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main.go
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main.go
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package main
import (
"bufio"
"bytes"
"crypto/ecdsa"
"crypto/rsa"
"crypto/x509"
"errors"
"flag"
"fmt"
"log"
"os"
"os/user"
"path"
"slices"
"strings"
"syscall"
"github.com/foxboron/ssh-tpm-agent/key"
"github.com/foxboron/ssh-tpm-agent/utils"
"github.com/google/go-tpm/tpm2"
"golang.org/x/crypto/ssh"
"golang.org/x/exp/slog"
"golang.org/x/term"
)
var Version string
const usage = `Usage:
ssh-tpm-keygen
Options:
-o, --owner-password Ask for the owner password.
-C Provide a comment with the key.
-f Output keyfile.
-N PIN for the key.
-t ecdsa | rsa Specify the type of key to create. Defaults to ecdsa
-b bits Number of bits in the key to create.
rsa: 2048 (default)
ecdsa: 256 (default) | 384 | 521
-I, --import PATH Import existing key into ssh-tpm-agent.
-A Generate host keys for all key types (rsa and ecdsa).
--supported List the supported keys of the TPM.
Generate new TPM sealed keys for ssh-tpm-agent.
TPM sealed keys are private keys created inside the Trusted Platform Module
(TPM) and sealed in .tpm suffixed files. They are bound to the hardware they
where produced on and can't be transferred to other machines.
Example:
$ ssh-tpm-keygen
Generating a sealed public/private ecdsa key pair.
Enter file in which to save the key (/home/user/.ssh/id_ecdsa):
Enter pin (empty for no pin):
Enter same pin again:
Your identification has been saved in /home/user/.ssh/id_ecdsa.tpm
Your public key has been saved in /home/user/.ssh/id_ecdsa.pub
The key fingerprint is:
SHA256:NCMJJ2La+q5tGcngQUQvEOJP3gPH8bMP98wJOEMV564
The key's randomart image is the color of television, tuned to a dead channel.`
func getStdin(s string, args ...any) (string, error) {
fmt.Printf(s, args...)
reader := bufio.NewReader(os.Stdin)
input, err := reader.ReadString('\n')
if err != nil {
return "", err
}
return strings.TrimSpace(input), nil
}
func getPin() []byte {
for {
fmt.Printf("Enter pin (empty for no pin): ")
pin1, err := term.ReadPassword(int(syscall.Stdin))
fmt.Println("")
if err != nil {
log.Fatal(err)
}
fmt.Printf("Confirm pin: ")
pin2, err := term.ReadPassword(int(syscall.Stdin))
fmt.Println("")
if err != nil {
log.Fatal(err)
}
if !bytes.Equal(pin1, pin2) {
fmt.Println("Passphrases do not match. Try again.")
continue
}
return pin1
}
}
func getOwnerPassword() []byte {
fmt.Printf("Enter owner password: ")
password, err := term.ReadPassword(int(syscall.Stdin))
fmt.Println("")
if err != nil {
log.Fatal(err)
}
return password
}
func main() {
flag.Usage = func() {
fmt.Println(usage)
}
var (
askOwnerPassword bool
comment, outputFile, keyPin string
keyType, importKey string
bits int
swtpmFlag, hostKeys, changePin bool
listsupported bool
)
defaultComment := func() string {
user, err := user.Current()
if err != nil {
slog.Error(err.Error())
os.Exit(1)
return ""
}
host, err := os.Hostname()
if err != nil {
slog.Error(err.Error())
os.Exit(1)
return ""
}
return user.Username + "@" + host
}()
flag.BoolVar(&askOwnerPassword, "o", false, "ask for the owner password")
flag.BoolVar(&askOwnerPassword, "owner-password", false, "ask for the owner password")
flag.StringVar(&comment, "C", defaultComment, "provide a comment, default to user@host")
flag.StringVar(&outputFile, "f", "", "output keyfile")
flag.StringVar(&keyPin, "N", "", "new pin for the key")
flag.StringVar(&keyType, "t", "ecdsa", "key to create")
flag.IntVar(&bits, "b", 0, "number of bits")
