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rc4_hmac.go
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rc4_hmac.go
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package crypto
import (
"bytes"
"context"
"crypto/hmac"
"crypto/md5"
"crypto/rand"
"crypto/rc4"
"encoding/asn1"
"encoding/binary"
"fmt"
"hash"
"github.com/oiweiwei/go-msrpc/ssp/gssapi"
"github.com/jcmturner/gokrb5/v8/asn1tools"
"github.com/jcmturner/gokrb5/v8/types"
)
var (
KRB5OID = asn1.ObjectIdentifier{1, 2, 840, 113554, 1, 2, 2}
)
type RC4HMAC struct {
// indicates whether this is an initiator.
init bool
// encryption key.
key types.EncryptionKey
}
func NewRC4Cipher(ctx context.Context, key types.EncryptionKey, isServer bool) (Cipher, error) {
return &RC4HMAC{init: !isServer, key: key}, nil
}
func (c *RC4HMAC) Wrap(ctx context.Context, seqNum uint64, forSign, forSeal [][]byte) ([]byte, error) {
b, err := c.wrap(ctx, seqNum, forSign, forSeal)
if err != nil {
return nil, fmt.Errorf("rc4-hmac: wrap: %w", err)
}
return b, nil
}
func (c *RC4HMAC) wrap(ctx context.Context, seqNum uint64, forSign, forSeal [][]byte) ([]byte, error) {
hdr := c.WrapHeader(ctx, seqNum)
_, err := rand.Read(hdr[24:32])
if err != nil {
return nil, err
}
// Ksign = HMAC(Kss, "signaturekey");
// Sgn_Cksum = MD5((int32)13, Token.Header, data);
// Sgn_Cksum = HMAC(Ksign, Sgn_Cksum);
cksum := c.hmac(c.hmac(c.key.KeyValue, []byte("signaturekey\x00")),
c.md5(int32(13), hdr[:8], hdr[24:32], forSign))
// memcpy(Token.SGN_CKSUM, Sgn_Cksum, 8);
copy(hdr[16:24], cksum[:8])
// for (i = 0; i < 16; i++) Klocal[i] = Kss[i] ^ 0xF0;
klocal := make([]byte, 16)
for i := range klocal {
klocal[i] = c.key.KeyValue[i] ^ 0xF0
}
// Kcrypt = HMAC(Klocal, (int32)0);
// Kcrypt = HMAC(Kcrypt, (int32)seq);
// RC4(Kcrypt, Token.Confounder);
cipher, _ := rc4.NewCipher(c.hmac(c.hmac(klocal, int32(0)), hdr[8:12]))
cipher.XORKeyStream(hdr[24:32], hdr[24:32])
for i := range forSeal {
cipher.XORKeyStream(forSeal[i], forSeal[i])
}
// Kseq = HMAC(Kss, (int32)0);
// Kseq = HMAC(Kseq, Token.SGN_CKSUM);
// RC4(Kseq, Token.SND_SEQ);
c.rc4(c.hmac(c.hmac(c.key.KeyValue, int32(0)), cksum[:8]), hdr[8:16])
return c.withASN1Header(ctx, hdr)
}
func (c *RC4HMAC) withASN1Header(ctx context.Context, b []byte) ([]byte, error) {
oid, err := asn1.Marshal(KRB5OID)
if err != nil {
return nil, fmt.Errorf("marshal krb5oid: %w", err)
}
return asn1tools.AddASNAppTag(append(oid, b...), 0), nil
}
func (c *RC4HMAC) Unwrap(ctx context.Context, seqNum uint64, forSign, forSeal [][]byte, sgn []byte) (bool, error) {
ok, err := c.unwrap(ctx, seqNum, forSign, forSeal, sgn)
if err != nil {
return ok, fmt.Errorf("rc4-hmac: unwrap: %w", err)
}
return ok, nil
}
func (c *RC4HMAC) unwrap(ctx context.Context, seqNum uint64, forSign, forSeal [][]byte, sgn []byte) (bool, error) {
if len(sgn) < 8 {
return false, gssapi.ErrDefectiveToken
}
hdr := c.WrapHeader(ctx, seqNum)
copy(hdr[24:32], sgn[len(sgn)-8:])
// for (i = 0; i < 16; i++) Klocal[i] = Kss[i] ^ 0xF0;
klocal := make([]byte, 16)
for i := range klocal {
klocal[i] = c.key.KeyValue[i] ^ 0xF0
}
// Kcrypt = HMAC(Klocal, (int32)0);
// Kcrypt = HMAC(Kcrypt, (int32)seq);
// RC4(Kcrypt, Token.Confounder);
cipher, _ := rc4.NewCipher(c.hmac(c.hmac(klocal, int32(0)), hdr[8:12]))
cipher.XORKeyStream(hdr[24:32], hdr[24:32])
for i := range forSeal {
cipher.XORKeyStream(forSeal[i], forSeal[i])
}
// Ksign = HMAC(Kss, "signaturekey");
// Sgn_Cksum = MD5((int32)13, Token.Header, data);
// Sgn_Cksum = HMAC(Ksign, Sgn_Cksum);
cksum := c.hmac(c.hmac(c.key.KeyValue, []byte("signaturekey\x00")),
c.md5(int32(13), hdr[:8], hdr[24:32], forSign))
// memcpy(Token.SGN_CKSUM, Sgn_Cksum, 8);
copy(hdr[16:24], cksum[:8])
// Kseq = HMAC(Kss, (int32)0);
// Kseq = HMAC(Kseq, Token.SGN_CKSUM);
// RC4(Kseq, Token.SND_SEQ);
c.rc4(c.hmac(c.hmac(c.key.KeyValue, int32(0)), cksum[:8]), hdr[8:16])
expSgn, err := c.withASN1Header(ctx, hdr)
if err != nil {
return false, err
}
// set decrypted confounder back.
