Merge pull request #322 from mtrmac/x-registry-supports-signatures

Add support for the X-Registry-Supports-Signatures API extension

integration/copy_test.go

@@ -473,6 +473,64 @@ func (s *CopySuite) TestCopyDockerSigstore(c *check.C) {
 	assertSkopeoSucceeds(c, "", "--tls-verify=false", "--policy", policy, "--registries.d", registriesDir, "copy", ourRegistry+"public/busybox", dirDest)
 }
 
+// atomic: and docker: X-Registry-Supports-Signatures works and interoperates
+func (s *CopySuite) TestCopyAtomicExtension(c *check.C) {
+	mech, _, err := signature.NewEphemeralGPGSigningMechanism([]byte{})
+	c.Assert(err, check.IsNil)
+	defer mech.Close()
+	if err := mech.SupportsSigning(); err != nil { // FIXME? Test that the reading/writing works using signatures from fixtures
+		c.Skip(fmt.Sprintf("Signing not supported: %v", err))
+	}
+
+	topDir, err := ioutil.TempDir("", "atomic-extension")
+	c.Assert(err, check.IsNil)
+	defer os.RemoveAll(topDir)
+	for _, subdir := range []string{"dirAA", "dirAD", "dirDA", "dirDD", "registries.d"} {
+		err := os.MkdirAll(filepath.Join(topDir, subdir), 0755)
+		c.Assert(err, check.IsNil)
+	}
+	registriesDir := filepath.Join(topDir, "registries.d")
+	dirDest := "dir:" + topDir
+	policy := fileFromFixture(c, "fixtures/policy.json", map[string]string{"@keydir@": s.gpgHome})
+	defer os.Remove(policy)
+
+	// Get an image to work with to an atomic: destination.  Also verifies that we can use Docker repositories without X-Registry-Supports-Signatures
+	assertSkopeoSucceeds(c, "", "--tls-verify=false", "--registries.d", registriesDir, "copy", "docker://busybox", "atomic:localhost:5000/myns/extension:unsigned")
+	// Pulling an unsigned image using atomic: fails.
+	assertSkopeoFails(c, ".*Source image rejected: A signature was required, but no signature exists.*",
+		"--tls-verify=false", "--policy", policy,
+		"copy", "atomic:localhost:5000/myns/extension:unsigned", dirDest+"/dirAA")
+	// The same when pulling using docker:
+	assertSkopeoFails(c, ".*Source image rejected: A signature was required, but no signature exists.*",
+		"--tls-verify=false", "--policy", policy, "--registries.d", registriesDir,
+		"copy", "docker://localhost:5000/myns/extension:unsigned", dirDest+"/dirAD")
+
+	// Sign the image using atomic:
+	assertSkopeoSucceeds(c, "", "--tls-verify=false",
+		"copy", "--sign-by", "personal@example.com", "atomic:localhost:5000/myns/extension:unsigned", "atomic:localhost:5000/myns/extension:atomic")
+	// Pulling the image using atomic: now succeeds.
+	assertSkopeoSucceeds(c, "", "--tls-verify=false", "--policy", policy,
+		"copy", "atomic:localhost:5000/myns/extension:atomic", dirDest+"/dirAA")
+	// The same when pulling using docker:
+	assertSkopeoSucceeds(c, "", "--tls-verify=false", "--policy", policy, "--registries.d", registriesDir,
+		"copy", "docker://localhost:5000/myns/extension:atomic", dirDest+"/dirAD")
+	// Both access methods result in the same data.
+	destructiveCheckDirImagesAreEqual(c, filepath.Join(topDir, "dirAA"), filepath.Join(topDir, "dirAD"))
+
+	// Get another image (different so that they don't share signatures, and sign it using docker://)
+	assertSkopeoSucceeds(c, "", "--tls-verify=false", "--registries.d", registriesDir,
+		"copy", "--sign-by", "personal@example.com", "docker://estesp/busybox:ppc64le", "atomic:localhost:5000/myns/extension:extension")
+	c.Logf("%s", combinedOutputOfCommand(c, "oc", "get", "istag", "extension:extension", "-o", "json"))
+	// Pulling the image using atomic: succeeds.
+	assertSkopeoSucceeds(c, "", "--debug", "--tls-verify=false", "--policy", policy,
+		"copy", "atomic:localhost:5000/myns/extension:extension", dirDest+"/dirDA")
+	// The same when pulling using docker:
+	assertSkopeoSucceeds(c, "", "--debug", "--tls-verify=false", "--policy", policy, "--registries.d", registriesDir,
+		"copy", "docker://localhost:5000/myns/extension:extension", dirDest+"/dirDD")
+	// Both access methods result in the same data.
+	destructiveCheckDirImagesAreEqual(c, filepath.Join(topDir, "dirDA"), filepath.Join(topDir, "dirDD"))
+}
+
 func (s *SkopeoSuite) TestCopySrcWithAuth(c *check.C) {
 	assertSkopeoSucceeds(c, "", "--tls-verify=false", "copy", "--dest-creds=testuser:testpassword", "docker://busybox", fmt.Sprintf("docker://%s/busybox:latest", s.regV2WithAuth.url))
 	dir1, err := ioutil.TempDir("", "copy-1")

