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

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.NewX 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.NewX
Required runtime conditions:
  - ecosystem: golang
  - language: go
  - packageManager: go@1.26.6
  - runtime: go@1.26.6

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:sha256:1aaf70d3dcd8254504ceb2a7877fb58e935916e3ad190510af2b7b7e6401c8be","contract":["chacha20poly1305.NewX creates a cipher.AEAD with NonceSize equal to NonceSizeX and Overhead equal to Overhead","chacha20poly1305.NewX rejects key with length not equal to KeySize","cipher.AEAD from NewX encrypts plaintext and decrypts back to original with correct nonce and additionalData","cipher.AEAD from NewX fails decryption when ciphertext is tampered or truncated","cipher.AEAD from NewX fails decryption when additionalData does not match","cipher.AEAD from NewX produces distinct ciphertexts for identical plaintext when nonce differs"],"goal":"verify golang.org/x/crypto/chacha20poly1305.NewX 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.NewX"]},"contractCommand":["go","run","./test"],"environment":{"arch":"x64","distro":"ubuntu","ecosystem":"golang","language":"go","libc":"glibc","libcVersion":"2.39","os":"linux","osVersionBucket":"24","packageManager":"go","packageManagerVersion":"1.26.6","runtime":"go","runtimeVersion":"1.26.6","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.NewX"],"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 v0.47.0 // 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/crypto v0.56.0 h1:GUh5Ii4J5jtcseSMiRqr1jXCNHoxjeV9Fmekc2oLy6Y=
golang.org/x/crypto v0.56.0/go.mod h1:OMW5y6CY9l38uPLmxU6l6pwcXp1obtLo3e6gT7gQR2I=
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/chacha20poly1305"
)

// Encrypt encrypts plaintext using XChaCha20-Poly1305.
func Encrypt(key, plaintext, additionalData []byte) ([]byte, []byte, error) {
	aead, err := chacha20poly1305.NewX(key)
	if err != nil {
		return nil, nil, err
	}
	nonce := make([]byte, aead.NonceSize())
	if _, err := io.ReadFull(rand.Reader, nonce); err != nil {
		return nil, nil, err
	}
	ciphertext := aead.Seal(nil, nonce, plaintext, additionalData)
	return nonce, ciphertext, nil
}

// Decrypt decrypts ciphertext using XChaCha20-Poly1305.
func Decrypt(key, nonce, ciphertext, additionalData []byte) ([]byte, error) {
	aead, err := chacha20poly1305.NewX(key)
	if err != nil {
		return nil, err
	}
	return aead.Open(nil, nonce, ciphertext, additionalData)
}

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

	plaintext := []byte("XChaCha20-Poly1305 sample message")
	additionalData := []byte("metadata-header")

	nonce, ciphertext, err := Encrypt(key, plaintext, additionalData)
	if err != nil {
		log.Fatalf("encryption failed: %v", err)
	}

	decrypted, err := Decrypt(key, nonce, ciphertext, additionalData)
	if err != nil {
		log.Fatalf("decryption failed: %v", err)
	}

	fmt.Printf("Plaintext: %s\n", string(decrypted))
	fmt.Printf("Ciphertext length: %d\n", len(ciphertext))
}

{
  "schemaVersion": 1,
  "goal": "verify golang.org/x/crypto/chacha20poly1305.NewX 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.NewX"
  ],
  "runtimeConditions": {
    "ecosystem": "golang",
    "language": "go",
    "packageManager": "go@1.26.6",
    "runtime": "go@1.26.6"
  }
}

package main

import (
	"bytes"
	"fmt"
	"os"

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

func main() {
	key := make([]byte, chacha20poly1305.KeySize)
	for i := range key {
		key[i] = byte(i + 1)
	}