copy(sgn[len(sgn)-8:], hdr[24:32])
return bytes.Equal(expSgn, sgn), nil
}
func (c *RC4HMAC) Size(ctx context.Context, conf bool) int {
sz := (16 /* header[16] */ + 8 /* cksum[8] */ + 13 /* asn1 header */)
if conf {
sz += 8 /* confounder[8] */
}
return sz
}
func (c *RC4HMAC) MakeSignature(ctx context.Context, seqNum uint64, forSign [][]byte) ([]byte, error) {
b, err := c.makeSignature(ctx, seqNum, forSign)
if err != nil {
return nil, fmt.Errorf("rc4-hmac: make signature: %w", err)
}
return b, nil
}
func (c *RC4HMAC) makeSignature(ctx context.Context, seqNum uint64, forSign [][]byte) ([]byte, error) {
hdr := c.MICHeader(ctx, seqNum)
// Ksign = HMAC(Kss, "signaturekey");
// Sgn_Cksum = MD5((int32)15, Token.Header, data);
// Sgn_Cksum = HMAC(Ksign, Sgn_Cksum);
cksum := c.hmac(c.hmac(c.key.KeyValue, []byte("signaturekey\x00")),
c.md5(int32(15), hdr[:8], forSign))
// memcpy(Token.SGN_CKSUM, Sgn_Cksum, 8);
copy(hdr[16:24], cksum[:8])
// Kseq = HMAC(Kss, (int32)0);
// Kseq = HMAC(Kseq, Token.SGN_CKSUM);
// RC4(Kseq, Token.SND_SEQ);
c.rc4(c.hmac(c.hmac(c.key.KeyValue, int32(0)), cksum[:8]), hdr[8:16])
return c.withASN1Header(ctx, hdr)
}
func (c *RC4HMAC) hmac(k []byte, data ...interface{}) []byte {
return c.digest(hmac.New(md5.New, k), data...)
}
func (c *RC4HMAC) md5(data ...interface{}) []byte {
return c.digest(md5.New(), data...)
}
func (c *RC4HMAC) rc4(key []byte, data []byte) {
cipher, _ := rc4.NewCipher(key)
cipher.XORKeyStream(data, data)
}
func (c *RC4HMAC) digest(h hash.Hash, data ...interface{}) []byte {
for _, d := range data {
switch d := d.(type) {
case []byte:
h.Write(d)
case [][]byte:
for i := range d {
h.Write(d[i])
}
default:
binary.Write(h, binary.LittleEndian, d)
}
}
return h.Sum(nil)
}
func (c *RC4HMAC) MICHeader(ctx context.Context, seqNum uint64) []byte {
hdr := make([]byte, 24)
// token_type 0x01 0x01
hdr[0] = 0x01
hdr[1] = 0x01
// HMAC
hdr[2] = 0x11
hdr[3] = 0x00
// filler.
hdr[4] = 0xff
hdr[5] = 0xff
hdr[6] = 0xff
hdr[7] = 0xff
// seq_number.
binary.BigEndian.PutUint32(hdr[8:12], uint32(seqNum))
// filler.
if !c.init {
hdr[12] = 0xff
hdr[13] = 0xff
hdr[14] = 0xff
hdr[15] = 0xff
}
return hdr
}
func (c *RC4HMAC) WrapHeader(ctx context.Context, seqNum uint64) []byte {
hdr := make([]byte, 32)
// token_id.
hdr[0] = 0x02
hdr[1] = 0x01
// sgn_alg.
hdr[2] = 0x11 // hmac
hdr[3] = 0x00
// seal_alg.
hdr[4] = 0x10
hdr[5] = 0x00
// filler.
hdr[6] = 0xff
hdr[7] = 0xff
// seq_number.
binary.BigEndian.PutUint32(hdr[8:12], uint32(seqNum))
// filler.
if !c.init {
hdr[12] = 0xff
hdr[13] = 0xff
hdr[14] = 0xff
hdr[15] = 0xff
}
return hdr
}