ethkey: Add new ethkey command line tool

It's a tool that serves as a command line interface to the basic key
management functionalities of geth.
It currently supports:
 - generating keyfiles
 - inspecting keyfiles (print public and private key)
 - signing messages
 - verifying signed messages

cmd/ethkey/README.md

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+ethkey
+======
+
+ethkey is a simple command-line tool for working with Ethereum keyfiles.
+
+
+# Usage
+
+### `ethkey generate`
+
+Generate a new keyfile.
+If you want to use an existing private key to use in the keyfile, it can be 
+specified by setting `--privatekey` with the location of the file containing the 
+private key.
+
+
+### `ethkey inspect <keyfile>`
+
+Print various information about the keyfile.
+Private key information can be printed by using the `--private` flag;
+make sure to use this feature with great caution!
+
+
+### `ethkey sign <keyfile> <message/file>`
+
+Sign the message with a keyfile.
+It is possible to refer to a file containing the message.
+
+
+### `ethkey verify <address> <signature> <message/file>`
+
+Verify the signature of the message.
+It is possible to refer to a file containing the message.
+
+
+## Passphrases
+
+For every command that uses a keyfile, you will be prompted to provide the 
+passphrase for decrypting the keyfile.  To avoid this message, it is possible
+to pass the passphrase by using the `--passphrase` flag pointing to a file that
+contains the passphrase.

cmd/ethkey/generate.go

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+package main
+
+import (
+	"crypto/ecdsa"
+	"crypto/rand"
+	"fmt"
+	"io/ioutil"
+	"os"
+	"path/filepath"
+
+	"github.com/ethereum/go-ethereum/accounts/keystore"
+	"github.com/ethereum/go-ethereum/cmd/utils"
+	"github.com/ethereum/go-ethereum/crypto"
+	"github.com/pborman/uuid"
+	"gopkg.in/urfave/cli.v1"
+)
+
+type outputGenerate struct {
+	Address      string
+	AddressEIP55 string
+}
+
+var commandGenerate = cli.Command{
+	Name:      "generate",
+	Usage:     "generate new keyfile",
+	ArgsUsage: "[ <keyfile> ]",
+	Description: `
+Generate a new keyfile.
+If you want to use an existing private key to use in the keyfile, it can be 
+specified by setting --privatekey with the location of the file containing the 
+private key.`,
+	Flags: []cli.Flag{
+		passphraseFlag,
+		jsonFlag,
+		cli.StringFlag{
+			Name: "privatekey",
+			Usage: "the file from where to read the private key to " +
+				"generate a keyfile for",
+		},
+	},
+	Action: func(ctx *cli.Context) error {
+		// Check if keyfile path given and make sure it doesn't already exist.
+		keyfilepath := ctx.Args().First()
+		if keyfilepath == "" {
+			keyfilepath = defaultKeyfileName
+		}
+		if _, err := os.Stat(keyfilepath); err == nil {
+			utils.Fatalf("Keyfile already exists at %s.", keyfilepath)
+		} else if !os.IsNotExist(err) {
+			utils.Fatalf("Error checking if keyfile exists: %v", err)
+		}
+
+		var privateKey *ecdsa.PrivateKey
+
+		// First check if a private key file is provided.
+		privateKeyFile := ctx.String("privatekey")
+		if privateKeyFile != "" {
+			privateKeyBytes, err := ioutil.ReadFile(privateKeyFile)
+			if err != nil {
+				utils.Fatalf("Failed to read the private key file '%s': %v",
+					privateKeyFile, err)
+			}
+
+			pk, err := crypto.HexToECDSA(string(privateKeyBytes))
+			if err != nil {
+				utils.Fatalf(
+					"Could not construct ECDSA private key from file content: %v",
+					err)
+			}
+			privateKey = pk
+		}
+
+		// If not loaded, generate random.
+		if privateKey == nil {
+			pk, err := ecdsa.GenerateKey(crypto.S256(), rand.Reader)
+			if err != nil {
+				utils.Fatalf("Failed to generate random private key: %v", err)
+			}
+			privateKey = pk
+		}
+
+		// Create the keyfile object with a random UUID.
+		id := uuid.NewRandom()
+		key := &keystore.Key{
+			Id:         id,
+			Address:    crypto.PubkeyToAddress(privateKey.PublicKey),
+			PrivateKey: privateKey,
+		}
+
+		// Encrypt key with passphrase.
+		passphrase := getPassPhrase(ctx, true)
+		keyjson, err := keystore.EncryptKey(key, passphrase,
+			keystore.StandardScryptN, keystore.StandardScryptP)
+		if err != nil {
+			utils.Fatalf("Error encrypting key: %v", err)
+		}
+
+		// Store the file to disk.
+		if err := os.MkdirAll(filepath.Dir(keyfilepath), 0700); err != nil {
+			utils.Fatalf("Could not create directory %s", filepath.Dir(keyfilepath))
+		}
+		if err := ioutil.WriteFile(keyfilepath, keyjson, 0600); err != nil {
+			utils.Fatalf("Failed to write keyfile to %s: %v", keyfilepath, err)
+		}
+
+		// Output some information.
+		out := outputGenerate{
+			Address: key.Address.Hex(),
+		}
+		if ctx.Bool(jsonFlag.Name) {
+			mustPrintJSON(out)
+		} else {
+			fmt.Println("Address:       ", out.Address)
+		}
+		return nil
+	},
+}

