open-vault/vendor/github.com/keybase/go-crypto/openpgp/ecdh/ecdh.go

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2017-02-08 07:13:15 +00:00
package ecdh
import (
"bytes"
"crypto"
"crypto/aes"
"crypto/elliptic"
"encoding/binary"
"errors"
"github.com/keybase/go-crypto/curve25519"
"io"
"math/big"
)
type PublicKey struct {
elliptic.Curve
X, Y *big.Int
}
type PrivateKey struct {
PublicKey
X *big.Int
}
// KDF implements Key Derivation Function as described in
// https://tools.ietf.org/html/rfc6637#section-7
func (e *PublicKey) KDF(S []byte, kdfParams []byte, hash crypto.Hash) []byte {
sLen := (e.Curve.Params().P.BitLen() + 7) / 8
buf := new(bytes.Buffer)
buf.Write([]byte{0, 0, 0, 1})
if sLen > len(S) {
// zero-pad the S. If we got invalid S (bigger than curve's
// P), we are going to produce invalid key. Garbage in,
// garbage out.
buf.Write(make([]byte, sLen-len(S)))
}
buf.Write(S)
buf.Write(kdfParams)
hashw := hash.New()
hashw.Write(buf.Bytes())
key := hashw.Sum(nil)
return key
}
// AESKeyUnwrap implements RFC 3394 Key Unwrapping. See
// http://tools.ietf.org/html/rfc3394#section-2.2.1
// Note: The second described algorithm ("index-based") is implemented
// here.
func AESKeyUnwrap(key, cipherText []byte) ([]byte, error) {
if len(cipherText)%8 != 0 {
return nil, errors.New("cipherText must by a multiple of 64 bits")
}
cipher, err := aes.NewCipher(key)
if err != nil {
return nil, err
}
nblocks := len(cipherText)/8 - 1
// 1) Initialize variables.
// - Set A = C[0]
var A [aes.BlockSize]byte
copy(A[:8], cipherText[:8])
// For i = 1 to n
// Set R[i] = C[i]
R := make([]byte, len(cipherText)-8)
copy(R, cipherText[8:])
// 2) Compute intermediate values.
for j := 5; j >= 0; j-- {
for i := nblocks - 1; i >= 0; i-- {
// B = AES-1(K, (A ^ t) | R[i]) where t = n*j+i
// A = MSB(64, B)
t := uint64(nblocks*j + i + 1)
At := binary.BigEndian.Uint64(A[:8]) ^ t
binary.BigEndian.PutUint64(A[:8], At)
copy(A[8:], R[i*8:i*8+8])
cipher.Decrypt(A[:], A[:])
// R[i] = LSB(B, 64)
copy(R[i*8:i*8+8], A[8:])
}
}
// 3) Output results.
// If A is an appropriate initial value (see 2.2.3),
for i := 0; i < 8; i++ {
if A[i] != 0xA6 {
return nil, errors.New("Failed to unwrap key (A is not IV)")
}
}
return R, nil
}
// AESKeyWrap implements RFC 3394 Key Wrapping. See
// https://tools.ietf.org/html/rfc3394#section-2.2.2
// Note: The second described algorithm ("index-based") is implemented
// here.
func AESKeyWrap(key, plainText []byte) ([]byte, error) {
if len(plainText)%8 != 0 {
return nil, errors.New("plainText must be a multiple of 64 bits")
}
cipher, err := aes.NewCipher(key) // NewCipher checks key size
if err != nil {
return nil, err
}
nblocks := len(plainText) / 8
// 1) Initialize variables.
var A [aes.BlockSize]byte
// Section 2.2.3.1 -- Initial Value
// http://tools.ietf.org/html/rfc3394#section-2.2.3.1
for i := 0; i < 8; i++ {
A[i] = 0xA6
}
// For i = 1 to n
// Set R[i] = P[i]
R := make([]byte, len(plainText))
copy(R, plainText)
// 2) Calculate intermediate values.
for j := 0; j <= 5; j++ {
for i := 0; i < nblocks; i++ {
// B = AES(K, A | R[i])
copy(A[8:], R[i*8:i*8+8])
cipher.Encrypt(A[:], A[:])
// (Assume B = A)
// A = MSB(64, B) ^ t where t = (n*j)+1
t := uint64(j*nblocks + i + 1)
At := binary.BigEndian.Uint64(A[:8]) ^ t
binary.BigEndian.PutUint64(A[:8], At)
// R[i] = LSB(64, B)
copy(R[i*8:i*8+8], A[8:])
}
}
// 3) Output results.
// Set C[0] = A
// For i = 1 to n
// C[i] = R[i]
return append(A[:8], R...), nil
}
// PadBuffer pads byte buffer buf to a length being multiple of
// blockLen. Additional bytes appended to the buffer have value of the
// number padded bytes. E.g. if the buffer is 3 bytes short of being
// 40 bytes total, the appended bytes will be [03, 03, 03].
func PadBuffer(buf []byte, blockLen int) []byte {
padding := blockLen - (len(buf) % blockLen)
if padding == 0 {
return buf
}
padBuf := make([]byte, padding)
for i := 0; i < padding; i++ {
padBuf[i] = byte(padding)
}
return append(buf, padBuf...)
