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go.crypto/bcrypt: add Cost function

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Extracts the cost used to generate a bcrypt hash from the hash itself.

R=agl, agl, dchest
CC=golang-dev
https://golang.org/cl/6810051
This commit is contained in:
Jeff Hodges
2012-10-31 12:35:46 -04:00
committed by Adam Langley
parent 1582bf0781
commit 2c5e207468
2 changed files with 42 additions and 8 deletions
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bcrypt/bcrypt.go
+18 -7
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@@ -76,7 +76,7 @@ var magicCipherData = []byte{
type hashed struct {
hash []byte
salt []byte
cost uint32 // allowed range is MinCost to MaxCost
cost int // allowed range is MinCost to MaxCost
major byte
minor byte
}
@@ -94,8 +94,7 @@ func GenerateFromPassword(password []byte, cost int) ([]byte, error) {
}
// CompareHashAndPassword compares a bcrypt hashed password with its possible
// plaintext equivalent. Note: Using bytes.Equal for this job is
// insecure. Returns nil on success, or an error on failure.
// plaintext equivalent. Returns nil on success, or an error on failure.
func CompareHashAndPassword(hashedPassword, password []byte) error {
p, err := newFromHash(hashedPassword)
if err != nil {
@@ -115,6 +114,18 @@ func CompareHashAndPassword(hashedPassword, password []byte) error {
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
@@ -127,7 +138,7 @@ func newFromPassword(password []byte, cost int) (*hashed, error) {
if err != nil {
return nil, err
}
p.cost = uint32(cost)
p.cost = cost
unencodedSalt := make([]byte, maxSaltSize)
_, err = io.ReadFull(rand.Reader, unencodedSalt)
@@ -172,11 +183,11 @@ func newFromHash(hashedSecret []byte) (*hashed, error) {
return p, nil
}
func bcrypt(password []byte, cost uint32, salt []byte) ([]byte, error) {
func bcrypt(password []byte, cost int, salt []byte) ([]byte, error) {
cipherData := make([]byte, len(magicCipherData))
copy(cipherData, magicCipherData)
c, err := expensiveBlowfishSetup(password, cost, salt)
c, err := expensiveBlowfishSetup(password, uint32(cost), salt)
if err != nil {
return nil, err
}
@@ -266,7 +277,7 @@ func (p *hashed) decodeCost(sbytes []byte) (int, error) {
if err != nil {
return -1, err
}
p.cost = uint32(cost)
p.cost = cost
return 3, nil
}