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/*
* keys.go - Functions and readers for getting passphrases and raw keys via
* the command line. Includes ability to hide the entered passphrase, or use a
* raw key as input.
*
* Copyright 2017 Google Inc.
* Author: Joe Richey (joerichey@google.com)
*
* Licensed under the Apache License, Version 2.0 (the "License"); you may not
* use this file except in compliance with the License. You may obtain a copy of
* the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
* WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
* License for the specific language governing permissions and limitations under
* the License.
*/
package main
import (
"fmt"
"io"
"log"
"os"
"github.com/pkg/errors"
"golang.org/x/crypto/ssh/terminal"
"github.com/google/fscrypt/actions"
"github.com/google/fscrypt/cmd"
"github.com/google/fscrypt/crypto"
"github.com/google/fscrypt/metadata"
"github.com/google/fscrypt/pam"
"github.com/google/fscrypt/util"
)
// The file descriptor for standard input
const stdinFd = 0
// actions.KeyFuncs for getting or creating cryptographic keys
var (
// getting an existing key
existingKeyFn = makeKeyFunc(true, false, "")
// getting an existing key when changing passphrases
oldExistingKeyFn = makeKeyFunc(true, false, "old ")
// creating a new key
createKeyFn = makeKeyFunc(false, true, "")
// creating a new key when changing passphrases
newCreateKeyFn = makeKeyFunc(false, true, "new ")
)
// passphraseReader is an io.Reader intended for terminal passphrase input. The
// struct is empty as the reader needs to maintain no internal state.
type passphraseReader struct{}
// Read gets input from the terminal until a newline is encountered. This read
// should be called with the maximum buffer size for the passphrase.
func (p passphraseReader) Read(buf []byte) (int, error) {
// We read one byte at a time to handle backspaces
position := 0
for {
if position == len(buf) {
return position, ErrMaxPassphrase
}
if _, err := io.ReadFull(os.Stdin, buf[position:position+1]); err != nil {
return position, err
}
switch buf[position] {
case '\r', '\n':
return position, io.EOF
case 3, 4:
return position, cmd.ErrCanceled
case 8, 127:
if position > 0 {
position--
}
default:
position++
}
}
}
// getPassphraseKey puts the terminal into raw mode for the entry of the user's
// passphrase into a key. If we are not reading from a terminal, just read into
// the passphrase into the key normally.
func getPassphraseKey(prompt string) (*crypto.Key, error) {
fmt.Fprint(cmd.Output, prompt)
// Only disable echo if stdin is actually a terminal.
if terminal.IsTerminal(stdinFd) {
state, err := terminal.MakeRaw(stdinFd)
if err != nil {
return nil, err
}
defer func() {
terminal.Restore(stdinFd, state)
fmt.Println() // To align input
}()
}
return crypto.NewKeyFromReader(passphraseReader{})
}
// makeKeyFunc creates an actions.KeyFunc. This function customizes the KeyFunc
// to whether or not it supports retrying, whether it confirms the passphrase,
// and custom prefix for printing (if any).
func makeKeyFunc(supportRetry, shouldConfirm bool, prefix string) actions.KeyFunc {
return func(info actions.ProtectorInfo, retry bool) (*crypto.Key, error) {
log.Printf("KeyFunc(%s, %v)", formatInfo(info), retry)
if retry {
if !supportRetry {
panic("this KeyFunc does not support retrying")
}
// Don't retry for non-interactive sessions
if cmd.QuietFlag.Value {
return nil, ErrWrongKey
}
fmt.Println("Incorrect Passphrase")
}
switch info.Source() {
case metadata.SourceType_pam_passphrase:
username := util.GetUser(int(info.UID())).Username
prompt := fmt.Sprintf("Enter %s%s: ", prefix, formatInfo(info))
key, err := getPassphraseKey(prompt)
if err != nil {
return nil, err
}
// To confirm, check that the passphrase is the user's
// login passphrase.
if shouldConfirm {
err = pam.IsUserLoginToken(username, key, cmd.QuietFlag.Value)
if err != nil {
key.Wipe()
return nil, err
}
}
return key, nil
case metadata.SourceType_custom_passphrase:
prompt := fmt.Sprintf("Enter %s%s: ", prefix, formatInfo(info))
key, err := getPassphraseKey(prompt)
if err != nil {
return nil, err
}
// To confirm, make sure the user types the same
// passphrase in again.
if shouldConfirm && !cmd.QuietFlag.Value {
key2, err := getPassphraseKey("Confirm passphrase: ")
if err != nil {
key.Wipe()
return nil, err
}
defer key2.Wipe()
if !key.Equals(key2) {
key.Wipe()
return nil, ErrPassphraseMismatch
}
}
return key, nil
case metadata.SourceType_raw_key:
// Only use prefixes with passphrase protectors.
if prefix != "" {
return nil, ErrNotPassphrase
}
prompt := fmt.Sprintf("Enter path to %s: ", formatInfo(info))
// Raw keys use a file containing the key data.
file, err := promptForKeyFile(prompt)
if err != nil {
return nil, err
}
defer file.Close()
fileInfo, err := file.Stat()
if err != nil {
return nil, err
}
if fileInfo.Size() != metadata.InternalKeyLen {
return nil, errors.Wrap(ErrKeyFileLength, file.Name())
}
return crypto.NewFixedLengthKeyFromReader(file, metadata.InternalKeyLen)
default:
return nil, ErrInvalidSource
}
}
}
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