golang.org/x/crypto v0.55.0: secretbox.Open

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 secretbox.Open in pkg:golang/golang.org/x/crypto@v0.55.0
Kind: HOW

Use EXACTLY these public packages and versions:
  - pkg:golang/golang.org/x/crypto@v0.55.0
Demonstrate these symbols/APIs:
  - secretbox.Open

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:sha256:19c3c892920825ed09fb16d1761e0c171d117fea3fb684f7241ff76c0aceb148","contract":["secretbox.Open authenticates and decrypts ciphertext created by Seal using the same key and nonce","secretbox.Open returns nil and false when ciphertext length is less than Overhead","secretbox.Open returns nil and false when ciphertext authentication fails due to corrupted data","secretbox.Open returns nil and false when decrypted with a mismatched nonce","secretbox.Open returns nil and false when decrypted with a mismatched key","secretbox.Open appends decrypted plaintext to the provided destination slice","secretbox.Open successfully decrypts an empty message"],"goal":"verify secretbox.Open in pkg:golang/golang.org/x/crypto@v0.55.0","kind":"HOW","packages":["pkg:golang/golang.org/x/crypto@v0.55.0"],"schemaVersion":1,"symbols":["secretbox.Open"]},"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@v0.55.0"],"schemaVersion":1,"subject":"pkg:golang/golang.org/x/crypto@v0.55.0","symbols":["secretbox.Open"],"verifierAdapter":"golang@1"}

module example.com/sample

go 1.26.6

require golang.org/x/crypto v0.55.0

golang.org/x/crypto v0.55.0 h1:+KWHjbgOaAQ66dh/YlkZKHlz9ZUlq61AFirAR9ntP8M=
golang.org/x/crypto v0.55.0/go.mod h1:uq0V9dE/fzQuJtbnL+2EhWOE63vo164FY8xqEnV9xis=

package main

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

	"golang.org/x/crypto/nacl/secretbox"
)

func main() {
	var secretKey [32]byte
	if _, err := io.ReadFull(rand.Reader, secretKey[:]); err != nil {
		log.Fatalf("failed to generate key: %v", err)
	}

	var nonce [24]byte
	if _, err := io.ReadFull(rand.Reader, nonce[:]); err != nil {
		log.Fatalf("failed to generate nonce: %v", err)
	}

	message := []byte("authenticated secret message")

	// Encrypt message using secretbox.Seal
	encrypted := secretbox.Seal(nil, message, &nonce, &secretKey)
	fmt.Printf("Encrypted length: %d bytes (Overhead: %d bytes)\n", len(encrypted), secretbox.Overhead)

	// Decrypt and authenticate using secretbox.Open
	decrypted, ok := secretbox.Open(nil, encrypted, &nonce, &secretKey)
	if !ok {
		log.Fatalf("decryption failed")
	}

	fmt.Printf("Decrypted message: %s\n", string(decrypted))
}

{
  "schemaVersion": 1,
  "goal": "verify secretbox.Open in pkg:golang/golang.org/x/crypto@v0.55.0",
  "kind": "HOW",
  "packages": [
    "pkg:golang/golang.org/x/crypto@v0.55.0"
  ],
  "symbols": [
    "secretbox.Open"
  ]
}

package main

import (
	"bytes"
	"crypto/rand"
	"fmt"
	"io"
	"os"

	"golang.org/x/crypto/nacl/secretbox"
)

func main() {
	var key [32]byte
	if _, err := io.ReadFull(rand.Reader, key[:]); err != nil {
		fmt.Fprintf(os.Stderr, "failed to read key: %v\n", err)
		os.Exit(1)
	}

	var nonce [24]byte
	if _, err := io.ReadFull(rand.Reader, nonce[:]); err != nil {
		fmt.Fprintf(os.Stderr, "failed to read nonce: %v\n", err)
		os.Exit(1)
	}

	message := []byte("contract test payload")
	sealed := secretbox.Seal(nil, message, &nonce, &key)

