diff --git a/acme/acme.go b/acme/acme.go
index 3902b94..6be00d1 100644
--- a/acme/acme.go
+++ b/acme/acme.go
@@ -31,7 +31,6 @@ import (
 	"crypto/x509/pkix"
 	"encoding/asn1"
 	"encoding/base64"
-	"encoding/hex"
 	"encoding/json"
 	"errors"
 	"fmt"
@@ -470,7 +469,7 @@ func (c *Client) WaitAuthorization(ctx context.Context, url string) (*Authorizat
 		// while waiting for a final authorization status.
 		d := retryAfter(res.Header.Get("Retry-After"))
 		if d == 0 {
-			// Given that the fastest challenges TLS-SNI and HTTP-01
+			// Given that the fastest challenges TLS-ALPN and HTTP-01
 			// require a CA to make at least 1 network round trip
 			// and most likely persist a challenge state,
 			// this default delay seems reasonable.
@@ -571,44 +570,21 @@ func (c *Client) HTTP01ChallengePath(token string) string {
 }
 
 // TLSSNI01ChallengeCert creates a certificate for TLS-SNI-01 challenge response.
+// Always returns an error.
 //
-// Deprecated: This challenge type is unused in both draft-02 and RFC versions of the ACME spec.
-func (c *Client) TLSSNI01ChallengeCert(token string, opt ...CertOption) (cert tls.Certificate, name string, err error) {
-	ka, err := keyAuth(c.Key.Public(), token)
-	if err != nil {
-		return tls.Certificate{}, "", err
-	}
-	b := sha256.Sum256([]byte(ka))
-	h := hex.EncodeToString(b[:])
-	name = fmt.Sprintf("%s.%s.acme.invalid", h[:32], h[32:])
-	cert, err = tlsChallengeCert([]string{name}, opt)
-	if err != nil {
-		return tls.Certificate{}, "", err
-	}
-	return cert, name, nil
+// Deprecated: This challenge type was only present in pre-standardized ACME
+// protocol drafts and is insecure for use in shared hosting environments.
+func (c *Client) TLSSNI01ChallengeCert(token string, opt ...CertOption) (tls.Certificate, string, error) {
+	return tls.Certificate{}, "", errPreRFC
 }
 
 // TLSSNI02ChallengeCert creates a certificate for TLS-SNI-02 challenge response.
+// Always returns an error.
 //
-// Deprecated: This challenge type is unused in both draft-02 and RFC versions of the ACME spec.
-func (c *Client) TLSSNI02ChallengeCert(token string, opt ...CertOption) (cert tls.Certificate, name string, err error) {
-	b := sha256.Sum256([]byte(token))
-	h := hex.EncodeToString(b[:])
-	sanA := fmt.Sprintf("%s.%s.token.acme.invalid", h[:32], h[32:])
-
-	ka, err := keyAuth(c.Key.Public(), token)
-	if err != nil {
-		return tls.Certificate{}, "", err
-	}
-	b = sha256.Sum256([]byte(ka))
-	h = hex.EncodeToString(b[:])
-	sanB := fmt.Sprintf("%s.%s.ka.acme.invalid", h[:32], h[32:])
-
-	cert, err = tlsChallengeCert([]string{sanA, sanB}, opt)
-	if err != nil {
-		return tls.Certificate{}, "", err
-	}
-	return cert, sanA, nil
+// Deprecated: This challenge type was only present in pre-standardized ACME
+// protocol drafts and is insecure for use in shared hosting environments.
+func (c *Client) TLSSNI02ChallengeCert(token string, opt ...CertOption) (tls.Certificate, string, error) {
+	return tls.Certificate{}, "", errPreRFC
 }
 
 // TLSALPN01ChallengeCert creates a certificate for TLS-ALPN-01 challenge response.
@@ -772,7 +748,7 @@ func defaultTLSChallengeCertTemplate() *x509.Certificate {
 	}
 }
 
