passphrase.go

// Imported from github.com/ethereum/go-ethereum/accounts/keystore/passphrase.go
// and github.com/ethereum/go-ethereum/accounts/keystore/presale.go

package keystore

import (
	"bytes"
	"crypto/aes"
	"crypto/cipher"
	"crypto/sha256"
	"encoding/hex"
	"encoding/json"
	"fmt"

	"github.com/google/uuid"
	"golang.org/x/crypto/pbkdf2"
	"golang.org/x/crypto/scrypt"

	"github.com/status-im/status-go/eth-node/crypto"
	"github.com/status-im/status-go/eth-node/types"
	"github.com/status-im/status-go/extkeys"
)

const (
	keyHeaderKDF = "scrypt"
)

type EncryptedKeyJSONV3 struct {
	Address         string     `json:"address"`
	Crypto          CryptoJSON `json:"crypto"`
	Id              string     `json:"id"`
	Version         int        `json:"version"`
	ExtendedKey     CryptoJSON `json:"extendedkey"`
	SubAccountIndex uint32     `json:"subaccountindex"`
}

type encryptedKeyJSONV1 struct {
	Address string     `json:"address"`
	Crypto  CryptoJSON `json:"crypto"`
	Id      string     `json:"id"`
	Version string     `json:"version"`
}

type CryptoJSON struct {
	Cipher       string                 `json:"cipher"`
	CipherText   string                 `json:"ciphertext"`
	CipherParams cipherparamsJSON       `json:"cipherparams"`
	KDF          string                 `json:"kdf"`
	KDFParams    map[string]interface{} `json:"kdfparams"`
	MAC          string                 `json:"mac"`
}

type cipherparamsJSON struct {
	IV string `json:"iv"`
}

// DecryptKey decrypts a key from a json blob, returning the private key itself.
func DecryptKey(keyjson []byte, auth string) (*types.Key, error) {
	// Parse the json into a simple map to fetch the key version
	m := make(map[string]interface{})
	if err := json.Unmarshal(keyjson, &m); err != nil {
		return nil, err
	}
	// Depending on the version try to parse one way or another
	var (
		keyBytes, keyId []byte
		err             error
		extKeyBytes     []byte
		extKey          *extkeys.ExtendedKey
	)

	subAccountIndex, ok := m["subaccountindex"].(float64)
	if !ok {
		subAccountIndex = 0
	}

	if version, ok := m["version"].(string); ok && version == "1" {
		k := new(encryptedKeyJSONV1)
		if err := json.Unmarshal(keyjson, k); err != nil {
			return nil, err
		}
		keyBytes, keyId, err = decryptKeyV1(k, auth)
		if err != nil {
			return nil, err
		}

		extKey, err = extkeys.NewKeyFromString(extkeys.EmptyExtendedKeyString)
	} else {
		k := new(EncryptedKeyJSONV3)
		if err := json.Unmarshal(keyjson, k); err != nil {
			return nil, err
		}
		keyBytes, keyId, err = decryptKeyV3(k, auth)
		if err != nil {
			return nil, err
		}

		extKeyBytes, err = decryptExtendedKey(k, auth)
		if err != nil {
			return nil, err
		}
		extKey, err = extkeys.NewKeyFromString(string(extKeyBytes))
	}
	// Handle any decryption errors and return the key
	if err != nil {
		return nil, err
	}
	key := crypto.ToECDSAUnsafe(keyBytes)

	id, err := uuid.FromBytes(keyId)
	if err != nil {
		return nil, err
	}

	return &types.Key{
		ID:              id,
		Address:         crypto.PubkeyToAddress(key.PublicKey),
		PrivateKey:      key,
		ExtendedKey:     extKey,
		SubAccountIndex: uint32(subAccountIndex),
	}, nil
}

func DecryptDataV3(cryptoJson CryptoJSON, auth string) ([]byte, error) {
	if cryptoJson.Cipher != "aes-128-ctr" {
		return nil, fmt.Errorf("Cipher not supported: %v", cryptoJson.Cipher)
	}
	mac, err := hex.DecodeString(cryptoJson.MAC)
	if err != nil {
		return nil, err
	}

	iv, err := hex.DecodeString(cryptoJson.CipherParams.IV)
	if err != nil {
		return nil, err
	}

	cipherText, err := hex.DecodeString(cryptoJson.CipherText)
	if err != nil {
		return nil, err
	}

	derivedKey, err := getKDFKey(cryptoJson, auth)
	if err != nil {
		return nil, err
	}

	calculatedMAC := crypto.Keccak256(derivedKey[16:32], cipherText)
	if !bytes.Equal(calculatedMAC, mac) {
		return nil, ErrDecrypt
	}

	plainText, err := aesCTRXOR(derivedKey[:16], cipherText, iv)
	if err != nil {
		return nil, err
	}
	return plainText, err
}

func decryptKeyV3(keyProtected *EncryptedKeyJSONV3, auth string) (keyBytes []byte, keyId []byte, err error) {
	if keyProtected.Version != version {
		return nil, nil, fmt.Errorf("Version not supported: %v", keyProtected.Version)
	}
	id, err := uuid.Parse(keyProtected.Id)
	if err != nil {
		return nil, nil, err
	}
	keyId = id[:]
	plainText, err := DecryptDataV3(keyProtected.Crypto, auth)
	if err != nil {
		return nil, nil, err
	}
	return plainText, keyId, err
}

func decryptKeyV1(keyProtected *encryptedKeyJSONV1, auth string) (keyBytes []byte, keyId []byte, err error) {
	id, err := uuid.Parse(keyProtected.Id)
	if err != nil {
		return nil, nil, err
	}
	keyId = id[:]

