diff --git a/go.mod b/go.mod
index cc95f887..936759b7 100644
--- a/go.mod
+++ b/go.mod
@@ -11,7 +11,7 @@ require (
 	github.com/google/certificate-transparency-go v1.1.8
 	github.com/in-toto/in-toto-golang v0.9.0
 	github.com/secure-systems-lab/go-securesystemslib v0.8.0
-	github.com/sigstore/protobuf-specs v0.2.1
+	github.com/sigstore/protobuf-specs v0.3.0
 	github.com/sigstore/rekor v1.3.5
 	github.com/sigstore/sigstore v1.8.2
 	github.com/sigstore/timestamp-authority v1.2.2
diff --git a/go.sum b/go.sum
index 3100f05d..f3115e90 100644
--- a/go.sum
+++ b/go.sum
@@ -249,8 +249,8 @@ github.com/sergi/go-diff v1.3.1 h1:xkr+Oxo4BOQKmkn/B9eMK0g5Kg/983T9DqqPHwYqD+8=
 github.com/sergi/go-diff v1.3.1/go.mod h1:aMJSSKb2lpPvRNec0+w3fl7LP9IOFzdc9Pa4NFbPK1I=
 github.com/shibumi/go-pathspec v1.3.0 h1:QUyMZhFo0Md5B8zV8x2tesohbb5kfbpTi9rBnKh5dkI=
 github.com/shibumi/go-pathspec v1.3.0/go.mod h1:Xutfslp817l2I1cZvgcfeMQJG5QnU2lh5tVaaMCl3jE=
-github.com/sigstore/protobuf-specs v0.2.1 h1:KIoM7E3C4uaK092q8YoSj/XSf9720f8dlsbYwwOmgEA=
-github.com/sigstore/protobuf-specs v0.2.1/go.mod h1:xPqQGnH/HllKuZ4VFPz/g+78epWM/NLRGl7Fuy45UdE=
+github.com/sigstore/protobuf-specs v0.3.0 h1:E49qS++llp4psM+3NNVEb+C4AD422bT9VkOQIPrNLpA=
+github.com/sigstore/protobuf-specs v0.3.0/go.mod h1:ynKzXpqr3dUj2Xk9O/5ZUhjnpi0F53DNi5AdH6pS3jc=
 github.com/sigstore/rekor v1.3.5 h1:QoVXcS7NppKY+rpbEFVHr4evGDZBBSh65X0g8PXoUkQ=
 github.com/sigstore/rekor v1.3.5/go.mod h1:CWqOk/fmnPwORQmm7SyDgB54GTJizqobbZ7yOP1lvw8=
 github.com/sigstore/sigstore v1.8.2 h1:0Ttjcn3V0fVQXlYq7+oHaaHkGFIt3ywm7SF4JTU/l8c=
diff --git a/pkg/bundle/bundle.go b/pkg/bundle/bundle.go
index 0aab8629..bd54575c 100644
--- a/pkg/bundle/bundle.go
+++ b/pkg/bundle/bundle.go
@@ -35,6 +35,8 @@ import (
 
 const SigstoreBundleMediaType01 = "application/vnd.dev.sigstore.bundle+json;version=0.1"
 const SigstoreBundleMediaType02 = "application/vnd.dev.sigstore.bundle+json;version=0.2"
+const SigstoreBundleMediaType03Legacy = "application/vnd.dev.sigstore.bundle+json;version=0.3"
+const SigstoreBundleMediaType03 = "application/vnd.dev.sigstore.bundle.v0.3+json"
 const IntotoMediaType = "application/vnd.in-toto+json"
 
 var ErrValidation = errors.New("validation error")
@@ -86,6 +88,12 @@ func (b *ProtobufBundle) validate() error {
 		if len(entries) > 0 && !b.hasInclusionProof {
 			return errors.New("inclusion proof missing in bundle (required for bundle v0.2)")
 		}
+	case SigstoreBundleMediaType03, SigstoreBundleMediaType03Legacy:
+		certs := b.Bundle.VerificationMaterial.GetX509CertificateChain()
+
+		if certs != nil {
+			return errors.New("verification material cannot be X.509 certificate chain (for bundle v0.3)")
+		}
 	default:
 		return ErrIncorrectMediaType
 	}
@@ -137,21 +145,26 @@ func (b *ProtobufBundle) VerificationContent() (verify.VerificationContent, erro
 	switch content := b.VerificationMaterial.GetContent().(type) {
 	case *protobundle.VerificationMaterial_X509CertificateChain:
 		certs := content.X509CertificateChain.GetCertificates()
-		certificates := make([]*x509.Certificate, len(certs))
-		var err error
-		for i, cert := range content.X509CertificateChain.GetCertificates() {
-			certificates[i], err = x509.ParseCertificate(cert.RawBytes)
-			if err != nil {
-				return nil, ErrValidationError(err)
-			}
-		}
-		if len(certificates) == 0 {
+		if len(certs) == 0 {
 			return nil, ErrMissingVerificationMaterial
 		}
-		certChain := &CertificateChain{
-			Certificates: certificates,
+		parsedCert, err := x509.ParseCertificate(certs[0].RawBytes)
+		if err != nil {
+			return nil, ErrValidationError(err)
+		}
+		cert := &Certificate{
+			Certificate: parsedCert,
+		}
+		return cert, nil
+	case *protobundle.VerificationMaterial_Certificate:
+		parsedCert, err := x509.ParseCertificate(content.Certificate.RawBytes)
+		if err != nil {
+			return nil, ErrValidationError(err)
+		}
+		cert := &Certificate{
+			Certificate: parsedCert,
 		}
-		return certChain, nil
+		return cert, nil
 	case *protobundle.VerificationMaterial_PublicKey:
 		pk := &PublicKey{
 			hint: content.PublicKey.Hint,
diff --git a/pkg/bundle/verification_content.go b/pkg/bundle/verification_content.go
index 8982ccf0..8e41e791 100644
--- a/pkg/bundle/verification_content.go
+++ b/pkg/bundle/verification_content.go
@@ -23,8 +23,8 @@ import (
 	"github.com/sigstore/sigstore-go/pkg/verify"
 )
 
