blob: 90ced3b58c9c202825200fcc7cf8239b23695d43 [file] [log] [blame]
package rfc8009
import (
"crypto/hmac"
"encoding/binary"
"encoding/hex"
"errors"
"golang.org/x/crypto/pbkdf2"
"gopkg.in/jcmturner/gokrb5.v7/crypto/etype"
"gopkg.in/jcmturner/gokrb5.v7/iana/etypeID"
)
const (
s2kParamsZero = 32768
)
// DeriveRandom for key derivation as defined in RFC 8009
func DeriveRandom(protocolKey, usage []byte, e etype.EType) ([]byte, error) {
h := e.GetHashFunc()()
return KDF_HMAC_SHA2(protocolKey, []byte("prf"), usage, h.Size(), e), nil
}
// DeriveKey derives a key from the protocol key based on the usage and the etype's specific methods.
//
// https://tools.ietf.org/html/rfc8009#section-5
//
// If the enctype is aes128-cts-hmac-sha256-128:
// Kc = KDF-HMAC-SHA2(base-key, usage | 0x99, 128)
// Ke = KDF-HMAC-SHA2(base-key, usage | 0xAA, 128)
// Ki = KDF-HMAC-SHA2(base-key, usage | 0x55, 128)
//
// If the enctype is aes256-cts-hmac-sha384-192:
// Kc = KDF-HMAC-SHA2(base-key, usage | 0x99, 192)
// Ke = KDF-HMAC-SHA2(base-key, usage | 0xAA, 256)
// Ki = KDF-HMAC-SHA2(base-key, usage | 0x55, 192)
func DeriveKey(protocolKey, label []byte, e etype.EType) []byte {
var context []byte
var kl int
// Key length is longer for aes256-cts-hmac-sha384-192 is it is a Ke or from StringToKey (where label is "kerberos")
if e.GetETypeID() == etypeID.AES256_CTS_HMAC_SHA384_192 {
switch label[len(label)-1] {
case 0x73:
// 0x73 is "s" so label could be kerberos meaning StringToKey so now check if the label is "kerberos"
kerblabel := []byte("kerberos")
if len(label) != len(kerblabel) {
break
}
for i, b := range label {
if b != kerblabel[i] {
kl = e.GetKeySeedBitLength()
break
}
}
if kl == 0 {
// This is StringToKey
kl = 256
}
case 0xAA:
// This is a Ke
kl = 256
}
}
if kl == 0 {
kl = e.GetKeySeedBitLength()
}
return e.RandomToKey(KDF_HMAC_SHA2(protocolKey, label, context, kl, e))
}
// RandomToKey returns a key from the bytes provided according to the definition in RFC 8009.
func RandomToKey(b []byte) []byte {
return b
}
// StringToKey returns a key derived from the string provided according to the definition in RFC 8009.
func StringToKey(secret, salt, s2kparams string, e etype.EType) ([]byte, error) {
i, err := S2KparamsToItertions(s2kparams)
if err != nil {
return nil, err
}
return StringToKeyIter(secret, salt, i, e)
}
// StringToKeyIter returns a key derived from the string provided according to the definition in RFC 8009.
func StringToKeyIter(secret, salt string, iterations int, e etype.EType) ([]byte, error) {
tkey := e.RandomToKey(StringToPBKDF2(secret, salt, iterations, e))
return e.DeriveKey(tkey, []byte("kerberos"))
}
// StringToPBKDF2 generates an encryption key from a pass phrase and salt string using the PBKDF2 function from PKCS #5 v2.0
func StringToPBKDF2(secret, salt string, iterations int, e etype.EType) []byte {
kl := e.GetKeyByteSize()
if e.GetETypeID() == etypeID.AES256_CTS_HMAC_SHA384_192 {
kl = 32
}
return pbkdf2.Key([]byte(secret), []byte(salt), iterations, kl, e.GetHashFunc())
}
// KDF_HMAC_SHA2 key derivation: https://tools.ietf.org/html/rfc8009#section-3
func KDF_HMAC_SHA2(protocolKey, label, context []byte, kl int, e etype.EType) []byte {
//k: Length in bits of the key to be outputted, expressed in big-endian binary representation in 4 bytes.
k := make([]byte, 4, 4)
binary.BigEndian.PutUint32(k, uint32(kl))
c := make([]byte, 4, 4)
binary.BigEndian.PutUint32(c, uint32(1))
c = append(c, label...)
c = append(c, byte(0))
if len(context) > 0 {
c = append(c, context...)
}
c = append(c, k...)
mac := hmac.New(e.GetHashFunc(), protocolKey)
mac.Write(c)
return mac.Sum(nil)[:(kl / 8)]
}
// GetSaltP returns the salt value based on the etype name: https://tools.ietf.org/html/rfc8009#section-4
func GetSaltP(salt, ename string) string {
b := []byte(ename)
b = append(b, byte(0))
b = append(b, []byte(salt)...)
return string(b)
}
// S2KparamsToItertions converts the string representation of iterations to an integer for RFC 8009.
func S2KparamsToItertions(s2kparams string) (int, error) {
var i uint32
if len(s2kparams) != 8 {
return s2kParamsZero, errors.New("Invalid s2kparams length")
}
b, err := hex.DecodeString(s2kparams)
if err != nil {
return s2kParamsZero, errors.New("Invalid s2kparams, cannot decode string to bytes")
}
i = binary.BigEndian.Uint32(b)
//buf := bytes.NewBuffer(b)
//err = binary.Read(buf, binary.BigEndian, &i)
if err != nil {
return s2kParamsZero, errors.New("Invalid s2kparams, cannot convert to big endian int32")
}
return int(i), nil
}