integration/fixtures/policy.json

@@ -13,6 +13,13 @@
                     "keyPath": "@keydir@/personal-pubkey.gpg"
                 }
             ],
+            "localhost:5000/myns/extension": [
+                {
+                    "type": "signedBy",
+                    "keyType": "GPGKeys",
+                    "keyPath": "@keydir@/personal-pubkey.gpg"
+                }
+            ],
             "docker.io/openshift": [
                 {
                     "type": "insecureAcceptAnything"
@@ -85,6 +92,13 @@
                     "keyType": "GPGKeys",
                     "keyPath": "@keydir@/personal-pubkey.gpg"
                 }
+            ],
+            "localhost:5000/myns/extension": [
+                {
+                    "type": "signedBy",
+                    "keyType": "GPGKeys",
+                    "keyPath": "@keydir@/personal-pubkey.gpg"
+                }
             ]
         }
     }

vendor/github.com/containers/image/docker/docker_client.go

@@ -18,8 +18,10 @@ import (
 	"github.com/containers/image/docker/reference"
 	"github.com/containers/image/types"
 	"github.com/containers/storage/pkg/homedir"
+	"github.com/docker/distribution/registry/client"
 	"github.com/docker/go-connections/sockets"
 	"github.com/docker/go-connections/tlsconfig"
+	"github.com/opencontainers/go-digest"
 	"github.com/pkg/errors"
 )
 
@@ -32,20 +34,38 @@ const (
 	dockerCfgFileName = "config.json"
 	dockerCfgObsolete = ".dockercfg"
 
-	baseURL       = "%s://%s/v2/"
-	baseURLV1     = "%s://%s/v1/_ping"
-	tagsURL       = "%s/tags/list"
-	manifestURL   = "%s/manifests/%s"
-	blobsURL      = "%s/blobs/%s"
-	blobUploadURL = "%s/blobs/uploads/"
+	resolvedPingV2URL       = "%s://%s/v2/"
+	resolvedPingV1URL       = "%s://%s/v1/_ping"
+	tagsPath                = "/v2/%s/tags/list"
+	manifestPath            = "/v2/%s/manifests/%s"
+	blobsPath               = "/v2/%s/blobs/%s"
+	blobUploadPath          = "/v2/%s/blobs/uploads/"
+	extensionsSignaturePath = "/extensions/v2/%s/signatures/%s"
 
 	minimumTokenLifetimeSeconds = 60
+
+	extensionSignatureSchemaVersion = 2        // extensionSignature.Version
+	extensionSignatureTypeAtomic    = "atomic" // extensionSignature.Type
 )
 
 // ErrV1NotSupported is returned when we're trying to talk to a
 // docker V1 registry.
 var ErrV1NotSupported = errors.New("can't talk to a V1 docker registry")
 
+// extensionSignature and extensionSignatureList come from github.com/openshift/origin/pkg/dockerregistry/server/signaturedispatcher.go:
+// signature represents a Docker image signature.
+type extensionSignature struct {
+	Version int    `json:"schemaVersion"` // Version specifies the schema version
+	Name    string `json:"name"`          // Name must be in "sha256:<digest>@signatureName" format
+	Type    string `json:"type"`          // Type is optional, of not set it will be defaulted to "AtomicImageV1"
+	Content []byte `json:"content"`       // Content contains the signature
+}
+
+// signatureList represents list of Docker image signatures.
+type extensionSignatureList struct {
+	Signatures []extensionSignature `json:"signatures"`
+}
+
 type bearerToken struct {
 	Token     string    `json:"token"`
 	ExpiresIn int       `json:"expires_in"`
@@ -54,15 +74,20 @@ type bearerToken struct {
 
