forked from containers/image
/
mechanism_gpgme.go
175 lines (161 loc) · 5.51 KB
/
mechanism_gpgme.go
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// +build !containers_image_openpgp
package signature
import (
"bytes"
"fmt"
"io/ioutil"
"os"
"github.com/mtrmac/gpgme"
)
// A GPG/OpenPGP signing mechanism, implemented using gpgme.
type gpgmeSigningMechanism struct {
ctx *gpgme.Context
ephemeralDir string // If not "", a directory to be removed on Close()
}
// newGPGSigningMechanismInDirectory returns a new GPG/OpenPGP signing mechanism, using optionalDir if not empty.
// The caller must call .Close() on the returned SigningMechanism.
func newGPGSigningMechanismInDirectory(optionalDir string) (SigningMechanism, error) {
ctx, err := newGPGMEContext(optionalDir)
if err != nil {
return nil, err
}
return &gpgmeSigningMechanism{
ctx: ctx,
ephemeralDir: "",
}, nil
}
// newEphemeralGPGSigningMechanism returns a new GPG/OpenPGP signing mechanism which
// recognizes _only_ public keys from the supplied blob, and returns the identities
// of these keys.
// The caller must call .Close() on the returned SigningMechanism.
func newEphemeralGPGSigningMechanism(blob []byte) (SigningMechanism, []string, error) {
dir, err := ioutil.TempDir("", "containers-ephemeral-gpg-")
if err != nil {
return nil, nil, err
}
removeDir := true
defer func() {
if removeDir {
os.RemoveAll(dir)
}
}()
ctx, err := newGPGMEContext(dir)
if err != nil {
return nil, nil, err
}
mech := &gpgmeSigningMechanism{
ctx: ctx,
ephemeralDir: dir,
}
keyIdentities, err := mech.importKeysFromBytes(blob)
if err != nil {
return nil, nil, err
}
removeDir = false
return mech, keyIdentities, nil
}
// newGPGMEContext returns a new *gpgme.Context, using optionalDir if not empty.
func newGPGMEContext(optionalDir string) (*gpgme.Context, error) {
ctx, err := gpgme.New()
if err != nil {
return nil, err
}
if err = ctx.SetProtocol(gpgme.ProtocolOpenPGP); err != nil {
return nil, err
}
if optionalDir != "" {
err := ctx.SetEngineInfo(gpgme.ProtocolOpenPGP, "", optionalDir)
if err != nil {
return nil, err
}
}
ctx.SetArmor(false)
ctx.SetTextMode(false)
return ctx, nil
}
func (m *gpgmeSigningMechanism) Close() error {
if m.ephemeralDir != "" {
os.RemoveAll(m.ephemeralDir) // Ignore an error, if any
}
return nil
}
// importKeysFromBytes imports public keys from the supplied blob and returns their identities.
// The blob is assumed to have an appropriate format (the caller is expected to know which one).
// NOTE: This may modify long-term state (e.g. key storage in a directory underlying the mechanism);
// but we do not make this public, it can only be used through newEphemeralGPGSigningMechanism.
func (m *gpgmeSigningMechanism) importKeysFromBytes(blob []byte) ([]string, error) {
inputData, err := gpgme.NewDataBytes(blob)
if err != nil {
return nil, err
}
res, err := m.ctx.Import(inputData)
if err != nil {
return nil, err
}
keyIdentities := []string{}
for _, i := range res.Imports {
if i.Result == nil {
keyIdentities = append(keyIdentities, i.Fingerprint)
}
}
return keyIdentities, nil
}
// SupportsSigning returns nil if the mechanism supports signing, or a SigningNotSupportedError.
func (m *gpgmeSigningMechanism) SupportsSigning() error {
return nil
}
// Sign creates a (non-detached) signature of input using keyIdentity.
// Fails with a SigningNotSupportedError if the mechanism does not support signing.
func (m *gpgmeSigningMechanism) Sign(input []byte, keyIdentity string) ([]byte, error) {
key, err := m.ctx.GetKey(keyIdentity, true)
if err != nil {
return nil, err
}
inputData, err := gpgme.NewDataBytes(input)
if err != nil {
return nil, err
}
var sigBuffer bytes.Buffer
sigData, err := gpgme.NewDataWriter(&sigBuffer)
if err != nil {
return nil, err
}
if err = m.ctx.Sign([]*gpgme.Key{key}, inputData, sigData, gpgme.SigModeNormal); err != nil {
return nil, err
}
return sigBuffer.Bytes(), nil
}
// Verify parses unverifiedSignature and returns the content and the signer's identity
func (m gpgmeSigningMechanism) Verify(unverifiedSignature []byte) (contents []byte, keyIdentity string, err error) {
signedBuffer := bytes.Buffer{}
signedData, err := gpgme.NewDataWriter(&signedBuffer)
if err != nil {
return nil, "", err
}
unverifiedSignatureData, err := gpgme.NewDataBytes(unverifiedSignature)
if err != nil {
return nil, "", err
}
_, sigs, err := m.ctx.Verify(unverifiedSignatureData, nil, signedData)
if err != nil {
return nil, "", err
}
if len(sigs) != 1 {
return nil, "", InvalidSignatureError{msg: fmt.Sprintf("Unexpected GPG signature count %d", len(sigs))}
}
sig := sigs[0]
// This is sig.Summary == gpgme.SigSumValid except for key trust, which we handle ourselves
if sig.Status != nil || sig.Validity == gpgme.ValidityNever || sig.ValidityReason != nil || sig.WrongKeyUsage {
// FIXME: Better error reporting eventually
return nil, "", InvalidSignatureError{msg: fmt.Sprintf("Invalid GPG signature: %#v", sig)}
}
return signedBuffer.Bytes(), sig.Fingerprint, nil
}
// UntrustedSignatureContents returns UNTRUSTED contents of the signature WITHOUT ANY VERIFICATION,
// along with a short identifier of the key used for signing.
// WARNING: The short key identifier (which correponds to "Key ID" for OpenPGP keys)
// is NOT the same as a "key identity" used in other calls ot this interface, and
// the values may have no recognizable relationship if the public key is not available.
func (m gpgmeSigningMechanism) UntrustedSignatureContents(untrustedSignature []byte) (untrustedContents []byte, shortKeyIdentifier string, err error) {
return gpgUntrustedSignatureContents(untrustedSignature)
}