path: root/accounts/presale.go

// Copyright 2016 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/>.

package accounts

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

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

// creates a Key and stores that in the given KeyStore by decrypting a presale key JSON
func importPreSaleKey(keyStore keyStore, keyJSON []byte, password string) (Account, *Key, error) {
    key, err := decryptPreSaleKey(keyJSON, password)
    if err != nil {
        return Account{}, nil, err
    }
    key.Id = uuid.NewRandom()
    a := Account{Address: key.Address, File: keyStore.JoinPath(keyFileName(key.Address))}
    err = keyStore.StoreKey(a.File, key, password)
    return a, key, err
}

func decryptPreSaleKey(fileContent []byte, password string) (key *Key, err error) {
    preSaleKeyStruct := struct {
        EncSeed string
        EthAddr string
        Email   string
        BtcAddr string
    }{}
    err = json.Unmarshal(fileContent, &preSaleKeyStruct)
    if err != nil {
        return nil, err
    }
    encSeedBytes, err := hex.DecodeString(preSaleKeyStruct.EncSeed)
    if err != nil {
        return nil, errors.New("invalid hex in encSeed")
    }
    iv := encSeedBytes[:16]
    cipherText := encSeedBytes[16:]
    /*
        See https://github.com/ethereum/pyethsaletool

        pyethsaletool generates the encryption key from password by
        2000 rounds of PBKDF2 with HMAC-SHA-256 using password as salt (:().
        16 byte key length within PBKDF2 and resulting key is used as AES key
    */
    passBytes := []byte(password)
    derivedKey := pbkdf2.Key(passBytes, passBytes, 2000, 16, sha256.New)
    plainText, err := aesCBCDecrypt(derivedKey, cipherText, iv)
    if err != nil {
        return nil, err
    }
    ethPriv := crypto.Keccak256(plainText)
    ecKey := crypto.ToECDSA(ethPriv)
    key = &Key{
        Id:         nil,
        Address:    crypto.PubkeyToAddress(ecKey.PublicKey),
        PrivateKey: ecKey,
    }
    derivedAddr := hex.EncodeToString(key.Address.Bytes()) // needed because .Hex() gives leading "0x"
    expectedAddr := preSaleKeyStruct.EthAddr
    if derivedAddr != expectedAddr {
        err = fmt.Errorf("decrypted addr '%s' not equal to expected addr '%s'", derivedAddr, expectedAddr)
    }
    return key, err
}

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)]
}