 // dockerClient is configuration for dealing with a single Docker registry.
 type dockerClient struct {
-	ctx             *types.SystemContext
-	registry        string
-	username        string
-	password        string
-	scheme          string // Cache of a value returned by a successful ping() if not empty
-	client          *http.Client
-	signatureBase   signatureStorageBase
-	challenges      []challenge
-	scope           authScope
+	// The following members are set by newDockerClient and do not change afterwards.
+	ctx           *types.SystemContext
+	registry      string
+	username      string
+	password      string
+	client        *http.Client
+	signatureBase signatureStorageBase
+	scope         authScope
+	// The following members are detected registry properties:
+	// They are set after a successful detectProperties(), and never change afterwards.
+	scheme             string // Empty value also used to indicate detectProperties() has not yet succeeded.
+	challenges         []challenge
+	supportsSignatures bool
+	// The following members are private state for setupRequestAuth, both are valid if token != nil.
 	token           *bearerToken
 	tokenExpiration time.Time
 }
@@ -209,15 +234,13 @@ func newDockerClient(ctx *types.SystemContext, ref dockerReference, write bool,
 }
 
 // makeRequest creates and executes a http.Request with the specified parameters, adding authentication and TLS options for the Docker client.
-// url is NOT an absolute URL, but a path relative to the /v2/ top-level API path.  The host name and schema is taken from the client or autodetected.
-func (c *dockerClient) makeRequest(method, url string, headers map[string][]string, stream io.Reader) (*http.Response, error) {
-	if c.scheme == "" {
-		if err := c.ping(); err != nil {
-			return nil, err
-		}
+// The host name and schema is taken from the client or autodetected, and the path is relative to it, i.e. the path usually starts with /v2/.
+func (c *dockerClient) makeRequest(method, path string, headers map[string][]string, stream io.Reader) (*http.Response, error) {
+	if err := c.detectProperties(); err != nil {
+		return nil, err
 	}
 
-	url = fmt.Sprintf(baseURL, c.scheme, c.registry) + url
+	url := fmt.Sprintf("%s://%s%s", c.scheme, c.registry, path)
 	return c.makeRequestToResolvedURL(method, url, headers, stream, -1, true)
 }
 
@@ -398,21 +421,28 @@ func getAuth(ctx *types.SystemContext, registry string) (string, string, error)
 	return "", "", nil
 }
 
-func (c *dockerClient) ping() error {
+// detectProperties detects various properties of the registry.
+// See the dockerClient documentation for members which are affected by this.
+func (c *dockerClient) detectProperties() error {
+	if c.scheme != "" {
+		return nil
+	}
+
 	ping := func(scheme string) error {
-		url := fmt.Sprintf(baseURL, scheme, c.registry)
+		url := fmt.Sprintf(resolvedPingV2URL, scheme, c.registry)
 		resp, err := c.makeRequestToResolvedURL("GET", url, nil, nil, -1, true)
 		logrus.Debugf("Ping %s err %#v", url, err)
 		if err != nil {
 			return err
 		}
 		defer resp.Body.Close()
-		logrus.Debugf("Ping %s status %d", scheme+"://"+c.registry+"/v2/", resp.StatusCode)
+		logrus.Debugf("Ping %s status %d", url, resp.StatusCode)
 		if resp.StatusCode != http.StatusOK && resp.StatusCode != http.StatusUnauthorized {
 			return errors.Errorf("error pinging repository, response code %d", resp.StatusCode)
 		}
 		c.challenges = parseAuthHeader(resp.Header)
 		c.scheme = scheme
+		c.supportsSignatures = resp.Header.Get("X-Registry-Supports-Signatures") == "1"
 		return nil
 	}
 	err := ping("https")
@@ -426,14 +456,14 @@ func (c *dockerClient) ping() error {
 		}
 		// best effort to understand if we're talking to a V1 registry
 		pingV1 := func(scheme string) bool {
-			url := fmt.Sprintf(baseURLV1, scheme, c.registry)
+			url := fmt.Sprintf(resolvedPingV1URL, scheme, c.registry)
 			resp, err := c.makeRequestToResolvedURL("GET", url, nil, nil, -1, true)
 			logrus.Debugf("Ping %s err %#v", url, err)
 			if err != nil {
 				return false
 			}
 			defer resp.Body.Close()
-			logrus.Debugf("Ping %s status %d", scheme+"://"+c.registry+"/v1/_ping", resp.StatusCode)
+			logrus.Debugf("Ping %s status %d", url, resp.StatusCode)
 			if resp.StatusCode != http.StatusOK && resp.StatusCode != http.StatusUnauthorized {
 				return false
 			}
@@ -450,6 +480,30 @@ func (c *dockerClient) ping() error {
 	return err
 }
 
