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

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.CompareHashAndPassword 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.CompareHashAndPassword

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:sha256:0c9ba4db6ab35a8857e2fe31ad968695dbfad866ed76235854f2399124d9329e","contract":["bcrypt.CompareHashAndPassword returns nil when password matches generated hash","bcrypt.CompareHashAndPassword returns ErrMismatchedHashAndPassword when password does not match","bcrypt.CompareHashAndPassword returns an error when hash is malformed","bcrypt.CompareHashAndPassword correctly verifies empty password against its hash","bcrypt.CompareHashAndPassword succeeds with hashes created at different cost levels"],"goal":"verify golang.org/x/crypto/bcrypt.CompareHashAndPassword 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.CompareHashAndPassword"]},"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@v0.21.0"],"schemaVersion":1,"subject":"pkg:golang/golang.org/x/crypto@v0.21.0","symbols":["golang.org/x/crypto/bcrypt.CompareHashAndPassword"],"verifierAdapter":"golang@1"}

module example.com/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 (
	"errors"
	"fmt"
	"log"

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

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

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

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

	// Verify mismatched password
	wrongPassword := []byte("incorrect-password")
	if err := bcrypt.CompareHashAndPassword(hash, wrongPassword); err != nil {
		if errors.Is(err, bcrypt.ErrMismatchedHashAndPassword) {
			fmt.Println("Mismatched password correctly rejected.")
		} else {
			log.Fatalf("Unexpected error: %v", err)
		}
	} else {
		log.Fatalf("Expected mismatched password error, but got success")
	}
}

{
  "schemaVersion": 1,
  "goal": "verify golang.org/x/crypto/bcrypt.CompareHashAndPassword 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.CompareHashAndPassword"
  ]
}

package main

import (
	"errors"
	"fmt"
	"os"

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

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

	// 1. bcrypt.CompareHashAndPassword returns nil when password matches generated hash
	hashDefault, err := bcrypt.GenerateFromPassword(password, bcrypt.DefaultCost)
	if err != nil {
		fmt.Fprintf(os.Stderr, "bcrypt.GenerateFromPassword failed: %v\n", err)
		os.Exit(1)
	}
	if err := bcrypt.CompareHashAndPassword(hashDefault, password); err != nil {
		fmt.Fprintf(os.Stderr, "bcrypt.CompareHashAndPassword failed for valid match: %v\n", err)
		os.Exit(1)
	}

	// 2. bcrypt.CompareHashAndPassword returns ErrMismatchedHashAndPassword when password does not match
	wrongPassword := []byte("wrong-password-sample")
	if err := bcrypt.CompareHashAndPassword(hashDefault, wrongPassword); !errors.Is(err, bcrypt.ErrMismatchedHashAndPassword) {
		fmt.Fprintf(os.Stderr, "Expected ErrMismatchedHashAndPassword, got: %v\n", err)
		os.Exit(1)
	}

	// 3. bcrypt.CompareHashAndPassword returns an error when hash is malformed
	malformedHash := []byte("$2a$10$malformedhashstringthatisnotvalid")
	if err := bcrypt.CompareHashAndPassword(malformedHash, password); err == nil {
		fmt.Fprintf(os.Stderr, "Expected error on malformed hash, got nil\n")
		os.Exit(1)
	}

	// 4. bcrypt.CompareHashAndPassword correctly verifies empty password against its hash
	emptyPassword := []byte("")
	emptyHash, err := bcrypt.GenerateFromPassword(emptyPassword, bcrypt.MinCost)
	if err != nil {
		fmt.Fprintf(os.Stderr, "Failed to hash empty password: %v\n", err)
		os.Exit(1)
	}
	if err := bcrypt.CompareHashAndPassword(emptyHash, emptyPassword); err != nil {
		fmt.Fprintf(os.Stderr, "Failed to verify empty password against empty hash: %v\n", err)
		os.Exit(1)
	}
	if err := bcrypt.CompareHashAndPassword(emptyHash, []byte("non-empty")); !errors.Is(err, bcrypt.ErrMismatchedHashAndPassword) {
		fmt.Fprintf(os.Stderr, "Expected ErrMismatchedHashAndPassword for non-empty password vs empty hash, got: %v\n", err)
		os.Exit(1)
	}

	// 5. bcrypt.CompareHashAndPassword succeeds with hashes created at different cost levels
	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 err := bcrypt.CompareHashAndPassword(hashMin, password); err != nil {
		fmt.Fprintf(os.Stderr, "bcrypt.CompareHashAndPassword failed for MinCost hash: %v\n", err)
		os.Exit(1)
	}
	if err := bcrypt.CompareHashAndPassword(hashDefault, password); err != nil {
		fmt.Fprintf(os.Stderr, "bcrypt.CompareHashAndPassword failed for DefaultCost hash: %v\n", err)
		os.Exit(1)
	}

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