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