golang.org/x/crypto v0.56.0: 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@v0.56.0
Kind: HOW

Use EXACTLY these public packages and versions:
  - pkg:golang/golang.org/x/crypto@v0.56.0
Demonstrate these symbols/APIs:
  - bcrypt.GenerateFromPassword

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:sha256:9fc7def6d231ec32ac8d9a2966c5fd76b8fa6ede9e87df2ff2b6fd383736ad2b","contract":["bcrypt.GenerateFromPassword generates a valid bcrypt hash with MinCost","bcrypt.GenerateFromPassword with cost \u003c MinCost automatically defaults to DefaultCost","bcrypt.GenerateFromPassword produces different hashes for identical passwords due to random salt","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@v0.56.0","kind":"HOW","packages":["pkg:golang/golang.org/x/crypto@v0.56.0"],"schemaVersion":1,"symbols":["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@v0.56.0"],"schemaVersion":1,"subject":"pkg:golang/golang.org/x/crypto@v0.56.0","symbols":["bcrypt.GenerateFromPassword"],"verifierAdapter":"golang@1"}

module example.com/sample

go 1.26.6

require golang.org/x/crypto v0.56.0

golang.org/x/crypto v0.56.0 h1:GUh5Ii4J5jtcseSMiRqr1jXCNHoxjeV9Fmekc2oLy6Y=
golang.org/x/crypto v0.56.0/go.mod h1:OMW5y6CY9l38uPLmxU6l6pwcXp1obtLo3e6gT7gQR2I=

package main

import (
	"bytes"
	"errors"
	"fmt"
	"log"

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

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

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

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

	// Verify mismatched password
	wrongPassword := []byte("incorrect-passphrase")
	if err := bcrypt.CompareHashAndPassword(hashed, wrongPassword); !errors.Is(err, bcrypt.ErrMismatchedHashAndPassword) {
		log.Fatalf("Expected ErrMismatchedHashAndPassword, got: %v", err)
	}
	fmt.Println("Wrong password correctly rejected.")

	// Verify rejection of passwords longer than 72 bytes
	longPassword := bytes.Repeat([]byte("a"), 73)
	if _, err := bcrypt.GenerateFromPassword(longPassword, bcrypt.MinCost); !errors.Is(err, bcrypt.ErrPasswordTooLong) {
		log.Fatalf("Expected ErrPasswordTooLong for 73-byte password, got: %v", err)
	}
	fmt.Println("Overlong password correctly rejected.")
}

{
  "schemaVersion": 1,
  "goal": "verify pkg:golang/golang.org/x/crypto@v0.56.0",
  "kind": "HOW",
  "packages": [
    "pkg:golang/golang.org/x/crypto@v0.56.0"
  ],
  "symbols": [
    "bcrypt.GenerateFromPassword"
  ]
}

package main

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

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

func main() {
	pass := []byte("example-contract-passphrase")

	// 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.GenerateFromPassword produces different hashes for identical passwords due to random salt
	hashedMin2, err := bcrypt.GenerateFromPassword(pass, bcrypt.MinCost)
	if err != nil {
		fmt.Fprintf(os.Stderr, "GenerateFromPassword second call failed: %v\n", err)
		os.Exit(1)
	}
	if bytes.Equal(hashedMin, hashedMin2) {
		fmt.Fprintf(os.Stderr, "GenerateFromPassword unexpectedly produced identical hashes for separate calls\n")
		os.Exit(1)
	}

	// 4. 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)
	}

	// 5. 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.")
}