+// getExtensionsSignatures returns signatures from the X-Registry-Supports-Signatures API extension,
+// using the original data structures.
+func (c *dockerClient) getExtensionsSignatures(ref dockerReference, manifestDigest digest.Digest) (*extensionSignatureList, error) {
+	path := fmt.Sprintf(extensionsSignaturePath, reference.Path(ref.ref), manifestDigest)
+	res, err := c.makeRequest("GET", path, nil, nil)
+	if err != nil {
+		return nil, err
+	}
+	defer res.Body.Close()
+	if res.StatusCode != http.StatusOK {
+		return nil, client.HandleErrorResponse(res)
+	}
+	body, err := ioutil.ReadAll(res.Body)
+	if err != nil {
+		return nil, err
+	}
+
+	var parsedBody extensionSignatureList
+	if err := json.Unmarshal(body, &parsedBody); err != nil {
+		return nil, errors.Wrapf(err, "Error decoding signature list")
+	}
+	return &parsedBody, nil
+}
+
 func getDefaultConfigDir(confPath string) string {
 	return filepath.Join(homedir.Get(), confPath)
 }

vendor/github.com/containers/image/docker/docker_image.go

@@ -40,8 +40,8 @@ func (i *Image) SourceRefFullName() string {
 
 // GetRepositoryTags list all tags available in the repository. Note that this has no connection with the tag(s) used for this specific image, if any.
 func (i *Image) GetRepositoryTags() ([]string, error) {
-	url := fmt.Sprintf(tagsURL, reference.Path(i.src.ref.ref))
-	res, err := i.src.c.makeRequest("GET", url, nil, nil)
+	path := fmt.Sprintf(tagsPath, reference.Path(i.src.ref.ref))
+	res, err := i.src.c.makeRequest("GET", path, nil, nil)
 	if err != nil {
 		return nil, err
 	}

vendor/github.com/containers/image/docker/docker_image_dest.go

@@ -2,6 +2,8 @@ package docker
 
 import (
 	"bytes"
+	"crypto/rand"
+	"encoding/json"
 	"fmt"
 	"io"
 	"io/ioutil"
@@ -70,7 +72,17 @@ func (d *dockerImageDestination) SupportedManifestMIMETypes() []string {
 // SupportsSignatures returns an error (to be displayed to the user) if the destination certainly can't store signatures.
 // Note: It is still possible for PutSignatures to fail if SupportsSignatures returns nil.
 func (d *dockerImageDestination) SupportsSignatures() error {
-	return errors.Errorf("Pushing signatures to a Docker Registry is not supported")
+	if err := d.c.detectProperties(); err != nil {
+		return err
+	}
+	switch {
+	case d.c.signatureBase != nil:
+		return nil
+	case d.c.supportsSignatures:
+		return nil
+	default:
+		return errors.Errorf("X-Registry-Supports-Signatures extension not supported, and lookaside is not configured")
+	}
 }
 
 // ShouldCompressLayers returns true iff it is desirable to compress layer blobs written to this destination.
@@ -111,16 +123,16 @@ func (d *dockerImageDestination) PutBlob(stream io.Reader, inputInfo types.BlobI
 	}
 
