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

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.Seal 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.Seal

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:sha256:0a29a0a8ea748a08a2b947c320f9928aea502a96439332977bed2aa02c700360","contract":["secretbox.Seal appends ciphertext of length len(message) + secretbox.Overhead to out slice","secretbox.Open authenticates and decrypts ciphertext sealed with secretbox.Seal using matching key and nonce","secretbox.Open returns false when ciphertext payload is modified","secretbox.Open returns false when decrypted with a different secret key","secretbox.Open returns false when decrypted with a different nonce","secretbox.Open returns false when ciphertext length is less than secretbox.Overhead","secretbox.Seal encrypts empty message producing an authentication tag of length secretbox.Overhead"],"goal":"verify secretbox.Seal 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.Seal"]},"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.Seal"],"verifierAdapter":"golang@1"}

module example.com/sample

go 1.26.6

require golang.org/x/crypto v0.55.0

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

golang.org/x/crypto v0.55.0 h1:+KWHjbgOaAQ66dh/YlkZKHlz9ZUlq61AFirAR9ntP8M=
golang.org/x/crypto v0.55.0/go.mod h1:uq0V9dE/fzQuJtbnL+2EhWOE63vo164FY8xqEnV9xis=
golang.org/x/sys v0.47.0 h1:o7XGOvZQCADBQQ4Y7VNq2dRWQR7JmOUW8Kxx4ZsNgWs=
golang.org/x/sys v0.47.0/go.mod h1:4GL1E5IUh+htKOUEOaiffhrAeqysfVGipDYzABqnCmw=

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("confidential payload")

	// Seal appends the encrypted and authenticated message to out
	encrypted := secretbox.Seal(nil, message, &nonce, &secretKey)
	fmt.Printf("Encrypted message length: %d (original %d + overhead %d)\n",
		len(encrypted), len(message), secretbox.Overhead)

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

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

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

package main

import (
	"bytes"
	"fmt"
	"os"

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

func main() {
	var key [32]byte
	var nonce [24]byte
	for i := range key {
		key[i] = byte(i + 1)
	}
	for i := range nonce {
		nonce[i] = byte(i + 10)
	}

	message := []byte("hello, secretbox!")
	outPrefix := []byte("prefix:")

	// 1. secretbox.Seal appends ciphertext of length len(message) + secretbox.Overhead to out slice
	sealed := secretbox.Seal(outPrefix, message, &nonce, &key)
	expectedLen := len(outPrefix) + len(message) + secretbox.Overhead
	if len(sealed) != expectedLen {
		fmt.Fprintf(os.Stderr, "Seal output length mismatch: got %d, want %d\n", len(sealed), expectedLen)
		os.Exit(1)
	}
	if !bytes.Equal(sealed[:len(outPrefix)], outPrefix) {
		fmt.Fprintf(os.Stderr, "Seal corrupted prefix slice\n")
		os.Exit(1)
	}

	// 2. secretbox.Open authenticates and decrypts ciphertext sealed with secretbox.Seal using matching key and nonce
	ciphertext := sealed[len(outPrefix):]
	decrypted, ok := secretbox.Open(nil, ciphertext, &nonce, &key)
	if !ok {
		fmt.Fprintf(os.Stderr, "Open failed to decrypt valid ciphertext\n")
		os.Exit(1)
	}
	if !bytes.Equal(decrypted, message) {
		fmt.Fprintf(os.Stderr, "Decrypted message mismatch: got %q, want %q\n", decrypted, message)
		os.Exit(1)
	}

	// 3. secretbox.Open returns false when ciphertext payload is modified
	tampered := make([]byte, len(ciphertext))
	copy(tampered, ciphertext)
	tampered[len(tampered)-1] ^= 0x01
	if _, ok := secretbox.Open(nil, tampered, &nonce, &key); ok {
		fmt.Fprintf(os.Stderr, "Open unexpectedly succeeded on tampered ciphertext\n")
		os.Exit(1)
	}

	// 4. secretbox.Open returns false when decrypted with a different secret key
	var wrongKey [32]byte
	copy(wrongKey[:], key[:])
	wrongKey[0] ^= 0xff
	if _, ok := secretbox.Open(nil, ciphertext, &nonce, &wrongKey); ok {
		fmt.Fprintf(os.Stderr, "Open unexpectedly succeeded with wrong key\n")
		os.Exit(1)
	}

	// 5. secretbox.Open returns false when decrypted with a different nonce
	var wrongNonce [24]byte
	copy(wrongNonce[:], nonce[:])
	wrongNonce[0] ^= 0xff
	if _, ok := secretbox.Open(nil, ciphertext, &wrongNonce, &key); ok {
		fmt.Fprintf(os.Stderr, "Open unexpectedly succeeded with wrong nonce\n")
		os.Exit(1)
	}

	// 6. secretbox.Open returns false when ciphertext length is less than secretbox.Overhead
	shortCiphertext := make([]byte, secretbox.Overhead-1)
	if _, ok := secretbox.Open(nil, shortCiphertext, &nonce, &key); ok {
		fmt.Fprintf(os.Stderr, "Open unexpectedly succeeded on ciphertext shorter than Overhead\n")
		os.Exit(1)
	}

	// 7. secretbox.Seal encrypts empty message producing an authentication tag of length secretbox.Overhead
	emptySealed := secretbox.Seal(nil, []byte{}, &nonce, &key)
	if len(emptySealed) != secretbox.Overhead {
		fmt.Fprintf(os.Stderr, "Seal empty message length mismatch: got %d, want %d\n", len(emptySealed), secretbox.Overhead)
		os.Exit(1)
	}
	decryptedEmpty, ok := secretbox.Open(nil, emptySealed, &nonce, &key)
	if !ok || len(decryptedEmpty) != 0 {
		fmt.Fprintf(os.Stderr, "Open failed to decrypt empty message\n")
		os.Exit(1)
	}

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