diff --git a/command_sign.go b/command_sign.go
index 5b09434a..efcf0bd5 100644
--- a/command_sign.go
+++ b/command_sign.go
@@ -6,10 +6,10 @@ import (
 	"io"
 	"os"
 
-	"github.com/github/smimesign/signature"
 	"github.com/pkg/errors"
 	"github.com/wlynch/smimecosign/fulcio"
 	"github.com/wlynch/smimecosign/git"
+	"github.com/wlynch/smimecosign/signature"
 )
 
 func commandSign() error {
diff --git a/command_verify.go b/command_verify.go
index ef4b7992..d5926c7b 100644
--- a/command_verify.go
+++ b/command_verify.go
@@ -8,10 +8,10 @@ import (
 	"io"
 	"os"
 
-	"github.com/github/smimesign/signature"
 	"github.com/pkg/errors"
 	"github.com/sigstore/cosign/cmd/cosign/cli/fulcio/fulcioroots"
 	"github.com/wlynch/smimecosign/git"
+	"github.com/wlynch/smimecosign/signature"
 )
 
 func commandVerify() error {
diff --git a/git/git.go b/git/git.go
index 2a164101..8adaf833 100644
--- a/git/git.go
+++ b/git/git.go
@@ -7,7 +7,6 @@ import (
 	"encoding/pem"
 
 	cms "github.com/github/smimesign/ietf-cms"
-	"github.com/github/smimesign/signature"
 	"github.com/go-git/go-git/v5/plumbing"
 	"github.com/go-git/go-git/v5/plumbing/object"
 	"github.com/pkg/errors"
@@ -15,6 +14,7 @@ import (
 	"github.com/sigstore/rekor/pkg/generated/models"
 	"github.com/wlynch/smimecosign/fulcio"
 	"github.com/wlynch/smimecosign/rekor"
+	"github.com/wlynch/smimecosign/signature"
 )
 
 func Sign(ctx context.Context, ident *fulcio.Identity, data []byte, opts signature.SignOptions) ([]byte, *x509.Certificate, error) {
diff --git a/go.mod b/go.mod
index 3c316a2e..3593e8f3 100644
--- a/go.mod
+++ b/go.mod
@@ -5,18 +5,17 @@ go 1.18
 require (
 	github.com/github/smimesign v0.2.0
 	github.com/go-git/go-git/v5 v5.4.2
+	github.com/go-openapi/runtime v0.24.0
 	github.com/go-openapi/strfmt v0.21.2
 	github.com/go-openapi/swag v0.21.1
 	github.com/pborman/getopt/v2 v2.1.0
 	github.com/pkg/errors v0.9.1
 	github.com/sigstore/cosign v1.8.1-0.20220502185546-8efb042c0427
 	github.com/sigstore/rekor v0.4.1-0.20220114213500-23f583409af3
+	github.com/sigstore/sigstore v1.2.1-0.20220424143412-3d41663116d5
 	golang.org/x/crypto v0.0.0-20220411220226-7b82a4e95df4
 )
 
