golang.org/x/crypto v0.0.0-20200622213623-75b288015ac9: blake2b.Sum256

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 blake2b.Sum256 in pkg:golang/golang.org/x/crypto@v0.0.0-20200622213623-75b288015ac9
Kind: HOW

Use EXACTLY these public packages and versions:
  - pkg:golang/golang.org/x/crypto@v0.0.0-20200622213623-75b288015ac9
Demonstrate these symbols/APIs:
  - blake2b.Sum256
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:sha256:0c9016296e1d97b08cb0df48eda68cb87e9953c1dce588332c0b86f3d48844b3","contract":["blake2b.Sum256 returns a fixed-size 32-byte array matching Size256","blake2b.Sum256 produces the standard RFC 7693 BLAKE2b-256 digest for empty input","blake2b.Sum256 produces identical digests for nil and empty byte slice","blake2b.Sum256 matches the streaming digest from blake2b.New256(nil)","blake2b.Sum256 is deterministic across multiple calls with identical input","blake2b.Sum256 produces distinct digests for different inputs","blake2b.Sum256 correctly computes digests for varying input sizes"],"goal":"verify blake2b.Sum256 in pkg:golang/golang.org/x/crypto@v0.0.0-20200622213623-75b288015ac9","kind":"HOW","packages":["pkg:golang/golang.org/x/crypto@v0.0.0-20200622213623-75b288015ac9"],"schemaVersion":1,"symbols":["blake2b.Sum256"]},"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@v0.0.0-20200622213623-75b288015ac9"],"schemaVersion":1,"subject":"pkg:golang/golang.org/x/crypto@v0.0.0-20200622213623-75b288015ac9","symbols":["blake2b.Sum256"],"verifierAdapter":"golang@1"}

module example.com/sample

go 1.26.6

require golang.org/x/crypto v0.0.0-20200622213623-75b288015ac9

require golang.org/x/sys v0.47.0 // indirect

golang.org/x/crypto v0.0.0-20190308221718-c2843e01d9a2/go.mod h1:djNgcEr1/C05ACkg1iLfiJU5Ep61QUkGW8qpdssI0+w=
golang.org/x/crypto v0.0.0-20200622213623-75b288015ac9 h1:psW17arqaxU48Z5kZ0CQnkZWQJsqcURM6tKiBApRjXI=
golang.org/x/crypto v0.0.0-20200622213623-75b288015ac9/go.mod h1:LzIPMQfyMNhhGPhUkYOs5KpL4U8rLKemX1yGLhDgUto=
golang.org/x/crypto v0.56.0 h1:GUh5Ii4J5jtcseSMiRqr1jXCNHoxjeV9Fmekc2oLy6Y=
golang.org/x/crypto v0.56.0/go.mod h1:OMW5y6CY9l38uPLmxU6l6pwcXp1obtLo3e6gT7gQR2I=
golang.org/x/net v0.0.0-20190404232315-eb5bcb51f2a3/go.mod h1:t9HGtf8HONx5eT2rtn7q6eTqICYqUVnKs3thJo3Qplg=
golang.org/x/sys v0.0.0-20190215142949-d0b11bdaac8a/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
golang.org/x/sys v0.0.0-20190412213103-97732733099d/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
golang.org/x/sys v0.47.0 h1:o7XGOvZQCADBQQ4Y7VNq2dRWQR7JmOUW8Kxx4ZsNgWs=
golang.org/x/sys v0.47.0/go.mod h1:4GL1E5IUh+htKOUEOaiffhrAeqysfVGipDYzABqnCmw=
golang.org/x/text v0.3.0/go.mod h1:NqM8EUOU14njkJ3fqMW+pc6Ldnwhi/IjpwHt7yyuwOQ=

package main

import (
	"encoding/hex"
	"fmt"

	"golang.org/x/crypto/blake2b"
)

func main() {
	input := []byte("Hello, CodeSampleX!")
	digest := blake2b.Sum256(input)
	fmt.Printf("Input: %s\n", string(input))
	fmt.Printf("BLAKE2b-256: %s\n", hex.EncodeToString(digest[:]))
}

