Add CLI-first yubicrypt buildHEADmain

3 files changed, 1092 insertions, 5 deletions

diff --git a/README.md b/README.md
index f554d81..fc98d94 100644
--- a/README.md
+++ b/README.md
@@ -1,6 +1,6 @@
-# yubicrypt

-

-An easy to use public key encryption program for your YubiKey.

+# yubicrypt
+
+An easy to use command-line public key encryption program for your YubiKey.
 

 Supported YubiKey algorithms:

 

@@ -33,7 +33,50 @@ sudo systemctl enable pcscd
 Check the status to ensure it's running  

 sudo systemctl status pcscd  

 

-![yubicrypt](img/1.png)

+## CLI usage
+
+Build the CLI:
+
+```sh
+go build -o yubicrypt .
+```
+
+Commands:
+
+```sh
+./yubicrypt help
+./yubicrypt cards
+./yubicrypt encrypt --key alice.crt -i msg.txt -o msg.yc
+printf '%s\n' "$PIV_PIN" | ./yubicrypt decrypt --pin-stdin -i msg.yc -o msg.txt
+printf '%s\n' "$PIV_PIN" | ./yubicrypt sign --pin-stdin -i msg.txt -o msg.sig.txt
+./yubicrypt verify -i msg.sig.txt --public-key
+./yubicrypt pad --text "message" -o padded.txt
+./yubicrypt unpad -i padded.txt -o message.txt
+```
+
+PIN options for `decrypt` and `sign`:
+
+- `--pin-stdin`: read the PIV PIN from the first stdin line.
+- `--pin-file FILE`: read the PIV PIN from the first line of a file.
+- `--pin PIN`: pass the PIV PIN directly. This is less safe because it can leak through shell history or process listings.
+- `--card-index N`: select the YubiKey index shown by `./yubicrypt cards`. The default is `0`.
+
+Common IO options:
+
+- `-i, --input FILE`: input file, or `-` for stdin.
+- `-o, --output FILE`: output file, or `-` for stdout.
+- `--text TEXT`: use literal text instead of reading input.
+- `--quiet`: suppress status output on stderr.
+
+## GUI build
+
+The old Fyne GUI is still available as an explicit build target:
+
+```sh
+go build -tags gui -o yubicrypt-gui .
+```
+
+![yubicrypt](img/1.png)
 

 The copy signature component is intended for usage of my [identicons](https://github.com/Ch1ffr3punk/identicons) program,    

 so that you can create your yubicrypt identicon for websites etc.  