 	// FIXME? Chunked upload, progress reporting, etc.
-	uploadURL := fmt.Sprintf(blobUploadURL, reference.Path(d.ref.ref))
-	logrus.Debugf("Uploading %s", uploadURL)
-	res, err := d.c.makeRequest("POST", uploadURL, nil, nil)
+	uploadPath := fmt.Sprintf(blobUploadPath, reference.Path(d.ref.ref))
+	logrus.Debugf("Uploading %s", uploadPath)
+	res, err := d.c.makeRequest("POST", uploadPath, nil, nil)
 	if err != nil {
 		return types.BlobInfo{}, err
 	}
 	defer res.Body.Close()
 	if res.StatusCode != http.StatusAccepted {
 		logrus.Debugf("Error initiating layer upload, response %#v", *res)
-		return types.BlobInfo{}, errors.Errorf("Error initiating layer upload to %s, status %d", uploadURL, res.StatusCode)
+		return types.BlobInfo{}, errors.Errorf("Error initiating layer upload to %s, status %d", uploadPath, res.StatusCode)
 	}
 	uploadLocation, err := res.Location()
 	if err != nil {
@@ -167,10 +179,10 @@ func (d *dockerImageDestination) HasBlob(info types.BlobInfo) (bool, int64, erro
 	if info.Digest == "" {
 		return false, -1, errors.Errorf(`"Can not check for a blob with unknown digest`)
 	}
-	checkURL := fmt.Sprintf(blobsURL, reference.Path(d.ref.ref), info.Digest.String())
+	checkPath := fmt.Sprintf(blobsPath, reference.Path(d.ref.ref), info.Digest.String())
 
-	logrus.Debugf("Checking %s", checkURL)
-	res, err := d.c.makeRequest("HEAD", checkURL, nil, nil)
+	logrus.Debugf("Checking %s", checkPath)
+	res, err := d.c.makeRequest("HEAD", checkPath, nil, nil)
 	if err != nil {
 		return false, -1, err
 	}
@@ -205,14 +217,14 @@ func (d *dockerImageDestination) PutManifest(m []byte) error {
 	if err != nil {
 		return err
 	}
-	url := fmt.Sprintf(manifestURL, reference.Path(d.ref.ref), refTail)
+	path := fmt.Sprintf(manifestPath, reference.Path(d.ref.ref), refTail)
 
 	headers := map[string][]string{}
 	mimeType := manifest.GuessMIMEType(m)
 	if mimeType != "" {
 		headers["Content-Type"] = []string{mimeType}
 	}
-	res, err := d.c.makeRequest("PUT", url, headers, bytes.NewReader(m))
+	res, err := d.c.makeRequest("PUT", path, headers, bytes.NewReader(m))
 	if err != nil {
 		return err
 	}
@@ -223,12 +235,32 @@ func (d *dockerImageDestination) PutManifest(m []byte) error {
 			logrus.Debugf("Error body %s", string(body))
 		}
 		logrus.Debugf("Error uploading manifest, status %d, %#v", res.StatusCode, res)
-		return errors.Errorf("Error uploading manifest to %s, status %d", url, res.StatusCode)
+		return errors.Errorf("Error uploading manifest to %s, status %d", path, res.StatusCode)
 	}
 	return nil
 }
 
 func (d *dockerImageDestination) PutSignatures(signatures [][]byte) error {
+	// Do not fail if we don’t really need to support signatures.
+	if len(signatures) == 0 {
+		return nil
+	}
+	if err := d.c.detectProperties(); err != nil {
+		return err
+	}
+	switch {
+	case d.c.signatureBase != nil:
+		return d.putSignaturesToLookaside(signatures)
+	case d.c.supportsSignatures:
+		return d.putSignaturesToAPIExtension(signatures)
+	default:
+		return errors.Errorf("X-Registry-Supports-Signatures extension not supported, and lookaside is not configured")
+	}
+}
+
+// putSignaturesToLookaside implements PutSignatures() from the lookaside location configured in s.c.signatureBase,
+// which is not nil.
+func (d *dockerImageDestination) putSignaturesToLookaside(signatures [][]byte) error {
 	// FIXME? This overwrites files one at a time, definitely not atomic.
 	// A failure when updating signatures with a reordered copy could lose some of them.
 
@@ -236,9 +268,6 @@ func (d *dockerImageDestination) PutSignatures(signatures [][]byte) error {
 	if len(signatures) == 0 {
 		return nil
 	}
-	if d.c.signatureBase == nil {
-		return errors.Errorf("Pushing signatures to a Docker Registry is not supported, and there is no applicable signature storage configured")
-	}
 
 	if d.manifestDigest.String() == "" {
 		// This shouldn’t happen, ImageDestination users are required to call PutManifest before PutSignatures
@@ -318,6 +347,82 @@ func (c *dockerClient) deleteOneSignature(url *url.URL) (missing bool, err error
 	}
 }
 