cmd/ethkey/inspect.go

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+package main
+
+import (
+	"encoding/hex"
+	"fmt"
+	"io/ioutil"
+
+	"github.com/ethereum/go-ethereum/accounts/keystore"
+	"github.com/ethereum/go-ethereum/cmd/utils"
+	"github.com/ethereum/go-ethereum/crypto"
+	"gopkg.in/urfave/cli.v1"
+)
+
+type outputInspect struct {
+	Address    string
+	PublicKey  string
+	PrivateKey string
+}
+
+var commandInspect = cli.Command{
+	Name:      "inspect",
+	Usage:     "inspect a keyfile",
+	ArgsUsage: "<keyfile>",
+	Description: `
+Print various information about the keyfile.
+Private key information can be printed by using the --private flag;
+make sure to use this feature with great caution!`,
+	Flags: []cli.Flag{
+		passphraseFlag,
+		jsonFlag,
+		cli.BoolFlag{
+			Name:  "private",
+			Usage: "include the private key in the output",
+		},
+	},
+	Action: func(ctx *cli.Context) error {
+		keyfilepath := ctx.Args().First()
+
+		// Read key from file.
+		keyjson, err := ioutil.ReadFile(keyfilepath)
+		if err != nil {
+			utils.Fatalf("Failed to read the keyfile at '%s': %v", keyfilepath, err)
+		}
+
+		// Decrypt key with passphrase.
+		passphrase := getPassPhrase(ctx, false)
+		key, err := keystore.DecryptKey(keyjson, passphrase)
+		if err != nil {
+			utils.Fatalf("Error decrypting key: %v", err)
+		}
+
+		// Output all relevant information we can retrieve.
+		showPrivate := ctx.Bool("private")
+		out := outputInspect{
+			Address: key.Address.Hex(),
+			PublicKey: hex.EncodeToString(
+				crypto.FromECDSAPub(&key.PrivateKey.PublicKey)),
+		}
+		if showPrivate {
+			out.PrivateKey = hex.EncodeToString(crypto.FromECDSA(key.PrivateKey))
+		}
+
+		if ctx.Bool(jsonFlag.Name) {
+			mustPrintJSON(out)
+		} else {
+			fmt.Println("Address:       ", out.Address)
+			fmt.Println("Public key:    ", out.PublicKey)
+			if showPrivate {
+				fmt.Println("Private key:   ", out.PrivateKey)
+			}
+		}
+		return nil
+	},
+}

cmd/ethkey/main.go

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+// Copyright 2017 The go-ethereum Authors
+// This file is part of go-ethereum.
+//
+// go-ethereum is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// go-ethereum 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 General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with go-ethereum. If not, see <http://www.gnu.org/licenses/>.
+
+package main
+
+import (
+	"fmt"
+	"os"
+
+	"github.com/ethereum/go-ethereum/cmd/utils"
+	"gopkg.in/urfave/cli.v1"
+)
+
+const (
+	defaultKeyfileName = "keyfile.json"
+)
+
+var (
+	gitCommit = "" // Git SHA1 commit hash of the release (set via linker flags)
+
+	app *cli.App // the main app instance
+)
+
+var ( // Commonly used command line flags.
+	passphraseFlag = cli.StringFlag{
+		Name:  "passwordfile",
+		Usage: "the file that contains the passphrase for the keyfile",
+	}
+
+	jsonFlag = cli.BoolFlag{
+		Name:  "json",
+		Usage: "output JSON instead of human-readable format",
+	}
+
+	messageFlag = cli.StringFlag{
+		Name:  "message",
+		Usage: "the file that contains the message to sign/verify",
+	}
+)
+
+// Configure the app instance.
+func init() {
+	app = utils.NewApp(gitCommit, "an Ethereum key manager")
+	app.Commands = []cli.Command{
+		commandGenerate,
+		commandInspect,
+		commandSignMessage,
+		commandVerifyMessage,
+	}
+}
+
+func main() {
+	if err := app.Run(os.Args); err != nil {
+		fmt.Fprintln(os.Stderr, err)
+		os.Exit(1)
+	}
+}