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package cryptokit
import (
"bytes"
"errors"
"fmt"
"os"
"os/exec"
"path/filepath"
"strings"
)
const maxOpenPGPMessageBytes = 64 << 20
type limitedBuffer struct {
buffer bytes.Buffer
limit int
}
func (b *limitedBuffer) Write(value []byte) (int, error) {
if b.buffer.Len() < b.limit {
remaining := b.limit - b.buffer.Len()
if len(value) > remaining {
_, _ = b.buffer.Write(value[:remaining])
} else {
_, _ = b.buffer.Write(value)
}
}
return len(value), nil
}
// OpenPGP support is delegated to the system GnuPG binary. This keeps Aegis
// compatible with the user's existing OpenPGP installation, including RSA,
// Ed25519 and X25519 keys, without embedding another keyring. Key material is
// imported into a temporary 0700 GNUPGHOME and removed after each operation.
func gpgBinary() (string, error) {
path, err := exec.LookPath("gpg")
if err != nil {
return "", errors.New("gpg is required for OpenPGP operations")
}
return path, nil
}
func withGPG(operation func(home string) error) error {
if _, err := gpgBinary(); err != nil {
return err
}
home, err := os.MkdirTemp("", "aegis-gpg-")
if err != nil {
return fmt.Errorf("create temporary OpenPGP home: %w", err)
}
defer os.RemoveAll(home)
if err := os.Chmod(home, 0o700); err != nil {
return fmt.Errorf("protect temporary OpenPGP home: %w", err)
}
return operation(home)
}
func runGPG(home string, args []string, input []byte, outputLimit int) ([]byte, string, error) {
binary, err := gpgBinary()
if err != nil {
return nil, "", err
}
base := []string{
"--batch", "--no-tty", "--no-options", "--no-auto-check-trustdb",
"--homedir", home,
}
cmd := exec.Command(binary, append(base, args...)...)
cmd.Stdin = bytes.NewReader(input)
var stdout limitedBuffer
var stderr bytes.Buffer
if outputLimit <= 0 {
outputLimit = maxOpenPGPMessageBytes
}
stdout.limit = outputLimit + 1
cmd.Stdout = &stdout
cmd.Stderr = &stderr
if err := cmd.Run(); err != nil {
return stdout.buffer.Bytes(), stderr.String(), fmt.Errorf("gpg %s: %w: %s", args[0], err, cleanGPGError(stderr.String()))
}
if stdout.buffer.Len() > outputLimit {
return nil, stderr.String(), fmt.Errorf("OpenPGP output exceeds the %d MiB limit", outputLimit/(1<<20))
}
return stdout.buffer.Bytes(), stderr.String(), nil
}
func cleanGPGError(value string) string {
value = strings.TrimSpace(value)
if len(value) > 1000 {
return value[:1000] + "..."
}
return value
}
func importOpenPGP(home, keyMaterial string) error {
if strings.TrimSpace(keyMaterial) == "" {
return errors.New("OpenPGP key material is required")
}
_, stderr, err := runGPG(home, []string{"--import"}, []byte(keyMaterial), 1<<20)
if err != nil {
return fmt.Errorf("import OpenPGP key: %w", err)
}
if strings.Contains(stderr, "no valid OpenPGP data found") {
return errors.New("no valid OpenPGP key found")
}
return nil
}
func listFingerprints(home string) ([]string, error) {
output, _, err := runGPG(home, []string{"--with-colons", "--list-keys"}, nil, 1<<20)
if err != nil {
return nil, fmt.Errorf("list OpenPGP keys: %w", err)
}
var fingerprints []string
for _, line := range strings.Split(string(output), "\n") {
fields := strings.Split(line, ":")
if len(fields) > 9 && fields[0] == "fpr" && fields[9] != "" {
fingerprints = append(fingerprints, fields[9])
}
}
if len(fingerprints) == 0 {
return nil, errors.New("no usable OpenPGP key found")
}
return fingerprints, nil
}
func writeGPGFile(home, name string, content []byte) (string, error) {
path := filepath.Join(home, name)
file, err := os.OpenFile(path, os.O_WRONLY|os.O_CREATE|os.O_TRUNC, 0o600)
if err != nil {
return "", fmt.Errorf("create temporary OpenPGP file: %w", err)
}
if _, err := file.Write(content); err != nil {
_ = file.Close()
return "", fmt.Errorf("write temporary OpenPGP file: %w", err)
}
if err := file.Close(); err != nil {
return "", fmt.Errorf("close temporary OpenPGP file: %w", err)
}
return path, nil
}
// SignOpenPGPDetached returns an ASCII-armored detached signature. The input
// must contain a private signing key supplied by the user.