-// Remove once https://github.com/github/smimesign/pull/108 is merged.
-replace github.com/github/smimesign => github.com/wlynch/smimesign v0.2.1-0.20220502200102-5d7d5b14387f
-
 require (
 	bitbucket.org/creachadair/shell v0.0.6 // indirect
 	cloud.google.com/go v0.100.2 // indirect
@@ -94,7 +93,6 @@ require (
 	github.com/go-openapi/jsonpointer v0.19.5 // indirect
 	github.com/go-openapi/jsonreference v0.19.6 // indirect
 	github.com/go-openapi/loads v0.21.1 // indirect
-	github.com/go-openapi/runtime v0.24.0 // indirect
 	github.com/go-openapi/spec v0.20.4 // indirect
 	github.com/go-openapi/validate v0.21.0 // indirect
 	github.com/go-piv/piv-go v1.9.0 // indirect
@@ -169,7 +167,6 @@ require (
 	github.com/sergi/go-diff v1.2.0 // indirect
 	github.com/shibumi/go-pathspec v1.3.0 // indirect
 	github.com/sigstore/fulcio v0.1.2-0.20220114150912-86a2036f9bc7 // indirect
-	github.com/sigstore/sigstore v1.2.1-0.20220424143412-3d41663116d5 // indirect
 	github.com/sirupsen/logrus v1.8.1 // indirect
 	github.com/skratchdot/open-golang v0.0.0-20200116055534-eef842397966 // indirect
 	github.com/soheilhy/cmux v0.1.5 // indirect
diff --git a/go.sum b/go.sum
index 5e6bf096..2a85617c 100644
--- a/go.sum
+++ b/go.sum
@@ -710,6 +710,8 @@ github.com/gin-contrib/sse v0.1.0/go.mod h1:RHrZQHXnP2xjPF+u1gW/2HnVO7nvIa9PG3Gm
 github.com/gin-gonic/gin v1.5.0/go.mod h1:Nd6IXA8m5kNZdNEHMBd93KT+mdY3+bewLgRvmCsR2Do=
 github.com/gin-gonic/gin v1.6.3/go.mod h1:75u5sXoLsGZoRN5Sgbi1eraJ4GU3++wFwWzhwvtwp4M=
 github.com/gin-gonic/gin v1.7.3/go.mod h1:jD2toBW3GZUr5UMcdrwQA10I7RuaFOl/SGeDjXkfUtY=
+github.com/github/smimesign v0.2.0 h1:Hho4YcX5N1I9XNqhq0fNx0Sts8MhLonHd+HRXVGNjvk=
+github.com/github/smimesign v0.2.0/go.mod h1:iZiiwNT4HbtGRVqCQu7uJPEZCuEE5sfSSttcnePkDl4=
 github.com/gliderlabs/ssh v0.2.2/go.mod h1:U7qILu1NlMHj9FlMhZLlkCdDnU1DBEAqr0aevW3Awn0=
 github.com/globalsign/mgo v0.0.0-20180905125535-1ca0a4f7cbcb/go.mod h1:xkRDCp4j0OGD1HRkm4kmhM+pmpv3AKq5SU7GMg4oO/Q=
 github.com/globalsign/mgo v0.0.0-20181015135952-eeefdecb41b8/go.mod h1:xkRDCp4j0OGD1HRkm4kmhM+pmpv3AKq5SU7GMg4oO/Q=
@@ -1965,8 +1967,6 @@ github.com/vmihailenco/msgpack/v4 v4.3.12 h1:07s4sz9IReOgdikxLTKNbBdqDMLsjPKXwvC
 github.com/vmihailenco/tagparser v0.1.1 h1:quXMXlA39OCbd2wAdTsGDlK9RkOk6Wuw+x37wVyIuWY=
 github.com/willf/bitset v1.1.11-0.20200630133818-d5bec3311243/go.mod h1:RjeCKbqT1RxIR/KWY6phxZiaY1IyutSBfGjNPySAYV4=
 github.com/willf/bitset v1.1.11/go.mod h1:83CECat5yLh5zVOf4P1ErAgKA5UDvKtgyUABdr3+MjI=
-github.com/wlynch/smimesign v0.2.1-0.20220502200102-5d7d5b14387f h1:IKLDd3pc2H3fTawZlEqnCyBiFs9c/nmTfOfD7Byo2aU=
-github.com/wlynch/smimesign v0.2.1-0.20220502200102-5d7d5b14387f/go.mod h1:iZiiwNT4HbtGRVqCQu7uJPEZCuEE5sfSSttcnePkDl4=
 github.com/xanzy/go-gitlab v0.31.0/go.mod h1:sPLojNBn68fMUWSxIJtdVVIP8uSBYqesTfDUseX11Ug=
 github.com/xanzy/go-gitlab v0.64.0 h1:rMgQdW9S1w3qvNAH2LYpFd2xh7KNLk+JWJd7sorNuTc=
 github.com/xanzy/go-gitlab v0.64.0/go.mod h1:F0QEXwmqiBUxCgJm8fE9S+1veX4XC9Z4cfaAbqwk4YM=
diff --git a/signature/sign.go b/signature/sign.go
new file mode 100644
index 00000000..79c294d1
--- /dev/null
+++ b/signature/sign.go
@@ -0,0 +1,148 @@
+package signature
+
+import (
+	"bytes"
+	"crypto"
+	"crypto/x509"
+	"encoding/pem"
+
+	cms "github.com/github/smimesign/ietf-cms"
+	"github.com/pkg/errors"
+)
+