	// 1. secretbox.Open authenticates and decrypts ciphertext created by Seal using the same key and nonce
	decrypted, ok := secretbox.Open(nil, sealed, &nonce, &key)
	if !ok {
		fmt.Fprintf(os.Stderr, "assertion 1 failed: secretbox.Open returned ok=false for valid ciphertext\n")
		os.Exit(1)
	}
	if !bytes.Equal(decrypted, message) {
		fmt.Fprintf(os.Stderr, "assertion 1 failed: decrypted %q does not match original %q\n", decrypted, message)
		os.Exit(1)
	}

	// 2. secretbox.Open returns nil and false when ciphertext length is less than Overhead
	shortCiphertext := make([]byte, secretbox.Overhead-1)
	if dec, ok := secretbox.Open(nil, shortCiphertext, &nonce, &key); ok || dec != nil {
		fmt.Fprintf(os.Stderr, "assertion 2 failed: expected nil, false for short ciphertext, got %v, %v\n", dec, ok)
		os.Exit(1)
	}

	// 3. secretbox.Open returns nil and false when ciphertext authentication fails due to corrupted data
	corrupted := make([]byte, len(sealed))
	copy(corrupted, sealed)
	corrupted[len(corrupted)-1] ^= 0x01
	if dec, ok := secretbox.Open(nil, corrupted, &nonce, &key); ok || dec != nil {
		fmt.Fprintf(os.Stderr, "assertion 3 failed: expected nil, false for corrupted ciphertext, got %v, %v\n", dec, ok)
		os.Exit(1)
	}

	// 4. secretbox.Open returns nil and false when decrypted with a mismatched nonce
	var wrongNonce [24]byte
	copy(wrongNonce[:], nonce[:])
	wrongNonce[0] ^= 0xff
	if dec, ok := secretbox.Open(nil, sealed, &wrongNonce, &key); ok || dec != nil {
		fmt.Fprintf(os.Stderr, "assertion 4 failed: expected nil, false for mismatched nonce, got %v, %v\n", dec, ok)
		os.Exit(1)
	}

	// 5. secretbox.Open returns nil and false when decrypted with a mismatched key
	var wrongKey [32]byte
	copy(wrongKey[:], key[:])
	wrongKey[0] ^= 0xff
	if dec, ok := secretbox.Open(nil, sealed, &nonce, &wrongKey); ok || dec != nil {
		fmt.Fprintf(os.Stderr, "assertion 5 failed: expected nil, false for mismatched key, got %v, %v\n", dec, ok)
		os.Exit(1)
	}

	// 6. secretbox.Open appends decrypted plaintext to the provided destination slice
	dstPrefix := []byte("header:")
	appended, ok := secretbox.Open(dstPrefix, sealed, &nonce, &key)
	if !ok {
		fmt.Fprintf(os.Stderr, "assertion 6 failed: open with destination buffer returned ok=false\n")
		os.Exit(1)
	}
	expectedAppended := append([]byte("header:"), message...)
	if !bytes.Equal(appended, expectedAppended) {
		fmt.Fprintf(os.Stderr, "assertion 6 failed: expected %q, got %q\n", expectedAppended, appended)
		os.Exit(1)
	}

	// 7. secretbox.Open successfully decrypts an empty message
	emptySealed := secretbox.Seal(nil, []byte{}, &nonce, &key)
	decEmpty, ok := secretbox.Open(nil, emptySealed, &nonce, &key)
	if !ok {
		fmt.Fprintf(os.Stderr, "assertion 7 failed: failed to decrypt empty message\n")
		os.Exit(1)
	}
	if len(decEmpty) != 0 {
		fmt.Fprintf(os.Stderr, "assertion 7 failed: expected empty slice, got length %d\n", len(decEmpty))
		os.Exit(1)
	}

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