armor.go

package crypto

import (
	"encoding/hex"
	"fmt"

	"github.com/pkg/errors"

	"github.com/tendermint/crypto/bcrypt"
	"github.com/tendermint/tendermint/crypto"
	"github.com/tendermint/tendermint/crypto/armor"
	"github.com/tendermint/tendermint/crypto/xsalsa20symmetric"

	"github.com/gridironzone/service-sdk-go/codec/legacy"
	cryptoAmino "github.com/gridironzone/service-sdk-go/crypto/codec"
	cryptotypes "github.com/gridironzone/service-sdk-go/crypto/types"
)

const (
	blockTypePrivKey = "TENDERMINT PRIVATE KEY"
	blockTypeKeyInfo = "TENDERMINT KEY INFO"
	blockTypePubKey  = "TENDERMINT PUBLIC KEY"

	defaultAlgo = "secp256k1"

	headerVersion = "version"
	headerType    = "type"
)

// BcryptSecurityParameter is security parameter var, and it can be changed within the lcd test.
// Making the bcrypt security parameter a var shouldn't be a security issue:
// One can't verify an invalid key by maliciously changing the bcrypt
// parameter during a runtime vulnerability. The main security
// threat this then exposes would be something that changes this during
// runtime before the user creates their key. This vulnerability must
// succeed to update this to that same value before every subsequent call
// to the keys command in future startups / or the attacker must get access
// to the filesystem. However, with a similar threat model (changing
// variables in runtime), one can cause the user to sign a different tx
// than what they see, which is a significantly cheaper attack then breaking
// a bcrypt hash. (Recall that the nonce still exists to break rainbow tables)
// For further notes on security parameter choice, see README.md
var BcryptSecurityParameter = 12

//-----------------------------------------------------------------
// add armor

// Armor the InfoBytes
func ArmorInfoBytes(bz []byte) string {
	header := map[string]string{
		headerType:    "Info",
		headerVersion: "0.0.0",
	}

	return armor.EncodeArmor(blockTypeKeyInfo, header, bz)
}

// Armor the PubKeyBytes
func ArmorPubKeyBytes(bz []byte, algo string) string {
	header := map[string]string{
		headerVersion: "0.0.1",
	}
	if algo != "" {
		header[headerType] = algo
	}

	return armor.EncodeArmor(blockTypePubKey, header, bz)
}

//-----------------------------------------------------------------
// remove armor

// Unarmor the InfoBytes
func UnarmorInfoBytes(armorStr string) ([]byte, error) {
	bz, header, err := unarmorBytes(armorStr, blockTypeKeyInfo)
	if err != nil {
		return nil, err
	}

	if header[headerVersion] != "0.0.0" {
		return nil, fmt.Errorf("unrecognized version: %v", header[headerVersion])
	}

	return bz, nil
}

// UnarmorPubKeyBytes returns the pubkey byte slice, a string of the algo type, and an error
func UnarmorPubKeyBytes(armorStr string) (bz []byte, algo string, err error) {
	bz, header, err := unarmorBytes(armorStr, blockTypePubKey)
	if err != nil {
		return nil, "", fmt.Errorf("couldn't unarmor bytes: %v", err)
	}

	switch header[headerVersion] {
	case "0.0.0":
		return bz, defaultAlgo, err
	case "0.0.1":
		if header[headerType] == "" {
			header[headerType] = defaultAlgo
		}

		return bz, header[headerType], err
	case "":
		return nil, "", fmt.Errorf("header's version field is empty")
	default:
		err = fmt.Errorf("unrecognized version: %v", header[headerVersion])
		return nil, "", err
	}
}

func unarmorBytes(armorStr, blockType string) (bz []byte, header map[string]string, err error) {
	bType, header, bz, err := armor.DecodeArmor(armorStr)
	if err != nil {
		return
	}

	if bType != blockType {
		err = fmt.Errorf("unrecognized armor type %q, expected: %q", bType, blockType)
		return
	}

	return
}

//-----------------------------------------------------------------
// encrypt/decrypt with armor

// Encrypt and armor the private key.
func EncryptArmorPrivKey(privKey cryptotypes.PrivKey, passphrase string, algo string) string {
	saltBytes, encBytes := encryptPrivKey(privKey, passphrase)
	header := map[string]string{
		"kdf":  "bcrypt",
		"salt": fmt.Sprintf("%X", saltBytes),
	}

	if algo != "" {
		header[headerType] = algo
	}

	armorStr := armor.EncodeArmor(blockTypePrivKey, header, encBytes)

	return armorStr
}

// encrypt the given privKey with the passphrase using a randomly
// generated salt and the xsalsa20 cipher. returns the salt and the
// encrypted priv key.
func encryptPrivKey(privKey cryptotypes.PrivKey, passphrase string) (saltBytes []byte, encBytes []byte) {
	saltBytes = crypto.CRandBytes(16)
	key, err := bcrypt.GenerateFromPassword(saltBytes, []byte(passphrase), BcryptSecurityParameter)

	if err != nil {
		panic(errors.Wrap(err, "error generating bcrypt key from passphrase"))
	}

	key = crypto.Sha256(key) // get 32 bytes
	privKeyBytes := legacy.Cdc.Amino.MustMarshalBinaryBare(privKey)

	return saltBytes, xsalsa20symmetric.EncryptSymmetric(privKeyBytes, key)
}

// UnarmorDecryptPrivKey returns the privkey byte slice, a string of the algo type, and an error
func UnarmorDecryptPrivKey(armorStr string, passphrase string) (privKey cryptotypes.PrivKey, algo string, err error) {
	blockType, header, encBytes, err := armor.DecodeArmor(armorStr)
	if err != nil {
		return privKey, "", err
	}

	if blockType != blockTypePrivKey {
		return privKey, "", fmt.Errorf("unrecognized armor type: %v", blockType)
	}

	if header["kdf"] != "bcrypt" {
		return privKey, "", fmt.Errorf("unrecognized KDF type: %v", header["kdf"])
	}

	if header["salt"] == "" {
		return privKey, "", fmt.Errorf("missing salt bytes")
	}

	saltBytes, err := hex.DecodeString(header["salt"])
	if err != nil {
		return privKey, "", fmt.Errorf("error decoding salt: %v", err.Error())
	}

	privKey, err = decryptPrivKey(saltBytes, encBytes, passphrase)

	if header[headerType] == "" {
		header[headerType] = defaultAlgo
	}

	return privKey, header[headerType], err
}

func decryptPrivKey(saltBytes []byte, encBytes []byte, passphrase string) (privKey cryptotypes.PrivKey, err error) {
	key, err := bcrypt.GenerateFromPassword(saltBytes, []byte(passphrase), BcryptSecurityParameter)
	if err != nil {
		return privKey, errors.Wrap(err, "error generating bcrypt key from passphrase")
	}

	key = crypto.Sha256(key) // Get 32 bytes

	privKeyBytes, err := xsalsa20symmetric.DecryptSymmetric(encBytes, key)
	if err != nil && err.Error() == "Ciphertext decryption failed" {
		return privKey, errors.New("wrong password")
	} else if err != nil {
		return privKey, err
	}

	return cryptoAmino.PrivKeyFromBytes(privKeyBytes)
}