-type CertificateChain struct {
-	Certificates []*x509.Certificate
+type Certificate struct {
+	*x509.Certificate
 }
 
 type PublicKey struct {
@@ -35,35 +35,27 @@ func (pk PublicKey) Hint() string {
 	return pk.hint
 }
 
-func (cc *CertificateChain) CompareKey(key any, _ root.TrustedMaterial) bool {
+func (c *Certificate) CompareKey(key any, _ root.TrustedMaterial) bool {
 	x509Key, ok := key.(*x509.Certificate)
 	if !ok {
 		return false
 	}
 
-	return cc.Certificates[0].Equal(x509Key)
+	return c.Certificate.Equal(x509Key)
 }
 
-func (cc *CertificateChain) ValidAtTime(t time.Time, _ root.TrustedMaterial) bool {
-	return !(cc.Certificates[0].NotAfter.Before(t) || cc.Certificates[0].NotBefore.After(t))
+func (c *Certificate) ValidAtTime(t time.Time, _ root.TrustedMaterial) bool {
+	return !(c.Certificate.NotAfter.Before(t) || c.Certificate.NotBefore.After(t))
 }
 
-func (cc *CertificateChain) HasCertificate() (x509.Certificate, bool) {
-	return *cc.Certificates[0], true
+func (c *Certificate) HasCertificate() (x509.Certificate, bool) {
+	return *c.Certificate, true
 }
 
-func (pk *PublicKey) HasCertificate() (x509.Certificate, bool) {
-	return x509.Certificate{}, false
-}
-
-func (cc *CertificateChain) HasPublicKey() (verify.PublicKeyProvider, bool) {
+func (c *Certificate) HasPublicKey() (verify.PublicKeyProvider, bool) {
 	return PublicKey{}, false
 }
 
-func (pk *PublicKey) HasPublicKey() (verify.PublicKeyProvider, bool) {
-	return *pk, true
-}
-
 func (pk *PublicKey) CompareKey(key any, tm root.TrustedMaterial) bool {
 	verifier, err := tm.PublicKeyVerifier(pk.hint)
 	if err != nil {
@@ -86,3 +78,11 @@ func (pk *PublicKey) ValidAtTime(t time.Time, tm root.TrustedMaterial) bool {
 	}
 	return verifier.ValidAtTime(t)
 }
+
+func (pk *PublicKey) HasCertificate() (x509.Certificate, bool) {
+	return x509.Certificate{}, false
+}
+
+func (pk *PublicKey) HasPublicKey() (verify.PublicKeyProvider, bool) {
+	return *pk, true
+}
diff --git a/pkg/root/trusted_root.go b/pkg/root/trusted_root.go
index 28d161d7..3101d1f6 100644
--- a/pkg/root/trusted_root.go
+++ b/pkg/root/trusted_root.go
@@ -154,7 +154,8 @@ func ParseTransparencyLogs(tlogs []*prototrustroot.TransparencyLogInstance) (tra
 				PublicKey:         ecKey,
 				SignatureHashFunc: crypto.SHA256,
 			}
-		case protocommon.PublicKeyDetails_PKCS1_RSA_PKCS1V5:
+		// This key format is deprecated, but currently in use for Sigstore staging instance
+		case protocommon.PublicKeyDetails_PKCS1_RSA_PKCS1V5: //nolint:staticcheck
 			key, err := x509.ParsePKCS1PublicKey(tlog.GetPublicKey().GetRawBytes())
 			if err != nil {
 				return nil, err
diff --git a/pkg/testing/ca/ca.go b/pkg/testing/ca/ca.go
index e592f1a1..ee1e4cfe 100644
--- a/pkg/testing/ca/ca.go
+++ b/pkg/testing/ca/ca.go
@@ -477,7 +477,7 @@ type TestEntity struct {
 }
 
 func (e *TestEntity) VerificationContent() (verify.VerificationContent, error) {
-	return &bundle.CertificateChain{Certificates: e.certChain}, nil
+	return &bundle.Certificate{Certificate: e.certChain[0]}, nil
 }
 
 func (e *TestEntity) HasInclusionPromise() bool {