diff --git a/cli.go b/cli.go
new file mode 100644
index 0000000..26f577f
--- /dev/null
+++ b/cli.go
@@ -0,0 +1,1041 @@
+//go:build !gui
+// +build !gui
+
+package main
+
+import (
+	"bufio"
+	"crypto"
+	"crypto/aes"
+	"crypto/cipher"
+	"crypto/ecdsa"
+	"crypto/ed25519"
+	"crypto/elliptic"
+	"crypto/rand"
+	"crypto/rsa"
+	"crypto/sha256"
+	"crypto/sha512"
+	"crypto/x509"
+	"encoding/asn1"
+	"encoding/base64"
+	"encoding/hex"
+	"encoding/pem"
+	"errors"
+	"flag"
+	"fmt"
+	"io"
+	"math/big"
+	"os"
+	"regexp"
+	"strings"
+
+	"github.com/awnumar/memguard"
+	"github.com/go-piv/piv-go/v2/piv"
+)
+
+type ecSignature struct{ R, S *big.Int }
+
+const (
+	AlgorithmECCP256 = "ECCP256"
+	AlgorithmECCP384 = "ECCP384"
+	AlgorithmED25519 = "ED25519"
+)
+
+const (
+	Ed25519SignatureSize = 64
+	Ed25519PublicKeySize = 32
+	Ed25519CombinedSize  = Ed25519SignatureSize + Ed25519PublicKeySize
+	minRSABits           = 2048
+)
+
+var supportedAlgorithms = map[string]bool{
+	AlgorithmECCP256: true,
+	AlgorithmECCP384: true,
+	AlgorithmED25519: true,
+}
+
+var curveToAlgorithm = map[elliptic.Curve]string{
+	elliptic.P256(): AlgorithmECCP256,
+	elliptic.P384(): AlgorithmECCP384,
+}
+
+var curveToHash = map[elliptic.Curve]crypto.Hash{
+	elliptic.P256(): crypto.SHA256,
+	elliptic.P384(): crypto.SHA384,
+}
+
+var supportedRSASizes = map[int]string{
+	2048: "RSA2048",
+	3072: "RSA3072",
+	4096: "RSA4096",
+}
+
+var yubiKeyIndex int
+
+type signatureInfo struct {
+	Algorithm       string
+	OriginalMessage []byte
+	PublicKey       []byte
+}
+
+func main() {
+	defer memguard.Purge()
+
+	if len(os.Args) == 1 {
+		printCLIHelp(os.Stdout)
+		return
+	}
+	if err := runCLI(os.Args[1:]); err != nil {
+		fmt.Fprintln(os.Stderr, "Error:", err)
+		os.Exit(1)
+	}
+}
+
+func runCLI(args []string) error {
+	if len(args) == 0 {
+		printCLIHelp(os.Stdout)
+		return nil
+	}
+
+	switch args[0] {
+	case "help", "-h", "--help":
+		printCLIHelp(os.Stdout)
+		return nil
+	case "version", "-v", "--version":
+		fmt.Println("yubicrypt v0.2.0")
+		return nil
+	case "encrypt", "enc":
+		return runEncryptCLI(args[1:])
+	case "decrypt", "dec":
+		return runDecryptCLI(args[1:])
+	case "sign":
+		return runSignCLI(args[1:])
+	case "verify":
+		return runVerifyCLI(args[1:])
+	case "pad":
+		return runPadCLI(args[1:])
+	case "unpad":
+		return runUnpadCLI(args[1:])
+	case "cards":
+		return runCardsCLI()
+	default:
+		return fmt.Errorf("unknown command %q; run `yubicrypt help`", args[0])
+	}
+}
+
+func printCLIHelp(w io.Writer) {
+	_, _ = io.WriteString(w, `Usage:
+  yubicrypt <command> [options]
+
+Commands:
+  encrypt   Encrypt with an RSA public certificate/key
+  decrypt   Decrypt with YubiKey PIV slot 9d
+  sign      Sign with YubiKey PIV slot 9c
+  verify    Verify an embedded yubicrypt signature
+  pad       ISO/IEC 7816-4 pad and Base64 encode
+  unpad     Base64 decode and remove padding
+  cards     List visible YubiKeys
+  version   Print version
+
+Common IO options:
+  -i, --input FILE     input file, or - for stdin (default -)
+  -o, --output FILE    output file, or - for stdout (default -)
+      --text TEXT      use TEXT instead of reading input
+      --quiet          suppress status lines on stderr
+
+PIN options for decrypt/sign:
+      --pin-stdin      read the PIV PIN from the first stdin line
+      --pin-file FILE  read the PIV PIN from the first line of FILE
+      --pin PIN        use PIN directly (less safe: shell history/process list)
+      --card-index N   YubiKey index from yubicrypt cards (default 0)
+
+Examples:
+  yubicrypt encrypt --key alice.crt -i msg.txt -o msg.yc
+  printf '%s\n' "$PIV_PIN" | yubicrypt decrypt --pin-stdin -i msg.yc -o msg.txt
+  printf '%s\n' "$PIV_PIN" | yubicrypt sign --pin-stdin -i msg.txt -o msg.sig.txt
+  yubicrypt verify -i msg.sig.txt --public-key
+`)
+}
+
+func newFlagSet(name string) *flag.FlagSet {
+	fs := flag.NewFlagSet(name, flag.ContinueOnError)
+	fs.SetOutput(os.Stderr)
+	return fs
+}
+
+func addIOFlags(fs *flag.FlagSet, input, output, text *string, quiet *bool) {
+	fs.StringVar(input, "input", "-", "input file, or - for stdin")
+	fs.StringVar(input, "i", "-", "input file, or - for stdin")
+	fs.StringVar(output, "output", "-", "output file, or - for stdout")