-// tlsChallengeCert creates a temporary certificate for TLS-SNI challenges
+// tlsChallengeCert creates a temporary certificate for TLS-ALPN challenges
 // with the given SANs and auto-generated public/private key pair.
 // The Subject Common Name is set to the first SAN to aid debugging.
 // To create a cert with a custom key pair, specify WithKey option.
diff --git a/acme/acme_test.go b/acme/acme_test.go
index d286888..a3118f4 100644
--- a/acme/acme_test.go
+++ b/acme/acme_test.go
@@ -9,7 +9,6 @@ import (
 	"context"
 	"crypto/rand"
 	"crypto/rsa"
-	"crypto/tls"
 	"crypto/x509"
 	"crypto/x509/pkix"
 	"encoding/base64"
@@ -22,8 +21,6 @@ import (
 	"net/http"
 	"net/http/httptest"
 	"reflect"
-	"sort"
-	"strings"
 	"testing"
 	"time"
 )
@@ -692,71 +689,6 @@ func TestLinkHeader(t *testing.T) {
 	}
 }
 
-func TestTLSSNI01ChallengeCert(t *testing.T) {
-	const (
-		token = "evaGxfADs6pSRb2LAv9IZf17Dt3juxGJ-PCt92wr-oA"
-		// echo -n <token.testKeyECThumbprint> | shasum -a 256
-		san = "dbbd5eefe7b4d06eb9d1d9f5acb4c7cd.a27d320e4b30332f0b6cb441734ad7b0.acme.invalid"
-	)
-
-	tlscert, name, err := newTestClient().TLSSNI01ChallengeCert(token)
-	if err != nil {
-		t.Fatal(err)
-	}
-
-	if n := len(tlscert.Certificate); n != 1 {
-		t.Fatalf("len(tlscert.Certificate) = %d; want 1", n)
-	}
-	cert, err := x509.ParseCertificate(tlscert.Certificate[0])
-	if err != nil {
-		t.Fatal(err)
-	}
-	if len(cert.DNSNames) != 1 || cert.DNSNames[0] != san {
-		t.Fatalf("cert.DNSNames = %v; want %q", cert.DNSNames, san)
-	}
-	if cert.DNSNames[0] != name {
-		t.Errorf("cert.DNSNames[0] != name: %q vs %q", cert.DNSNames[0], name)
-	}
-	if cn := cert.Subject.CommonName; cn != san {
-		t.Errorf("cert.Subject.CommonName = %q; want %q", cn, san)
-	}
-}
-
-func TestTLSSNI02ChallengeCert(t *testing.T) {
-	const (
-		token = "evaGxfADs6pSRb2LAv9IZf17Dt3juxGJ-PCt92wr-oA"
-		// echo -n evaGxfADs6pSRb2LAv9IZf17Dt3juxGJ-PCt92wr-oA | shasum -a 256
-		sanA = "7ea0aaa69214e71e02cebb18bb867736.09b730209baabf60e43d4999979ff139.token.acme.invalid"
-		// echo -n <token.testKeyECThumbprint> | shasum -a 256
-		sanB = "dbbd5eefe7b4d06eb9d1d9f5acb4c7cd.a27d320e4b30332f0b6cb441734ad7b0.ka.acme.invalid"
-	)
-
-	tlscert, name, err := newTestClient().TLSSNI02ChallengeCert(token)
-	if err != nil {
-		t.Fatal(err)
-	}
-
-	if n := len(tlscert.Certificate); n != 1 {
-		t.Fatalf("len(tlscert.Certificate) = %d; want 1", n)
-	}
-	cert, err := x509.ParseCertificate(tlscert.Certificate[0])
-	if err != nil {
-		t.Fatal(err)
-	}
-	names := []string{sanA, sanB}
-	if !reflect.DeepEqual(cert.DNSNames, names) {
-		t.Fatalf("cert.DNSNames = %v;\nwant %v", cert.DNSNames, names)
-	}
-	sort.Strings(cert.DNSNames)
-	i := sort.SearchStrings(cert.DNSNames, name)
-	if i >= len(cert.DNSNames) || cert.DNSNames[i] != name {
-		t.Errorf("%v doesn't have %q", cert.DNSNames, name)
-	}
-	if cn := cert.Subject.CommonName; cn != sanA {
-		t.Errorf("CommonName = %q; want %q", cn, sanA)
-	}
-}
-
 func TestTLSALPN01ChallengeCert(t *testing.T) {
 	const (
 		token   = "evaGxfADs6pSRb2LAv9IZf17Dt3juxGJ-PCt92wr-oA"
@@ -813,6 +745,7 @@ func TestTLSChallengeCertOpt(t *testing.T) {
 	if err != nil {
 		t.Fatal(err)
 	}
+	domain := "example.com"
 	tmpl := &x509.Certificate{
 		SerialNumber: big.NewInt(2),
 		Subject:      pkix.Name{Organization: []string{"Test"}},
@@ -821,52 +754,43 @@ func TestTLSChallengeCertOpt(t *testing.T) {
 	opts := []CertOption{WithKey(key), WithTemplate(tmpl)}
 
