diff --git a/linux/hci/smp/context.go b/linux/hci/smp/context.go
index 0dbdcde..1149f0c 100644
--- a/linux/hci/smp/context.go
+++ b/linux/hci/smp/context.go
@@ -89,7 +89,7 @@ func (p *pairingContext) checkPasskeyConfirm() error {
 	kax := MarshalPublicKeyX(p.scECDHKeys.public)
 	nb := p.remoteRandom
 	i := p.passKeyIteration
-	key := p.authData.Passkey
+	key := p.authData.GetPasskey()
 
 	//this gets the bit of the passkey for the current iteration
 	z := 0x80 | (byte)((key&(1<<uint(i)))>>uint(i))
@@ -114,7 +114,7 @@ func (p *pairingContext) checkPasskeyConfirm() error {
 	return nil
 }
 
-//todo: key should be set at the beginning
+// todo: key should be set at the beginning
 func (p *pairingContext) generatePassKeyConfirm() ([]byte, []byte) {
 	kbx := MarshalPublicKeyX(p.scRemotePubKey)
 	kax := MarshalPublicKeyX(p.scECDHKeys.public)
@@ -125,7 +125,7 @@ func (p *pairingContext) generatePassKeyConfirm() ([]byte, []byte) {
 	}
 
 	i := p.passKeyIteration
-	z := 0x80 | (byte)((p.authData.Passkey&(1<<uint(i)))>>uint(i))
+	z := 0x80 | (byte)((p.authData.GetPasskey()&(1<<uint(i)))>>uint(i))
 
 	calcConf, err := smpF4(kax, kbx, nai, z)
 	if err != nil {
@@ -176,7 +176,7 @@ func (p *pairingContext) checkDHKeyCheck() error {
 	ra := make([]byte, 16)
 	if p.pairingType == Passkey {
 		keyBytes := make([]byte, 4)
-		binary.BigEndian.PutUint32(keyBytes, uint32(p.authData.Passkey))
+		binary.BigEndian.PutUint32(keyBytes, uint32(p.authData.GetPasskey()))
 		ra[12] = keyBytes[0]
 		ra[13] = keyBytes[1]
 		ra[14] = keyBytes[2]
@@ -230,7 +230,7 @@ func (p *pairingContext) checkLegacyConfirm() error {
 
 	k := make([]byte, 16)
 	if p.pairingType == Passkey {
-		k = getLegacyParingTK(p.authData.Passkey)
+		k = getLegacyParingTK(p.authData.GetPasskey())
 	}
 	c1, err := smpC1(k, sRand, preq, pres,
 		p.localAddrType,
diff --git a/linux/hci/smp/handler.go b/linux/hci/smp/handler.go
index 97d2007..f94c67c 100644
--- a/linux/hci/smp/handler.go
+++ b/linux/hci/smp/handler.go
@@ -151,7 +151,7 @@ func onLegacyRandom(t *transport) ([]byte, error) {
 	//calculate STK
 	var k []byte
 	if t.pairing.pairingType == Passkey {
-		k = getLegacyParingTK(t.pairing.authData.Passkey)
+		k = getLegacyParingTK(t.pairing.authData.GetPasskey())
 	} else {
 		k = getLegacyParingTK(0)
 	}
@@ -314,8 +314,8 @@ func continuePassKeyPairing(t *transport) {
 	t.send(out)
 }
 
-//Core spec v5.0 Vol 3, Part H, 2.3.5.1
-//Tables 2.6, 2.7, and 2.8
+// Core spec v5.0 Vol 3, Part H, 2.3.5.1
+// Tables 2.6, 2.7, and 2.8
 var ioCapsTableSC = [][]int{
 	{JustWorks, JustWorks, Passkey, JustWorks, Passkey},
 	{JustWorks, NumericComp, Passkey, JustWorks, NumericComp},
diff --git a/linux/hci/smp/transport.go b/linux/hci/smp/transport.go
index 0499c77..4b6e0d1 100644
--- a/linux/hci/smp/transport.go
+++ b/linux/hci/smp/transport.go
@@ -153,7 +153,7 @@ func (t *transport) sendDHKeyCheck() error {
 	rb := make([]byte, 16)
 	if t.pairing.pairingType == Passkey {
 		keyBytes := make([]byte, 4)
-		binary.BigEndian.PutUint32(keyBytes, uint32(t.pairing.authData.Passkey))
+		binary.BigEndian.PutUint32(keyBytes, uint32(t.pairing.authData.GetPasskey()))
 		rb[12] = keyBytes[0]
 		rb[13] = keyBytes[1]
 		rb[14] = keyBytes[2]
@@ -198,7 +198,7 @@ func (t *transport) sendMConfirm() error {
 
 	k := make([]byte, 16)
 	if t.pairing.pairingType == Passkey {
-		k = getLegacyParingTK(t.pairing.authData.Passkey)
+		k = getLegacyParingTK(t.pairing.authData.GetPasskey())
 	}
 
 	c1, err := smpC1(k, r, preq, pres,
diff --git a/smp.go b/smp.go
index 980a199..02d8958 100644
--- a/smp.go
+++ b/smp.go
@@ -1,6 +1,26 @@
 package ble
 
 type AuthData struct {
+	// Passkey is the numeric passkey for pairing.
 	Passkey int
+
+	// PasskeyFn is a function that returns the passkey for pairing.
+	// If Passkey is not set, this function will be called to
+	// retrieve the passkey.
+	PasskeyFn func() int
+
+	// OOBData is the out-of-band data for pairing.
 	OOBData []byte
-}
\ No newline at end of file
+}
+
+// GetPasskey returns the passkey for pairing. If Passkey is not set,
+// it calls PasskeyFn to populate it.
+func (a *AuthData) GetPasskey() int {
+	if a.Passkey != 0 {
+		return a.Passkey
+	}
+	if a.PasskeyFn != nil {
+		a.Passkey = a.PasskeyFn()
+	}
+	return a.Passkey
+}