	mac, err := hex.DecodeString(keyProtected.Crypto.MAC)
	if err != nil {
		return nil, nil, err
	}

	iv, err := hex.DecodeString(keyProtected.Crypto.CipherParams.IV)
	if err != nil {
		return nil, nil, err
	}

	cipherText, err := hex.DecodeString(keyProtected.Crypto.CipherText)
	if err != nil {
		return nil, nil, err
	}

	derivedKey, err := getKDFKey(keyProtected.Crypto, auth)
	if err != nil {
		return nil, nil, err
	}

	calculatedMAC := crypto.Keccak256(derivedKey[16:32], cipherText)
	if !bytes.Equal(calculatedMAC, mac) {
		return nil, nil, ErrDecrypt
	}

	plainText, err := aesCBCDecrypt(crypto.Keccak256(derivedKey[:16])[:16], cipherText, iv)
	if err != nil {
		return nil, nil, err
	}
	return plainText, keyId, err
}

func decryptExtendedKey(keyProtected *EncryptedKeyJSONV3, auth string) (plainText []byte, err error) {
	if len(keyProtected.ExtendedKey.CipherText) == 0 {
		return []byte(extkeys.EmptyExtendedKeyString), nil
	}

	if keyProtected.Version != version {
		return nil, fmt.Errorf("Version not supported: %v", keyProtected.Version)
	}

	if keyProtected.ExtendedKey.Cipher != "aes-128-ctr" {
		return nil, fmt.Errorf("Cipher not supported: %v", keyProtected.ExtendedKey.Cipher)
	}

	mac, err := hex.DecodeString(keyProtected.ExtendedKey.MAC)
	if err != nil {
		return nil, err
	}

	iv, err := hex.DecodeString(keyProtected.ExtendedKey.CipherParams.IV)
	if err != nil {
		return nil, err
	}

	cipherText, err := hex.DecodeString(keyProtected.ExtendedKey.CipherText)
	if err != nil {
		return nil, err
	}

	derivedKey, err := getKDFKey(keyProtected.ExtendedKey, auth)
	if err != nil {
		return nil, err
	}

	calculatedMAC := crypto.Keccak256(derivedKey[16:32], cipherText)
	if !bytes.Equal(calculatedMAC, mac) {
		return nil, ErrDecrypt
	}

	plainText, err = aesCTRXOR(derivedKey[:16], cipherText, iv)
	if err != nil {
		return nil, err
	}
	return plainText, err
}

func getKDFKey(cryptoJSON CryptoJSON, auth string) ([]byte, error) {
	authArray := []byte(auth)
	salt, err := hex.DecodeString(cryptoJSON.KDFParams["salt"].(string))
	if err != nil {
		return nil, err
	}
	dkLen := ensureInt(cryptoJSON.KDFParams["dklen"])

	if cryptoJSON.KDF == keyHeaderKDF {
		n := ensureInt(cryptoJSON.KDFParams["n"])
		r := ensureInt(cryptoJSON.KDFParams["r"])
		p := ensureInt(cryptoJSON.KDFParams["p"])
		return scrypt.Key(authArray, salt, n, r, p, dkLen)

	} else if cryptoJSON.KDF == "pbkdf2" {
		c := ensureInt(cryptoJSON.KDFParams["c"])
		prf := cryptoJSON.KDFParams["prf"].(string)
		if prf != "hmac-sha256" {
			return nil, fmt.Errorf("Unsupported PBKDF2 PRF: %s", prf)
		}
		key := pbkdf2.Key(authArray, salt, c, dkLen, sha256.New)
		return key, nil
	}

	return nil, fmt.Errorf("Unsupported KDF: %s", cryptoJSON.KDF)
}

// TODO: can we do without this when unmarshalling dynamic JSON?
// why do integers in KDF params end up as float64 and not int after
// unmarshal?
func ensureInt(x interface{}) int {
	res, ok := x.(int)
	if !ok {
		res = int(x.(float64))
	}
	return res
}

func aesCTRXOR(key, inText, iv []byte) ([]byte, error) {
	// AES-128 is selected due to size of encryptKey.
	aesBlock, err := aes.NewCipher(key)
	if err != nil {
		return nil, err
	}
	stream := cipher.NewCTR(aesBlock, iv)
	outText := make([]byte, len(inText))
	stream.XORKeyStream(outText, inText)
	return outText, err
}

func aesCBCDecrypt(key, cipherText, iv []byte) ([]byte, error) {
	aesBlock, err := aes.NewCipher(key)
	if err != nil {
		return nil, err
	}
	decrypter := cipher.NewCBCDecrypter(aesBlock, iv)
	paddedPlaintext := make([]byte, len(cipherText))
	decrypter.CryptBlocks(paddedPlaintext, cipherText)
	plaintext := pkcs7Unpad(paddedPlaintext)
	if plaintext == nil {
		return nil, ErrDecrypt
	}
	return plaintext, err
}

// From https://leanpub.com/gocrypto/read#leanpub-auto-block-cipher-modes
func pkcs7Unpad(in []byte) []byte {
	if len(in) == 0 {
		return nil
	}

	padding := in[len(in)-1]
	if int(padding) > len(in) || padding > aes.BlockSize {
		return nil
	} else if padding == 0 {
		return nil
	}

	for i := len(in) - 1; i > len(in)-int(padding)-1; i-- {
		if in[i] != padding {
			return nil
		}
	}
	return in[:len(in)-int(padding)]
}

func RawKeyToCryptoJSON(rawKeyFile []byte) (cj CryptoJSON, e error) {
	var keyJSON EncryptedKeyJSONV3
	if e := json.Unmarshal(rawKeyFile, &keyJSON); e != nil {
		return cj, fmt.Errorf("failed to read key file: %s", e)
	}

	return keyJSON.Crypto, e
}