func SignOpenPGPDetached(message []byte, privateKeyArmor string) (string, error) {
var signature []byte
err := withGPG(func(home string) error {
if err := importOpenPGP(home, privateKeyArmor); err != nil {
return err
}
output, _, err := runGPG(home, []string{"--armor", "--detach-sign", "--output", "-"}, message, 1<<20)
if err != nil {
return fmt.Errorf("sign OpenPGP message: %w", err)
}
signature = output
return nil
})
return string(signature), err
}
// VerifyOpenPGPDetached verifies an ASCII-armored or binary detached
// signature using public or private OpenPGP key material supplied by the user.
func VerifyOpenPGPDetached(message []byte, signature, publicKeyArmor string) error {
return withGPG(func(home string) error {
if err := importOpenPGP(home, publicKeyArmor); err != nil {
return err
}
signaturePath, err := writeGPGFile(home, "signature.asc", []byte(signature))
if err != nil {
return err
}
messagePath, err := writeGPGFile(home, "message.bin", message)
if err != nil {
return err
}
if _, _, err := runGPG(home, []string{"--verify", signaturePath, messagePath}, nil, 1<<20); err != nil {
return fmt.Errorf("verify OpenPGP signature: %w", err)
}
return nil
})
}
// EncryptOpenPGP encrypts a message to every entity in the supplied armored
// public key ring. If privateSignerArmor is non-empty, it also signs the
// message with the supplied private key. The result is ASCII armored.
func EncryptOpenPGP(message []byte, recipientKeyArmor, privateSignerArmor string) (string, error) {
var encrypted []byte
err := withGPG(func(home string) error {
if err := importOpenPGP(home, recipientKeyArmor); err != nil {
return err
}
recipientFingerprints, err := listFingerprints(home)
if err != nil {
return err
}
args := []string{"--armor", "--trust-model", "always", "--encrypt", "--output", "-"}
for _, fingerprint := range recipientFingerprints {
args = append(args, "--recipient", fingerprint)
}
if strings.TrimSpace(privateSignerArmor) != "" {
if err := importOpenPGP(home, privateSignerArmor); err != nil {
return err
}
signerFingerprints, err := listFingerprints(home)
if err != nil {
return err
}
args = append(args, "--sign", "--local-user", signerFingerprints[0])
}
output, _, err := runGPG(home, args, message, maxOpenPGPMessageBytes)
if err != nil {
return fmt.Errorf("encrypt OpenPGP message: %w", err)
}
encrypted = output
return nil
})
return string(encrypted), err
}
// DecryptOpenPGP decrypts an ASCII-armored or binary OpenPGP message with a
// user-provided private key. A bad embedded signature is rejected.
func DecryptOpenPGP(message []byte, privateKeyArmor string) ([]byte, error) {
var plaintext []byte
err := withGPG(func(home string) error {
if err := importOpenPGP(home, privateKeyArmor); err != nil {
return err
}
output, status, err := runGPG(home, []string{"--status-fd", "2", "--decrypt", "--output", "-"}, message, maxOpenPGPMessageBytes)
if strings.Contains(status, "[GNUPG:] BADSIG") || strings.Contains(status, "[GNUPG:] ERRSIG") {
return errors.New("authenticate OpenPGP message: invalid signature")
}
if err != nil {
return fmt.Errorf("decrypt OpenPGP message: %w", err)
}
plaintext = output
return nil
})
return plaintext, err
}
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