golang.org/x/crypto v0.11.1-0.20230711161743-2e82bdd1719d: chacha20poly1305.KeySize

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/chacha20poly1305.KeySize in pkg:golang/golang.org/x/crypto@v0.11.1-0.20230711161743-2e82bdd1719d
Kind: HOW

Use EXACTLY these public packages and versions:
  - pkg:golang/golang.org/x/crypto@v0.11.1-0.20230711161743-2e82bdd1719d
Demonstrate these symbols/APIs:
  - golang.org/x/crypto/chacha20poly1305.KeySize

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:sha256:9e2d223453d28ec2eb9df070b522328b0feb71055fe75b59d5555697adbe667d","contract":["chacha20poly1305.KeySize is exactly 32 bytes","chacha20poly1305.New succeeds when key length equals KeySize","chacha20poly1305.New returns error when key length is shorter than KeySize","chacha20poly1305.New returns error when key length is longer than KeySize","chacha20poly1305.New returns error when key is empty","chacha20poly1305.NewX succeeds when key length equals KeySize","chacha20poly1305.NewX returns error when key length differs from KeySize","AEAD cipher created with KeySize key successfully encrypts and decrypts payload"],"goal":"verify golang.org/x/crypto/chacha20poly1305.KeySize in pkg:golang/golang.org/x/crypto@v0.11.1-0.20230711161743-2e82bdd1719d","kind":"HOW","packages":["pkg:golang/golang.org/x/crypto@v0.11.1-0.20230711161743-2e82bdd1719d"],"schemaVersion":1,"symbols":["golang.org/x/crypto/chacha20poly1305.KeySize"]},"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@v0.11.1-0.20230711161743-2e82bdd1719d"],"schemaVersion":1,"subject":"pkg:golang/golang.org/x/crypto@v0.11.1-0.20230711161743-2e82bdd1719d","symbols":["golang.org/x/crypto/chacha20poly1305.KeySize"],"verifierAdapter":"golang@1"}

module example.com/sample

go 1.26.6

require golang.org/x/crypto v0.11.1-0.20230711161743-2e82bdd1719d

require golang.org/x/sys v0.10.0 // indirect

golang.org/x/crypto v0.11.1-0.20230711161743-2e82bdd1719d h1:LiA25/KWKuXfIq5pMIBq1s5hz3HQxhJJSu/SUGlD+SM=
golang.org/x/crypto v0.11.1-0.20230711161743-2e82bdd1719d/go.mod h1:xgJhtzW8F9jGdVFWZESrid1U1bjeNy4zgy5cRr/CIio=
golang.org/x/sys v0.10.0 h1:SqMFp9UcQJZa+pmYuAKjd9xq1f0j5rLcDIk0mj4qAsA=
golang.org/x/sys v0.10.0/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=

package main

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

	"golang.org/x/crypto/chacha20poly1305"
)

func main() {
	// ChaCha20-Poly1305 requires a 256-bit (32-byte) key.
	key := make([]byte, chacha20poly1305.KeySize)
	if _, err := io.ReadFull(rand.Reader, key); err != nil {
		log.Fatalf("failed to generate random key: %v", err)
	}
	fmt.Printf("Generated key with KeySize = %d bytes\n", len(key))

	aead, err := chacha20poly1305.New(key)
	if err != nil {
		log.Fatalf("failed to create cipher: %v", err)
	}

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

	plaintext := []byte("example data to encrypt")
	additionalData := []byte("example associated data")

	ciphertext := aead.Seal(nil, nonce, plaintext, additionalData)
	fmt.Printf("Encrypted %d bytes into %d bytes of ciphertext\n", len(plaintext), len(ciphertext))

	decrypted, err := aead.Open(nil, nonce, ciphertext, additionalData)
	if err != nil {
		log.Fatalf("decryption failed: %v", err)
	}
	fmt.Printf("Decrypted message: %s\n", string(decrypted))

	// Demonstrate rejection of invalid key length
	invalidKey := make([]byte, chacha20poly1305.KeySize-1)
	if _, err := chacha20poly1305.New(invalidKey); err != nil {
		fmt.Printf("Correctly rejected key of invalid size %d: %v\n", len(invalidKey), err)
	}
}