flag.StringVar(&importKey, "I", "", "import key")
flag.StringVar(&importKey, "import", "", "import key")
flag.BoolVar(&changePin, "p", false, "change pin")
flag.BoolVar(&swtpmFlag, "swtpm", false, "use swtpm instead of actual tpm")
flag.BoolVar(&hostKeys, "A", false, "generate host keys")
flag.BoolVar(&listsupported, "supported", false, "list tpm caps")
flag.Parse()
tpm, err := utils.TPM(swtpmFlag)
if err != nil {
log.Fatal(err)
}
defer tpm.Close()
if bits == 0 {
if keyType == "ecdsa" {
bits = 256
}
if keyType == "rsa" {
bits = 2048
}
}
supportedECCBitsizes := key.SupportedECCAlgorithms(tpm)
if listsupported {
fmt.Printf("ecdsa bit lengths:")
for _, alg := range key.SupportedECCAlgorithms(tpm) {
fmt.Printf(" %d", alg)
}
fmt.Println()
fmt.Println("rsa bit lengths: 2048")
os.Exit(0)
}
// Ask for owner password
var ownerPassword []byte
if askOwnerPassword {
ownerPassword = getOwnerPassword()
} else {
ownerPassword = []byte("")
}
// Generate host keys
if hostKeys {
// Mimics the `ssh-keygen -A -f ./something` behaviour
outputPath := "/etc/ssh"
if outputFile != "" {
outputPath = path.Join(outputFile, outputPath)
}
lookup := map[string]struct {
alg tpm2.TPMAlgID
bits int
}{
"rsa": {alg: tpm2.TPMAlgRSA, bits: 2048},
"ecdsa": {alg: tpm2.TPMAlgECDSA, bits: 256},
}
for n, t := range lookup {
filename := fmt.Sprintf("ssh_tpm_host_%s_key", n)
privatekeyFilename := path.Join(outputPath, filename+".tpm")
pubkeyFilename := path.Join(outputPath, filename+".pub")
if utils.FileExists(privatekeyFilename) {
continue
}
slog.Info("Generating new host key", slog.String("algorithm", strings.ToUpper(n)))
k, err := key.CreateKey(tpm, t.alg, t.bits, ownerPassword, []byte(""), defaultComment)
if err != nil {
log.Fatal(err)
}
if err := os.WriteFile(pubkeyFilename, k.AuthorizedKey(), 0o600); err != nil {
log.Fatal(err)
}
encodedkey, err := k.Encode()
if err != nil {
log.Fatal(err)
}
if err := os.WriteFile(privatekeyFilename, encodedkey, 0o600); err != nil {
log.Fatal(err)
}
slog.Info("Wrote private key", slog.String("filename", privatekeyFilename))
}
os.Exit(0)
}
var tpmkeyType tpm2.TPMAlgID
var filename string
var privatekeyFilename string
var pubkeyFilename string
switch keyType {
case "ecdsa":
tpmkeyType = tpm2.TPMAlgECC
filename = "id_ecdsa"
if !slices.Contains(supportedECCBitsizes, bits) {
log.Fatalf("invalid ecdsa key length: TPM does not support %v bits", bits)
}
case "rsa":
tpmkeyType = tpm2.TPMAlgRSA
filename = "id_rsa"
}
if outputFile != "" {
filename = outputFile
} else {
filename = path.Join(utils.SSHDir(), filename)
}
if changePin {
b, err := os.ReadFile(filename)
if err != nil {
log.Fatal(err)
}
k, err := key.DecodeKey(b)
if err != nil {
log.Fatal(err)
}
if k.Description() != "" {
fmt.Printf("Key has comment '%s'\n", k.Description())
}
if outputFile == "" {
filename, err = getStdin("Enter file in which the key is (%s): ", filename)
if err != nil {
log.Fatal(err)
}
}
fmt.Printf("Enter old pin: ")
oldPin, err := term.ReadPassword(int(syscall.Stdin))
if err != nil {
log.Fatal(err)
}
fmt.Printf("\nEnter new pin (empty for no pin): ")
newPin, err := term.ReadPassword(int(syscall.Stdin))
if err != nil {
log.Fatal(err)
}
fmt.Printf("\nEnter same pin: ")
newPin2, err := term.ReadPassword(int(syscall.Stdin))
if err != nil {
log.Fatal(err)
}
if !bytes.Equal(newPin, newPin2) {
log.Fatal("Pin do not match. Try again.")
}
fmt.Println()
newkey, err := key.ChangeAuth(tpm, ownerPassword, k, oldPin, newPin)
if err != nil {
log.Fatal("Failed changing pin on the key.")
