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

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.ErrMismatchedHashAndPassword 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.ErrMismatchedHashAndPassword
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:sha256:44ed39c216b345bfe4f8191833c19ce2c2b1f170e7d87550aacea07a578f97fd","contract":["bcrypt.CompareHashAndPassword returns ErrMismatchedHashAndPassword when password does not match hash","errors.Is identifies ErrMismatchedHashAndPassword from CompareHashAndPassword error","bcrypt.ErrMismatchedHashAndPassword error message equals 'crypto/bcrypt: hashedPassword is not the hash of the given password'","bcrypt.CompareHashAndPassword returns ErrMismatchedHashAndPassword for empty password against non-empty hash","bcrypt.CompareHashAndPassword returns ErrMismatchedHashAndPassword when hash payload is corrupted","bcrypt.CompareHashAndPassword returns nil for matching password and does not match ErrMismatchedHashAndPassword"],"goal":"verify golang.org/x/crypto/bcrypt.ErrMismatchedHashAndPassword 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.ErrMismatchedHashAndPassword"]},"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.ErrMismatchedHashAndPassword"],"verifierAdapter":"golang@1"}

module example.com/sample

go 1.22

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("secure-password-123")
	wrongPassword := []byte("incorrect-password-456")

	// Generate a bcrypt hash from the correct password
	hash, err := bcrypt.GenerateFromPassword(password, bcrypt.DefaultCost)
	if err != nil {
		log.Fatalf("failed to generate bcrypt hash: %v", err)
	}

	// Compare with incorrect password; expect ErrMismatchedHashAndPassword
	err = bcrypt.CompareHashAndPassword(hash, wrongPassword)
	if errors.Is(err, bcrypt.ErrMismatchedHashAndPassword) {
		fmt.Printf("detected expected mismatch error: %v\n", err)
	} else {
		log.Fatalf("expected ErrMismatchedHashAndPassword, got: %v", err)
	}

	// Compare with the matching password; expect nil error
	if err := bcrypt.CompareHashAndPassword(hash, password); err != nil {
		log.Fatalf("expected successful comparison, got: %v", err)
	}
	fmt.Println("password verified successfully")
}

{
  "schemaVersion": 1,
  "goal": "verify golang.org/x/crypto/bcrypt.ErrMismatchedHashAndPassword 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.ErrMismatchedHashAndPassword"
  ],
  "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() {
	password := []byte("contract-password-alpha")
	wrongPassword := []byte("contract-password-beta")

	hash, err := bcrypt.GenerateFromPassword(password, bcrypt.MinCost)
	if err != nil {
		fmt.Fprintf(os.Stderr, "setup failed to generate hash: %v\n", err)
		os.Exit(1)
	}

	// 1. bcrypt.CompareHashAndPassword returns ErrMismatchedHashAndPassword when password does not match hash
	errMismatch := bcrypt.CompareHashAndPassword(hash, wrongPassword)
	if errMismatch == nil || !errors.Is(errMismatch, bcrypt.ErrMismatchedHashAndPassword) {
		fmt.Fprintf(os.Stderr, "assertion 1 failed: expected ErrMismatchedHashAndPassword, got %v\n", errMismatch)
		os.Exit(1)
	}

	// 2. errors.Is identifies ErrMismatchedHashAndPassword from CompareHashAndPassword error
	if !errors.Is(errMismatch, bcrypt.ErrMismatchedHashAndPassword) {
		fmt.Fprintf(os.Stderr, "assertion 2 failed: errors.Is failed to identify ErrMismatchedHashAndPassword\n")
		os.Exit(1)
	}

	// 3. bcrypt.ErrMismatchedHashAndPassword error message equals 'crypto/bcrypt: hashedPassword is not the hash of the given password'
	expectedMsg := "crypto/bcrypt: hashedPassword is not the hash of the given password"
	if bcrypt.ErrMismatchedHashAndPassword.Error() != expectedMsg {
		fmt.Fprintf(os.Stderr, "assertion 3 failed: expected %q, got %q\n", expectedMsg, bcrypt.ErrMismatchedHashAndPassword.Error())
		os.Exit(1)
	}

	// 4. bcrypt.CompareHashAndPassword returns ErrMismatchedHashAndPassword for empty password against non-empty hash
	emptyErr := bcrypt.CompareHashAndPassword(hash, []byte(""))
	if !errors.Is(emptyErr, bcrypt.ErrMismatchedHashAndPassword) {
		fmt.Fprintf(os.Stderr, "assertion 4 failed: expected ErrMismatchedHashAndPassword, got %v\n", emptyErr)
		os.Exit(1)
	}

	// 5. bcrypt.CompareHashAndPassword returns ErrMismatchedHashAndPassword when hash payload is corrupted
	corruptedHash := make([]byte, len(hash))
	copy(corruptedHash, hash)
	if corruptedHash[len(corruptedHash)-1] == 'a' {
		corruptedHash[len(corruptedHash)-1] = 'b'
	} else {
		corruptedHash[len(corruptedHash)-1] = 'a'
	}
	corruptedErr := bcrypt.CompareHashAndPassword(corruptedHash, password)
	if !errors.Is(corruptedErr, bcrypt.ErrMismatchedHashAndPassword) {
		fmt.Fprintf(os.Stderr, "assertion 5 failed: expected ErrMismatchedHashAndPassword, got %v\n", corruptedErr)
		os.Exit(1)
	}

	// 6. bcrypt.CompareHashAndPassword returns nil for matching password and does not match ErrMismatchedHashAndPassword
	matchErr := bcrypt.CompareHashAndPassword(hash, password)
	if matchErr != nil {
		fmt.Fprintf(os.Stderr, "assertion 6 failed: expected nil for matching password, got %v\n", matchErr)
		os.Exit(1)
	}
	if errors.Is(matchErr, bcrypt.ErrMismatchedHashAndPassword) {
		fmt.Fprintf(os.Stderr, "assertion 6 failed: nil should not match ErrMismatchedHashAndPassword\n")
		os.Exit(1)
	}

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