golang.org/x/crypto v0.39.0: xts.NewCipher

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/xts.NewCipher in pkg:golang/golang.org/x/crypto@v0.39.0
Kind: HOW

Use EXACTLY these public packages and versions:
  - pkg:golang/golang.org/x/crypto@v0.39.0
Demonstrate these symbols/APIs:
  - golang.org/x/crypto/xts.NewCipher

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:f78975b8dff20f09d179a9637fb81b46ae2582eed64f26054dddb3916d29d2f5","contract":["xts.NewCipher(aes.NewCipher, 32-byte key) returns a non-nil *xts.Cipher with nil error","Cipher.Encrypt and Cipher.Decrypt round-trip a 32-byte sector using the same sectorNum","xts.NewCipher rejects odd-length keys with a non-nil error"],"goal":"verify golang.org/x/crypto/xts.NewCipher in pkg:golang/golang.org/x/crypto@v0.39.0","kind":"HOW","packages":["pkg:golang/golang.org/x/crypto@v0.39.0"],"schemaVersion":1,"symbols":["golang.org/x/crypto/xts.NewCipher"]},"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@v0.39.0"],"schemaVersion":1,"subject":"pkg:golang/golang.org/x/crypto@v0.39.0","symbols":["golang.org/x/crypto/xts.NewCipher"],"verifierAdapter":"golang@1"}

module sample

go 1.24

require golang.org/x/crypto v0.39.0

golang.org/x/crypto v0.39.0 h1:SHs+kF4LP+f+p14esP5jAoDpHU8Gu/v9lFRK6IT5imM=
golang.org/x/crypto v0.39.0/go.mod h1:L+Xg3Wf6HoL4Bn4238Z6ft6KfEpN0tJGo53AAPC632U=

{
  "schemaVersion": 1,
  "goal": "verify golang.org/x/crypto/xts.NewCipher in pkg:golang/golang.org/x/crypto@v0.39.0",
  "kind": "HOW",
  "packages": [
    "pkg:golang/golang.org/x/crypto@v0.39.0"
  ],
  "symbols": [
    "golang.org/x/crypto/xts.NewCipher"
  ]
}

package main

import (
	"bytes"
	"crypto/aes"
	"fmt"
	"os"

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

func main() {
	// XTS requires a double-length key (two 16-byte AES-128 keys = 32 bytes,
	// or two 32-byte AES-256 keys = 64 bytes).
	key := make([]byte, 32)
	for i := range key {
		key[i] = byte(i + 1)
	}

	c, err := xts.NewCipher(aes.NewCipher, key)
	if err != nil {
		fmt.Fprintf(os.Stderr, "expected NewCipher to succeed with 32-byte key, got: %v\n", err)
		os.Exit(1)
	}
	if c == nil {
		fmt.Fprintln(os.Stderr, "expected non-nil Cipher")
		os.Exit(1)
	}

	// Encrypt and decrypt a 32-byte sector (must be at least 16 bytes)
	plaintext := []byte("0123456789abcdeffedcba9876543210")
	ciphertext := make([]byte, len(plaintext))
	sectorNum := uint64(42)

	c.Encrypt(ciphertext, plaintext, sectorNum)
	if bytes.Equal(ciphertext, plaintext) {
		fmt.Fprintln(os.Stderr, "expected ciphertext to differ from plaintext")
		os.Exit(1)
	}

	decrypted := make([]byte, len(ciphertext))
	c.Decrypt(decrypted, ciphertext, sectorNum)
	if !bytes.Equal(decrypted, plaintext) {
		fmt.Fprintf(os.Stderr, "expected decrypted text to match plaintext, got %x\n", decrypted)
		os.Exit(1)
	}

	// Verify odd key length rejection (must be even length so it splits into two equal keys)
	_, err = xts.NewCipher(aes.NewCipher, make([]byte, 31))
	if err == nil {
		fmt.Fprintln(os.Stderr, "expected NewCipher to reject odd-length key")
		os.Exit(1)
	}
}