path: root/accounts/key_store_passphrase.go

// Copyright 2014 The go-ethereum Authors
// This file is part of the go-ethereum library.
//
// The go-ethereum library is free software: you can redistribute it and/or modify
// it under the terms of the GNU Lesser General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// The go-ethereum library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU Lesser General Public License for more details.
//
// You should have received a copy of the GNU Lesser General Public License
// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.

/*

This key store behaves as KeyStorePlain with the difference that
the private key is encrypted and on disk uses another JSON encoding.

The crypto is documented at https://github.com/ethereum/wiki/wiki/Web3-Secret-Storage-Definition

*/

package accounts

import (
    "bytes"
    "crypto/aes"
    "crypto/sha256"
    "encoding/hex"
    "encoding/json"
    "fmt"
    "io/ioutil"
    "path/filepath"

    "github.com/ethereum/go-ethereum/common"
    "github.com/ethereum/go-ethereum/crypto"
    "github.com/ethereum/go-ethereum/crypto/randentropy"
    "github.com/pborman/uuid"
    "golang.org/x/crypto/pbkdf2"
    "golang.org/x/crypto/scrypt"
)

const (
    keyHeaderKDF = "scrypt"

    // n,r,p = 2^18, 8, 1 uses 256MB memory and approx 1s CPU time on a modern CPU.
    StandardScryptN = 1 << 18
    StandardScryptP = 1

    // n,r,p = 2^12, 8, 6 uses 4MB memory and approx 100ms CPU time on a modern CPU.
    LightScryptN = 1 << 12
    LightScryptP = 6

    scryptR     = 8
    scryptDKLen = 32
)

type keyStorePassphrase struct {
    keysDirPath string
    scryptN     int
    scryptP     int
}

func (ks keyStorePassphrase) GetKey(addr common.Address, filename, auth string) (*Key, error) {
    // Load the key from the keystore and decrypt its contents
    keyjson, err := ioutil.ReadFile(filename)
    if err != nil {
        return nil, err
    }
    key, err := DecryptKey(keyjson, auth)
    if err != nil {
        return nil, err
    }
    // Make sure we're really operating on the requested key (no swap attacks)
    if key.Address != addr {
        return nil, fmt.Errorf("key content mismatch: have account %x, want %x", key.Address, addr)
    }
    return key, nil
}

func (ks keyStorePassphrase) StoreKey(filename string, key *Key, auth string) error {
    keyjson, err := EncryptKey(key, auth, ks.scryptN, ks.scryptP)
    if err != nil {
        return err
    }
    return writeKeyFile(filename, keyjson)
}

func (ks keyStorePassphrase) JoinPath(filename string) string {
    if filepath.IsAbs(filename) {
        return filename
    } else {
        return filepath.Join(ks.keysDirPath, filename)
    }
}

// EncryptKey encrypts a key using the specified scrypt parameters into a json
// blob that can be decrypted later on.
func EncryptKey(key *Key, auth string, scryptN, scryptP int) ([]byte, error) {
    authArray := []byte(auth)
    salt := randentropy.GetEntropyCSPRNG(32)
    derivedKey, err := scrypt.Key(authArray, salt, scryptN, scryptR, scryptP, scryptDKLen)
    if err != nil {
        return nil, err
    }
    encryptKey := derivedKey[:16]
    keyBytes := crypto.FromECDSA(key.PrivateKey)

    iv := randentropy.GetEntropyCSPRNG(aes.BlockSize) // 16
    cipherText, err := aesCTRXOR(encryptKey, keyBytes, iv)
    if err != nil {
        return nil, err
    }
    mac := crypto.Keccak256(derivedKey[16:32], cipherText)

    scryptParamsJSON := make(map[string]interface{}, 5)
    scryptParamsJSON["n"] = scryptN
    scryptParamsJSON["r"] = scryptR
    scryptParamsJSON["p"] = scryptP
    scryptParamsJSON["dklen"] = scryptDKLen
    scryptParamsJSON["salt"] = hex.EncodeToString(salt)

    cipherParamsJSON := cipherparamsJSON{
        IV: hex.EncodeToString(iv),
    }

    cryptoStruct := cryptoJSON{
        Cipher:       "aes-128-ctr",
        CipherText:   hex.EncodeToString(cipherText),
        CipherParams: cipherParamsJSON,
        KDF:          "scrypt",
        KDFParams:    scryptParamsJSON,
        MAC:          hex.EncodeToString(mac),
    }
    encryptedKeyJSONV3 := encryptedKeyJSONV3{
        hex.EncodeToString(key.Address[:]),
        cryptoStruct,
        key.Id.String(),
        version,
    }
    return json.Marshal(encryptedKeyJSONV3)
}

// DecryptKey decrypts a key from a json blob, returning the private key itself.
func DecryptKey(keyjson []byte, auth string) (*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
    )
    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)
    } else {
        k := new(encryptedKeyJSONV3)
        if err := json.Unmarshal(keyjson, k); err != nil {
            return nil, err
        }
        keyBytes, keyId, err = decryptKeyV3(k, auth)
    }
    // Handle any decryption errors and return the key
    if err != nil {
        return nil, err
    }
    key := crypto.ToECDSA(keyBytes)
    return &Key{
        Id:         uuid.UUID(keyId),
        Address:    crypto.PubkeyToAddress(key.PublicKey),
        PrivateKey: key,
    }, nil
}

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)
    }

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

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

func decryptKeyV1(keyProtected *encryptedKeyJSONV1, auth string) (keyBytes []byte, keyId []byte, err error) {
    keyId = uuid.Parse(keyProtected.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 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 == "scrypt" {
        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
}