+	fs.StringVar(output, "o", "-", "output file, or - for stdout")
+	fs.StringVar(text, "text", "", "literal input text")
+	fs.BoolVar(quiet, "quiet", false, "suppress status lines on stderr")
+}
+
+func addPINFlags(fs *flag.FlagSet, pin, pinFile *string, pinStdin *bool) {
+	fs.StringVar(pin, "pin", "", "PIV PIN (less safe: shell history/process list)")
+	fs.StringVar(pinFile, "pin-file", "", "file containing the PIV PIN on the first line")
+	fs.BoolVar(pinStdin, "pin-stdin", false, "read the PIV PIN from the first stdin line")
+	fs.IntVar(&yubiKeyIndex, "card-index", 0, "YubiKey index from `yubicrypt cards`")
+}
+
+func runEncryptCLI(args []string) error {
+	var input, output, text, key string
+	var quiet bool
+	fs := newFlagSet("encrypt")
+	addIOFlags(fs, &input, &output, &text, &quiet)
+	fs.StringVar(&key, "key", "", "RSA public certificate/key file")
+	if err := fs.Parse(args); err != nil {
+		return err
+	}
+	if key == "" {
+		return fmt.Errorf("encrypt requires --key")
+	}
+
+	stdin := bufio.NewReader(os.Stdin)
+	data, err := readInput(input, text, stdin)
+	if err != nil {
+		return fmt.Errorf("read input: %w", err)
+	}
+	result, err := encryptData(data, key)
+	if err != nil {
+		return err
+	}
+	if err := writeOutput(output, []byte(result)); err != nil {
+		return fmt.Errorf("write output: %w", err)
+	}
+	logStatus(quiet, "encrypted %d bytes", len(data))
+	return nil
+}
+
+func runDecryptCLI(args []string) error {
+	var input, output, text, pin, pinFile string
+	var quiet, pinStdin bool
+	fs := newFlagSet("decrypt")
+	addIOFlags(fs, &input, &output, &text, &quiet)
+	addPINFlags(fs, &pin, &pinFile, &pinStdin)
+	if err := fs.Parse(args); err != nil {
+		return err
+	}
+
+	stdin := bufio.NewReader(os.Stdin)
+	pivPIN, err := readPIN(pin, pinFile, pinStdin, stdin)
+	if err != nil {
+		return err
+	}
+	data, err := readInput(input, text, stdin)
+	if err != nil {
+		return fmt.Errorf("read input: %w", err)
+	}
+	result, err := decryptData(data, pivPIN)
+	if err != nil {
+		return err
+	}
+	if err := writeOutput(output, result); err != nil {
+		return fmt.Errorf("write output: %w", err)
+	}
+	logStatus(quiet, "decrypted %d bytes", len(result))
+	return nil
+}
+
+func runSignCLI(args []string) error {
+	var input, output, text, pin, pinFile string
+	var quiet, pinStdin, force bool
+	fs := newFlagSet("sign")
+	addIOFlags(fs, &input, &output, &text, &quiet)
+	addPINFlags(fs, &pin, &pinFile, &pinStdin)
+	fs.BoolVar(&force, "force", false, "allow signing input that already contains a yubicrypt signature")
+	if err := fs.Parse(args); err != nil {
+		return err
+	}
+
+	stdin := bufio.NewReader(os.Stdin)
+	pivPIN, err := readPIN(pin, pinFile, pinStdin, stdin)
+	if err != nil {
+		return err
+	}
+	data, err := readInput(input, text, stdin)
+	if err != nil {
+		return fmt.Errorf("read input: %w", err)
+	}
+	if !force && containsSignatureBlock(data) {
+		return fmt.Errorf("input already contains a yubicrypt signature; use --force to sign anyway")
+	}
+	result, err := signData(data, pivPIN)
+	if err != nil {
+		return err
+	}
+	if err := writeOutput(output, []byte(result)); err != nil {
+		return fmt.Errorf("write output: %w", err)
+	}
+	logStatus(quiet, "signed %d bytes", len(data))
+	return nil
+}
+
+func runVerifyCLI(args []string) error {
+	var input, output, text, messageOutput string
+	var quiet, publicKeyOnly bool
+	fs := newFlagSet("verify")
+	fs.StringVar(&input, "input", "-", "input file, or - for stdin")
+	fs.StringVar(&input, "i", "-", "input file, or - for stdin")
+	fs.StringVar(&text, "text", "", "literal input text")
+	fs.BoolVar(&quiet, "quiet", false, "suppress success output")
+	fs.BoolVar(&publicKeyOnly, "public-key", false, "print embedded public key hex only")
+	fs.StringVar(&messageOutput, "message-output", "", "write verified original message to file")
+	fs.StringVar(&output, "output", "", "alias for --message-output")
+	fs.StringVar(&output, "o", "", "alias for --message-output")
+	if err := fs.Parse(args); err != nil {
+		return err
+	}
+	if output != "" && messageOutput == "" {
+		messageOutput = output
+	}
+
+	stdin := bufio.NewReader(os.Stdin)
+	data, err := readInput(input, text, stdin)