+type SignOptions struct {
+	// Make a detached signature
+	Detached bool
+	// URL of RFC3161 timestamp authority to use for timestamping
+	TimestampAuthority string
+	// Create ascii armored output
+	Armor bool
+	// IncludeCerts specifies what certs to include in the resulting signature.
+	// -3 is the same as -2, but ommits issuer when cert has Authority Information Access extension.
+	// -2 includes all certs except root.
+	// -1 includes all certs.
+	// 0 includes no certs.
+	// 1 includes leaf cert.
+	// >1 includes n from the leaf.
+	IncludeCerts int
+}
+
+// Identity is a copy of smimesign.Identity to allow for compatibility without
+// needing a dependency on the whole package. This can be removed once
+// https://github.com/github/smimesign/pull/108 is merged.
+type Identity interface {
+	// Certificate gets the identity's certificate.
+	Certificate() (*x509.Certificate, error)
+	// CertificateChain attempts to get the identity's full certificate chain.
+	CertificateChain() ([]*x509.Certificate, error)
+	// Signer gets a crypto.Signer that uses the identity's private key.
+	Signer() (crypto.Signer, error)
+	// Delete deletes this identity from the system.
+	Delete() error
+	// Close any manually managed memory held by the Identity.
+	Close()
+}
+
+// Sign signs a given payload for the given identity.
+// The resulting signature and cert used is returned.
+func Sign(ident Identity, body []byte, opts SignOptions) ([]byte, *x509.Certificate, error) {
+	cert, err := ident.Certificate()
+	if err != nil {
+		return nil, nil, errors.Wrap(err, "failed to get idenity certificate")
+	}
+	signer, err := ident.Signer()
+	if err != nil {
+		return nil, nil, errors.Wrap(err, "failed to get idenity signer")
+	}
+
+	sd, err := cms.NewSignedData(body)
+	if err != nil {
+		return nil, nil, errors.Wrap(err, "failed to create signed data")
+	}
+
+	if err := sd.Sign([]*x509.Certificate{cert}, signer); err != nil {
+		return nil, nil, errors.Wrap(err, "failed to sign message")
+	}
+	if opts.Detached {
+		sd.Detached()
+	}
+
+	if len(opts.TimestampAuthority) > 0 {
+		if err = sd.AddTimestamps(opts.TimestampAuthority); err != nil {
+			return nil, nil, errors.Wrap(err, "failed to add timestamp")
+		}
+	}
+
+	chain, err := ident.CertificateChain()
+	if err != nil {
+		return nil, nil, errors.Wrap(err, "failed to get idenity certificate chain")
+	}
+	if chain, err = certsForSignature(chain, opts.IncludeCerts); err != nil {
+		return nil, nil, err
+	}
+	if err := sd.SetCertificates(chain); err != nil {
+		return nil, nil, errors.Wrap(err, "failed to set certificates")
+	}
+
+	der, err := sd.ToDER()
+	if err != nil {
+		return nil, nil, errors.Wrap(err, "failed to serialize signature")
+	}
+
+	if opts.Armor {
+		return pem.EncodeToMemory(&pem.Block{
+			Type:  "SIGNED MESSAGE",
+			Bytes: der,
+		}), cert, nil
+	} else {
+		return der, cert, nil
+	}
+}
+
+// certsForSignature determines which certificates to include in the signature
+// based on the --include-certs option specified by the user.
+func certsForSignature(chain []*x509.Certificate, include int) ([]*x509.Certificate, error) {
+	if include < -3 {
+		include = -2 // default
+	}
+	if include > len(chain) {
+		include = len(chain)
+	}
+
+	switch include {
+	case -3:
+		for i := len(chain) - 1; i > 0; i-- {
