diff --git a/marshal.go b/marshal.go
new file mode 100644
index 0000000..e94339b
--- /dev/null
+++ b/marshal.go
@@ -0,0 +1,25 @@
+package pkcs7
+
+import "encoding/asn1"
+
+func (p7 *PKCS7) Marshal() ([]byte, error) {
+	var contentType asn1.ObjectIdentifier
+	switch p7.raw.(type) {
+	case signedData:
+		contentType = OIDSignedData
+	case envelopedData:
+		contentType = OIDEnvelopedData
+	case encryptedData:
+		contentType = OIDEncryptedData
+	default:
+		return nil, ErrUnsupportedContentType
+	}
+	inner, err := asn1.Marshal(p7.raw)
+	if err != nil {
+		return nil, err
+	}
+	return asn1.Marshal(contentInfo{
+		ContentType: contentType,
+		Content:     asn1.RawValue{Class: 2, Tag: 0, Bytes: inner, IsCompound: true},
+	})
+}
diff --git a/marshal_test.go b/marshal_test.go
new file mode 100644
index 0000000..204b450
--- /dev/null
+++ b/marshal_test.go
@@ -0,0 +1,60 @@
+package pkcs7
+
+import (
+	"bytes"
+	"crypto/x509"
+	"encoding/pem"
+	"os"
+	"testing"
+)
+
+func TestPKCS7_Marshal(t *testing.T) {
+	content := []byte("Hello World")
+	rootCert, err := createTestCertificateByIssuer("PKCS7 Test Root CA", nil, x509.SHA256WithRSA, true)
+	if err != nil {
+		t.Fatalf("cannot generate root cert: %s", err)
+	}
+	truststore := x509.NewCertPool()
+	truststore.AddCert(rootCert.Certificate)
+	signerCert, err := createTestCertificateByIssuer("PKCS7 Test Signer Cert", rootCert, x509.SHA256WithRSA, false)
+	if err != nil {
+		t.Fatalf("cannot generate signer cert: %s", err)
+	}
+	toBeSigned, err := NewSignedData(content)
+	if err != nil {
+		t.Fatalf("cannot initialize signed data: %s", err)
+	}
+
+	// Set the digest to match the end entity cert
+	signerDigest, _ := getDigestOIDForSignatureAlgorithm(signerCert.Certificate.SignatureAlgorithm)
+	toBeSigned.SetDigestAlgorithm(signerDigest)
+
+	if err := toBeSigned.AddSignerChain(signerCert.Certificate, *signerCert.PrivateKey, nil, SignerInfoConfig{}); err != nil {
+		t.Fatalf("cannot add signer: %s", err)
+	}
+	signed, err := toBeSigned.Finish()
+	if err != nil {
+		t.Fatalf("cannot finish signing data: %s", err)
+	}
+	pem.Encode(os.Stdout, &pem.Block{Type: "PKCS7", Bytes: signed})
+
+	p7, err := Parse(signed)
+	if err != nil {
+		t.Fatalf("cannot parse signed data: %s", err)
+	}
+
+	marshaled, err := p7.Marshal()
+	if err != nil {
+		t.Fatalf("cannot marshal signed data: %s", err)
+	}
+	p7Reparsed, err := Parse(marshaled)
+	if err != nil {
+		t.Fatalf("cannot reparse signed data: %s", err)
+	}
+	if !bytes.Equal(p7.Content, p7Reparsed.Content) {
+		t.Errorf("content was not found in the reparsed data:\n\tExpected: %s\n\tActual: %s", p7.Content, p7Reparsed.Content)
+	}
+	if err := p7Reparsed.VerifyWithChain(truststore); err != nil {
+		t.Errorf("cannot verify reparsed data: %s", err)
+	}
+}
diff --git a/sign.go b/sign.go
index 31c3654..8ecc18d 100644
--- a/sign.go
+++ b/sign.go
@@ -23,6 +23,34 @@ type SignedData struct {
 	encryptionOid       asn1.ObjectIdentifier
 }
 
