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package cryptokit
import (
"bytes"
"errors"
"fmt"
"os"
"os/exec"
"path/filepath"
"strings"
)
const maxYubiCryptMessageBytes = 64 << 20
var yubiCryptCandidates = []string{
"/home/gabriel1/bin/yubicrypt",
"/home/gabriel1/bin/yubicrpt-cli",
"/home/gabriel1/Projects/yubicrpt-cli/yubicrypt",
"/home/gabriel1/Projects/yubicrpt-cli/yubicrpt-cli",
"/usr/local/bin/yubicrypt",
"/usr/bin/yubicrypt",
}
// FindYubiCryptCLI returns the optional yubicrypt-cli executable. An explicit
// AEGIS_YUBICRYPT_CLI path takes precedence over the standard locations.
func FindYubiCryptCLI() (string, error) {
if configured := strings.TrimSpace(os.Getenv("AEGIS_YUBICRYPT_CLI")); configured != "" {
if isExecutableBinary(configured) {
return configured, nil
}
return "", fmt.Errorf("AEGIS_YUBICRYPT_CLI is not executable: %s", configured)
}
for _, candidate := range yubiCryptCandidates {
if isExecutableBinary(candidate) {
return candidate, nil
}
}
if path, err := exec.LookPath("yubicrypt"); err == nil {
return path, nil
}
return "", errors.New("yubicrypt-cli executable not found; set AEGIS_YUBICRYPT_CLI or install yubicrypt")
}
func isExecutableBinary(path string) bool {
info, err := os.Stat(path)
return err == nil && info.Mode().IsRegular() && info.Mode()&0o111 != 0
}
func runYubiCrypt(args []string, input []byte) ([]byte, error) {
executable, err := FindYubiCryptCLI()
if err != nil {
return nil, err
}
command := exec.Command(executable, args...)
command.Stdin = bytes.NewReader(input)
var stdout limitedBuffer
var stderr bytes.Buffer
stdout.limit = maxYubiCryptMessageBytes + 1
command.Stdout = &stdout
command.Stderr = &stderr
if err := command.Run(); err != nil {
return nil, fmt.Errorf("yubicrypt %s: %w: %s", firstCommandArg(args), err, cleanCommandError(stderr.String()))
}
if stdout.buffer.Len() > maxYubiCryptMessageBytes {
return nil, errors.New("yubicrypt output exceeds the 64 MiB limit")
}
return stdout.buffer.Bytes(), nil
}
func firstCommandArg(args []string) string {
if len(args) == 0 {
return "operation"
}
return args[0]
}
func cleanCommandError(value string) string {
value = strings.TrimSpace(value)
if len(value) > 1000 {
return value[:1000] + "..."
}
if value == "" {
return "command failed"
}
return value
}
func withYubiTemp(operation func(directory string) error) error {
directory, err := os.MkdirTemp("", "aegis-yubicrypt-")
if err != nil {
return fmt.Errorf("create temporary YubiCrypt directory: %w", err)
}
defer os.RemoveAll(directory)
if err := os.Chmod(directory, 0o700); err != nil {
return fmt.Errorf("protect temporary YubiCrypt directory: %w", err)
}
return operation(directory)
}
func writeYubiTemp(directory, name string, data []byte) (string, error) {
path := filepath.Join(directory, name)
file, err := os.OpenFile(path, os.O_WRONLY|os.O_CREATE|os.O_TRUNC, 0o600)
if err != nil {
return "", fmt.Errorf("create temporary YubiCrypt input: %w", err)
}
if _, err := file.Write(data); err != nil {
_ = file.Close()
return "", fmt.Errorf("write temporary YubiCrypt input: %w", err)
}
if err := file.Close(); err != nil {
return "", fmt.Errorf("close temporary YubiCrypt input: %w", err)
}
return path, nil
}
func checkYubiMessageSize(message []byte) error {
if len(message) > maxYubiCryptMessageBytes {
return errors.New("message exceeds the 64 MiB limit")
}
return nil
}
// EncryptYubiCrypt encrypts with an RSA public certificate/key accepted by
// yubicrypt-cli. The private decryption key remains inside the YubiKey PIV
// slot 9d and is never read by Aegis.
