122 lines
4 KiB
Go
122 lines
4 KiB
Go
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// Note: Consider the API unstable until the code supports at least three different image formats or transports.
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package signature
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import (
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"bytes"
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"fmt"
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"github.com/mtrmac/gpgme"
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)
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// SigningMechanism abstracts a way to sign binary blobs and verify their signatures.
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// FIXME: Eventually expand on keyIdentity (namespace them between mechanisms to
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// eliminate ambiguities, support CA signatures and perhaps other key properties)
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type SigningMechanism interface {
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// ImportKeysFromBytes imports public keys from the supplied blob and returns their identities.
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// The blob is assumed to have an appropriate format (the caller is expected to know which one).
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// NOTE: This may modify long-term state (e.g. key storage in a directory underlying the mechanism).
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ImportKeysFromBytes(blob []byte) ([]string, error)
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// Sign creates a (non-detached) signature of input using keyidentity
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Sign(input []byte, keyIdentity string) ([]byte, error)
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// Verify parses unverifiedSignature and returns the content and the signer's identity
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Verify(unverifiedSignature []byte) (contents []byte, keyIdentity string, err error)
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}
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// A GPG/OpenPGP signing mechanism.
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type gpgSigningMechanism struct {
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ctx *gpgme.Context
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}
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// NewGPGSigningMechanism returns a new GPG/OpenPGP signing mechanism.
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func NewGPGSigningMechanism() (SigningMechanism, error) {
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return newGPGSigningMechanismInDirectory("")
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}
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// newGPGSigningMechanismInDirectory returns a new GPG/OpenPGP signing mechanism, using optionalDir if not empty.
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func newGPGSigningMechanismInDirectory(optionalDir string) (SigningMechanism, error) {
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ctx, err := gpgme.New()
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if err != nil {
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return nil, err
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}
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if err = ctx.SetProtocol(gpgme.ProtocolOpenPGP); err != nil {
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return nil, err
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}
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if optionalDir != "" {
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err := ctx.SetEngineInfo(gpgme.ProtocolOpenPGP, "", optionalDir)
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if err != nil {
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return nil, err
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}
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}
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ctx.SetArmor(false)
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ctx.SetTextMode(false)
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return gpgSigningMechanism{ctx: ctx}, nil
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}
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// ImportKeysFromBytes implements SigningMechanism.ImportKeysFromBytes
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func (m gpgSigningMechanism) ImportKeysFromBytes(blob []byte) ([]string, error) {
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inputData, err := gpgme.NewDataBytes(blob)
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if err != nil {
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return nil, err
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}
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res, err := m.ctx.Import(inputData)
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if err != nil {
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return nil, err
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}
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keyIdentities := []string{}
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for _, i := range res.Imports {
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if i.Result == nil {
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keyIdentities = append(keyIdentities, i.Fingerprint)
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}
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}
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return keyIdentities, nil
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}
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// Sign implements SigningMechanism.Sign
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func (m gpgSigningMechanism) Sign(input []byte, keyIdentity string) ([]byte, error) {
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key, err := m.ctx.GetKey(keyIdentity, true)
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if err != nil {
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return nil, err
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}
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inputData, err := gpgme.NewDataBytes(input)
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if err != nil {
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return nil, err
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}
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var sigBuffer bytes.Buffer
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sigData, err := gpgme.NewDataWriter(&sigBuffer)
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if err != nil {
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return nil, err
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}
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if err = m.ctx.Sign([]*gpgme.Key{key}, inputData, sigData, gpgme.SigModeNormal); err != nil {
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return nil, err
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}
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return sigBuffer.Bytes(), nil
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}
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// Verify implements SigningMechanism.Verify
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func (m gpgSigningMechanism) Verify(unverifiedSignature []byte) (contents []byte, keyIdentity string, err error) {
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signedBuffer := bytes.Buffer{}
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signedData, err := gpgme.NewDataWriter(&signedBuffer)
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if err != nil {
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return nil, "", err
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}
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unverifiedSignatureData, err := gpgme.NewDataBytes(unverifiedSignature)
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if err != nil {
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return nil, "", err
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}
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_, sigs, err := m.ctx.Verify(unverifiedSignatureData, nil, signedData)
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if err != nil {
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return nil, "", err
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}
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if len(sigs) != 1 {
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return nil, "", InvalidSignatureError{msg: fmt.Sprintf("Unexpected GPG signature count %d", len(sigs))}
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}
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sig := sigs[0]
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// This is sig.Summary == gpgme.SigSumValid except for key trust, which we handle ourselves
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if sig.Status != nil || sig.Validity == gpgme.ValidityNever || sig.ValidityReason != nil || sig.WrongKeyUsage {
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// FIXME: Better error reporting eventually
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return nil, "", InvalidSignatureError{msg: fmt.Sprintf("Invalid GPG signature: %#v", sig)}
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}
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return signedBuffer.Bytes(), sig.Fingerprint, nil
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}
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