Initial vault: single-binary post-quantum file vault

Strip Fury back to its vault functionality in one `vault` command:
genkey, init, add (file or directory, optional folder inside the vault),
list, get, mv and rm.

The hybrid FrodoKEM-640 + ML-KEM-768 encryption core is kept under
internal/pqcrypt. Signing, policies, profiles, backups, SSH remotes,
FIDO2, agents, provenance and compression are removed.

internal/term/term.go

@@ -0,0 +1,89 @@
+package term
+
+import (
+	"fmt"
+	"os"
+	"runtime"
+
+	"golang.org/x/term"
+)
+
+// enableVirtualTerminalProcessing tries to enable virtual terminal processing
+// on Windows. If it fails, avoid using escape sequences to prevent weird
+// characters being printed to the console.
+var enableVirtualTerminalProcessing func(out *os.File) error
+
+// clearLine clears the current line on the terminal, or opens a new line if
+// terminal escape codes don't work.
+func clearLine(out *os.File) {
+	const (
+		CUI = "\033["   // Control Sequence Introducer
+		CPL = CUI + "F" // Cursor Previous Line
+		EL  = CUI + "K" // Erase in Line
+	)
+
+	// First, open a new line, which is guaranteed to work everywhere. Then, try
+	// to erase the line above with escape codes, if possible.
+	//
+	// (We use CRLF instead of LF to work around an apparent bug in WSL2's
+	// handling of CONOUT$. Only when running a Windows binary from WSL2, the
+	// cursor would not go back to the start of the line with a simple LF.
+	// Honestly, it's impressive CONIN$ and CONOUT$ work at all inside WSL2.)
+	fmt.Fprintf(out, "\r\n")
+	if enableVirtualTerminalProcessing == nil || enableVirtualTerminalProcessing(out) == nil {
+		fmt.Fprintf(out, CPL+EL)
+	}
+}
+
+// WithTerminal runs f with the terminal input and output files, if available.
+// WithTerminal does not open a non-terminal stdin, so the caller does not need
+// to check if stdin is in use.
+func WithTerminal(f func(in, out *os.File) error) error {
+	if runtime.GOOS == "windows" {
+		in, err := os.OpenFile("CONIN$", os.O_RDWR, 0)
+		if err != nil {
+			return err
+		}
+		defer in.Close()
+		out, err := os.OpenFile("CONOUT$", os.O_WRONLY, 0)
+		if err != nil {
+			return err
+		}
+		defer out.Close()
+		return f(in, out)
+	} else if tty, err := os.OpenFile("/dev/tty", os.O_RDWR, 0); err == nil {
+		defer tty.Close()
+		return f(tty, tty)
+	} else if term.IsTerminal(int(os.Stdin.Fd())) {
+		return f(os.Stdin, os.Stdin)
+	} else {
+		return fmt.Errorf("standard input is not a terminal, and /dev/tty is not available: %v", err)
+	}
+}
+
+// ReadSecret reads a value from the terminal with no echo. The prompt is ephemeral.
+func ReadSecret(prompt string) (s []byte, err error) {
+	err = WithTerminal(func(in, out *os.File) error {
+		fmt.Fprintf(out, "%s ", prompt)
+		defer clearLine(out)
+		s, err = term.ReadPassword(int(in.Fd()))
+		return err
+	})
+	return
+}
+
+// ReadPassphrase returns the passphrase from the environment variable env if
+// it is set, otherwise prompts on the terminal.
+func ReadPassphrase(prompt, env string) (string, error) {
+	if p, ok := os.LookupEnv(env); ok {
+		if p == "" {
+			return "", fmt.Errorf("%s is set but empty", env)
+		}
+		return p, nil
+	}
+	p, err := ReadSecret(prompt)
+	if err != nil {
+		return "", fmt.Errorf("could not read passphrase (set %s for non-interactive use): %v", env, err)
+	}
+	return string(p), nil
+}

internal/term/term_windows.go

@@ -0,0 +1,46 @@
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+package term
+
+import (
+	"errors"
+	"os"
+	"syscall"
+
+	"golang.org/x/sys/windows"
+)
+
+func init() {
+	enableVirtualTerminalProcessing = func(out *os.File) error {
+		// Some instances of the Windows Console (e.g., cmd.exe and Windows PowerShell)
+		// do not have the virtual terminal processing enabled, which is necessary to
+		// make terminal escape sequences work. For this reason the clearLine function
+		// may not properly work. Here we enable the virtual terminal processing, if
+		// possible.
+		//
+		// See https://learn.microsoft.com/en-us/windows/console/console-virtual-terminal-sequences.
+
+		const (
+			ENABLE_PROCESSED_OUTPUT            uint32 = 0x1
+			ENABLE_VIRTUAL_TERMINAL_PROCESSING uint32 = 0x4
+		)
+
+		kernel32DLL := windows.NewLazySystemDLL("Kernel32.dll")
+		setConsoleMode := kernel32DLL.NewProc("SetConsoleMode")
+
+		var mode uint32
+		if err := syscall.GetConsoleMode(syscall.Handle(out.Fd()), &mode); err != nil {
+			return err
+		}
+
+		mode |= ENABLE_PROCESSED_OUTPUT
+		mode |= ENABLE_VIRTUAL_TERMINAL_PROCESSING
+
+		// If the SetConsoleMode function fails, the return value is zero.
+		// See https://learn.microsoft.com/en-us/windows/console/setconsolemode#return-value.
+		if ret, _, _ := setConsoleMode.Call(out.Fd(), uintptr(mode)); ret == 0 {
+			return errors.New("SetConsoleMode failed")
+		}
+		return nil
+	}
+}