golang.org/x/crypto v0.37.0: 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@v0.37.0
Kind: HOW

Use EXACTLY these public packages and versions:
  - pkg:golang/golang.org/x/crypto@v0.37.0

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:sha256:01e9945284dd7409402f8628d4c060b44a09eb59d08b2a360e4962b3484f2e66","contract":["bcrypt.GenerateFromPassword generates a valid bcrypt hash with MinCost","bcrypt.GenerateFromPassword with cost \u003c MinCost automatically defaults to DefaultCost","bcrypt.CompareHashAndPassword returns nil when password matches hash","bcrypt.CompareHashAndPassword returns ErrMismatchedHashAndPassword when password does not match","bcrypt.Cost returns the integer cost value extracted from a valid bcrypt hash","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@v0.37.0","kind":"HOW","packages":["pkg:golang/golang.org/x/crypto@v0.37.0"],"schemaVersion":1,"symbols":["bcrypt.CompareHashAndPassword","bcrypt.Cost","bcrypt.GenerateFromPassword"]},"contractCommand":["go","run","./test"],"environment":{"arch":"x64","distro":"ubuntu","ecosystem":"golang","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@v0.37.0"],"schemaVersion":1,"subject":"pkg:golang/golang.org/x/crypto@v0.37.0","symbols":["bcrypt.CompareHashAndPassword","bcrypt.Cost","bcrypt.GenerateFromPassword"],"verifierAdapter":"golang@1"}

module example.com/sample

go 1.26.6

require golang.org/x/crypto v0.37.0

golang.org/x/crypto v0.37.0 h1:kJNSjF/Xp7kU0iB2Z+9viTPMW4EqqsrywMXLJOOsXSE=
golang.org/x/crypto v0.37.0/go.mod h1:vg+k43peMZ0pUMhYmVAWysMK35e6ioLh3wB8ZCAfbVc=

package main

import (
	"errors"
	"fmt"
	"log"

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

func main() {
	password := []byte("secret-passphrase-42")

	// Generate bcrypt hash using DefaultCost
	hashed, err := bcrypt.GenerateFromPassword(password, bcrypt.DefaultCost)
	if err != nil {
		log.Fatalf("GenerateFromPassword failed: %v", err)
	}
	fmt.Printf("Generated hash: %s\n", string(hashed))

	// Extract cost from hash
	cost, err := bcrypt.Cost(hashed)
	if err != nil {
		log.Fatalf("Cost inspection failed: %v", err)
	}
	fmt.Printf("Extracted cost: %d (DefaultCost: %d)\n", cost, bcrypt.DefaultCost)

	// Verify correct password
	if err := bcrypt.CompareHashAndPassword(hashed, password); err != nil {
		log.Fatalf("Password verification failed: %v", err)
	}
	fmt.Println("Password verified successfully.")

	// Verify wrong password
	wrongPassword := []byte("wrong-passphrase")
	if err := bcrypt.CompareHashAndPassword(hashed, wrongPassword); err != nil {
		if errors.Is(err, bcrypt.ErrMismatchedHashAndPassword) {
			fmt.Println("Wrong password correctly rejected with ErrMismatchedHashAndPassword.")
		} else {
			log.Fatalf("Unexpected error for wrong password: %v", err)
		}
	}
}

{
  "schemaVersion": 1,
  "goal": "verify pkg:golang/golang.org/x/crypto@v0.37.0",
  "kind": "HOW",
  "packages": [
    "pkg:golang/golang.org/x/crypto@v0.37.0"
  ],
  "symbols": [
    "bcrypt.CompareHashAndPassword",
    "bcrypt.Cost",
    "bcrypt.GenerateFromPassword"
  ]
}

package main

import (
	"bytes"
	"errors"
	"fmt"
	"os"

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

func main() {
	pass := []byte("correct-horse-battery-staple")