	// 1. chacha20poly1305.NewX creates a cipher.AEAD with NonceSize equal to NonceSizeX and Overhead equal to Overhead
	aead, err := chacha20poly1305.NewX(key)
	if err != nil {
		fmt.Fprintf(os.Stderr, "FAIL: NewX failed with valid key: %v\n", err)
		os.Exit(1)
	}
	if aead.NonceSize() != chacha20poly1305.NonceSizeX {
		fmt.Fprintf(os.Stderr, "FAIL: expected NonceSize %d, got %d\n", chacha20poly1305.NonceSizeX, aead.NonceSize())
		os.Exit(1)
	}
	if aead.Overhead() != chacha20poly1305.Overhead {
		fmt.Fprintf(os.Stderr, "FAIL: expected Overhead %d, got %d\n", chacha20poly1305.Overhead, aead.Overhead())
		os.Exit(1)
	}

	// 2. chacha20poly1305.NewX rejects key with length not equal to KeySize
	shortKey := make([]byte, chacha20poly1305.KeySize-1)
	if _, err := chacha20poly1305.NewX(shortKey); err == nil {
		fmt.Fprintf(os.Stderr, "FAIL: NewX expected error for short key, got nil\n")
		os.Exit(1)
	}
	longKey := make([]byte, chacha20poly1305.KeySize+1)
	if _, err := chacha20poly1305.NewX(longKey); err == nil {
		fmt.Fprintf(os.Stderr, "FAIL: NewX expected error for long key, got nil\n")
		os.Exit(1)
	}

	// 3. cipher.AEAD from NewX encrypts plaintext and decrypts back to original with correct nonce and additionalData
	plaintext := []byte("confidential payload for contract testing")
	additionalData := []byte("authenticated-associated-data")
	nonce := make([]byte, chacha20poly1305.NonceSizeX)
	for i := range nonce {
		nonce[i] = byte(i * 3)
	}

	ciphertext := aead.Seal(nil, nonce, plaintext, additionalData)
	if len(ciphertext) != len(plaintext)+aead.Overhead() {
		fmt.Fprintf(os.Stderr, "FAIL: expected ciphertext length %d, got %d\n", len(plaintext)+aead.Overhead(), len(ciphertext))
		os.Exit(1)
	}

	decrypted, err := aead.Open(nil, nonce, ciphertext, additionalData)
	if err != nil {
		fmt.Fprintf(os.Stderr, "FAIL: Open failed to decrypt valid ciphertext: %v\n", err)
		os.Exit(1)
	}
	if !bytes.Equal(decrypted, plaintext) {
		fmt.Fprintf(os.Stderr, "FAIL: decrypted content does not match original plaintext\n")
		os.Exit(1)
	}

	// 4. cipher.AEAD from NewX fails decryption when ciphertext is tampered or truncated
	tamperedCiphertext := make([]byte, len(ciphertext))
	copy(tamperedCiphertext, ciphertext)
	tamperedCiphertext[0] ^= 0xff
	if _, err := aead.Open(nil, nonce, tamperedCiphertext, additionalData); err == nil {
		fmt.Fprintf(os.Stderr, "FAIL: Open expected error on tampered ciphertext, got nil\n")
		os.Exit(1)
	}

	truncatedCiphertext := ciphertext[:len(ciphertext)-1]
	if _, err := aead.Open(nil, nonce, truncatedCiphertext, additionalData); err == nil {
		fmt.Fprintf(os.Stderr, "FAIL: Open expected error on truncated ciphertext, got nil\n")
		os.Exit(1)
	}

	// 5. cipher.AEAD from NewX fails decryption when additionalData does not match
	corruptedAD := []byte("mismatched-associated-data")
	if _, err := aead.Open(nil, nonce, ciphertext, corruptedAD); err == nil {
		fmt.Fprintf(os.Stderr, "FAIL: Open expected error on mismatched additionalData, got nil\n")
		os.Exit(1)
	}

	// 6. cipher.AEAD from NewX produces distinct ciphertexts for identical plaintext when nonce differs
	nonceAlt := make([]byte, chacha20poly1305.NonceSizeX)
	copy(nonceAlt, nonce)
	nonceAlt[0] ^= 0x01

	ciphertextAlt := aead.Seal(nil, nonceAlt, plaintext, additionalData)
	if bytes.Equal(ciphertext, ciphertextAlt) {
		fmt.Fprintf(os.Stderr, "FAIL: expected different ciphertexts for different nonces\n")
		os.Exit(1)
	}

	fmt.Println("PASS: all contract assertions passed")
}