diff --git a/internal/certificate/generate.go b/internal/certificate/generate.go
index 21d7e27..c98a6aa 100644
--- a/internal/certificate/generate.go
+++ b/internal/certificate/generate.go
@@ -61,7 +61,7 @@ func GenerateLeaf(
 	}
 
 	// Sign certificate using CA
-	_, cert, err := pki.SignCertificate(template, caCert, pk.Public(), caPk)
+	cert, err := pki.SignCertificate(template, caCert, pk.Public(), caPk)
 	return cert, pk, err
 }
 
@@ -94,6 +94,6 @@ func GenerateCA(
 	}
 
 	// self sign the root CA
-	_, cert, err := pki.SignCertificate(template, template, pk.Public(), pk)
+	cert, err := pki.SignCertificate(template, template, pk.Public(), pk)
 	return cert, pk, err
 }
diff --git a/internal/errors/errors.go b/internal/errors/errors.go
deleted file mode 100644
index 43d69e8..0000000
--- a/internal/errors/errors.go
+++ /dev/null
@@ -1,25 +0,0 @@
-/*
-Copyright 2020 The cert-manager Authors.
-
-Licensed under the Apache License, Version 2.0 (the "License");
-you may not use this file except in compliance with the License.
-You may obtain a copy of the License at
-
-    http://www.apache.org/licenses/LICENSE-2.0
-
-Unless required by applicable law or agreed to in writing, software
-distributed under the License is distributed on an "AS IS" BASIS,
-WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-See the License for the specific language governing permissions and
-limitations under the License.
-*/
-
-package errors
-
-import "fmt"
-
-type invalidDataError struct{ error }
-
-func NewInvalidData(str string, obj ...any) error {
-	return &invalidDataError{error: fmt.Errorf(str, obj...)}
-}
diff --git a/internal/pki/csr.go b/internal/pki/csr.go
index 67c4728..5d2ed9b 100644
--- a/internal/pki/csr.go
+++ b/internal/pki/csr.go
@@ -33,12 +33,11 @@ import (
 // *x509.Certificate crt and an issuer.
 // publicKey is the public key of the signee, and signerKey is the private
 // key of the signer.
-// It returns a PEM encoded copy of the Certificate as well as a *x509.Certificate
-// which can be used for reading the encoded values.
-func SignCertificate(template *x509.Certificate, issuerCert *x509.Certificate, publicKey crypto.PublicKey, signerKey any) ([]byte, *x509.Certificate, error) {
+// It returns a parsed *x509.Certificate on success.
+func SignCertificate(template *x509.Certificate, issuerCert *x509.Certificate, publicKey crypto.PublicKey, signerKey any) (*x509.Certificate, error) {
 	typedSigner, ok := signerKey.(crypto.Signer)
 	if !ok {
-		return nil, nil, fmt.Errorf("didn't get an expected Signer in call to SignCertificate")
+		return nil, fmt.Errorf("didn't get an expected Signer in call to SignCertificate")
 	}
 
 	var pubKeyAlgo x509.PublicKeyAlgorithm
@@ -64,32 +63,26 @@ func SignCertificate(template *x509.Certificate, issuerCert *x509.Certificate, p
 		sigAlgoArg = nil // ignored by signatureAlgorithmFromPublicKey
 
 	default:
-		return nil, nil, fmt.Errorf("unknown public key type on signing certificate: %T", issuerCert.PublicKey)
+		return nil, fmt.Errorf("unknown public key type on signing certificate: %T", issuerCert.PublicKey)
 	}
 
 	var err error
 	template.SignatureAlgorithm, err = signatureAlgorithmFromPublicKey(pubKeyAlgo, sigAlgoArg)
 	if err != nil {
-		return nil, nil, err
+		return nil, err
 	}
 
 	derBytes, err := x509.CreateCertificate(rand.Reader, template, issuerCert, publicKey, signerKey)
 	if err != nil {
-		return nil, nil, fmt.Errorf("error creating x509 certificate: %s", err.Error())
+		return nil, fmt.Errorf("error creating x509 certificate: %w", err)
 	}
 
 	cert, err := x509.ParseCertificate(derBytes)
 	if err != nil {
-		return nil, nil, fmt.Errorf("error decoding DER certificate bytes: %s", err.Error())
-	}
-
-	pemBytes := bytes.NewBuffer([]byte{})
-	err = pem.Encode(pemBytes, &pem.Block{Type: "CERTIFICATE", Bytes: derBytes})
-	if err != nil {
-		return nil, nil, fmt.Errorf("error encoding certificate PEM: %s", err.Error())
+		return nil, fmt.Errorf("error decoding DER certificate bytes: %w", err)
 	}
 
-	return pemBytes.Bytes(), cert, err
+	return cert, nil
 }
 
 // EncodeX509 will encode a single *x509.Certificate into PEM format.
diff --git a/internal/pki/generate.go b/internal/pki/generate.go
index 5b701ab..176cce6 100644
--- a/internal/pki/generate.go
+++ b/internal/pki/generate.go
@@ -65,26 +65,22 @@ func encodePKCS8PrivateKey(pk any) ([]byte, error) {
 func encodeECPrivateKey(pk *ecdsa.PrivateKey) ([]byte, error) {
 	keyBytes, err := x509.MarshalECPrivateKey(pk)
 	if err != nil {
-		return nil, fmt.Errorf("error encoding private key: %s", err.Error())
+		return nil, fmt.Errorf("error encoding private key: %w", err)
 	}
 	block := &pem.Block{Type: "EC PRIVATE KEY", Bytes: keyBytes}
 
