golang.org/x/crypto v0.47.0: bcrypt.MaxCost

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/bcrypt.MaxCost in pkg:golang/golang.org/x/crypto@v0.47.0
Kind: HOW

Use EXACTLY these public packages and versions:
  - pkg:golang/golang.org/x/crypto@v0.47.0
Demonstrate these symbols/APIs:
  - golang.org/x/crypto/bcrypt.MaxCost

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:sha256:2bcdda0bcce0bbd91755c719b6a75c7114004c2723f2ae19fc85e8fa5622de93","contract":["bcrypt.MaxCost is 31 representing maximum allowable bcrypt hashing cost","bcrypt.GenerateFromPassword returns InvalidCostError when cost exceeds bcrypt.MaxCost","bcrypt.Cost returns bcrypt.MaxCost when parsing valid hash formatted with maximum cost","bcrypt.Cost returns InvalidCostError when parsing hash with cost exceeding bcrypt.MaxCost","bcrypt.InvalidCostError formatted error string includes bcrypt.MaxCost as upper bound"],"goal":"verify golang.org/x/crypto/bcrypt.MaxCost in pkg:golang/golang.org/x/crypto@v0.47.0","kind":"HOW","packages":["pkg:golang/golang.org/x/crypto@v0.47.0"],"schemaVersion":1,"symbols":["golang.org/x/crypto/bcrypt.MaxCost"]},"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@v0.47.0"],"schemaVersion":1,"subject":"pkg:golang/golang.org/x/crypto@v0.47.0","symbols":["golang.org/x/crypto/bcrypt.MaxCost"],"verifierAdapter":"golang@1"}

module example.com/sample

go 1.26.6

require golang.org/x/crypto v0.47.0

golang.org/x/crypto v0.47.0 h1:V6e3FRj+n4dbpw86FJ8Fv7XVOql7TEwpHapKoMJ/GO8=
golang.org/x/crypto v0.47.0/go.mod h1:ff3Y9VzzKbwSSEzWqJsJVBnWmRwRSHt/6Op5n9bQc4A=

package main

import (
	"errors"
	"fmt"

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

func main() {
	// bcrypt.MaxCost represents the upper limit for hashing cost (31)
	fmt.Printf("Bcrypt maximum allowed cost: %d\n", bcrypt.MaxCost)

	// Attempting to generate a password hash with cost exceeding MaxCost returns InvalidCostError
	_, err := bcrypt.GenerateFromPassword([]byte("example-secret"), bcrypt.MaxCost+1)
	var invalidCostErr bcrypt.InvalidCostError
	if errors.As(err, &invalidCostErr) {
		fmt.Printf("Rejected invalid cost %d: %v\n", int(invalidCostErr), err)
	}

	// Parsing a valid bcrypt hash with MaxCost
	maxCostHash := []byte("$2a$31$usesomesillystringfore2uDLvp1AK2Q68Lp7FI0d5BOmvnoZZGW")
	cost, err := bcrypt.Cost(maxCostHash)
	if err != nil {
		fmt.Printf("Failed to inspect cost: %v\n", err)
		return
	}
	fmt.Printf("Inspected hash cost matching MaxCost: %d\n", cost)
}

{
  "schemaVersion": 1,
  "goal": "verify golang.org/x/crypto/bcrypt.MaxCost in pkg:golang/golang.org/x/crypto@v0.47.0",
  "kind": "HOW",
  "packages": [
    "pkg:golang/golang.org/x/crypto@v0.47.0"
  ],
  "symbols": [
    "golang.org/x/crypto/bcrypt.MaxCost"
  ]
}

package main

import (
	"errors"
	"fmt"
	"os"

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

func main() {
	// Assertion 1: bcrypt.MaxCost is 31 representing maximum allowable bcrypt hashing cost
	if bcrypt.MaxCost != 31 {
		fmt.Fprintf(os.Stderr, "assertion 1 failed: expected bcrypt.MaxCost == 31, got %d\n", bcrypt.MaxCost)
		os.Exit(1)
	}

	// Assertion 2: bcrypt.GenerateFromPassword returns InvalidCostError when cost exceeds bcrypt.MaxCost
	password := []byte("contract-verification-password")
	_, err := bcrypt.GenerateFromPassword(password, bcrypt.MaxCost+1)
	var invalidCostErr bcrypt.InvalidCostError
	if !errors.As(err, &invalidCostErr) {
		fmt.Fprintf(os.Stderr, "assertion 2 failed: expected InvalidCostError, got %v\n", err)
		os.Exit(1)
	}
	if int(invalidCostErr) != bcrypt.MaxCost+1 {
		fmt.Fprintf(os.Stderr, "assertion 2 failed: expected InvalidCostError(%d), got %d\n", bcrypt.MaxCost+1, int(invalidCostErr))
		os.Exit(1)
	}

	// Assertion 3: bcrypt.Cost returns bcrypt.MaxCost when parsing valid hash formatted with maximum cost
	validMaxCostHash := []byte("$2a$31$usesomesillystringfore2uDLvp1AK2Q68Lp7FI0d5BOmvnoZZGW")
	cost, err := bcrypt.Cost(validMaxCostHash)
	if err != nil {
		fmt.Fprintf(os.Stderr, "assertion 3 failed: Cost returned error on validMaxCostHash: %v\n", err)
		os.Exit(1)
	}
	if cost != bcrypt.MaxCost {
		fmt.Fprintf(os.Stderr, "assertion 3 failed: expected cost %d, got %d\n", bcrypt.MaxCost, cost)
		os.Exit(1)
	}

	// Assertion 4: bcrypt.Cost returns InvalidCostError when parsing hash with cost exceeding bcrypt.MaxCost
	hashExceedingMaxCost := []byte("$2a$32$usesomesillystringfore2uDLvp1AK2Q68Lp7FI0d5BOmvnoZZGW")
	_, err = bcrypt.Cost(hashExceedingMaxCost)
	if !errors.As(err, &invalidCostErr) {
		fmt.Fprintf(os.Stderr, "assertion 4 failed: expected InvalidCostError for cost 32, got %v\n", err)
		os.Exit(1)
	}
	if int(invalidCostErr) != 32 {
		fmt.Fprintf(os.Stderr, "assertion 4 failed: expected InvalidCostError(32), got %d\n", int(invalidCostErr))
		os.Exit(1)
	}

	// Assertion 5: bcrypt.InvalidCostError formatted error string includes bcrypt.MaxCost as upper bound
	expectedErr := fmt.Sprintf("crypto/bcrypt: cost 32 is outside allowed inclusive range %d..%d", bcrypt.MinCost, bcrypt.MaxCost)
	if invalidCostErr.Error() != expectedErr {
		fmt.Fprintf(os.Stderr, "assertion 5 failed: expected error %q, got %q\n", expectedErr, invalidCostErr.Error())
		os.Exit(1)
	}

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