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// Copyright 2011 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// Package bcrypt implements Provos and Mazières's bcrypt adaptive hashing
// algorithm. See http://www.usenix.org/event/usenix99/provos/provos.pdf
package bcrypt // import "golang.org/x/crypto/bcrypt"
// The code is a port of Provos and Mazières's C implementation.
import (
"crypto/rand"
"crypto/subtle"
"errors"
"fmt"
"io"
"strconv"
"golang.org/x/crypto/blowfish"
)
const (
MinCost int = 4 // the minimum allowable cost as passed in to GenerateFromPassword
MaxCost int = 31 // the maximum allowable cost as passed in to GenerateFromPassword
DefaultCost int = 10 // the cost that will actually be set if a cost below MinCost is passed into GenerateFromPassword
)
// The error returned from CompareHashAndPassword when a password and hash do
// not match.
var ErrMismatchedHashAndPassword = errors.New("crypto/bcrypt: hashedPassword is not the hash of the given password")
// The error returned from CompareHashAndPassword when a hash is too short to
// be a bcrypt hash.
var ErrHashTooShort = errors.New("crypto/bcrypt: hashedSecret too short to be a bcrypted password")
// The error returned from CompareHashAndPassword when a hash was created with
// a bcrypt algorithm newer than this implementation.
type HashVersionTooNewError byte
func (hv HashVersionTooNewError) Error() string {
return fmt.Sprintf("crypto/bcrypt: bcrypt algorithm version '%c' requested is newer than current version '%c'", byte(hv), majorVersion)
}
// The error returned from CompareHashAndPassword when a hash starts with something other than '$'
type InvalidHashPrefixError byte
func (ih InvalidHashPrefixError) Error() string {
return fmt.Sprintf("crypto/bcrypt: bcrypt hashes must start with '$', but hashedSecret started with '%c'", byte(ih))
}
type InvalidCostError int
func (ic InvalidCostError) Error() string {
return fmt.Sprintf("crypto/bcrypt: cost %d is outside allowed range (%d,%d)", int(ic), int(MinCost), int(MaxCost))
}
const (
majorVersion = '2'
minorVersion = 'a'
maxSaltSize = 16
maxCryptedHashSize = 23
encodedSaltSize = 22
encodedHashSize = 31
minHashSize = 59
)
// magicCipherData is an IV for the 64 Blowfish encryption calls in
// bcrypt(). It's the string "OrpheanBeholderScryDoubt" in big-endian bytes.
var magicCipherData = []byte{
0x4f, 0x72, 0x70, 0x68,
0x65, 0x61, 0x6e, 0x42,
0x65, 0x68, 0x6f, 0x6c,
0x64, 0x65, 0x72, 0x53,
0x63, 0x72, 0x79, 0x44,
0x6f, 0x75, 0x62, 0x74,
}
type hashed struct {
hash []byte
salt []byte
cost int // allowed range is MinCost to MaxCost
major byte
minor byte
}
// GenerateFromPassword returns the bcrypt hash of the password at the given
// cost. If the cost given is less than MinCost, the cost will be set to
// DefaultCost, instead. Use CompareHashAndPassword, as defined in this package,
// to compare the returned hashed password with its cleartext version.
func GenerateFromPassword(password []byte, cost int) ([]byte, error) {
p, err := newFromPassword(password, cost)
if err != nil {
return nil, err
}
return p.Hash(), nil
}
// CompareHashAndPassword compares a bcrypt hashed password with its possible
// plaintext equivalent. Returns nil on success, or an error on failure.
func CompareHashAndPassword(hashedPassword, password []byte) error {
p, err := newFromHash(hashedPassword)
if err != nil {
return err
}
otherHash, err := bcrypt(password, p.cost, p.salt)
if err != nil {
return err
}
otherP := &hashed{otherHash, p.salt, p.cost, p.major, p.minor}
if subtle.ConstantTimeCompare(p.Hash(), otherP.Hash()) == 1 {
return nil
}
return ErrMismatchedHashAndPassword
}
// Cost returns the hashing cost used to create the given hashed
// password. When, in the future, the hashing cost of a password system needs
// to be increased in order to adjust for greater computational power, this
// function allows one to establish which passwords need to be updated.