+	if err != nil {
+		return fmt.Errorf("read input: %w", err)
+	}
+	info, err := verifySignedData(data)
+	if err != nil {
+		return err
+	}
+	if messageOutput != "" {
+		if err := writeOutput(messageOutput, info.OriginalMessage); err != nil {
+			return fmt.Errorf("write verified message: %w", err)
+		}
+	}
+	if publicKeyOnly {
+		fmt.Fprintln(os.Stdout, hex.EncodeToString(info.PublicKey))
+		return nil
+	}
+	if !quiet {
+		fmt.Fprintf(os.Stdout, "OK %s signature valid; message=%d bytes; public_key=%s\n",
+			info.Algorithm, len(info.OriginalMessage), hex.EncodeToString(info.PublicKey))
+	}
+	return nil
+}
+
+func runPadCLI(args []string) error {
+	var input, output, text string
+	var quiet bool
+	fs := newFlagSet("pad")
+	addIOFlags(fs, &input, &output, &text, &quiet)
+	if err := fs.Parse(args); err != nil {
+		return err
+	}
+
+	stdin := bufio.NewReader(os.Stdin)
+	data, err := readInput(input, text, stdin)
+	if err != nil {
+		return fmt.Errorf("read input: %w", err)
+	}
+	padded := securePadMessage(data)
+	encoded := formatBase64RFC(base64.StdEncoding.EncodeToString(padded))
+	if err := writeOutput(output, []byte(encoded)); err != nil {
+		return fmt.Errorf("write output: %w", err)
+	}
+	logStatus(quiet, "padded %d -> %d bytes", len(data), len(padded))
+	return nil
+}
+
+func runUnpadCLI(args []string) error {
+	var input, output, text string
+	var quiet bool
+	fs := newFlagSet("unpad")
+	addIOFlags(fs, &input, &output, &text, &quiet)
+	if err := fs.Parse(args); err != nil {
+		return err
+	}
+
+	stdin := bufio.NewReader(os.Stdin)
+	data, err := readInput(input, text, stdin)
+	if err != nil {
+		return fmt.Errorf("read input: %w", err)
+	}
+	decoded, err := decodeBase64Clean(data)
+	if err != nil {
+		return err
+	}
+	defer memguard.WipeBytes(decoded)
+	result, err := secureUnpadMessage(decoded)
+	if err != nil {
+		return err
+	}
+	if err := writeOutput(output, result); err != nil {
+		return fmt.Errorf("write output: %w", err)
+	}
+	logStatus(quiet, "unpadded %d bytes", len(result))
+	return nil
+}
+
+func runCardsCLI() error {
+	cards, err := piv.Cards()
+	if err != nil {
+		return fmt.Errorf("list cards: %w", err)
+	}
+	if len(cards) == 0 {
+		return fmt.Errorf("no smart card found")
+	}
+	for i, card := range cards {
+		fmt.Fprintf(os.Stdout, "%d\t%s\n", i, card)
+	}
+	return nil
+}
+
+func readInput(path, text string, stdin *bufio.Reader) ([]byte, error) {
+	if text != "" {
+		return []byte(text), nil
+	}
+	if path == "" || path == "-" {
+		return io.ReadAll(stdin)
+	}
+	return os.ReadFile(path)
+}
+
+func writeOutput(path string, data []byte) error {
+	if path == "" || path == "-" {
+		_, err := os.Stdout.Write(data)
+		return err
+	}
+	return os.WriteFile(path, data, 0600)
+}
+
+func firstLine(data []byte) string {
+	line := string(data)
+	if i := strings.IndexAny(line, "\r\n"); i >= 0 {
+		line = line[:i]
+	}
+	return strings.TrimSpace(line)
+}
+
+func readPIN(pin, pinFile string, pinStdin bool, stdin *bufio.Reader) (string, error) {
+	switch {
+	case pin != "":
+		return pin, nil
+	case pinFile != "":
+		data, err := os.ReadFile(pinFile)
+		if err != nil {
+			return "", fmt.Errorf("read PIN file: %w", err)
+		}
+		defer memguard.WipeBytes(data)
+		p := firstLine(data)
+		if p == "" {
+			return "", fmt.Errorf("PIN file is empty")
+		}
+		return p, nil
+	case pinStdin:
+		line, err := stdin.ReadString('\n')
+		if err != nil && err != io.EOF {
+			return "", fmt.Errorf("read PIN from stdin: %w", err)
+		}
+		p := strings.TrimRight(line, "\r\n")
+		if p == "" {
+			return "", fmt.Errorf("stdin PIN is empty")
+		}
+		return p, nil
+	default:
+		return "", fmt.Errorf("PIV PIN required; use --pin-stdin, --pin-file, or --pin")
+	}
+}
+
+func logStatus(quiet bool, format string, args ...any) {
+	if quiet {
+		return
+	}
+	fmt.Fprintf(os.Stderr, format+"\n", args...)
+}
+
+func containsSignatureBlock(data []byte) bool {
+	s := string(data)
+	for algo := range supportedAlgorithms {
+		if strings.Contains(s, "-----BEGIN "+algo+" SIGNATURE-----") {
+			return true
+		}
+	}
+	return false
+}
+
+func signData(data []byte, pin string) (string, error) {
+	pinGuard := memguard.NewBufferFromBytes([]byte(pin))
+	defer pinGuard.Destroy()
