golang.org/x/crypto v0.21.0: bcrypt.MinCost

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.MinCost in pkg:golang/golang.org/x/crypto@v0.21.0
Kind: HOW

Use EXACTLY these public packages and versions:
  - pkg:golang/golang.org/x/crypto@v0.21.0
Demonstrate these symbols/APIs:
  - golang.org/x/crypto/bcrypt.MinCost
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:cf11618f8b3c84b2a6bad6798d17e8ae52eccf39c4ff94ca6831e8403c278c3f","contract":["bcrypt.MinCost equals 4","bcrypt.GenerateFromPassword produces valid hash with cost equal to bcrypt.MinCost","bcrypt.GenerateFromPassword sets cost to DefaultCost when requested cost is below bcrypt.MinCost","bcrypt.CompareHashAndPassword validates matching password and rejects mismatched password for MinCost hash"],"goal":"verify golang.org/x/crypto/bcrypt.MinCost in pkg:golang/golang.org/x/crypto@v0.21.0","kind":"HOW","packages":["pkg:golang/golang.org/x/crypto@v0.21.0"],"schemaVersion":1,"symbols":["golang.org/x/crypto/bcrypt.MinCost"]},"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@v0.21.0"],"schemaVersion":1,"subject":"pkg:golang/golang.org/x/crypto@v0.21.0","symbols":["golang.org/x/crypto/bcrypt.MinCost"],"verifierAdapter":"golang@1"}

module sample

go 1.26.6

require golang.org/x/crypto v0.21.0

golang.org/x/crypto v0.21.0 h1:X31++rzVUdKhX5sWmSOFZxx8UW/ldWx55cbf08iNAMA=
golang.org/x/crypto v0.21.0/go.mod h1:0BP7YvVV9gBbVKyeTG0Gyn+gZm94bibOW5BjDEYAOMs=

package main

import (
	"fmt"

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

// HashPassword hashes a password using bcrypt.MinCost.
func HashPassword(password []byte) ([]byte, error) {
	return bcrypt.GenerateFromPassword(password, bcrypt.MinCost)
}

// VerifyPassword verifies a password against a hash generated with bcrypt.
func VerifyPassword(hashedPassword, password []byte) error {
	return bcrypt.CompareHashAndPassword(hashedPassword, password)
}

// GetHashCost returns the bcrypt cost of the provided hash.
func GetHashCost(hashedPassword []byte) (int, error) {
	return bcrypt.Cost(hashedPassword)
}

func main() {
	password := []byte("sample-secret-password")
	hashed, err := HashPassword(password)
	if err != nil {
		panic(err)
	}

	cost, err := GetHashCost(hashed)
	if err != nil {
		panic(err)
	}
	fmt.Printf("Bcrypt MinCost: %d, Hash Cost: %d\n", bcrypt.MinCost, cost)

	if err := VerifyPassword(hashed, password); err != nil {
		panic(err)
	}
	fmt.Println("Password verified successfully")
}

{
  "schemaVersion": 1,
  "goal": "verify golang.org/x/crypto/bcrypt.MinCost in pkg:golang/golang.org/x/crypto@v0.21.0",
  "kind": "HOW",
  "packages": [
    "pkg:golang/golang.org/x/crypto@v0.21.0"
  ],
  "symbols": [
    "golang.org/x/crypto/bcrypt.MinCost"
  ],
  "runtimeConditions": {
    "ecosystem": "golang",
    "language": "go",
    "packageManager": "go@1.26.6",
    "runtime": "go@1.26.6"
  }
}

package main

import (
	"errors"
	"fmt"
	"os"

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

func main() {
	// 1. bcrypt.MinCost equals 4
	{
		if bcrypt.MinCost != 4 {
			fmt.Fprintf(os.Stderr, "FAIL: expected MinCost == 4, got %d\n", bcrypt.MinCost)
			os.Exit(1)
		}
	}

	// 2. bcrypt.GenerateFromPassword produces valid hash with cost equal to bcrypt.MinCost
	var minCostHash []byte
	password := []byte("secure-sample-password")
	{
		var err error
		minCostHash, err = bcrypt.GenerateFromPassword(password, bcrypt.MinCost)
		if err != nil {
			fmt.Fprintf(os.Stderr, "FAIL: GenerateFromPassword failed with MinCost: %v\n", err)
			os.Exit(1)
		}
		cost, err := bcrypt.Cost(minCostHash)
		if err != nil {
			fmt.Fprintf(os.Stderr, "FAIL: Cost failed for minCostHash: %v\n", err)
			os.Exit(1)
		}
		if cost != bcrypt.MinCost {
			fmt.Fprintf(os.Stderr, "FAIL: expected Cost %d, got %d\n", bcrypt.MinCost, cost)
			os.Exit(1)
		}
	}

	// 3. bcrypt.GenerateFromPassword sets cost to DefaultCost when requested cost is below bcrypt.MinCost
	{
		fallbackHash, err := bcrypt.GenerateFromPassword(password, bcrypt.MinCost-1)
		if err != nil {
			fmt.Fprintf(os.Stderr, "FAIL: GenerateFromPassword failed with cost below MinCost: %v\n", err)
			os.Exit(1)
		}
		cost, err := bcrypt.Cost(fallbackHash)
		if err != nil {
			fmt.Fprintf(os.Stderr, "FAIL: Cost failed for fallbackHash: %v\n", err)
			os.Exit(1)
		}
		if cost != bcrypt.DefaultCost {
			fmt.Fprintf(os.Stderr, "FAIL: expected DefaultCost %d for cost < MinCost, got %d\n", bcrypt.DefaultCost, cost)
			os.Exit(1)
		}
	}

	// 4. bcrypt.CompareHashAndPassword validates matching password and rejects mismatched password for MinCost hash
	{
		if err := bcrypt.CompareHashAndPassword(minCostHash, password); err != nil {
			fmt.Fprintf(os.Stderr, "FAIL: CompareHashAndPassword failed for correct password: %v\n", err)
			os.Exit(1)
		}
		wrongPassword := []byte("wrong-password-value")
		if err := bcrypt.CompareHashAndPassword(minCostHash, wrongPassword); err == nil {
			fmt.Fprintf(os.Stderr, "FAIL: CompareHashAndPassword unexpectedly succeeded for wrong password\n")
			os.Exit(1)
		} else if !errors.Is(err, bcrypt.ErrMismatchedHashAndPassword) {
			fmt.Fprintf(os.Stderr, "FAIL: expected ErrMismatchedHashAndPassword, got %v\n", err)
			os.Exit(1)
		}
	}

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