}
// UnpadBuffer verifies that buffer contains proper padding and
// returns buffer without the padding, or nil if the padding was
// invalid.
func UnpadBuffer(buf []byte, dataLen int) []byte {
padding := len(buf) - dataLen
outBuf := buf[:dataLen]
for i := dataLen; i < len(buf); i++ {
if buf[i] != byte(padding) {
// Invalid padding - bail out
return nil
}
}
return outBuf
}
func (e *PublicKey) Encrypt(random io.Reader, kdfParams []byte, plain []byte, hash crypto.Hash, kdfKeySize int) (Vx *big.Int, Vy *big.Int, C []byte, err error) {
// Vx, Vy - encryption key
// Note for Curve 25519 - curve25519 library already does key
// clamping in scalarMult, so we can use generic random scalar
// generation from elliptic.
priv, Vx, Vy, err := elliptic.GenerateKey(e.Curve, random)
if err != nil {
return nil, nil, nil, err
}
// Sx, Sy - shared secret
Sx, _ := e.Curve.ScalarMult(e.X, e.Y, priv)
// Encrypt the payload with KDF-ed S as the encryption key. Pass
// the ciphertext along with V to the recipient. Recipient can
// generate S using V and their priv key, and then KDF(S), on
// their own, to get encryption key and decrypt the ciphertext,
// revealing encryption key for symmetric encryption later.
plain = PadBuffer(plain, 8)
key := e.KDF(Sx.Bytes(), kdfParams, hash)
// Take only as many bytes from key as the key length (the hash
// result might be bigger)
encrypted, err := AESKeyWrap(key[:kdfKeySize], plain)
return Vx, Vy, encrypted, nil
}
func (e *PrivateKey) DecryptShared(X, Y *big.Int) []byte {
Sx, _ := e.Curve.ScalarMult(X, Y, e.X.Bytes())
return Sx.Bytes()
}
func countBits(buffer []byte) int {
var headerLen int
switch buffer[0] {
case 0x4:
headerLen = 3
case 0x40:
headerLen = 7
default:
// Unexpected header - but we can still count the bits.
val := buffer[0]
headerLen = 0
for val > 0 {
val = val / 2
headerLen++
}
}
return headerLen + (len(buffer)-1)*8
}
// elliptic.Marshal and elliptic.Unmarshal only marshals uncompressed
// 0x4 MPI types. These functions will check if the curve is cv25519,
// and if so, use 0x40 compressed type to (un)marshal. Otherwise,
// elliptic.(Un)marshal will be called.
// Marshal encodes point into either 0x4 uncompressed point form, or
// 0x40 compressed point for Curve 25519.
func Marshal(curve elliptic.Curve, x, y *big.Int) (buf []byte, bitSize int) {
// NOTE: Read more about MPI encoding in the RFC:
// https://tools.ietf.org/html/rfc4880#section-3.2
// We are required to encode size in bits, counting from the most-
// significant non-zero bit. So assuming that the buffer never
// starts with 0x00, we only need to count bits in the first byte
// - and in current implentation it will always be 0x4 or 0x40.
cv, ok := curve25519.ToCurve25519(curve)
if ok {
buf = cv.MarshalType40(x, y)
} else {
buf = elliptic.Marshal(curve, x, y)
}
return buf, countBits(buf)
}
// Unmarshal converts point, serialized by Marshal, into x, y pair.
// For 0x40 compressed points (for Curve 25519), y will always be 0.
// It is an error if point is not on the curve, On error, x = nil.
func Unmarshal(curve elliptic.Curve, data []byte) (x, y *big.Int) {
cv, ok := curve25519.ToCurve25519(curve)
if ok {
return cv.UnmarshalType40(data)
}
return elliptic.Unmarshal(curve, data)
}
func GenerateKey(curve elliptic.Curve, random io.Reader) (priv *PrivateKey, err error) {
var privBytes []byte
var Vx, Vy *big.Int
if _, ok := curve25519.ToCurve25519(curve); ok {
privBytes = make([]byte, 32)
_, err = io.ReadFull(random, privBytes)
if err != nil {
return nil, err
}
// NOTE: PGP expect scalars in reverse order than Curve 25519
// go library. That's why this trimming is backwards compared
// to curve25519.go
privBytes[31] &= 248
privBytes[0] &= 127
privBytes[0] |= 64
Vx,Vy = curve.ScalarBaseMult(privBytes)
} else {
privBytes, Vx, Vy, err = elliptic.GenerateKey(curve, random)
if err != nil {
return nil, err
}
}
priv = &PrivateKey{}
priv.X = new(big.Int).SetBytes(privBytes)
priv.PublicKey.Curve = curve
priv.PublicKey.X = Vx
priv.PublicKey.Y = Vy
return priv, nil
}