}
encodedkey, err := newkey.Encode()
if err != nil {
log.Fatal(err)
}
if err := os.WriteFile(filename, encodedkey, 0o600); err != nil {
log.Fatal(err)
}
fmt.Println("Your identification has been saved with the new pin.")
os.Exit(0)
}
// Only used with -I/--import
var toImportKey any
if importKey != "" {
fmt.Println("Sealing an existing public/private ecdsa key pair.")
filename = importKey
pem, err := os.ReadFile(importKey)
if err != nil {
log.Fatal(err)
}
var kerr *ssh.PassphraseMissingError
var rawKey any
rawKey, err = ssh.ParseRawPrivateKey(pem)
if errors.As(err, &kerr) {
for {
fmt.Printf("Enter existing password (empty for no pin): ")
pin, err := term.ReadPassword(int(syscall.Stdin))
fmt.Println("")
if err != nil {
log.Fatal(err)
}
rawKey, err = ssh.ParseRawPrivateKeyWithPassphrase(pem, pin)
if err == nil {
break
} else if errors.Is(err, x509.IncorrectPasswordError) {
fmt.Println("Wrong password, try again.")
continue
} else {
log.Fatal(err)
}
}
}
switch key := rawKey.(type) {
case *ecdsa.PrivateKey:
toImportKey = *key
if !slices.Contains(supportedECCBitsizes, key.Params().BitSize) {
log.Fatalf("invalid ecdsa key length: TPM does not support %v bits", key.Params().BitSize)
}
case *rsa.PrivateKey:
if key.N.BitLen() != 2048 {
log.Fatal("can only support 2048 bit RSA")
}
toImportKey = *key
default:
log.Fatal("unsupported key type")
}
pubPem, err := os.ReadFile(importKey + ".pub")
if err != nil {
log.Fatalf("can't find corresponding public key: %v", err)
}
_, c, _, _, err := ssh.ParseAuthorizedKey(pubPem)
if err != nil {
log.Fatal("can't parse public key", err)
}
comment = c
} else {
fmt.Printf("Generating a sealed public/private %s key pair.\n", keyType)
filenameInput, err := getStdin("Enter file in which to save the key (%s): ", filename)
if err != nil {
log.Fatal(err)
}
if filenameInput != "" {
filename = strings.TrimSuffix(filenameInput, ".tpm")
}
}
privatekeyFilename = filename + ".tpm"
pubkeyFilename = filename + ".pub"
if utils.FileExists(privatekeyFilename) {
fmt.Printf("%s already exists.\n", privatekeyFilename)
s, err := getStdin("Overwrite (y/n)?")
if err != nil {
log.Fatal(err)
}
if s != "y" {
return
}
}
if utils.FileExists(pubkeyFilename) {
fmt.Printf("%s already exists.\n", pubkeyFilename)
s, err := getStdin("Overwrite (y/n)?")
if err != nil {
log.Fatal(err)
}
if s != "y" {
return
}
}
var pin []byte
if keyPin != "" {
pin = []byte(keyPin)
} else {
pinInput := getPin()
if bytes.Equal(pin, []byte("")) {
pin = []byte(pinInput)
}
}
var k *key.Key
if importKey != "" {
// TODO: Read public key for comment
k, err = key.ImportKey(tpm, ownerPassword, toImportKey, pin, comment)
if err != nil {
log.Fatal(err)
}
} else {
k, err = key.CreateKey(tpm, tpmkeyType, bits, ownerPassword, pin, comment)
if err != nil {
log.Fatal(err)
}
}
if importKey == "" {
if err := os.WriteFile(pubkeyFilename, k.AuthorizedKey(), 0o600); err != nil {
log.Fatal(err)
}
}
encodedkey, err := k.Encode()
if err != nil {
log.Fatal(err)
}
if err := os.WriteFile(privatekeyFilename, encodedkey, 0o600); err != nil {
log.Fatal(err)
}
fmt.Printf("Your identification has been saved in %s\n", privatekeyFilename)
if importKey == "" {
fmt.Printf("Your public key has been saved in %s\n", pubkeyFilename)
}
fmt.Printf("The key fingerprint is:\n")
fmt.Println(k.Fingerprint())
fmt.Println("The key's randomart image is the color of television, tuned to a dead channel.")
}