golang.org/x/crypto v0.39.0: cast5.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 cast5.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:
  - cast5.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:sha256:822e0e23c62899ad51f5fd7d8d4c46f58744d27e2c55580bfa1364be78a62e74","contract":["cast5.NewCipher returns a *cast5.Cipher with BlockSize() == 8 for keys between 5 and 16 bytes (such as cast5.KeySize = 16)","Cipher.Encrypt and Cipher.Decrypt round-trip an 8-byte block back to the original plaintext","cast5.NewCipher returns a non-nil error when key length is outside [5, 16] bytes (e.g. 4 or 17 bytes)"],"goal":"verify cast5.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":["cast5.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":["cast5.NewCipher"],"verifierAdapter":"golang@1"}

module sample

go 1.23.0

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 cast5.NewCipher in pkg:golang/golang.org/x/crypto@v0.39.0",
  "kind": "HOW",
  "packages": [
    "pkg:golang/golang.org/x/crypto@v0.39.0"
  ],
  "symbols": [
    "cast5.NewCipher"
  ]
}

package main

import (
	"bytes"
	"log"

	"golang.org/x/crypto/cast5"
)

func main() {
	key := []byte("0123456789abcdef") // 16-byte key (cast5.KeySize)
	c, err := cast5.NewCipher(key)
	if err != nil {
		log.Fatalf("expected nil error for 16-byte key, got %v", err)
	}
	if c.BlockSize() != cast5.BlockSize || c.BlockSize() != 8 {
		log.Fatalf("expected block size 8, got %d", c.BlockSize())
	}

	plaintext := []byte("8byteblk")
	ciphertext := make([]byte, cast5.BlockSize)
	decrypted := make([]byte, cast5.BlockSize)

	c.Encrypt(ciphertext, plaintext)
	if bytes.Equal(ciphertext, plaintext) {
		log.Fatalf("expected ciphertext to differ from plaintext")
	}

	c.Decrypt(decrypted, ciphertext)
	if !bytes.Equal(decrypted, plaintext) {
		log.Fatalf("round-trip decrypt mismatch: got %q, want %q", decrypted, plaintext)
	}

	if _, err := cast5.NewCipher([]byte("short")[:4]); err == nil {
		log.Fatalf("expected error for 4-byte key (<5 bytes)")
	}
	if _, err := cast5.NewCipher(make([]byte, 17)); err == nil {
		log.Fatalf("expected error for 17-byte key (>16 bytes)")
	}
}