golang.org/x/crypto v0.36.0: bcrypt.CompareHashAndPassword, bcrypt.Cost, bcrypt.GenerateFromPassword

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 pkg:golang/golang.org/x/crypto@v0.36.0
Kind: HOW

Use EXACTLY these public packages and versions:
  - pkg:golang/golang.org/x/crypto@v0.36.0
Demonstrate these symbols/APIs:
  - golang.org/x/crypto/bcrypt.CompareHashAndPassword
  - golang.org/x/crypto/bcrypt.Cost
  - golang.org/x/crypto/bcrypt.GenerateFromPassword

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:fa0ee977c1661fc13011f4271716681342ad430895253b4289a2ab14f1751530","contract":["bcrypt.GenerateFromPassword generates a valid bcrypt hash with MinCost","bcrypt.Cost returns the integer cost value extracted from a valid bcrypt hash","bcrypt.GenerateFromPassword with cost 0 automatically defaults to DefaultCost","bcrypt.CompareHashAndPassword returns nil when password matches hash","bcrypt.CompareHashAndPassword returns ErrMismatchedHashAndPassword when password does not match","bcrypt.GenerateFromPassword rejects password exceeding 72 bytes with ErrPasswordTooLong","bcrypt.GenerateFromPassword rejects cost exceeding MaxCost with InvalidCostError"],"goal":"verify pkg:golang/golang.org/x/crypto@v0.36.0","kind":"HOW","packages":["pkg:golang/golang.org/x/crypto@v0.36.0"],"schemaVersion":1,"symbols":["golang.org/x/crypto/bcrypt.CompareHashAndPassword","golang.org/x/crypto/bcrypt.Cost","golang.org/x/crypto/bcrypt.GenerateFromPassword"]},"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@v0.36.0"],"schemaVersion":1,"subject":"pkg:golang/golang.org/x/crypto@v0.36.0","symbols":["golang.org/x/crypto/bcrypt.CompareHashAndPassword","golang.org/x/crypto/bcrypt.Cost","golang.org/x/crypto/bcrypt.GenerateFromPassword"],"verifierAdapter":"golang@1"}

module example.com/sample

go 1.26.6

require golang.org/x/crypto v0.36.0

require golang.org/x/sys v0.31.0 // indirect

golang.org/x/crypto v0.36.0 h1:AnAEvhDddvBdpY+uR+MyHmuZzzNqXSe/GvuDeob5L34=
golang.org/x/crypto v0.36.0/go.mod h1:Y4J0ReaxCR1IMaabaSMugxJES1EpwhBHhv2bDHklZvc=
golang.org/x/sys v0.31.0 h1:ioabZlmFYtWhL+TRYpcnNlLwhyxaM9kWTDEmfnprqik=
golang.org/x/sys v0.31.0/go.mod h1:BJP2sWEmIv4KK5OTEluFJCKSidICx8ciO85XgH3Ak8k=

package main

import (
	"errors"
	"fmt"
	"log"

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

func main() {
	password := []byte("secure-user-password-123")

	// 1. Hash password with DefaultCost
	hash, err := bcrypt.GenerateFromPassword(password, bcrypt.DefaultCost)
	if err != nil {
		log.Fatalf("Failed to generate bcrypt hash: %v", err)
	}
	fmt.Printf("Generated bcrypt hash: %s\n", string(hash))

	// 2. Extract cost from generated hash
	cost, err := bcrypt.Cost(hash)
	if err != nil {
		log.Fatalf("Failed to get hash cost: %v", err)
	}
	fmt.Printf("Bcrypt hash cost: %d\n", cost)

	// 3. Verify matching password
	if err := bcrypt.CompareHashAndPassword(hash, password); err != nil {
		log.Fatalf("Password verification failed: %v", err)
	}
	fmt.Println("Password verification succeeded.")