 	return pem.EncodeToMemory(block), nil
 }
 
-// PublicKeysEqual compares two given public keys for equality.
-// The definition of "equality" depends on the type of the public keys.
-// Returns true if the keys are the same, false if they differ or an error if
-// the key type of `a` cannot be determined.
-func PublicKeysEqual(a, b crypto.PublicKey) (bool, error) {
-	switch pub := a.(type) {
-	case *rsa.PublicKey:
-		return pub.Equal(b), nil
-	case *ecdsa.PublicKey:
-		return pub.Equal(b), nil
-	case ed25519.PublicKey:
-		return pub.Equal(b), nil
-	default:
-		return false, fmt.Errorf("unrecognised public key type: %T", a)
+type publicKeyEqual interface {
+	Equal(crypto.PublicKey) bool
+}
+
+// PublicKeysEqual compares two public keys for equivalence across supported types.
+func PublicKeysEqual(a, b any) (bool, error) {
+	if ak, ok := a.(publicKeyEqual); ok {
+		return ak.Equal(b), nil
 	}
+
+	return false, fmt.Errorf("unsupported public key type %T", a)
 }
diff --git a/internal/pki/parse.go b/internal/pki/parse.go
index 8f727a0..e56d867 100644
--- a/internal/pki/parse.go
+++ b/internal/pki/parse.go
@@ -20,8 +20,7 @@ import (
 	"crypto"
 	"crypto/x509"
 	"encoding/pem"
-
-	"github.com/cert-manager/webhook-cert-lib/internal/errors"
+	"fmt"
 )
 
 // DecodeX509CertificateBytes will decode a PEM encoded x509 Certificate.
@@ -50,13 +49,13 @@ func DecodeX509CertificateSetBytes(certBytes []byte) ([]*x509.Certificate, error
 		// parse the tls certificate
 		cert, err := x509.ParseCertificate(block.Bytes)
 		if err != nil {
-			return nil, errors.NewInvalidData("error parsing TLS certificate: %s", err.Error())
+			return nil, fmt.Errorf("error parsing TLS certificate: %w", err)
 		}
 		certs = append(certs, cert)
 	}
 
 	if len(certs) == 0 {
-		return nil, errors.NewInvalidData("error decoding certificate PEM block")
+		return nil, fmt.Errorf("error decoding certificate PEM block")
 	}
 
 	return certs, nil
@@ -68,40 +67,40 @@ func DecodePrivateKeyBytes(keyBytes []byte) (crypto.Signer, error) {
 	// decode the private key pem
 	block, _ := pem.Decode(keyBytes)
 	if block == nil {
-		return nil, errors.NewInvalidData("error decoding private key PEM block")
+		return nil, fmt.Errorf("error decoding private key PEM block")
 	}
 
 	switch block.Type {
 	case "PRIVATE KEY":
 		key, err := x509.ParsePKCS8PrivateKey(block.Bytes)
 		if err != nil {
-			return nil, errors.NewInvalidData("error parsing pkcs#8 private key: %s", err.Error())
+			return nil, fmt.Errorf("error parsing pkcs#8 private key: %w", err)
 		}
 
 		signer, ok := key.(crypto.Signer)
 		if !ok {
-			return nil, errors.NewInvalidData("error parsing pkcs#8 private key: invalid key type")
+			return nil, fmt.Errorf("error parsing pkcs#8 private key: invalid key type")
 		}
 		return signer, nil
 	case "EC PRIVATE KEY":
 		key, err := x509.ParseECPrivateKey(block.Bytes)
 		if err != nil {
-			return nil, errors.NewInvalidData("error parsing ecdsa private key: %s", err.Error())
+			return nil, fmt.Errorf("error parsing ecdsa private key: %w", err)
 		}
 
 		return key, nil
 	case "RSA PRIVATE KEY":
 		key, err := x509.ParsePKCS1PrivateKey(block.Bytes)
 		if err != nil {
-			return nil, errors.NewInvalidData("error parsing rsa private key: %s", err.Error())
+			return nil, fmt.Errorf("error parsing rsa private key: %w", err)
 		}
 
 		err = key.Validate()
 		if err != nil {
-			return nil, errors.NewInvalidData("rsa private key failed validation: %s", err.Error())
+			return nil, fmt.Errorf("rsa private key failed validation: %w", err)
 		}
 		return key, nil
 	default:
-		return nil, errors.NewInvalidData("unknown private key type: %s", block.Type)
+		return nil, fmt.Errorf("unknown private key type: %s", block.Type)
 	}
 }
diff --git a/internal/pki/tls.go b/internal/pki/tls.go
index 27c973c..9f3ab0d 100644
--- a/internal/pki/tls.go
+++ b/internal/pki/tls.go
@@ -22,6 +22,7 @@ import (
 	"crypto/x509"
 )
 
+// ToTLSCertificate converts a x509.Certificate and a crypto.Signer to a tls.Certificate.
 func ToTLSCertificate(cert *x509.Certificate, pk crypto.Signer) (tls.Certificate, error) {
 	pkData, err := EncodePrivateKey(pk)
 	if err != nil {
diff --git a/pkg/authority/ca_secret_controller_test.go b/pkg/authority/ca_secret_controller_test.go
index a71bc20..0bdb311 100644
--- a/pkg/authority/ca_secret_controller_test.go
+++ b/pkg/authority/ca_secret_controller_test.go
@@ -59,7 +59,7 @@ func Test__caRequiresRegeneration(t *testing.T) {
 		if mod != nil {
 			mod(cert)
 		}
-		_, cert, err = pki.SignCertificate(cert, cert, pk.Public(), pk)
+		cert, err = pki.SignCertificate(cert, cert, pk.Public(), pk)
 		assert.NoError(t, err)
 		certBytes, err := pki.EncodeX509(cert)
 		assert.NoError(t, err)