+// CopyWithUnsignedAttributes creates a copy of the PKCS7 struct with different unsigned attributes.
+func (p7 *PKCS7) CopyWithUnsignedAttributes(unauthenticatedAttrs ...Attribute) (*PKCS7, error) {
+	rawData, isSignedData := p7.raw.(signedData)
+	if !isSignedData {
+		return nil, ErrUnsupportedContentType
+	}
+
+	// Make a copy of the signer infos since we change them
+	rawData.SignerInfos = append([]signerInfo{}, rawData.SignerInfos...)
+	for i := range rawData.SignerInfos {
+		err := rawData.SignerInfos[i].SetUnauthenticatedAttributes(unauthenticatedAttrs)
+		if err != nil {
+			return nil, err
+		}
+	}
+	certs, err := rawData.Certificates.Parse()
+	if err != nil {
+		return nil, err
+	}
+	return &PKCS7{
+		Content:      p7.Content,
+		Certificates: certs,
+		CRLs:         rawData.CRLs,
+		Signers:      rawData.SignerInfos,
+		raw:          rawData,
+	}, nil
+}
+
 // NewSignedData takes data and initializes a PKCS7 SignedData struct that is
 // ready to be signed via AddSigner. The digest algorithm is set to SHA1 by default
 // and can be changed by calling SetDigestAlgorithm.
diff --git a/sign_test.go b/sign_test.go
index 0ba6324..ee1a2c4 100644
--- a/sign_test.go
+++ b/sign_test.go
@@ -264,3 +264,63 @@ func fromHex(s string) *big.Int {
 	}
 	return result
 }
+
+func TestCopyWithUnsignedAttributes(t *testing.T) {
+	content := []byte("Hello World")
+	rootCert, err := createTestCertificateByIssuer("PKCS7 Test Root CA", nil, x509.SHA256WithRSA, true)
+	if err != nil {
+		t.Fatalf("cannot generate root cert: %s", err)
+	}
+	truststore := x509.NewCertPool()
+	truststore.AddCert(rootCert.Certificate)
+	signerCert, err := createTestCertificateByIssuer("PKCS7 Test Signer Cert", rootCert, x509.SHA256WithRSA, false)
+	if err != nil {
+		t.Fatalf("cannot generate signer cert: %s", err)
+	}
+	toBeSigned, err := NewSignedData(content)
+	if err != nil {
+		t.Fatalf("cannot initialize signed data: %s", err)
+	}
+
+	// Set the digest to match the end entity cert
+	signerDigest, _ := getDigestOIDForSignatureAlgorithm(signerCert.Certificate.SignatureAlgorithm)
+	toBeSigned.SetDigestAlgorithm(signerDigest)
+
+	if err := toBeSigned.AddSignerChain(signerCert.Certificate, *signerCert.PrivateKey, nil, SignerInfoConfig{}); err != nil {
+		t.Fatalf("cannot add signer: %s", err)
+	}
+	signed, err := toBeSigned.Finish()
+	if err != nil {
+		t.Fatalf("cannot finish signing data: %s", err)
+	}
+	pem.Encode(os.Stdout, &pem.Block{Type: "PKCS7", Bytes: signed})
+
+	p7, err := Parse(signed)
+	if err != nil {
+		t.Fatalf("cannot parse signed data: %s", err)
+	}
+	testOid := asn1.ObjectIdentifier{2, 3, 4, 5, 6, 7}
+	testValue := "TestValue"
+	p7, err = p7.CopyWithUnsignedAttributes(Attribute{
+		Type:  testOid,
+		Value: testValue,
+	})
+	if err != nil {
+		t.Fatalf("cannot copy signed data: %s", err)
+	}
+
+	if !bytes.Equal(content, p7.Content) {
+		t.Errorf("content was not found in the copied data:\n\tExpected: %s\n\tActual: %s", content, p7.Content)
+	}
+	if err := p7.VerifyWithChain(truststore); err != nil {
+		t.Errorf("cannot verify copied data: %s", err)
+	}
+
+	var copiedValue string
+	if err := p7.UnmarshalUnsignedAttribute(testOid, &copiedValue); err != nil {
+		t.Fatalf("could not unmarshal attribute: %s", err)
+	}
+	if copiedValue != testValue {
+		t.Errorf("incorrect attribute value: %s", copiedValue)
+	}
+}
diff --git a/verify.go b/verify.go
index 2c6f32c..e1fed88 100644
--- a/verify.go
+++ b/verify.go
@@ -189,6 +189,19 @@ func (p7 *PKCS7) UnmarshalSignedAttribute(attributeType asn1.ObjectIdentifier, o
 	return unmarshalAttribute(attributes, attributeType, out)
 }
 
+// UnmarshalUnsignedAttribute decodes a single attribute from the signer info
+func (p7 *PKCS7) UnmarshalUnsignedAttribute(attributeType asn1.ObjectIdentifier, out interface{}) error {
+	sd, ok := p7.raw.(signedData)
+	if !ok {
+		return errors.New("pkcs7: payload is not signedData content")
+	}
+	if len(sd.SignerInfos) < 1 {
+		return errors.New("pkcs7: payload has no signers")
+	}
+	attributes := sd.SignerInfos[0].UnauthenticatedAttributes
+	return unmarshalAttribute(attributes, attributeType, out)
+}
+
 func parseSignedData(data []byte) (*PKCS7, error) {
 	var sd signedData
 	asn1.Unmarshal(data, &sd)
@@ -337,6 +350,14 @@ func getCertFromCertsByIssuerAndSerial(certs []*x509.Certificate, ias issuerAndS
 	return nil
 }
 
+type AttributeNotFoundError struct {
+	AttributeType asn1.ObjectIdentifier
+}
+
+func (a AttributeNotFoundError) Error() string {
+	return fmt.Sprintf("pkcs7: attribute %s does not exist", a.AttributeType)
+}
+
 func unmarshalAttribute(attrs []attribute, attributeType asn1.ObjectIdentifier, out interface{}) error {
 	for _, attr := range attrs {
 		if attr.Type.Equal(attributeType) {
@@ -344,5 +365,5 @@ func unmarshalAttribute(attrs []attribute, attributeType asn1.ObjectIdentifier,
 			return err
 		}
 	}
-	return errors.New("pkcs7: attribute type not in attributes")
+	return AttributeNotFoundError{AttributeType: attributeType}
 }