+
+	normalizedData := normalizeToRFCCompliantCRLF(data)
+	sig, algo, err := signDataInternal(pinGuard.Bytes(), normalizedData)
+	if err != nil {
+		return "", fmt.Errorf("signing failed: %w", err)
+	}
+
+	sep := "\r\n"
+	if len(normalizedData) > 0 {
+		last := string(normalizedData[len(normalizedData)-1:])
+		if last == "\n" && !(len(normalizedData) >= 2 && string(normalizedData[len(normalizedData)-2:]) == "\r\n") {
+			sep = "\n"
+		}
+	}
+
+	return string(normalizedData) + sep +
+		"-----BEGIN " + algo + " SIGNATURE-----" + sep +
+		formatSignatureRFC(sig) +
+		"-----END " + algo + " SIGNATURE-----" + sep, nil
+}
+
+func signDataInternal(pin, data []byte) (string, string, error) {
+	yk, err := openYubiKey(yubiKeyIndex)
+	if err != nil {
+		return "", "", err
+	}
+	defer yk.Close()
+
+	cert, err := yk.Certificate(piv.SlotSignature)
+	if err != nil {
+		return "", "", fmt.Errorf("failed to get certificate from signature slot: %w", err)
+	}
+
+	if ed25519PubKey, ok := cert.PublicKey.(ed25519.PublicKey); ok {
+		hash := sha256.Sum256(data)
+		return signEd25519Data(string(pin), hash[:], ed25519PubKey, yk)
+	}
+
+	pubKey, ok := cert.PublicKey.(*ecdsa.PublicKey)
+	if !ok {
+		return "", "", fmt.Errorf("public key is not ECDSA or Ed25519")
+	}
+
+	algorithm, exists := curveToAlgorithm[pubKey.Curve]
+	if !exists {
+		return "", "", fmt.Errorf("unsupported curve: %v", pubKey.Curve)
+	}
+
+	hashFunc := curveToHash[pubKey.Curve]
+	var digest []byte
+	switch hashFunc {
+	case crypto.SHA256:
+		h := sha256.New()
+		h.Write(data)
+		digest = h.Sum(nil)
+	case crypto.SHA384:
+		h := sha512.New384()
+		h.Write(data)
+		digest = h.Sum(nil)
+	default:
+		return "", "", fmt.Errorf("unsupported hash algorithm for curve")
+	}
+
+	auth := piv.KeyAuth{PIN: string(pin)}
+	priv, err := yk.PrivateKey(piv.SlotSignature, cert.PublicKey, auth)
+	if err != nil {
+		return "", "", fmt.Errorf("failed to get private key: %w", err)
+	}
+
+	signer, ok := priv.(crypto.Signer)
+	if !ok {
+		return "", "", fmt.Errorf("key does not implement crypto.Signer")
+	}
+
+	asn1sig, err := signer.Sign(rand.Reader, digest, nil)
+	if err != nil {
+		return "", "", fmt.Errorf("signing failed: %w", err)
+	}
+
+	var sig ecSignature
+	if _, err := asn1.Unmarshal(asn1sig, &sig); err != nil {
+		return "", "", fmt.Errorf("ASN.1 unmarshal failed: %w", err)
+	}
+
+	curveSize := (pubKey.Curve.Params().BitSize + 7) / 8
+	var raw []byte
+	raw = append(raw, safePad(pubKey.X.Bytes(), curveSize)...)
+	raw = append(raw, safePad(pubKey.Y.Bytes(), curveSize)...)
+	raw = append(raw, safePad(sig.R.Bytes(), curveSize)...)
+	raw = append(raw, safePad(sig.S.Bytes(), curveSize)...)
+
+	return hex.EncodeToString(raw), algorithm, nil
+}
+
+func signEd25519Data(pin string, hash []byte, pubKey ed25519.PublicKey, yk *piv.YubiKey) (string, string, error) {
+	auth := piv.KeyAuth{PIN: pin}
+	priv, err := yk.PrivateKey(piv.SlotSignature, pubKey, auth)
+	if err != nil {
+		return "", "", fmt.Errorf("failed to get private key: %w", err)
+	}
+
+	signer, ok := priv.(crypto.Signer)
+	if !ok {
+		return "", "", fmt.Errorf("key does not implement crypto.Signer")
+	}
+
+	signature, err := signer.Sign(rand.Reader, hash, crypto.Hash(0))
+	if err != nil {
+		return "", "", fmt.Errorf("Ed25519 signing failed: %w", err)
+	}
+
+	combined := append(pubKey, signature...)
+	return hex.EncodeToString(combined), AlgorithmED25519, nil
+}
+
+func verifySignedData(data []byte) (*signatureInfo, error) {
+	s := string(normalizeToRFCCompliantCRLF(data))
+	var algorithm string
+	beginIndex := -1
+	beginMarker := ""
+
+	for algo := range supportedAlgorithms {
+		marker := "-----BEGIN " + algo + " SIGNATURE-----"
+		if idx := strings.Index(s, marker); idx >= 0 {
+			algorithm = algo
+			beginIndex = idx
+			beginMarker = marker
+			break
+		}
+	}
+	if algorithm == "" {
+		return nil, fmt.Errorf("no supported signature block found")
+	}
+
+	endMarker := "-----END " + algorithm + " SIGNATURE-----"
+	hexStart := beginIndex + len(beginMarker)
+	endRel := strings.Index(s[hexStart:], endMarker)
+	if endRel < 0 {
+		return nil, fmt.Errorf("invalid signature block format")
+	}
+
+	original := []byte(s[:beginIndex])
+	original = bytesTrimOneLineEnding(original)