	// 4. Verify mismatched password
	wrongPassword := []byte("wrong-password-attempt")
	if err := bcrypt.CompareHashAndPassword(hash, wrongPassword); err != nil {
		if errors.Is(err, bcrypt.ErrMismatchedHashAndPassword) {
			fmt.Println("Correctly rejected mismatched password.")
		} else {
			log.Fatalf("Unexpected error on wrong password: %v", err)
		}
	}
}

{
  "schemaVersion": 1,
  "goal": "verify pkg:golang/golang.org/x/crypto@v0.36.0",
  "kind": "HOW",
  "packages": [
    "pkg:golang/golang.org/x/crypto@v0.36.0"
  ],
  "symbols": [
    "golang.org/x/crypto/bcrypt.CompareHashAndPassword",
    "golang.org/x/crypto/bcrypt.Cost",
    "golang.org/x/crypto/bcrypt.GenerateFromPassword"
  ]
}

package main

import (
	"errors"
	"fmt"
	"os"

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

func main() {
	password := []byte("contract-test-password-456")

	// 1. bcrypt.GenerateFromPassword generates a valid bcrypt hash with MinCost
	hashMin, err := bcrypt.GenerateFromPassword(password, bcrypt.MinCost)
	if err != nil {
		fmt.Fprintf(os.Stderr, "bcrypt.GenerateFromPassword failed with MinCost: %v\n", err)
		os.Exit(1)
	}
	if len(hashMin) == 0 {
		fmt.Fprintf(os.Stderr, "Generated hash is empty\n")
		os.Exit(1)
	}

	// 2. bcrypt.Cost returns the integer cost value extracted from a valid bcrypt hash
	cost, err := bcrypt.Cost(hashMin)
	if err != nil {
		fmt.Fprintf(os.Stderr, "bcrypt.Cost failed: %v\n", err)
		os.Exit(1)
	}
	if cost != bcrypt.MinCost {
		fmt.Fprintf(os.Stderr, "bcrypt.Cost mismatch: got %d, want %d\n", cost, bcrypt.MinCost)
		os.Exit(1)
	}

	// 3. bcrypt.GenerateFromPassword with cost 0 automatically defaults to DefaultCost
	hashDefault, err := bcrypt.GenerateFromPassword(password, 0)
	if err != nil {
		fmt.Fprintf(os.Stderr, "bcrypt.GenerateFromPassword failed with cost 0: %v\n", err)
		os.Exit(1)
	}
	costDefault, err := bcrypt.Cost(hashDefault)
	if err != nil {
		fmt.Fprintf(os.Stderr, "bcrypt.Cost failed for default hash: %v\n", err)
		os.Exit(1)
	}
	if costDefault != bcrypt.DefaultCost {
		fmt.Fprintf(os.Stderr, "Expected DefaultCost (%d), got %d\n", bcrypt.DefaultCost, costDefault)
		os.Exit(1)
	}

	// 4. bcrypt.CompareHashAndPassword returns nil when password matches hash
	if err := bcrypt.CompareHashAndPassword(hashMin, password); err != nil {
		fmt.Fprintf(os.Stderr, "bcrypt.CompareHashAndPassword failed for matching password: %v\n", err)
		os.Exit(1)
	}

	// 5. bcrypt.CompareHashAndPassword returns ErrMismatchedHashAndPassword when password does not match
	wrongPassword := []byte("incorrect-test-password")
	if err := bcrypt.CompareHashAndPassword(hashMin, wrongPassword); !errors.Is(err, bcrypt.ErrMismatchedHashAndPassword) {
		fmt.Fprintf(os.Stderr, "Expected ErrMismatchedHashAndPassword, got: %v\n", err)
		os.Exit(1)
	}

	// 6. bcrypt.GenerateFromPassword rejects password exceeding 72 bytes with ErrPasswordTooLong
	longPassword := make([]byte, 73)
	for i := range longPassword {
		longPassword[i] = 'a'
	}
	if _, err := bcrypt.GenerateFromPassword(longPassword, bcrypt.MinCost); !errors.Is(err, bcrypt.ErrPasswordTooLong) {
		fmt.Fprintf(os.Stderr, "Expected ErrPasswordTooLong for 73-byte password, got: %v\n", err)
		os.Exit(1)
	}

	// 7. bcrypt.GenerateFromPassword rejects cost exceeding MaxCost with InvalidCostError
	if _, err := bcrypt.GenerateFromPassword(password, bcrypt.MaxCost+1); err == nil {
		fmt.Fprintf(os.Stderr, "Expected error when cost exceeds MaxCost, got nil\n")
		os.Exit(1)
	} else {
		var invalidCostErr bcrypt.InvalidCostError
		if !errors.As(err, &invalidCostErr) {
			fmt.Fprintf(os.Stderr, "Expected bcrypt.InvalidCostError, got %T: %v\n", err, err)
			os.Exit(1)
		}
	}

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