sigtool/internal/pb/wrap.go
Sudhi Herle 00542dec02 Major breaking changes: Reworked file encryption scheme
* all encryption now uses ephmeral curve25519 keys
* sender can identify themselves by providing a signing key
* sign/verify now uses a string prefix for calculating checksum of the
  incoming message + known prefix [prevents us from verifying unknown
  blobs]
* encrypt/decrypt key is now expanded with a known prefix _and_ the
  header checksum
* protobuf definition changed to include an encrypted sender
  identification blob (sender public key)
* moved protobuf files into an internal/pb directory
* general code rearrangement to make it easy to find files
* added extra validation for reading all keys
* bumped version to 1.0.0
2020-03-20 17:40:52 -07:00

97 lines
2.1 KiB
Go

// wrap.go - wrap keys and sender as needed
//
// (c) 2016 Sudhi Herle <sudhi@herle.net>
//
// Licensing Terms: GPLv2
//
// If you need a commercial license for this work, please contact
// the author.
//
// This software does not come with any express or implied
// warranty; it is provided "as is". No claim is made to its
// suitability for any purpose.
//
package pb
import (
"crypto/aes"
"crypto/cipher"
"crypto/rand"
"crypto/sha256"
"fmt"
"io"
)
const (
WrapReceiverNonce = "Receiver PK"
WrapSenderNonce = "Sender PK"
)
// Wrap sender's PK with the data encryption key
func WrapSenderPK(pk []byte, k, salt []byte) ([]byte, error) {
aes, err := aes.NewCipher(k)
if err != nil {
return nil, fmt.Errorf("wrap: %s", err)
}
ae, err := cipher.NewGCM(aes)
if err != nil {
return nil, fmt.Errorf("wrap: %s", err)
}
nonce := MakeNonce([]byte(WrapSenderNonce), salt)
buf := make([]byte, ae.Overhead()+len(pk))
out := ae.Seal(buf[:0], nonce[:ae.NonceSize()], pk, nil)
return out, nil
}
// Given a wrapped PK of sender 's', unwrap it using the given key and salt
func (s *Sender) UnwrapPK(k, salt []byte) ([]byte, error) {
aes, err := aes.NewCipher(k)
if err != nil {
return nil, fmt.Errorf("uwrap-sender: %s", err)
}
ae, err := cipher.NewGCM(aes)
if err != nil {
return nil, fmt.Errorf("unwrap-sender: %s", err)
}
nonce := MakeNonce([]byte(WrapSenderNonce), salt)
want := 32 + ae.Overhead()
if len(s.Pk) != want {
return nil, fmt.Errorf("unwrap-sender: incorrect decrypt bytes (need %d, saw %d)", want, 32)
}
out := make([]byte, 32)
pk, err := ae.Open(out[:0], nonce[:ae.NonceSize()], s.Pk, nil)
if err != nil {
return nil, fmt.Errorf("unwrap-sender: %s", err)
}
return pk, nil
}
func MakeNonce(v ...[]byte) []byte {
h := sha256.New()
for _, x := range v {
h.Write(x)
}
return h.Sum(nil)[:]
}
func Clamp(k []byte) []byte {
k[0] &= 248
k[31] &= 127
k[31] |= 64
return k
}
func Randread(b []byte) []byte {
_, err := io.ReadFull(rand.Reader, b)
if err != nil {
panic(fmt.Sprintf("can't read %d bytes of random data: %s", len(b), err))
}
return b
}