func EncryptYubiCrypt(message []byte, recipientKeyPEM string) ([]byte, error) {
if err := checkYubiMessageSize(message); err != nil {
return nil, err
}
if strings.TrimSpace(recipientKeyPEM) == "" {
return nil, errors.New("YubiCrypt RSA recipient certificate is required")
}
var result []byte
err := withYubiTemp(func(directory string) error {
messagePath, err := writeYubiTemp(directory, "message.bin", message)
if err != nil {
return err
}
keyPath, err := writeYubiTemp(directory, "recipient.pem", []byte(recipientKeyPEM))
if err != nil {
return err
}
result, err = runYubiCrypt([]string{
"encrypt", "--quiet", "--key", keyPath, "--input", messagePath, "--output", "-",
}, nil)
if err != nil {
return fmt.Errorf("YubiCrypt encryption failed: %w", err)
}
return nil
})
return result, err
}
func requireYubiPIN(pin string) ([]byte, error) {
pin = strings.TrimRight(pin, "\r\n")
if pin == "" {
return nil, errors.New("YubiKey PIV PIN is required")
}
return []byte(pin + "\n"), nil
}
// SignYubiCrypt signs with the YubiKey PIV slot 9c. The PIN is sent through
// stdin to yubicrypt-cli and is not placed in command arguments or logs.
func SignYubiCrypt(message []byte, pin string) ([]byte, error) {
if err := checkYubiMessageSize(message); err != nil {
return nil, err
}
pinInput, err := requireYubiPIN(pin)
if err != nil {
return nil, err
}
var result []byte
err = withYubiTemp(func(directory string) error {
messagePath, err := writeYubiTemp(directory, "message.bin", message)
if err != nil {
return err
}
result, err = runYubiCrypt([]string{
"sign", "--quiet", "--pin-stdin", "--input", messagePath, "--output", "-",
}, pinInput)
if err != nil {
return fmt.Errorf("YubiCrypt signing failed: %w", err)
}
return nil
})
return result, err
}
// DecryptYubiCrypt decrypts with the YubiKey PIV slot 9d. The ciphertext is
// kept in a temporary file while the PIN is supplied only on stdin.
func DecryptYubiCrypt(ciphertext []byte, pin string) ([]byte, error) {
if err := checkYubiMessageSize(ciphertext); err != nil {
return nil, err
}
pinInput, err := requireYubiPIN(pin)
if err != nil {
return nil, err
}
var result []byte
err = withYubiTemp(func(directory string) error {
ciphertextPath, err := writeYubiTemp(directory, "ciphertext.yc", ciphertext)
if err != nil {
return err
}
result, err = runYubiCrypt([]string{
"decrypt", "--quiet", "--pin-stdin", "--input", ciphertextPath, "--output", "-",
}, pinInput)
if err != nil {
return fmt.Errorf("YubiCrypt decryption failed: %w", err)
}
return nil
})
return result, err
}
// VerifyYubiCrypt verifies a yubicrypt signature block and returns the
// original message only after the CLI has authenticated it.
func VerifyYubiCrypt(signedMessage []byte) ([]byte, error) {
if err := checkYubiMessageSize(signedMessage); err != nil {
return nil, err
}
var result []byte
err := withYubiTemp(func(directory string) error {
signedPath, err := writeYubiTemp(directory, "signed.yc", signedMessage)
if err != nil {
return err
}
result, err = runYubiCrypt([]string{
"verify", "--quiet", "--input", signedPath, "--message-output", "-",
}, nil)
if err != nil {
return fmt.Errorf("YubiCrypt verification failed: %w", err)
}
return nil
})
return result, err
}
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