+	hexPart := s[hexStart : hexStart+endRel]
+	hexPart = regexp.MustCompile(`[\r\n\s\t]+`).ReplaceAllString(hexPart, "")
+
+	combined, err := hex.DecodeString(hexPart)
+	if err != nil {
+		return nil, fmt.Errorf("hex decode failed: %w", err)
+	}
+
+	var verificationErr error
+	switch algorithm {
+	case AlgorithmED25519:
+		hash := sha256.Sum256(original)
+		verificationErr = verifyEd25519(hash[:], combined)
+	case AlgorithmECCP256, AlgorithmECCP384:
+		verificationErr = verifyECDSA(original, combined, algorithm)
+	default:
+		verificationErr = fmt.Errorf("unsupported algorithm: %s", algorithm)
+	}
+	if verificationErr != nil {
+		return nil, verificationErr
+	}
+
+	publicKey, err := extractPublicKeyFromSignature(combined, algorithm)
+	if err != nil {
+		return nil, err
+	}
+	return &signatureInfo{
+		Algorithm:       algorithm,
+		OriginalMessage: original,
+		PublicKey:       publicKey,
+	}, nil
+}
+
+func extractPublicKeyFromSignature(combined []byte, algorithm string) ([]byte, error) {
+	switch algorithm {
+	case AlgorithmED25519:
+		if len(combined) != Ed25519CombinedSize {
+			return nil, fmt.Errorf("invalid Ed25519 signature block")
+		}
+		return combined[:Ed25519PublicKeySize], nil
+	case AlgorithmECCP256, AlgorithmECCP384:
+		var curve elliptic.Curve
+		switch algorithm {
+		case AlgorithmECCP256:
+			curve = elliptic.P256()
+		case AlgorithmECCP384:
+			curve = elliptic.P384()
+		}
+		curveSize := (curve.Params().BitSize + 7) / 8
+		expectedBytes := 4 * curveSize
+		if len(combined) != expectedBytes {
+			return nil, fmt.Errorf("invalid signature block size: expected %d, got %d", expectedBytes, len(combined))
+		}
+		return combined[:2*curveSize], nil
+	default:
+		return nil, fmt.Errorf("unsupported algorithm: %s", algorithm)
+	}
+}
+
+func verifyEd25519(dataHash, combined []byte) error {
+	if len(combined) != Ed25519CombinedSize {
+		return fmt.Errorf("invalid Ed25519 signature block")
+	}
+	publicKey := combined[:Ed25519PublicKeySize]
+	signature := combined[Ed25519PublicKeySize:]
+	if !ed25519.Verify(ed25519.PublicKey(publicKey), dataHash, signature) {
+		return fmt.Errorf("Ed25519 signature verification failed")
+	}
+	return nil
+}
+
+func verifyECDSA(data, combined []byte, algorithm string) error {
+	var curve elliptic.Curve
+	var hashFunc crypto.Hash
+	switch algorithm {
+	case AlgorithmECCP256:
+		curve = elliptic.P256()
+		hashFunc = crypto.SHA256
+	case AlgorithmECCP384:
+		curve = elliptic.P384()
+		hashFunc = crypto.SHA384
+	default:
+		return fmt.Errorf("unsupported ECDSA algorithm: %s", algorithm)
+	}
+
+	curveSize := (curve.Params().BitSize + 7) / 8
+	expectedBytes := 4 * curveSize
+	if len(combined) != expectedBytes {
+		return fmt.Errorf("invalid signature block size: expected %d, got %d", expectedBytes, len(combined))
+	}
+
+	x := new(big.Int).SetBytes(safePad(combined[0:curveSize], curveSize))
+	y := new(big.Int).SetBytes(safePad(combined[curveSize:2*curveSize], curveSize))
+	r := new(big.Int).SetBytes(safePad(combined[2*curveSize:3*curveSize], curveSize))
+	s := new(big.Int).SetBytes(safePad(combined[3*curveSize:], curveSize))
+
+	if !curve.IsOnCurve(x, y) {
+		return fmt.Errorf("public key point (X,Y) is not on the curve %s", curve.Params().Name)
+	}
+
+	pub := &ecdsa.PublicKey{Curve: curve, X: x, Y: y}
+	var digest []byte
+	switch hashFunc {
+	case crypto.SHA256:
+		h := sha256.New()
+		h.Write(data)
+		digest = h.Sum(nil)
+	case crypto.SHA384:
+		h := sha512.New384()
+		h.Write(data)
+		digest = h.Sum(nil)
+	}
+
+	if !ecdsa.Verify(pub, digest, r, s) {
+		return fmt.Errorf("signature verification failed")
+	}
+	return nil
+}
+
+func encryptData(data []byte, pubKeyFile string) (string, error) {
+	pubKey, err := loadRSAPublicKey(pubKeyFile)
+	if err != nil {
+		return "", fmt.Errorf("failed to load public key: %w", err)
+	}
+
+	aesKeyGuard := memguard.NewBuffer(32)
+	defer aesKeyGuard.Destroy()
+	if _, err := rand.Read(aesKeyGuard.Bytes()); err != nil {
+		return "", fmt.Errorf("failed to generate AES key: %w", err)
+	}
+
+	encryptedKey, err := rsa.EncryptPKCS1v15(rand.Reader, pubKey, aesKeyGuard.Bytes())
+	if err != nil {
+		return "", fmt.Errorf("RSA encryption failed: %w", err)
+	}
