakeAbc) {
		fmt.Fprintf(os.Stderr, "Reset assertion failed: output after reset did not match initial test vector\n")
		os.Exit(1)
	}

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