+// putSignaturesToAPIExtension implements PutSignatures() using the X-Registry-Supports-Signatures API extension.
+func (d *dockerImageDestination) putSignaturesToAPIExtension(signatures [][]byte) error {
+	// Skip dealing with the manifest digest, or reading the old state, if not necessary.
+	if len(signatures) == 0 {
+		return nil
+	}
+
+	if d.manifestDigest.String() == "" {
+		// This shouldn’t happen, ImageDestination users are required to call PutManifest before PutSignatures
+		return errors.Errorf("Unknown manifest digest, can't add signatures")
+	}
+
+	// Because image signatures are a shared resource in Atomic Registry, the default upload
+	// always adds signatures.  Eventually we should also allow removing signatures,
+	// but the X-Registry-Supports-Signatures API extension does not support that yet.
+
+	existingSignatures, err := d.c.getExtensionsSignatures(d.ref, d.manifestDigest)
+	if err != nil {
+		return err
+	}
+	existingSigNames := map[string]struct{}{}
+	for _, sig := range existingSignatures.Signatures {
+		existingSigNames[sig.Name] = struct{}{}
+	}
+
+sigExists:
+	for _, newSig := range signatures {
+		for _, existingSig := range existingSignatures.Signatures {
+			if existingSig.Version == extensionSignatureSchemaVersion && existingSig.Type == extensionSignatureTypeAtomic && bytes.Equal(existingSig.Content, newSig) {
+				continue sigExists
+			}
+		}
+
+		// The API expect us to invent a new unique name. This is racy, but hopefully good enough.
+		var signatureName string
+		for {
+			randBytes := make([]byte, 16)
+			n, err := rand.Read(randBytes)
+			if err != nil || n != 16 {
+				return errors.Wrapf(err, "Error generating random signature len %d", n)
+			}
+			signatureName = fmt.Sprintf("%s@%032x", d.manifestDigest.String(), randBytes)
+			if _, ok := existingSigNames[signatureName]; !ok {
+				break
+			}
+		}
+		sig := extensionSignature{
+			Version: extensionSignatureSchemaVersion,
+			Name:    signatureName,
+			Type:    extensionSignatureTypeAtomic,
+			Content: newSig,
+		}
+		body, err := json.Marshal(sig)
+		if err != nil {
+			return err
+		}
+
+		path := fmt.Sprintf(extensionsSignaturePath, reference.Path(d.ref.ref), d.manifestDigest.String())
+		res, err := d.c.makeRequest("PUT", path, nil, bytes.NewReader(body))
+		if err != nil {
+			return err
+		}
+		defer res.Body.Close()
+		if res.StatusCode != http.StatusCreated {
+			body, err := ioutil.ReadAll(res.Body)
+			if err == nil {
+				logrus.Debugf("Error body %s", string(body))
+			}
+			logrus.Debugf("Error uploading signature, status %d, %#v", res.StatusCode, res)
+			return errors.Errorf("Error uploading signature to %s, status %d", path, res.StatusCode)
+		}
+	}
+
+	return nil
+}
+
 // Commit marks the process of storing the image as successful and asks for the image to be persisted.
 // WARNING: This does not have any transactional semantics:
 // - Uploaded data MAY be visible to others before Commit() is called

vendor/github.com/containers/image/docker/docker_image_src.go

@@ -93,10 +93,10 @@ func (s *dockerImageSource) GetManifest() ([]byte, string, error) {
 }
 
 func (s *dockerImageSource) fetchManifest(tagOrDigest string) ([]byte, string, error) {
-	url := fmt.Sprintf(manifestURL, reference.Path(s.ref.ref), tagOrDigest)
+	path := fmt.Sprintf(manifestPath, reference.Path(s.ref.ref), tagOrDigest)
 	headers := make(map[string][]string)
 	headers["Accept"] = s.requestedManifestMIMETypes
-	res, err := s.c.makeRequest("GET", url, headers, nil)
+	res, err := s.c.makeRequest("GET", path, headers, nil)
 	if err != nil {
 		return nil, "", err
 	}
@@ -179,9 +179,9 @@ func (s *dockerImageSource) GetBlob(info types.BlobInfo) (io.ReadCloser, int64,
 		return s.getExternalBlob(info.URLs)
 	}
 
