golang.org/x/crypto v0.37.0: bcrypt.InvalidCostError

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.InvalidCostError in 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
Demonstrate these symbols/APIs:
  - golang.org/x/crypto/bcrypt.InvalidCostError

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:ea363451fb499a125af4fba69e2f9ad871246ff869cf4b7dee24d79d7a07690a","contract":["bcrypt.InvalidCostError represents an int cost value outside allowable range 4 to 31","bcrypt.GenerateFromPassword returns InvalidCostError when requested cost exceeds bcrypt.MaxCost","bcrypt.Cost returns InvalidCostError when parsing hash with cost below bcrypt.MinCost","bcrypt.Cost returns InvalidCostError when parsing hash with cost exceeding bcrypt.MaxCost","bcrypt.CompareHashAndPassword returns InvalidCostError when given hash with invalid cost","bcrypt.InvalidCostError Error method formats error string naming invalid cost and allowed range"],"goal":"verify golang.org/x/crypto/bcrypt.InvalidCostError in pkg:golang/golang.org/x/crypto@v0.37.0","kind":"HOW","packages":["pkg:golang/golang.org/x/crypto@v0.37.0"],"schemaVersion":1,"symbols":["golang.org/x/crypto/bcrypt.InvalidCostError"]},"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@v0.37.0"],"schemaVersion":1,"subject":"pkg:golang/golang.org/x/crypto@v0.37.0","symbols":["golang.org/x/crypto/bcrypt.InvalidCostError"],"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"

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

func main() {
	// Attempting to hash with a cost greater than bcrypt.MaxCost returns bcrypt.InvalidCostError
	password := []byte("example-secret-passphrase")
	_, err := bcrypt.GenerateFromPassword(password, 32)
	var invalidCostErr bcrypt.InvalidCostError
	if errors.As(err, &invalidCostErr) {
		fmt.Printf("Detected invalid cost during password hashing: %d (error: %v)\n", int(invalidCostErr), err)
	}

	// Parsing an existing bcrypt hash with a cost below bcrypt.MinCost returns bcrypt.InvalidCostError
	lowCostHash := []byte("$2a$03$usesomesillystringfore2uDLvp1AK2Q68Lp7FI0d5BOmvnoZZGW")
	cost, err := bcrypt.Cost(lowCostHash)
	if errors.As(err, &invalidCostErr) {
		fmt.Printf("Detected invalid cost during hash inspection: %d (error: %v)\n", int(invalidCostErr), err)
	} else {
		fmt.Printf("Cost inspected: %d\n", cost)
	}
}

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

package main

import (
	"errors"
	"fmt"
	"os"

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

func main() {
	// Assertion 1: bcrypt.InvalidCostError represents an int cost value outside allowable range 4 to 31
	errVal := bcrypt.InvalidCostError(3)
	if int(errVal) != 3 {
		fmt.Fprintf(os.Stderr, "assertion 1 failed: expected int value 3, got %d\n", int(errVal))
		os.Exit(1)
	}

	// Assertion 2: bcrypt.GenerateFromPassword returns InvalidCostError when requested cost exceeds bcrypt.MaxCost
	password := []byte("contract-verification-password")
	_, err := bcrypt.GenerateFromPassword(password, bcrypt.MaxCost+1)
	var invalidCostErr bcrypt.InvalidCostError
	if !errors.As(err, &invalidCostErr) {
		fmt.Fprintf(os.Stderr, "assertion 2 failed: expected InvalidCostError, got %v\n", err)
		os.Exit(1)
	}
	if int(invalidCostErr) != bcrypt.MaxCost+1 {
		fmt.Fprintf(os.Stderr, "assertion 2 failed: expected cost %d, got %d\n", bcrypt.MaxCost+1, int(invalidCostErr))
		os.Exit(1)
	}

	// Assertion 3: bcrypt.Cost returns InvalidCostError when parsing hash with cost below bcrypt.MinCost
	lowCostHash := []byte("$2a$03$usesomesillystringfore2uDLvp1AK2Q68Lp7FI0d5BOmvnoZZGW")
	_, err = bcrypt.Cost(lowCostHash)
	if !errors.As(err, &invalidCostErr) {
		fmt.Fprintf(os.Stderr, "assertion 3 failed: expected InvalidCostError for cost 3, got %v\n", err)
		os.Exit(1)
	}
	if int(invalidCostErr) != 3 {
		fmt.Fprintf(os.Stderr, "assertion 3 failed: expected cost 3, got %d\n", int(invalidCostErr))
		os.Exit(1)
	}

	// Assertion 4: bcrypt.Cost returns InvalidCostError when parsing hash with cost exceeding bcrypt.MaxCost
	highCostHash := []byte("$2a$32$usesomesillystringfore2uDLvp1AK2Q68Lp7FI0d5BOmvnoZZGW")
	_, err = bcrypt.Cost(highCostHash)
	if !errors.As(err, &invalidCostErr) {
		fmt.Fprintf(os.Stderr, "assertion 4 failed: expected InvalidCostError for cost 32, got %v\n", err)
		os.Exit(1)
	}
	if int(invalidCostErr) != 32 {
		fmt.Fprintf(os.Stderr, "assertion 4 failed: expected cost 32, got %d\n", int(invalidCostErr))
		os.Exit(1)
	}

	// Assertion 5: bcrypt.CompareHashAndPassword returns InvalidCostError when given hash with invalid cost
	err = bcrypt.CompareHashAndPassword(lowCostHash, password)
	if !errors.As(err, &invalidCostErr) {
		fmt.Fprintf(os.Stderr, "assertion 5 failed: expected InvalidCostError from CompareHashAndPassword, got %v\n", err)
		os.Exit(1)
	}
	if int(invalidCostErr) != 3 {
		fmt.Fprintf(os.Stderr, "assertion 5 failed: expected cost 3, got %d\n", int(invalidCostErr))
		os.Exit(1)
	}

	// Assertion 6: bcrypt.InvalidCostError Error method formats error string naming invalid cost and allowed range
	errFormatted := bcrypt.InvalidCostError(32)
	expectedErrorMsg := fmt.Sprintf("crypto/bcrypt: cost 32 is outside allowed range (%d,%d)", bcrypt.MinCost, bcrypt.MaxCost)
	if errFormatted.Error() != expectedErrorMsg {
		fmt.Fprintf(os.Stderr, "assertion 6 failed: expected %q, got %q\n", expectedErrorMsg, errFormatted.Error())
		os.Exit(1)
	}

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