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Merge pull request #207 from mtrmac/openpgp
Allow choosing between a gpgme and openpgp signature backend using a build tag
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,175 @@ | ||
| // +build !containers_image_openpgp | ||
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| package signature | ||
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| import ( | ||
| "bytes" | ||
| "fmt" | ||
| "io/ioutil" | ||
| "os" | ||
|
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| "github.com/mtrmac/gpgme" | ||
| ) | ||
|
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| // 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() | ||
| } | ||
|
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||
| // 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 | ||
| } | ||
|
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| // 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 | ||
| } | ||
|
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| removeDir = false | ||
| return mech, keyIdentities, nil | ||
| } | ||
|
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| // 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 | ||
| } | ||
|
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||
| func (m *gpgmeSigningMechanism) Close() error { | ||
| if m.ephemeralDir != "" { | ||
| os.RemoveAll(m.ephemeralDir) // Ignore an error, if any | ||
| } | ||
| return nil | ||
| } | ||
|
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||
| // 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 | ||
| } | ||
|
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||
| // SupportsSigning returns nil if the mechanism supports signing, or a SigningNotSupportedError. | ||
| func (m *gpgmeSigningMechanism) SupportsSigning() error { | ||
| return nil | ||
| } | ||
|
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||
| // 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 | ||
| } | ||
|
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||
| // 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 | ||
| } | ||
|
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||
| // 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) | ||
| } |
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