 	client := newTestClient()
-	cert1, _, err := client.TLSSNI01ChallengeCert("token", opts...)
-	if err != nil {
-		t.Fatal(err)
-	}
-	cert2, _, err := client.TLSSNI02ChallengeCert("token", opts...)
+	cert, err := client.TLSALPN01ChallengeCert("token", domain, opts...)
 	if err != nil {
 		t.Fatal(err)
 	}
 
-	for i, tlscert := range []tls.Certificate{cert1, cert2} {
-		// verify generated cert private key
-		tlskey, ok := tlscert.PrivateKey.(*rsa.PrivateKey)
-		if !ok {
-			t.Errorf("%d: tlscert.PrivateKey is %T; want *rsa.PrivateKey", i, tlscert.PrivateKey)
-			continue
-		}
-		if tlskey.D.Cmp(key.D) != 0 {
-			t.Errorf("%d: tlskey.D = %v; want %v", i, tlskey.D, key.D)
-		}
-		// verify generated cert public key
-		x509Cert, err := x509.ParseCertificate(tlscert.Certificate[0])
-		if err != nil {
-			t.Errorf("%d: %v", i, err)
-			continue
-		}
-		tlspub, ok := x509Cert.PublicKey.(*rsa.PublicKey)
-		if !ok {
-			t.Errorf("%d: x509Cert.PublicKey is %T; want *rsa.PublicKey", i, x509Cert.PublicKey)
-			continue
-		}
-		if tlspub.N.Cmp(key.N) != 0 {
-			t.Errorf("%d: tlspub.N = %v; want %v", i, tlspub.N, key.N)
-		}
-		// verify template option
-		sn := big.NewInt(2)
-		if x509Cert.SerialNumber.Cmp(sn) != 0 {
-			t.Errorf("%d: SerialNumber = %v; want %v", i, x509Cert.SerialNumber, sn)
-		}
-		org := []string{"Test"}
-		if !reflect.DeepEqual(x509Cert.Subject.Organization, org) {
-			t.Errorf("%d: Subject.Organization = %+v; want %+v", i, x509Cert.Subject.Organization, org)
-		}
-		for _, v := range x509Cert.DNSNames {
-			if !strings.HasSuffix(v, ".acme.invalid") {
-				t.Errorf("%d: invalid DNSNames element: %q", i, v)
-			}
+	// verify generated cert private key
+	tlskey, ok := cert.PrivateKey.(*rsa.PrivateKey)
+	if !ok {
+		t.Fatalf("tlscert.PrivateKey is %T; want *rsa.PrivateKey", cert.PrivateKey)
+	}
+	if tlskey.D.Cmp(key.D) != 0 {
+		t.Errorf("tlskey.D = %v; want %v", tlskey.D, key.D)
+	}
+	// verify generated cert public key
+	x509Cert, err := x509.ParseCertificate(cert.Certificate[0])
+	if err != nil {
+		t.Fatal(err)
+	}
+	tlspub, ok := x509Cert.PublicKey.(*rsa.PublicKey)
+	if !ok {
+		t.Fatalf("x509Cert.PublicKey is %T; want *rsa.PublicKey", x509Cert.PublicKey)
+	}
+	if tlspub.N.Cmp(key.N) != 0 {
+		t.Errorf("tlspub.N = %v; want %v", tlspub.N, key.N)
+	}
+	// verify template option
+	sn := big.NewInt(2)
+	if x509Cert.SerialNumber.Cmp(sn) != 0 {
+		t.Errorf("SerialNumber = %v; want %v", x509Cert.SerialNumber, sn)
+	}
+	org := []string{"Test"}
+	if !reflect.DeepEqual(x509Cert.Subject.Organization, org) {
+		t.Errorf("Subject.Organization = %+v; want %+v", x509Cert.Subject.Organization, org)
+	}
+	for _, v := range x509Cert.DNSNames {
+		if v != domain {
+			t.Errorf("invalid DNSNames element: %q", v)
 		}
 	}
 }