{
  "schemaVersion": 1,
  "goal": "verify golang.org/x/crypto/chacha20poly1305.KeySize in pkg:golang/golang.org/x/crypto@v0.11.1-0.20230711161743-2e82bdd1719d",
  "kind": "HOW",
  "packages": [
    "pkg:golang/golang.org/x/crypto@v0.11.1-0.20230711161743-2e82bdd1719d"
  ],
  "symbols": [
    "golang.org/x/crypto/chacha20poly1305.KeySize"
  ]
}

package main

import (
	"bytes"
	"fmt"
	"os"

	"golang.org/x/crypto/chacha20poly1305"
)

func main() {
	// 1. chacha20poly1305.KeySize is exactly 32 bytes
	if chacha20poly1305.KeySize != 32 {
		fmt.Fprintf(os.Stderr, "assertion 1 failed: expected KeySize 32, got %d\n", chacha20poly1305.KeySize)
		os.Exit(1)
	}

	key := make([]byte, chacha20poly1305.KeySize)
	for i := range key {
		key[i] = byte(i)
	}

	// 2. chacha20poly1305.New succeeds when key length equals KeySize
	aead, err := chacha20poly1305.New(key)
	if err != nil {
		fmt.Fprintf(os.Stderr, "assertion 2 failed: expected nil error, got %v\n", err)
		os.Exit(1)
	}
	if aead == nil {
		fmt.Fprintf(os.Stderr, "assertion 2 failed: expected non-nil cipher\n")
		os.Exit(1)
	}

	// 3. chacha20poly1305.New returns error when key length is shorter than KeySize
	shortKey := key[:chacha20poly1305.KeySize-1]
	if _, err := chacha20poly1305.New(shortKey); err == nil {
		fmt.Fprintf(os.Stderr, "assertion 3 failed: expected error for key shorter than KeySize, got nil\n")
		os.Exit(1)
	}

	// 4. chacha20poly1305.New returns error when key length is longer than KeySize
	longKey := append(key, 0xFF)
	if _, err := chacha20poly1305.New(longKey); err == nil {
		fmt.Fprintf(os.Stderr, "assertion 4 failed: expected error for key longer than KeySize, got nil\n")
		os.Exit(1)
	}

	// 5. chacha20poly1305.New returns error when key is empty
	if _, err := chacha20poly1305.New([]byte{}); err == nil {
		fmt.Fprintf(os.Stderr, "assertion 5 failed: expected error for empty key, got nil\n")
		os.Exit(1)
	}

	// 6. chacha20poly1305.NewX succeeds when key length equals KeySize
	aeadX, err := chacha20poly1305.NewX(key)
	if err != nil {
		fmt.Fprintf(os.Stderr, "assertion 6 failed: expected nil error for NewX with KeySize key, got %v\n", err)
		os.Exit(1)
	}
	if aeadX == nil {
		fmt.Fprintf(os.Stderr, "assertion 6 failed: expected non-nil cipher from NewX\n")
		os.Exit(1)
	}

	// 7. chacha20poly1305.NewX returns error when key length differs from KeySize
	if _, err := chacha20poly1305.NewX(shortKey); err == nil {
		fmt.Fprintf(os.Stderr, "assertion 7 failed: expected error for NewX with short key, got nil\n")
		os.Exit(1)
	}
	if _, err := chacha20poly1305.NewX(longKey); err == nil {
		fmt.Fprintf(os.Stderr, "assertion 7 failed: expected error for NewX with long key, got nil\n")
		os.Exit(1)
	}

	// 8. AEAD cipher created with KeySize key successfully encrypts and decrypts payload
	nonce := make([]byte, aead.NonceSize())
	for i := range nonce {
		nonce[i] = byte(i + 10)
	}
	plaintext := []byte("contract-verification-payload")
	ad := []byte("contract-additional-data")
	ciphertext := aead.Seal(nil, nonce, plaintext, ad)
	decrypted, err := aead.Open(nil, nonce, ciphertext, ad)
	if err != nil {
		fmt.Fprintf(os.Stderr, "assertion 8 failed: Open failed: %v\n", err)
		os.Exit(1)
	}
	if !bytes.Equal(decrypted, plaintext) {
		fmt.Fprintf(os.Stderr, "assertion 8 failed: decrypted bytes do not match plaintext\n")
		os.Exit(1)
	}

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