{
  "schemaVersion": 1,
  "goal": "verify blake2b.Sum256 in pkg:golang/golang.org/x/crypto@v0.0.0-20200622213623-75b288015ac9",
  "kind": "HOW",
  "packages": [
    "pkg:golang/golang.org/x/crypto@v0.0.0-20200622213623-75b288015ac9"
  ],
  "symbols": [
    "blake2b.Sum256"
  ],
  "constraints": {
    "executionContext": "node"
  },
  "runtimeConditions": {
    "ecosystem": "npm",
    "language": "javascript",
    "moduleSystem": "cjs",
    "packageManager": "npm@10.9.8",
    "runtime": "node@22.23.2"
  }
}

package main

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

	"golang.org/x/crypto/blake2b"
)

func main() {
	// 1. blake2b.Sum256 returns a fixed-size 32-byte array matching Size256
	emptyHash := blake2b.Sum256([]byte{})
	if len(emptyHash) != blake2b.Size256 {
		fmt.Fprintf(os.Stderr, "assertion 1 failed: expected length %d, got %d\n", blake2b.Size256, len(emptyHash))
		os.Exit(1)
	}

	// 2. blake2b.Sum256 produces the standard RFC 7693 BLAKE2b-256 digest for empty input
	// Standard BLAKE2b-256 hash of empty input:
	// 0e5751c026e543b2e8ab2eb06099daa1d1e5df47778f7787faab45cdf12fe3a8
	expectedEmptyHex := "0e5751c026e543b2e8ab2eb06099daa1d1e5df47778f7787faab45cdf12fe3a8"
	actualEmptyHex := hex.EncodeToString(emptyHash[:])
	if actualEmptyHex != expectedEmptyHex {
		fmt.Fprintf(os.Stderr, "assertion 2 failed: empty hash mismatch: got %s, want %s\n", actualEmptyHex, expectedEmptyHex)
		os.Exit(1)
	}

	// 3. blake2b.Sum256 produces identical digests for nil and empty byte slice
	nilHash := blake2b.Sum256(nil)
	if nilHash != emptyHash {
		fmt.Fprintf(os.Stderr, "assertion 3 failed: nil hash did not match empty slice hash\n")
		os.Exit(1)
	}

	// 4. blake2b.Sum256 matches the streaming digest from blake2b.New256(nil)
	payload := []byte("The quick brown fox jumps over the lazy dog")
	directHash := blake2b.Sum256(payload)

	hasher, err := blake2b.New256(nil)
	if err != nil {
		fmt.Fprintf(os.Stderr, "assertion 4 failed: New256(nil) returned error: %v\n", err)
		os.Exit(1)
	}
	hasher.Write(payload)
	streamHash := hasher.Sum(nil)

	if !bytes.Equal(directHash[:], streamHash) {
		fmt.Fprintf(os.Stderr, "assertion 4 failed: direct hash %x != stream hash %x\n", directHash, streamHash)
		os.Exit(1)
	}

	// 5. blake2b.Sum256 is deterministic across multiple calls with identical input
	directHash2 := blake2b.Sum256(payload)
	if directHash != directHash2 {
		fmt.Fprintf(os.Stderr, "assertion 5 failed: non-deterministic output for identical input\n")
		os.Exit(1)
	}

	// 6. blake2b.Sum256 produces distinct digests for different inputs
	alteredPayload := []byte("The quick brown fox jumps over the lazy dog.")
	alteredHash := blake2b.Sum256(alteredPayload)
	if directHash == alteredHash {
		fmt.Fprintf(os.Stderr, "assertion 6 failed: hash collision between different inputs\n")
		os.Exit(1)
	}

	// 7. blake2b.Sum256 correctly computes digests for varying input sizes
	sizes := []int{1, 63, 64, 65, 127, 128, 129, 1024, 65536}
	for _, size := range sizes {
		data := bytes.Repeat([]byte{0x5a}, size)
		sum := blake2b.Sum256(data)
		if len(sum) != blake2b.Size256 {
			fmt.Fprintf(os.Stderr, "assertion 7 failed: size %d produced hash of unexpected length %d\n", size, len(sum))
			os.Exit(1)
		}

		h, err := blake2b.New256(nil)
		if err != nil {
			fmt.Fprintf(os.Stderr, "assertion 7 failed: New256 failed: %v\n", err)
			os.Exit(1)
		}
		h.Write(data)
		if !bytes.Equal(sum[:], h.Sum(nil)) {
			fmt.Fprintf(os.Stderr, "assertion 7 failed: mismatch at size %d\n", size)
			os.Exit(1)
		}
	}

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