	// 1. bcrypt.GenerateFromPassword generates a valid bcrypt hash with MinCost
	hashedMin, err := bcrypt.GenerateFromPassword(pass, bcrypt.MinCost)
	if err != nil {
		fmt.Fprintf(os.Stderr, "GenerateFromPassword(MinCost) failed: %v\n", err)
		os.Exit(1)
	}
	if len(hashedMin) == 0 {
		fmt.Fprintf(os.Stderr, "GenerateFromPassword returned empty hash\n")
		os.Exit(1)
	}
	if !bytes.HasPrefix(hashedMin, []byte("$2a$")) && !bytes.HasPrefix(hashedMin, []byte("$2b$")) && !bytes.HasPrefix(hashedMin, []byte("$2y$")) {
		fmt.Fprintf(os.Stderr, "GenerateFromPassword produced invalid bcrypt header: %s\n", string(hashedMin))
		os.Exit(1)
	}

	// 2. bcrypt.GenerateFromPassword with cost < MinCost automatically defaults to DefaultCost
	hashedDefault, err := bcrypt.GenerateFromPassword(pass, 0)
	if err != nil {
		fmt.Fprintf(os.Stderr, "GenerateFromPassword(0) failed: %v\n", err)
		os.Exit(1)
	}
	defaultCost, err := bcrypt.Cost(hashedDefault)
	if err != nil || defaultCost != bcrypt.DefaultCost {
		fmt.Fprintf(os.Stderr, "Cost for cost=0 hash expected %d, got %d (err: %v)\n", bcrypt.DefaultCost, defaultCost, err)
		os.Exit(1)
	}

	// 3. bcrypt.CompareHashAndPassword returns nil when password matches hash
	if err := bcrypt.CompareHashAndPassword(hashedMin, pass); err != nil {
		fmt.Fprintf(os.Stderr, "CompareHashAndPassword failed on matching password: %v\n", err)
		os.Exit(1)
	}

	// 4. bcrypt.CompareHashAndPassword returns ErrMismatchedHashAndPassword when password does not match
	wrongPass := []byte("incorrect-horse-battery-staple")
	if err := bcrypt.CompareHashAndPassword(hashedMin, wrongPass); err == nil {
		fmt.Fprintf(os.Stderr, "CompareHashAndPassword unexpectedly succeeded on mismatched password\n")
		os.Exit(1)
	} else if !errors.Is(err, bcrypt.ErrMismatchedHashAndPassword) {
		fmt.Fprintf(os.Stderr, "CompareHashAndPassword returned wrong error: got %v, want %v\n", err, bcrypt.ErrMismatchedHashAndPassword)
		os.Exit(1)
	}

	// 5. bcrypt.Cost returns the integer cost value extracted from a valid bcrypt hash
	cost, err := bcrypt.Cost(hashedMin)
	if err != nil {
		fmt.Fprintf(os.Stderr, "Cost returned error for valid hash: %v\n", err)
		os.Exit(1)
	}
	if cost != bcrypt.MinCost {
		fmt.Fprintf(os.Stderr, "Cost mismatch: got %d, want %d\n", cost, bcrypt.MinCost)
		os.Exit(1)
	}

	// 6. bcrypt.GenerateFromPassword rejects password exceeding 72 bytes with ErrPasswordTooLong
	longPass := bytes.Repeat([]byte("a"), 73)
	if _, err := bcrypt.GenerateFromPassword(longPass, bcrypt.MinCost); err == nil {
		fmt.Fprintf(os.Stderr, "GenerateFromPassword should fail for password > 72 bytes\n")
		os.Exit(1)
	} else if !errors.Is(err, bcrypt.ErrPasswordTooLong) {
		fmt.Fprintf(os.Stderr, "GenerateFromPassword returned wrong error for long password: got %v, want %v\n", err, bcrypt.ErrPasswordTooLong)
		os.Exit(1)
	}

	// 7. bcrypt.GenerateFromPassword rejects cost exceeding MaxCost with InvalidCostError
	var invalidCostErr bcrypt.InvalidCostError
	if _, err := bcrypt.GenerateFromPassword(pass, bcrypt.MaxCost+1); err == nil {
		fmt.Fprintf(os.Stderr, "GenerateFromPassword should fail for cost above MaxCost\n")
		os.Exit(1)
	} else if !errors.As(err, &invalidCostErr) {
		fmt.Fprintf(os.Stderr, "GenerateFromPassword returned wrong error type for high cost: %v\n", err)
		os.Exit(1)
	}

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