cmd/fscrypt: setup, encrypt, unlock commands

This commit adds in the framework for adding commands and subcommands to
the fscrypt tool. This commit adds in the "setup", "encrypt", and
"unlock" commands. Additional information can be found by running:
    fscrypt <command> --help.

This commit defines how flags are parsed and errors are handled. It also
creates an extensible framework for prompting the user for information.

Change-Id: I159d7f44ee2b2bbc5e072f0802850e082d9a13ce

1 files changed, 198 insertions, 0 deletions

diff --git a/cmd/fscrypt/keys.go b/cmd/fscrypt/keys.go
new file mode 100644
index 0000000..45dc294
--- /dev/null
+++ b/cmd/fscrypt/keys.go
@@ -0,0 +1,198 @@
+/*
+ * 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"
+
+	"fscrypt/actions"
+	"fscrypt/crypto"
+	"fscrypt/metadata"
+	"fscrypt/pam"
+)
+
+// 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, "")
+	// creating a new key
+	createKeyFn = makeKeyFunc(false, true, "")
+)
+
+// 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, 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) {
+	if !quietFlag.Value {
+		fmt.Printf(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 quietFlag.Value {
+				return nil, ErrWrongKey
+			}
+			fmt.Println("Incorrect Passphrase")
+		}
+
+		switch info.Source() {
+		case metadata.SourceType_pam_passphrase:
+			prompt := fmt.Sprintf("Enter %slogin passphrase for %s: ",
+				prefix, getUsername(info.UID()))
+			key, err := getPassphraseKey(prompt)
+			if err != nil {
+				return nil, err
+			}
+
+			// To confirm, check that the passphrase is the user's
+			// login passphrase.
+			if shouldConfirm {
+				username := getUsername(info.UID())
+				ok, err := pam.IsUserLoginToken(username, key)
+				if err != nil {
+					key.Wipe()
+					return nil, err
+				}
+				if !ok {
+					key.Wipe()
+					return nil, ErrPAMPassphrase
+				}
+			}
+			return key, nil
+
+		case metadata.SourceType_custom_passphrase:
+			prompt := fmt.Sprintf("Enter %scustom passphrase for protector %q: ",
+				prefix, info.Name())
+			key, err := getPassphraseKey(prompt)
+			if err != nil {
+				return nil, err
+			}
+
+			// To confirm, make sure the user types the same
+			// passphrase in again.
+			if shouldConfirm && !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 key file for protector %q: ", info.Name())
+			// 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
+		}
+	}
+}