+			issuer, cert := chain[i], chain[i-1]
+
+			// remove issuer when cert has AIA extension
+			if bytes.Equal(issuer.RawSubject, cert.RawIssuer) && len(cert.IssuingCertificateURL) > 0 {
+				chain = chain[0:i]
+			}
+		}
+		return chainWithoutRoot(chain), nil
+	case -2:
+		return chainWithoutRoot(chain), nil
+	case -1:
+		return chain, nil
+	default:
+		return chain[0:include], nil
+	}
+}
+
+// Returns the provided chain, having removed the root certificate, if present.
+// This includes removing the cert itself if the chain is a single self-signed
+// cert.
+func chainWithoutRoot(chain []*x509.Certificate) []*x509.Certificate {
+	if len(chain) == 0 {
+		return chain
+	}
+
+	lastIdx := len(chain) - 1
+	last := chain[lastIdx]
+
+	if bytes.Equal(last.RawIssuer, last.RawSubject) {
+		return chain[0:lastIdx]
+	}
+
+	return chain
+}
diff --git a/signature/signature_test.go b/signature/signature_test.go
new file mode 100644
index 00000000..fe32c2bb
--- /dev/null
+++ b/signature/signature_test.go
@@ -0,0 +1,57 @@
+package signature
+
+import (
+	"crypto"
+	"crypto/x509"
+	"fmt"
+	"testing"
+
+	"github.com/github/smimesign/fakeca"
+)
+
+type identity struct {
+	Identity
+	base *fakeca.Identity
+}
+
+func (i *identity) Certificate() (*x509.Certificate, error) {
+	return i.base.Certificate, nil
+}
+
+func (i *identity) CertificateChain() ([]*x509.Certificate, error) {
+	return i.base.Chain(), nil
+}
+
+func (i *identity) Signer() (crypto.Signer, error) {
+	return i.base.PrivateKey, nil
+}
+
+// TestSignVerify is a basic test to ensure that the Sign/Verify funcs can be
+// used with each other. We're assuming that the actual signature format has
+// been more thoroghly vetted in other packages (i.e. ietf-cms).
+func TestSignVerify(t *testing.T) {
+	id := &identity{
+		base: fakeca.New(),
+	}
+	data := []byte("tacocat")
+
+	sig, _, err := Sign(id, data, SignOptions{
+		Detached: true,
+		Armor:    true,
+		// Fake CA outputs self-signed certs, so we need to use -1 to make sure
+		// the self-signed cert itself is included in the chain, otherwise
+		// Verify cannot find a cert to use for verification.
+		IncludeCerts: -1,
+	})
+	if err != nil {
+		t.Fatalf("Sign() = %v", err)
+	}
+
+	fmt.Println(id.base.Chain())
+	if _, err := Verify(data, sig, true, x509.VerifyOptions{
+		// Trust the fake CA
+		Roots: id.base.ChainPool(),
+	}); err != nil {
+		t.Fatalf("Verify() = %v", err)
+	}
+}
diff --git a/signature/verify.go b/signature/verify.go
new file mode 100644
index 00000000..85b453b5
--- /dev/null
+++ b/signature/verify.go
@@ -0,0 +1,34 @@
+package signature
+
+import (
+	"crypto/x509"
+	"encoding/pem"
+
+	cms "github.com/github/smimesign/ietf-cms"
+	"github.com/pkg/errors"
+)
+
+// Verify verifies a signature for a given identity.
+//
+// WARNING: this function doesn't do any revocation checking.
+func Verify(body, sig []byte, detached bool, opts x509.VerifyOptions) ([][][]*x509.Certificate, error) {
+	// Try decoding as PEM
+	var der []byte
+	if blk, _ := pem.Decode(sig); blk != nil {
+		der = blk.Bytes
+	} else {
+		der = sig
+	}
+
+	// Parse signature
+	sd, err := cms.ParseSignedData(der)
+	if err != nil {
+		return nil, errors.Wrap(err, "failed to parse signature")
+	}
+
+	if detached {
+		return sd.VerifyDetached(body, opts)
+	} else {
+		return sd.Verify(opts)
+	}
+}