+	defer memguard.WipeBytes(encryptedKey)
+
+	encryptedData, err := encryptAES(data, aesKeyGuard.Bytes())
+	if err != nil {
+		return "", fmt.Errorf("AES encryption failed: %w", err)
+	}
+	defer memguard.WipeBytes(encryptedData)
+
+	combined := append(encryptedKey, encryptedData...)
+	defer memguard.WipeBytes(combined)
+
+	return formatBase64RFC(base64.StdEncoding.EncodeToString(combined)), nil
+}
+
+func decryptData(data []byte, pin string) ([]byte, error) {
+	pinGuard := memguard.NewBufferFromBytes([]byte(pin))
+	defer pinGuard.Destroy()
+
+	combined, err := decodeBase64Clean(data)
+	if err != nil {
+		return nil, err
+	}
+	defer memguard.WipeBytes(combined)
+
+	yk, err := openYubiKey(yubiKeyIndex)
+	if err != nil {
+		return nil, fmt.Errorf("failed to open YubiKey: %w", err)
+	}
+	defer yk.Close()
+
+	cert, err := yk.Certificate(piv.SlotKeyManagement)
+	if err != nil {
+		return nil, fmt.Errorf("failed to get certificate from slot 9d: %w", err)
+	}
+
+	rsaPubKey, ok := cert.PublicKey.(*rsa.PublicKey)
+	if !ok {
+		return nil, fmt.Errorf("certificate does not contain RSA public key")
+	}
+	if err := checkRSASecurity(rsaPubKey, "on YubiKey"); err != nil {
+		return nil, err
+	}
+
+	keySize := rsaPubKey.Size()
+	if len(combined) < keySize {
+		return nil, fmt.Errorf("ciphertext too short")
+	}
+
+	encryptedKey := combined[:keySize]
+	encryptedData := combined[keySize:]
+
+	auth := piv.KeyAuth{PIN: string(pinGuard.Bytes())}
+	priv, err := yk.PrivateKey(piv.SlotKeyManagement, cert.PublicKey, auth)
+	if err != nil {
+		return nil, fmt.Errorf("failed to get private key: %w", err)
+	}
+
+	decrypter, ok := priv.(crypto.Decrypter)
+	if !ok {
+		return nil, fmt.Errorf("private key does not support decryption")
+	}
+
+	decryptedPayload, err := decrypter.Decrypt(rand.Reader, encryptedKey, nil)
+	if err != nil {
+		return nil, fmt.Errorf("RSA decryption failed: %w", err)
+	}
+	defer memguard.WipeBytes(decryptedPayload)
+
+	if len(decryptedPayload) != 32 {
+		return nil, fmt.Errorf("invalid AES key size")
+	}
+
+	decryptedData, err := decryptAES(encryptedData, decryptedPayload)
+	if err != nil {
+		return nil, fmt.Errorf("AES decryption failed: %w", err)
+	}
+	return decryptedData, nil
+}
+
+func checkRSASecurity(pubKey *rsa.PublicKey, context string) error {
+	keySize := pubKey.N.BitLen()
+	if keySize < minRSABits {
+		return fmt.Errorf("insecure %d-bit RSA key %s - minimum is %d-bit", keySize, context, minRSABits)
+	}
+	if _, supported := supportedRSASizes[keySize]; !supported {
+		fmt.Fprintf(os.Stderr, "WARNING: %d-bit RSA key %s - supported sizes are 2048, 3072, 4096 bits\n", keySize, context)
+	}
+	if keySize == 1024 {
+		fmt.Fprintf(os.Stderr, "CRITICAL WARNING: 1024-bit RSA keys %s are insecure and should not be used!\n", context)
+	}
+	return nil
+}
+
+func loadRSAPublicKey(filename string) (*rsa.PublicKey, error) {
+	data, err := os.ReadFile(filename)
+	if err != nil {
+		return nil, fmt.Errorf("failed to read public key file: %w", err)
+	}
+	defer memguard.WipeBytes(data)
+
+	block, _ := pem.Decode(data)
+	if block == nil {
+		return nil, fmt.Errorf("no data found in file")
+	}
+
+	switch block.Type {
+	case "CERTIFICATE":
+		cert, err := x509.ParseCertificate(block.Bytes)
+		if err != nil {
+			return nil, fmt.Errorf("failed to parse certificate: %w", err)
+		}
+		pubKey, ok := cert.PublicKey.(*rsa.PublicKey)
+		if !ok {
+			return nil, fmt.Errorf("certificate does not contain RSA public key")
+		}
+		if err := checkRSASecurity(pubKey, "in certificate "+filename); err != nil {
+			return nil, err
+		}
+		return pubKey, nil
+	case "PUBLIC KEY":
+		pubInterface, err := x509.ParsePKIXPublicKey(block.Bytes)
+		if err != nil {
+			return nil, fmt.Errorf("failed to parse public key: %w", err)
+		}
+		pubKey, ok := pubInterface.(*rsa.PublicKey)
+		if !ok {
+			return nil, fmt.Errorf("not an RSA public key")
+		}
+		if err := checkRSASecurity(pubKey, "in file "+filename); err != nil {
+			return nil, err
+		}
+		return pubKey, nil
+	case "RSA PUBLIC KEY":
+		pubKey, err := x509.ParsePKCS1PublicKey(block.Bytes)
+		if err != nil {
+			return nil, fmt.Errorf("failed to parse RSA public key: %w", err)
+		}
+		if err := checkRSASecurity(pubKey, "in file "+filename); err != nil {