func Cost(hashedPassword []byte) (int, error) {
p, err := newFromHash(hashedPassword)
if err != nil {
return 0, err
}
return p.cost, nil
}
func newFromPassword(password []byte, cost int) (*hashed, error) {
if cost < MinCost {
cost = DefaultCost
}
p := new(hashed)
p.major = majorVersion
p.minor = minorVersion
err := checkCost(cost)
if err != nil {
return nil, err
}
p.cost = cost
unencodedSalt := make([]byte, maxSaltSize)
_, err = io.ReadFull(rand.Reader, unencodedSalt)
if err != nil {
return nil, err
}
p.salt = base64Encode(unencodedSalt)
hash, err := bcrypt(password, p.cost, p.salt)
if err != nil {
return nil, err
}
p.hash = hash
return p, err
}
func newFromHash(hashedSecret []byte) (*hashed, error) {
if len(hashedSecret) < minHashSize {
return nil, ErrHashTooShort
}
p := new(hashed)
n, err := p.decodeVersion(hashedSecret)
if err != nil {
return nil, err
}
hashedSecret = hashedSecret[n:]
n, err = p.decodeCost(hashedSecret)
if err != nil {
return nil, err
}
hashedSecret = hashedSecret[n:]
// The "+2" is here because we'll have to append at most 2 '=' to the salt
// when base64 decoding it in expensiveBlowfishSetup().
p.salt = make([]byte, encodedSaltSize, encodedSaltSize+2)
copy(p.salt, hashedSecret[:encodedSaltSize])
hashedSecret = hashedSecret[encodedSaltSize:]
p.hash = make([]byte, len(hashedSecret))
copy(p.hash, hashedSecret)
return p, nil
}
func bcrypt(password []byte, cost int, salt []byte) ([]byte, error) {
cipherData := make([]byte, len(magicCipherData))
copy(cipherData, magicCipherData)
c, err := expensiveBlowfishSetup(password, uint32(cost), salt)
if err != nil {
return nil, err
}
for i := 0; i < 24; i += 8 {
for j := 0; j < 64; j++ {
c.Encrypt(cipherData[i:i+8], cipherData[i:i+8])
}
}
// Bug compatibility with C bcrypt implementations. We only encode 23 of
// the 24 bytes encrypted.
hsh := base64Encode(cipherData[:maxCryptedHashSize])
return hsh, nil
}
func expensiveBlowfishSetup(key []byte, cost uint32, salt []byte) (*blowfish.Cipher, error) {
csalt, err := base64Decode(salt)
if err != nil {
return nil, err
}
// Bug compatibility with C bcrypt implementations. They use the trailing
// NULL in the key string during expansion.
// We copy the key to prevent changing the underlying array.
ckey := append(key[:len(key):len(key)], 0)
c, err := blowfish.NewSaltedCipher(ckey, csalt)
if err != nil {
return nil, err
}
var i, rounds uint64
rounds = 1 << cost
for i = 0; i < rounds; i++ {
blowfish.ExpandKey(ckey, c)
blowfish.ExpandKey(csalt, c)
}
return c, nil
}
func (p *hashed) Hash() []byte {
arr := make([]byte, 60)
arr[0] = '$'
arr[1] = p.major
n := 2
if p.minor != 0 {
arr[2] = p.minor
n = 3
}
arr[n] = '$'
n++
copy(arr[n:], []byte(fmt.Sprintf("%02d", p.cost)))
n += 2
arr[n] = '$'
n++
copy(arr[n:], p.salt)
n += encodedSaltSize
copy(arr[n:], p.hash)
n += encodedHashSize
return arr[:n]
}
func (p *hashed) decodeVersion(sbytes []byte) (int, error) {
if sbytes[0] != '$' {
return -1, InvalidHashPrefixError(sbytes[0])
}
if sbytes[1] > majorVersion {
return -1, HashVersionTooNewError(sbytes[1])
}
p.major = sbytes[1]
n := 3
if sbytes[2] != '$' {
p.minor = sbytes[2]
n++
}
return n, nil
}
// sbytes should begin where decodeVersion left off.
func (p *hashed) decodeCost(sbytes []byte) (int, error) {
cost, err := strconv.Atoi(string(sbytes[0:2]))
if err != nil {
return -1, err
}
err = checkCost(cost)
if err != nil {
return -1, err
}
p.cost = cost
return 3, nil
}
func (p *hashed) String() string {
return fmt.Sprintf("&{hash: %#v, salt: %#v, cost: %d, major: %c, minor: %c}", string(p.hash), p.salt, p.cost, p.major, p.minor)
}
func checkCost(cost int) error {
if cost < MinCost || cost > MaxCost {
return InvalidCostError(cost)
}
return nil
}