golang.org/x/crypto v0.0.0-20220525230936-793ad666bf5e: 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@v0.0.0-20220525230936-793ad666bf5e
Kind: HOW

Use EXACTLY these public packages and versions:
  - pkg:golang/golang.org/x/crypto@v0.0.0-20220525230936-793ad666bf5e

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:f0589b7de1220b477ea58bcf03026138013984ff5a0e29095f58b8b21e1c25da","contract":["bcrypt.GenerateFromPassword generates a valid $2a$ bcrypt hash with MinCost","bcrypt.GenerateFromPassword with cost \u003c MinCost defaults to DefaultCost","bcrypt.Cost extracts the integer cost from a valid bcrypt hash","bcrypt.CompareHashAndPassword returns nil when password matches the hash","bcrypt.CompareHashAndPassword returns ErrMismatchedHashAndPassword when password does not match","bcrypt.CompareHashAndPassword returns ErrHashTooShort when hash is shorter than 59 bytes","bcrypt.GenerateFromPassword returns InvalidCostError when cost exceeds MaxCost","bcrypt.CompareHashAndPassword returns InvalidHashPrefixError when hash does not start with '$'"],"goal":"verify pkg:golang/golang.org/x/crypto@v0.0.0-20220525230936-793ad666bf5e","kind":"HOW","packages":["pkg:golang/golang.org/x/crypto@v0.0.0-20220525230936-793ad666bf5e"],"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","schemaVersion":1},"license":"MIT-0","packages":["pkg:golang/golang.org/x/crypto@v0.0.0-20220525230936-793ad666bf5e"],"schemaVersion":1,"subject":"pkg:golang/golang.org/x/crypto@v0.0.0-20220525230936-793ad666bf5e","symbols":["bcrypt.CompareHashAndPassword","bcrypt.Cost","bcrypt.GenerateFromPassword"],"verifierAdapter":"golang@1"}

module example.com/sample

go 1.26.6

require golang.org/x/crypto v0.0.0-20220525230936-793ad666bf5e

golang.org/x/crypto v0.0.0-20220525230936-793ad666bf5e h1:T8NU3HyQ8ClP4SEE+KbFlg6n0NhuTsN4MyznaarGsZM=
golang.org/x/crypto v0.0.0-20220525230936-793ad666bf5e/go.mod h1:IxCIyHEi3zRg3s0A5j5BB6A9Jmi73HwBIUl50j+osU4=

package main

import (
	"errors"
	"fmt"
	"log"

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

func main() {
	secret := []byte("example-passphrase-2026")

	hash, err := bcrypt.GenerateFromPassword(secret, bcrypt.MinCost)
	if err != nil {
		log.Fatalf("GenerateFromPassword failed: %v", err)
	}
	fmt.Printf("Hash prefix: %s\n", string(hash[:7]))

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

	if err := bcrypt.CompareHashAndPassword(hash, secret); err != nil {
		log.Fatalf("CompareHashAndPassword failed: %v", err)
	}

	if err := bcrypt.CompareHashAndPassword(hash, []byte("wrong-secret")); !errors.Is(err, bcrypt.ErrMismatchedHashAndPassword) {
		log.Fatalf("Expected ErrMismatchedHashAndPassword, got: %v", err)
	}
	fmt.Println("Verification succeeded.")
}

{
  "schemaVersion": 1,
  "goal": "verify pkg:golang/golang.org/x/crypto@v0.0.0-20220525230936-793ad666bf5e",
  "kind": "HOW",
  "packages": [
    "pkg:golang/golang.org/x/crypto@v0.0.0-20220525230936-793ad666bf5e"
  ]
}

package main

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

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

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

	// 1. bcrypt.GenerateFromPassword generates a valid $2a$ bcrypt hash with MinCost
	minHash, err := bcrypt.GenerateFromPassword(secret, bcrypt.MinCost)
	if err != nil {
		fmt.Fprintf(os.Stderr, "GenerateFromPassword(MinCost) failed: %v\n", err)
		os.Exit(1)
	}
	if !bytes.HasPrefix(minHash, []byte("$2a$04$")) {
		fmt.Fprintf(os.Stderr, "unexpected hash prefix for MinCost: %s\n", string(minHash))
		os.Exit(1)
	}

	// 2. bcrypt.GenerateFromPassword with cost < MinCost defaults to DefaultCost
	defHash, err := bcrypt.GenerateFromPassword(secret, bcrypt.MinCost-1)
	if err != nil {
		fmt.Fprintf(os.Stderr, "GenerateFromPassword(MinCost-1) failed: %v\n", err)
		os.Exit(1)
	}
	defCost, err := bcrypt.Cost(defHash)
	if err != nil || defCost != bcrypt.DefaultCost {
		fmt.Fprintf(os.Stderr, "expected DefaultCost %d, got %d (err=%v)\n", bcrypt.DefaultCost, defCost, err)
		os.Exit(1)
	}

	// 3. bcrypt.Cost extracts the integer cost from a valid bcrypt hash
	cost, err := bcrypt.Cost(minHash)
	if err != nil || cost != bcrypt.MinCost {
		fmt.Fprintf(os.Stderr, "expected MinCost %d, got %d (err=%v)\n", bcrypt.MinCost, cost, err)
		os.Exit(1)
	}

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

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

	// 6. bcrypt.CompareHashAndPassword returns ErrHashTooShort when hash is shorter than 59 bytes
	if err := bcrypt.CompareHashAndPassword([]byte("$2a$04$short"), secret); !errors.Is(err, bcrypt.ErrHashTooShort) {
		fmt.Fprintf(os.Stderr, "expected ErrHashTooShort, got: %v\n", err)
		os.Exit(1)
	}

	// 7. bcrypt.GenerateFromPassword returns InvalidCostError when cost exceeds MaxCost
	var invalidCostErr bcrypt.InvalidCostError
	if _, err := bcrypt.GenerateFromPassword(secret, bcrypt.MaxCost+1); !errors.As(err, &invalidCostErr) {
		fmt.Fprintf(os.Stderr, "expected InvalidCostError, got: %v\n", err)
		os.Exit(1)
	}

	// 8. bcrypt.CompareHashAndPassword returns InvalidHashPrefixError when hash does not start with '$'
	var invalidPrefixErr bcrypt.InvalidHashPrefixError
	badPrefix := []byte("2a$04$0123456789abcdef0123456789abcdef0123456789abcdef0123456789")
	if err := bcrypt.CompareHashAndPassword(badPrefix, secret); !errors.As(err, &invalidPrefixErr) {
		fmt.Fprintf(os.Stderr, "expected InvalidHashPrefixError, got: %v\n", err)
		os.Exit(1)
	}

	fmt.Println("Contract passed.")
}