diff --git a/cipher_suites.go b/cipher_suites.go
index afe5129..914491d 100644
--- a/cipher_suites.go
+++ b/cipher_suites.go
@@ -96,7 +96,7 @@ func macSHA1(version uint16, key []byte) macFunction {
 
 type macFunction interface {
 	Size() int
-	MAC(seq, data []byte) []byte
+	MAC(digestBuf, seq, data []byte) []byte
 }
 
 // ssl30MAC implements the SSLv3 MAC function, as defined in
@@ -114,7 +114,7 @@ var ssl30Pad1 = [48]byte{0x36, 0x36, 0x36, 0x36, 0x36, 0x36, 0x36, 0x36, 0x36, 0
 
 var ssl30Pad2 = [48]byte{0x5c, 0x5c, 0x5c, 0x5c, 0x5c, 0x5c, 0x5c, 0x5c, 0x5c, 0x5c, 0x5c, 0x5c, 0x5c, 0x5c, 0x5c, 0x5c, 0x5c, 0x5c, 0x5c, 0x5c, 0x5c, 0x5c, 0x5c, 0x5c, 0x5c, 0x5c, 0x5c, 0x5c, 0x5c, 0x5c, 0x5c, 0x5c, 0x5c, 0x5c, 0x5c, 0x5c, 0x5c, 0x5c, 0x5c, 0x5c, 0x5c, 0x5c, 0x5c, 0x5c, 0x5c, 0x5c, 0x5c, 0x5c}
 
-func (s ssl30MAC) MAC(seq, record []byte) []byte {
+func (s ssl30MAC) MAC(digestBuf, seq, record []byte) []byte {
 	padLength := 48
 	if s.h.Size() == 20 {
 		padLength = 40
@@ -127,13 +127,13 @@ func (s ssl30MAC) MAC(seq, record []byte) []byte {
 	s.h.Write(record[:1])
 	s.h.Write(record[3:5])
 	s.h.Write(record[recordHeaderLen:])
-	digest := s.h.Sum(nil)
+	digestBuf = s.h.Sum(digestBuf[:0])
 
 	s.h.Reset()
 	s.h.Write(s.key)
 	s.h.Write(ssl30Pad2[:padLength])
-	s.h.Write(digest)
-	return s.h.Sum(nil)
+	s.h.Write(digestBuf)
+	return s.h.Sum(digestBuf[:0])
 }
 
 // tls10MAC implements the TLS 1.0 MAC function. RFC 2246, section 6.2.3.
@@ -145,11 +145,11 @@ func (s tls10MAC) Size() int {
 	return s.h.Size()
 }
 
-func (s tls10MAC) MAC(seq, record []byte) []byte {
+func (s tls10MAC) MAC(digestBuf, seq, record []byte) []byte {
 	s.h.Reset()
 	s.h.Write(seq)
 	s.h.Write(record)
-	return s.h.Sum(nil)
+	return s.h.Sum(digestBuf[:0])
 }
 
 func rsaKA() keyAgreement {
diff --git a/conn.go b/conn.go
index b8fa273..6a03fa8 100644
--- a/conn.go
+++ b/conn.go
@@ -118,6 +118,9 @@ type halfConn struct {
 
 	nextCipher interface{} // next encryption state
 	nextMac    macFunction // next MAC algorithm
+
+	// used to save allocating a new buffer for each MAC.
+	inDigestBuf, outDigestBuf []byte
 }
 
 // prepareCipherSpec sets the encryption and MAC states
@@ -280,12 +283,13 @@ func (hc *halfConn) decrypt(b *block) (bool, alert) {
 		b.data[4] = byte(n)
 		b.resize(recordHeaderLen + n)
 		remoteMAC := payload[n:]
-		localMAC := hc.mac.MAC(hc.seq[0:], b.data)
+		localMAC := hc.mac.MAC(hc.inDigestBuf, hc.seq[0:], b.data)
 		hc.incSeq()
 
 		if subtle.ConstantTimeCompare(localMAC, remoteMAC) != 1 || paddingGood != 255 {
 			return false, alertBadRecordMAC
 		}
+		hc.inDigestBuf = localMAC
 	}
 
 	return true, 0
@@ -312,12 +316,13 @@ func padToBlockSize(payload []byte, blockSize int) (prefix, finalBlock []byte) {
 func (hc *halfConn) encrypt(b *block) (bool, alert) {
 	// mac
 	if hc.mac != nil {
-		mac := hc.mac.MAC(hc.seq[0:], b.data)
+		mac := hc.mac.MAC(hc.outDigestBuf, hc.seq[0:], b.data)
 		hc.incSeq()
 
 		n := len(b.data)
 		b.resize(n + len(mac))
 		copy(b.data[n:], mac)
+		hc.outDigestBuf = mac
 	}
 
 	payload := b.data[recordHeaderLen:]
diff --git a/handshake_client.go b/handshake_client.go
index b4337f2..e39e59c 100644
--- a/handshake_client.go
+++ b/handshake_client.go
@@ -231,10 +231,10 @@ func (c *Conn) clientHandshake() error {
 
 	if cert != nil {
 		certVerify := new(certificateVerifyMsg)
-		var digest [36]byte
-		copy(digest[0:16], finishedHash.serverMD5.Sum(nil))
-		copy(digest[16:36], finishedHash.serverSHA1.Sum(nil))
-		signed, err := rsa.SignPKCS1v15(c.config.rand(), c.config.Certificates[0].PrivateKey, crypto.MD5SHA1, digest[0:])
+		digest := make([]byte, 0, 36)
+		digest = finishedHash.serverMD5.Sum(digest)
+		digest = finishedHash.serverSHA1.Sum(digest)
+		signed, err := rsa.SignPKCS1v15(c.config.rand(), c.config.Certificates[0].PrivateKey, crypto.MD5SHA1, digest)
 		if err != nil {
 			return c.sendAlert(alertInternalError)
 		}
diff --git a/handshake_server.go b/handshake_server.go
index bbb23c0..89c000d 100644
--- a/handshake_server.go
+++ b/handshake_server.go
@@ -234,9 +234,9 @@ FindCipherSuite:
 			return c.sendAlert(alertUnexpectedMessage)
 		}
 
-		digest := make([]byte, 36)
-		copy(digest[0:16], finishedHash.serverMD5.Sum(nil))
-		copy(digest[16:36], finishedHash.serverSHA1.Sum(nil))
+		digest := make([]byte, 0, 36)
+		digest = finishedHash.serverMD5.Sum(digest)
+		digest = finishedHash.serverSHA1.Sum(digest)
 		err = rsa.VerifyPKCS1v15(pub, crypto.MD5SHA1, digest, certVerify.signature)
 		if err != nil {
 			c.sendAlert(alertBadCertificate)