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aesgcm_aead.go
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aesgcm_aead.go
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package crypto
import (
"crypto/aes"
"crypto/cipher"
"encoding/binary"
"errors"
"github.com/Psiphon-Labs/psiphon-tunnel-core/psiphon/common/quic/gquic-go/internal/protocol"
)
type aeadAESGCM struct {
otherIV []byte
myIV []byte
encrypter cipher.AEAD
decrypter cipher.AEAD
}
var _ AEAD = &aeadAESGCM{}
const ivLen = 12
// NewAEADAESGCM creates a AEAD using AES-GCM
func NewAEADAESGCM(otherKey []byte, myKey []byte, otherIV []byte, myIV []byte) (AEAD, error) {
// the IVs need to be at least 8 bytes long, otherwise we can't compute the nonce
if len(otherIV) != ivLen || len(myIV) != ivLen {
return nil, errors.New("AES-GCM: expected 12 byte IVs")
}
encrypterCipher, err := aes.NewCipher(myKey)
if err != nil {
return nil, err
}
encrypter, err := cipher.NewGCM(encrypterCipher)
if err != nil {
return nil, err
}
decrypterCipher, err := aes.NewCipher(otherKey)
if err != nil {
return nil, err
}
decrypter, err := cipher.NewGCM(decrypterCipher)
if err != nil {
return nil, err
}
return &aeadAESGCM{
otherIV: otherIV,
myIV: myIV,
encrypter: encrypter,
decrypter: decrypter,
}, nil
}
func (aead *aeadAESGCM) Open(dst, src []byte, packetNumber protocol.PacketNumber, associatedData []byte) ([]byte, error) {
return aead.decrypter.Open(dst, aead.makeNonce(aead.otherIV, packetNumber), src, associatedData)
}
func (aead *aeadAESGCM) Seal(dst, src []byte, packetNumber protocol.PacketNumber, associatedData []byte) []byte {
return aead.encrypter.Seal(dst, aead.makeNonce(aead.myIV, packetNumber), src, associatedData)
}
func (aead *aeadAESGCM) makeNonce(iv []byte, packetNumber protocol.PacketNumber) []byte {
nonce := make([]byte, ivLen)
binary.BigEndian.PutUint64(nonce[ivLen-8:], uint64(packetNumber))
for i := 0; i < ivLen; i++ {
nonce[i] ^= iv[i]
}
return nonce
}
func (aead *aeadAESGCM) Overhead() int {
return aead.encrypter.Overhead()
}