Move manifest package to schema1

As we begin our march towards multi-arch, we must prepare for the reality of
multiple manifest schemas. This is the beginning of a set of changes to
facilitate this. We are both moving this package into its target position where
it may live peacefully next to other manfiest versions.

Signed-off-by: Stephen J Day <stephen.day@docker.com>

manifest/schema1/verify.go

@@ -0,0 +1,32 @@
+package schema1
+
+import (
+	"crypto/x509"
+
+	"github.com/Sirupsen/logrus"
+	"github.com/docker/libtrust"
+)
+
+// Verify verifies the signature of the signed manifest returning the public
+// keys used during signing.
+func Verify(sm *SignedManifest) ([]libtrust.PublicKey, error) {
+	js, err := libtrust.ParsePrettySignature(sm.Raw, "signatures")
+	if err != nil {
+		logrus.WithField("err", err).Debugf("(*SignedManifest).Verify")
+		return nil, err
+	}
+
+	return js.Verify()
+}
+
+// VerifyChains verifies the signature of the signed manifest against the
+// certificate pool returning the list of verified chains. Signatures without
+// an x509 chain are not checked.
+func VerifyChains(sm *SignedManifest, ca *x509.CertPool) ([][]*x509.Certificate, error) {
+	js, err := libtrust.ParsePrettySignature(sm.Raw, "signatures")
+	if err != nil {
+		return nil, err
+	}
+
+	return js.VerifyChains(ca)
+}