-	url := fmt.Sprintf(blobsURL, reference.Path(s.ref.ref), info.Digest.String())
-	logrus.Debugf("Downloading %s", url)
-	res, err := s.c.makeRequest("GET", url, nil, nil)
+	path := fmt.Sprintf(blobsPath, reference.Path(s.ref.ref), info.Digest.String())
+	logrus.Debugf("Downloading %s", path)
+	res, err := s.c.makeRequest("GET", path, nil, nil)
 	if err != nil {
 		return nil, 0, err
 	}
@@ -193,10 +193,22 @@ func (s *dockerImageSource) GetBlob(info types.BlobInfo) (io.ReadCloser, int64,
 }
 
 func (s *dockerImageSource) GetSignatures() ([][]byte, error) {
-	if s.c.signatureBase == nil { // Skip dealing with the manifest digest if not necessary.
+	if err := s.c.detectProperties(); err != nil {
+		return nil, err
+	}
+	switch {
+	case s.c.signatureBase != nil:
+		return s.getSignaturesFromLookaside()
+	case s.c.supportsSignatures:
+		return s.getSignaturesFromAPIExtension()
+	default:
 		return [][]byte{}, nil
 	}
+}
 
+// getSignaturesFromLookaside implements GetSignatures() from the lookaside location configured in s.c.signatureBase,
+// which is not nil.
+func (s *dockerImageSource) getSignaturesFromLookaside() ([][]byte, error) {
 	if err := s.ensureManifestIsLoaded(); err != nil {
 		return nil, err
 	}
@@ -261,6 +273,30 @@ func (s *dockerImageSource) getOneSignature(url *url.URL) (signature []byte, mis
 	}
 }
 
+// getSignaturesFromAPIExtension implements GetSignatures() using the X-Registry-Supports-Signatures API extension.
+func (s *dockerImageSource) getSignaturesFromAPIExtension() ([][]byte, error) {
+	if err := s.ensureManifestIsLoaded(); err != nil {
+		return nil, err
+	}
+	manifestDigest, err := manifest.Digest(s.cachedManifest)
+	if err != nil {
+		return nil, err
+	}
+
+	parsedBody, err := s.c.getExtensionsSignatures(s.ref, manifestDigest)
+	if err != nil {
+		return nil, err
+	}
+
+	var sigs [][]byte
+	for _, sig := range parsedBody.Signatures {
+		if sig.Version == extensionSignatureSchemaVersion && sig.Type == extensionSignatureTypeAtomic {
+			sigs = append(sigs, sig.Content)
+		}
+	}
+	return sigs, nil
+}
+
 // deleteImage deletes the named image from the registry, if supported.
 func deleteImage(ctx *types.SystemContext, ref dockerReference) error {
 	c, err := newDockerClient(ctx, ref, true, "push")
@@ -277,8 +313,8 @@ func deleteImage(ctx *types.SystemContext, ref dockerReference) error {
 	if err != nil {
 		return err
 	}
-	getURL := fmt.Sprintf(manifestURL, reference.Path(ref.ref), refTail)
-	get, err := c.makeRequest("GET", getURL, headers, nil)
+	getPath := fmt.Sprintf(manifestPath, reference.Path(ref.ref), refTail)
+	get, err := c.makeRequest("GET", getPath, headers, nil)
 	if err != nil {
 		return err
 	}
@@ -296,11 +332,11 @@ func deleteImage(ctx *types.SystemContext, ref dockerReference) error {
 	}
 
 	digest := get.Header.Get("Docker-Content-Digest")
-	deleteURL := fmt.Sprintf(manifestURL, reference.Path(ref.ref), digest)
+	deletePath := fmt.Sprintf(manifestPath, reference.Path(ref.ref), digest)
 
 	// When retrieving the digest from a registry >= 2.3 use the following header:
 	//   "Accept": "application/vnd.docker.distribution.manifest.v2+json"
-	delete, err := c.makeRequest("DELETE", deleteURL, headers, nil)
+	delete, err := c.makeRequest("DELETE", deletePath, headers, nil)
 	if err != nil {
 		return err
 	}
@@ -311,7 +347,7 @@ func deleteImage(ctx *types.SystemContext, ref dockerReference) error {
 		return err
 	}
 	if delete.StatusCode != http.StatusAccepted {
-		return errors.Errorf("Failed to delete %v: %s (%v)", deleteURL, string(body), delete.Status)
+		return errors.Errorf("Failed to delete %v: %s (%v)", deletePath, string(body), delete.Status)
 	}
 
 	if c.signatureBase != nil {