cmd/ethkey: new command line tool for keys (#15438)

ethkey is a new 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/inspect.go

@@ -0,0 +1,74 @@
+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
+	},
+}