attachment_crypto.go

package cryptoutil

import (
	"bytes"
	"crypto/cipher"
	"fmt"
	"io"
	"math/big"

	libp2pcrypto "github.com/libp2p/go-libp2p-core/crypto"
	"go.uber.org/zap"
	"golang.org/x/crypto/chacha20poly1305"
	"golang.org/x/crypto/hkdf"
	"golang.org/x/crypto/nacl/secretbox"
	"golang.org/x/crypto/sha3"

	"berty.tech/berty/v2/go/internal/streamutil"
	"berty.tech/berty/v2/go/pkg/errcode"
	"berty.tech/berty/v2/go/pkg/protocoltypes"
)

// ⚠⚠⚠ FIXME: Needs thorough security review ⚠⚠⚠

const (
	attachmentCipherblockSize = 64 * 1024
	attachmentNonceIV         = 0
	attachmentKeyV0Prefix     = "/libp2psk+xchacha20poly1305_64_0/" // TODO: replace when multikey rolls out
)

// - DATA ENCRYPTION

type attachmentCipher struct {
	nonce    *big.Int
	nonceBuf [chacha20poly1305.NonceSizeX]byte
	aead     cipher.AEAD
}

func attachmentNewCipher(sk libp2pcrypto.PrivKey) (*attachmentCipher, error) {
	key, err := SeedFromEd25519PrivateKey(sk)
	if err != nil {
		return nil, errcode.ErrInvalidInput.Wrap(err)
	}
	if len(key) < chacha20poly1305.KeySize {
		return nil, errcode.ErrInvalidInput.Wrap(fmt.Errorf("bad key size, got %d, expected to be >= %d", len(key), chacha20poly1305.KeySize))
	}

	aead, err := chacha20poly1305.NewX(key[:chacha20poly1305.KeySize])
	if err != nil {
		return nil, errcode.ErrCryptoCipherInit.Wrap(err)
	}

	ac := attachmentCipher{
		aead:  aead,
		nonce: big.NewInt(attachmentNonceIV),
	}

	return &ac, nil
}

var bigOne = big.NewInt(1)

func AttachmentSealer(plaintext io.Reader, l *zap.Logger) (libp2pcrypto.PrivKey, *io.PipeReader, error) {
	sk, _, err := libp2pcrypto.GenerateKeyPair(libp2pcrypto.Ed25519, 0)
	if err != nil {
		return nil, nil, errcode.ErrCryptoKeyGeneration.Wrap(err)
	}

	ac, err := attachmentNewCipher(sk)
	if err != nil {
		return nil, nil, errcode.ErrCryptoCipherInit.Wrap(err)
	}

	return sk, streamutil.FuncBlockTransformer(make([]byte, attachmentCipherblockSize-ac.aead.Overhead()), plaintext, l, func(pt []byte) ([]byte, error) {
		bigIntFillBytes(ac.nonce, ac.nonceBuf[:])

		ct := ac.aead.Seal([]byte(nil), ac.nonceBuf[:], pt, []byte(nil))

		ac.nonce.Add(ac.nonce, bigOne)

		return ct, nil
	}), nil
}

func AttachmentOpener(ciphertext io.Reader, sk libp2pcrypto.PrivKey, l *zap.Logger) (*io.PipeReader, error) {
	ac, err := attachmentNewCipher(sk)
	if err != nil {
		return nil, errcode.ErrCryptoCipherInit.Wrap(err)
	}

	return streamutil.FuncBlockTransformer(make([]byte, attachmentCipherblockSize), ciphertext, l, func(ct []byte) ([]byte, error) {
		bigIntFillBytes(ac.nonce, ac.nonceBuf[:])

		pt, err := ac.aead.Open([]byte(nil), ac.nonceBuf[:], ct, []byte(nil))
		if err != nil {
			return nil, errcode.ErrCryptoDecrypt.Wrap(err)
		}

		ac.nonce.Add(ac.nonce, bigOne)

		return pt, nil
	}), nil
}

// - KEY SERIALIZATION

func attachmentKeyMarshal(sk libp2pcrypto.PrivKey) ([]byte, error) {
	skBytes, err := libp2pcrypto.MarshalPrivateKey(sk)
	if err != nil {
		return nil, errcode.ErrSerialization.Wrap(err)
	}

	return append([]byte(attachmentKeyV0Prefix), skBytes...), nil
}

func attachmentKeyUnmarshal(s []byte) (libp2pcrypto.PrivKey, error) {
	if len(s) <= len(attachmentKeyV0Prefix) || !bytes.Equal(s[:len(attachmentKeyV0Prefix)], []byte(attachmentKeyV0Prefix)) {
		return nil, errcode.ErrInvalidInput.Wrap(fmt.Errorf("invalid secret prefix"))
	}
	skBytes := s[len(attachmentKeyV0Prefix):]

	sk, err := libp2pcrypto.UnmarshalPrivateKey(skBytes)
	if err != nil {
		return nil, errcode.ErrDeserialization.Wrap(err)
	}

	return sk, nil
}

// - CID ENCRYPTION

func attachmentCIDEncryptionKey(source *[KeySize]byte) (*[KeySize]byte, error) {
	hkdf := hkdf.New(sha3.New256, source[:], nil, []byte("cid encryption v0"))

	var key [KeySize]byte
	if _, err := io.ReadFull(hkdf, key[:]); err != nil {
		return nil, errcode.ErrStreamRead.Wrap(err)
	}

	return &key, nil
}

func attachmentCIDEncrypt(sk *[KeySize]byte, cid []byte) ([]byte, error) {
	nonce, err := GenerateNonce()
	if err != nil {
		return nil, errcode.ErrCryptoNonceGeneration.Wrap(err)
	}

	return append(nonce[:], secretbox.Seal(nil, cid, nonce, sk)...), nil
}

func attachmentCIDDecrypt(sk *[KeySize]byte, eCID []byte) ([]byte, error) {
	if len(eCID) <= NonceSize {
		return nil, errcode.ErrInvalidInput.Wrap(fmt.Errorf("encrypted cid too small, got %v, expected to be > %v", len(eCID), NonceSize))
	}

	var nonce [NonceSize]byte
	_ = copy(nonce[:], eCID[:NonceSize])

	cid, ok := secretbox.Open(nil, eCID[NonceSize:], &nonce, sk)
	if !ok {
		return nil, errcode.ErrCryptoDecrypt
	}

	return cid, nil
}

func AttachmentCIDSliceEncrypt(g *protocoltypes.Group, cids [][]byte) ([][]byte, error) {
	sk, err := attachmentCIDEncryptionKey(GetSharedSecret(g))
	if err != nil {
		return nil, errcode.ErrCryptoKeyDerivation.Wrap(err)
	}
	return mapBufArray(cids, func(cid []byte) ([]byte, error) { return attachmentCIDEncrypt(sk, cid) })
}

func AttachmentCIDSliceDecrypt(g *protocoltypes.Group, eCIDs [][]byte) ([][]byte, error) {
	sk, err := attachmentCIDEncryptionKey(GetSharedSecret(g))
	if err != nil {
		return nil, errcode.ErrCryptoKeyDerivation.Wrap(err)
	}
	return mapBufArray(eCIDs, func(eCID []byte) ([]byte, error) { return attachmentCIDDecrypt(sk, eCID) })
}