golang.org/x/crypto v0.0.0-20201203163018-be400aefbc4c: bcrypt.DefaultCost

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.DefaultCost in pkg:golang/golang.org/x/crypto@v0.0.0-20201203163018-be400aefbc4c
Kind: HOW

Use EXACTLY these public packages and versions:
  - pkg:golang/golang.org/x/crypto@v0.0.0-20201203163018-be400aefbc4c
Demonstrate these symbols/APIs:
  - golang.org/x/crypto/bcrypt.DefaultCost

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:a6e24ed7816f11fbb7057daf5ee3da208fdc1af0cd170eda03be1b313b2d3105","contract":["bcrypt.DefaultCost is defined with value 10","bcrypt.DefaultCost is within MinCost and MaxCost inclusive","bcrypt.GenerateFromPassword with DefaultCost yields hash with DefaultCost","bcrypt.GenerateFromPassword with zero cost defaults to DefaultCost","bcrypt.GenerateFromPassword with cost below MinCost defaults to DefaultCost","bcrypt.CompareHashAndPassword successfully validates hash produced with DefaultCost"],"goal":"verify golang.org/x/crypto/bcrypt.DefaultCost in pkg:golang/golang.org/x/crypto@v0.0.0-20201203163018-be400aefbc4c","kind":"HOW","packages":["pkg:golang/golang.org/x/crypto@v0.0.0-20201203163018-be400aefbc4c"],"schemaVersion":1,"symbols":["golang.org/x/crypto/bcrypt.DefaultCost"]},"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@v0.0.0-20201203163018-be400aefbc4c"],"schemaVersion":1,"subject":"pkg:golang/golang.org/x/crypto@v0.0.0-20201203163018-be400aefbc4c","symbols":["golang.org/x/crypto/bcrypt.DefaultCost"],"verifierAdapter":"golang@1"}

module example.com/sample

go 1.24

require golang.org/x/crypto v0.0.0-20201203163018-be400aefbc4c

golang.org/x/crypto v0.0.0-20190308221718-c2843e01d9a2/go.mod h1:djNgcEr1/C05ACkg1iLfiJU5Ep61QUkGW8qpdssI0+w=
golang.org/x/crypto v0.0.0-20201203163018-be400aefbc4c h1:9HhBz5L/UjnK9XLtiZhYAdue5BVKep3PMmS2LuPDt8k=
golang.org/x/crypto v0.0.0-20201203163018-be400aefbc4c/go.mod h1:jdWPYTVW3xRLrWPugEBEK3UY2ZEsg3UU495nc5E+M+I=
golang.org/x/net v0.0.0-20190404232315-eb5bcb51f2a3/go.mod h1:t9HGtf8HONx5eT2rtn7q6eTqICYqUVnKs3thJo3Qplg=
golang.org/x/sys v0.0.0-20190215142949-d0b11bdaac8a/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
golang.org/x/sys v0.0.0-20191026070338-33540a1f6037/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
golang.org/x/term v0.0.0-20201117132131-f5c789dd3221/go.mod h1:Nr5EML6q2oocZ2LXRh80K7BxOlk5/8JxuGnuhpl+muw=
golang.org/x/text v0.3.0/go.mod h1:NqM8EUOU14njkJ3fqMW+pc6Ldnwhi/IjpwHt7yyuwOQ=

package main

import (
	"fmt"
	"log"

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

func main() {
	password := []byte("sample-secret-password")

	fmt.Printf("bcrypt.DefaultCost: %d\n", bcrypt.DefaultCost)

	hash, err := bcrypt.GenerateFromPassword(password, bcrypt.DefaultCost)
	if err != nil {
		log.Fatalf("GenerateFromPassword failed: %v", err)
	}

	cost, err := bcrypt.Cost(hash)
	if err != nil {
		log.Fatalf("Cost failed: %v", err)
	}
	fmt.Printf("Hash cost: %d\n", cost)

	if err := bcrypt.CompareHashAndPassword(hash, password); err != nil {
		log.Fatalf("CompareHashAndPassword failed: %v", err)
	}
	fmt.Println("Password verified.")
}

{
  "schemaVersion": 1,
  "goal": "verify golang.org/x/crypto/bcrypt.DefaultCost in pkg:golang/golang.org/x/crypto@v0.0.0-20201203163018-be400aefbc4c",
  "kind": "HOW",
  "packages": [
    "pkg:golang/golang.org/x/crypto@v0.0.0-20201203163018-be400aefbc4c"
  ],
  "symbols": [
    "golang.org/x/crypto/bcrypt.DefaultCost"
  ]
}

package main

import (
	"fmt"
	"os"

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

func main() {
	password := []byte("contract-secret-password")

	if bcrypt.DefaultCost != 10 {
		fmt.Fprintf(os.Stderr, "expected DefaultCost 10, got %d\n", bcrypt.DefaultCost)
		os.Exit(1)
	}

	if bcrypt.DefaultCost < bcrypt.MinCost || bcrypt.DefaultCost > bcrypt.MaxCost {
		fmt.Fprintf(os.Stderr, "DefaultCost %d outside [%d, %d]\n", bcrypt.DefaultCost, bcrypt.MinCost, bcrypt.MaxCost)
		os.Exit(1)
	}

	hashDefault, err := bcrypt.GenerateFromPassword(password, bcrypt.DefaultCost)
	if err != nil {
		fmt.Fprintf(os.Stderr, "GenerateFromPassword(DefaultCost) failed: %v\n", err)
		os.Exit(1)
	}
	costDefault, err := bcrypt.Cost(hashDefault)
	if err != nil {
		fmt.Fprintf(os.Stderr, "Cost(hashDefault) failed: %v\n", err)
		os.Exit(1)
	}
	if costDefault != bcrypt.DefaultCost {
		fmt.Fprintf(os.Stderr, "expected cost %d, got %d\n", bcrypt.DefaultCost, costDefault)
		os.Exit(1)
	}

	hashZero, err := bcrypt.GenerateFromPassword(password, 0)
	if err != nil {
		fmt.Fprintf(os.Stderr, "GenerateFromPassword(0) failed: %v\n", err)
		os.Exit(1)
	}
	costZero, err := bcrypt.Cost(hashZero)
	if err != nil {
		fmt.Fprintf(os.Stderr, "Cost(hashZero) failed: %v\n", err)
		os.Exit(1)
	}
	if costZero != bcrypt.DefaultCost {
		fmt.Fprintf(os.Stderr, "expected cost %d for 0 input, got %d\n", bcrypt.DefaultCost, costZero)
		os.Exit(1)
	}

	hashBelowMin, err := bcrypt.GenerateFromPassword(password, bcrypt.MinCost-1)
	if err != nil {
		fmt.Fprintf(os.Stderr, "GenerateFromPassword(MinCost-1) failed: %v\n", err)
		os.Exit(1)
	}
	costBelowMin, err := bcrypt.Cost(hashBelowMin)
	if err != nil {
		fmt.Fprintf(os.Stderr, "Cost(hashBelowMin) failed: %v\n", err)
		os.Exit(1)
	}
	if costBelowMin != bcrypt.DefaultCost {
		fmt.Fprintf(os.Stderr, "expected cost %d for below-min input, got %d\n", bcrypt.DefaultCost, costBelowMin)
		os.Exit(1)
	}

	if err := bcrypt.CompareHashAndPassword(hashDefault, password); err != nil {
		fmt.Fprintf(os.Stderr, "CompareHashAndPassword failed: %v\n", err)
		os.Exit(1)
	}

	fmt.Println("contract ok")
}