+			return nil, err
+		}
+		return pubKey, nil
+	default:
+		return nil, fmt.Errorf("unsupported type: %s, expected CERTIFICATE, PUBLIC KEY or RSA PUBLIC KEY", block.Type)
+	}
+}
+
+func encryptAES(data, key []byte) ([]byte, error) {
+	block, err := aes.NewCipher(key)
+	if err != nil {
+		return nil, err
+	}
+	gcm, err := cipher.NewGCM(block)
+	if err != nil {
+		return nil, err
+	}
+	nonce := make([]byte, gcm.NonceSize())
+	if _, err := rand.Read(nonce); err != nil {
+		return nil, err
+	}
+	return gcm.Seal(nonce, nonce, data, nil), nil
+}
+
+func decryptAES(data, key []byte) ([]byte, error) {
+	block, err := aes.NewCipher(key)
+	if err != nil {
+		return nil, err
+	}
+	gcm, err := cipher.NewGCM(block)
+	if err != nil {
+		return nil, err
+	}
+	nonceSize := gcm.NonceSize()
+	if len(data) < nonceSize {
+		return nil, fmt.Errorf("ciphertext too short")
+	}
+	nonce, ciphertext := data[:nonceSize], data[nonceSize:]
+	plaintext, err := gcm.Open(nil, nonce, ciphertext, nil)
+	if err != nil {
+		return nil, err
+	}
+	return plaintext, nil
+}
+
+func openYubiKey(index int) (*piv.YubiKey, error) {
+	cards, err := piv.Cards()
+	if err != nil {
+		return nil, fmt.Errorf("failed to list cards: %w", err)
+	}
+	if len(cards) == 0 {
+		return nil, fmt.Errorf("no smart card found")
+	}
+
+	count := 0
+	for _, card := range cards {
+		if strings.Contains(strings.ToLower(card), "yubikey") {
+			if count == index {
+				return piv.Open(card)
+			}
+			count++
+		}
+	}
+	return nil, fmt.Errorf("no YubiKey found at index %d", index)
+}
+
+func normalizeToRFCCompliantCRLF(data []byte) []byte {
+	s := string(data)
+	s = strings.ReplaceAll(s, "\r\n", "\n")
+	s = strings.ReplaceAll(s, "\r", "\n")
+	s = strings.ReplaceAll(s, "\n", "\r\n")
+	return []byte(s)
+}
+
+func formatSignatureRFC(sig string) string {
+	var result strings.Builder
+	for i := 0; i < len(sig); i += 64 {
+		end := i + 64
+		if end > len(sig) {
+			end = len(sig)
+		}
+		result.WriteString(sig[i:end])
+		result.WriteString("\r\n")
+	}
+	return result.String()
+}
+
+func formatBase64RFC(data string) string {
+	var result strings.Builder
+	for i := 0; i < len(data); i += 76 {
+		end := i + 76
+		if end > len(data) {
+			end = len(data)
+		}
+		result.WriteString(data[i:end])
+		result.WriteString("\r\n")
+	}
+	return result.String()
+}
+
+func securePadMessage(data []byte) []byte {
+	const blockSize = 4096
+	paddingNeeded := blockSize - (len(data) % blockSize)
+	if paddingNeeded == blockSize {
+		return data
+	}
+	paddedData := make([]byte, len(data)+paddingNeeded)
+	copy(paddedData, data)
+	paddedData[len(data)] = 0x80
+	return paddedData
+}
+
+func secureUnpadMessage(data []byte) ([]byte, error) {
+	if len(data) == 0 {
+		return nil, errors.New("cannot unpad empty data")
+	}
+	if len(data)%4096 != 0 {
+		return nil, errors.New("invalid block size for unpadding")
+	}
+
+	lastIndex := -1
+	for i := len(data) - 1; i >= 0; i-- {
+		if data[i] == 0x80 {
+			lastIndex = i
+			break
+		}
+		if data[i] != 0x00 {
+			return nil, errors.New("invalid padding format: unexpected non-zero byte")
+		}
+	}
+	if lastIndex == -1 {
+		return nil, errors.New("no padding marker found")
+	}
+	return data[:lastIndex], nil
+}
+
+func safePad(b []byte, size int) []byte {
+	if len(b) > size {
+		return b[len(b)-size:]
+	}
+	return append(make([]byte, size-len(b)), b...)
+}
+
+func bytesTrimOneLineEnding(data []byte) []byte {
+	if len(data) >= 2 && data[len(data)-2] == '\r' && data[len(data)-1] == '\n' {
+		return data[:len(data)-2]
+	}
+	if len(data) >= 1 && data[len(data)-1] == '\n' {
+		return data[:len(data)-1]
+	}
+	return data
+}
+
+func decodeBase64Clean(data []byte) ([]byte, error) {
+	s := string(data)
+	s = strings.ReplaceAll(s, "\r", "")
+	s = strings.ReplaceAll(s, "\n", "")
+	s = strings.ReplaceAll(s, " ", "")
+	decoded, err := base64.StdEncoding.DecodeString(s)
+	if err != nil {
+		return nil, fmt.Errorf("base64 decode failed: %w", err)
+	}
+	return decoded, nil
+}
diff --git a/yubicrypt.go b/yubicrypt.go
index f614750..abc0c74 100644
--- a/yubicrypt.go
+++ b/yubicrypt.go
@@ -1,4 +1,7 @@
-package main

+//go:build gui
+// +build gui
+
+package main
 

 import (

 	"crypto"