diff --git a/attest/attest.go b/attest/attest.go
index 6ce145f..79efed3 100644
--- a/attest/attest.go
+++ b/attest/attest.go
@@ -85,11 +85,11 @@ const (
 )
 
 type aik interface {
-	Close(*TPM) error
-	Marshal() ([]byte, error)
-	ActivateCredential(tpm *TPM, in EncryptedCredential) ([]byte, error)
-	Quote(t *TPM, nonce []byte, alg HashAlg) (*Quote, error)
-	AttestationParameters() AttestationParameters
+	close(*platformTPM) error
+	marshal() ([]byte, error)
+	activateCredential(tpm *platformTPM, in EncryptedCredential) ([]byte, error)
+	quote(t *platformTPM, nonce []byte, alg HashAlg) (*Quote, error)
+	attestationParameters() AttestationParameters
 }
 
 // AIK represents a key which can be used for attestation.
@@ -99,7 +99,7 @@ type AIK struct {
 
 // Close unloads the AIK from the system.
 func (k *AIK) Close(t *TPM) error {
-	return k.aik.Close(t)
+	return k.aik.close(t.tpm)
 }
 
 // Marshal encodes the AIK in a format that can be reloaded with tpm.LoadAIK().
@@ -107,7 +107,7 @@ func (k *AIK) Close(t *TPM) error {
 // it as a later time. Users SHOULD NOT attempt to interpret or extract values
 // from this blob.
 func (k *AIK) Marshal() ([]byte, error) {
-	return k.aik.Marshal()
+	return k.aik.marshal()
 }
 
 // ActivateCredential decrypts the secret using the key to prove that the AIK
@@ -115,18 +115,18 @@ func (k *AIK) Marshal() ([]byte, error) {
 //
 // This operation is synonymous with TPM2_ActivateCredential.
 func (k *AIK) ActivateCredential(tpm *TPM, in EncryptedCredential) (secret []byte, err error) {
-	return k.aik.ActivateCredential(tpm, in)
+	return k.aik.activateCredential(tpm.tpm, in)
 }
 
 // Quote returns a quote over the platform state, signed by the AIK.
 func (k *AIK) Quote(tpm *TPM, nonce []byte, alg HashAlg) (*Quote, error) {
-	return k.aik.Quote(tpm, nonce, alg)
+	return k.aik.quote(tpm.tpm, nonce, alg)
 }
 
 // Parameters returns information about the AIK, typically used to generate
 // a credential activation challenge.
 func (k *AIK) AttestationParameters() AttestationParameters {
-	return k.aik.AttestationParameters()
+	return k.aik.attestationParameters()
 }
 
 // AIKConfig encapsulates parameters for minting keys. This type is defined
diff --git a/attest/attest_simulated_tpm20_test.go b/attest/attest_simulated_tpm20_test.go
index af7108f..73deecd 100644
--- a/attest/attest_simulated_tpm20_test.go
+++ b/attest/attest_simulated_tpm20_test.go
@@ -13,6 +13,9 @@
 // the License.
 
 // +build !localtest !tpm12
+// +build cgo
+
+// NOTE: simulator requires cgo, hence the build tag.
 
 package attest
 
@@ -30,12 +33,12 @@ func setupSimulatedTPM(t *testing.T) (*simulator.Simulator, *TPM) {
 	if err != nil {
 		t.Fatal(err)
 	}
-	return tpm, &TPM{
+	return tpm, &TPM{&platformTPM{
 		version: TPMVersion20,
 		interf:  TPMInterfaceKernelManaged,
 		sysPath: "/dev/tpmrm0",
 		rwc:     tpm,
-	}
+	}}
 }
 
 func TestSimTPM20EK(t *testing.T) {
@@ -195,7 +198,7 @@ func TestSimTPM20Persistence(t *testing.T) {
 	sim, tpm := setupSimulatedTPM(t)
 	defer sim.Close()
 
-	ekHnd, _, err := tpm.getPrimaryKeyHandle(commonEkEquivalentHandle)
+	ekHnd, _, err := tpm.tpm.getPrimaryKeyHandle(commonEkEquivalentHandle)
 	if err != nil {
 		t.Fatalf("getPrimaryKeyHandle() failed: %v", err)
 	}
@@ -203,7 +206,7 @@ func TestSimTPM20Persistence(t *testing.T) {
 		t.Fatalf("bad EK-equivalent handle: got 0x%x, wanted 0x%x", ekHnd, commonEkEquivalentHandle)
 	}
 
-	ekHnd, p, err := tpm.getPrimaryKeyHandle(commonEkEquivalentHandle)
+	ekHnd, p, err := tpm.tpm.getPrimaryKeyHandle(commonEkEquivalentHandle)
 	if err != nil {
 		t.Fatalf("second getPrimaryKeyHandle() failed: %v", err)
 	}
diff --git a/attest/attest_tpm12_test.go b/attest/attest_tpm12_test.go
index 7b2e2c8..a29c760 100644
--- a/attest/attest_tpm12_test.go
+++ b/attest/attest_tpm12_test.go
@@ -91,12 +91,9 @@ func TestNewAIK(t *testing.T) {
 	tpm := openTPM12(t)
 	defer tpm.Close()
 
-	aik, err := tpm.NewAIK(nil)
-	if err != nil {
+	if _, err := tpm.NewAIK(nil); err != nil {
 		t.Fatalf("NewAIK failed: %v", err)
 	}
-	k := aik.aik.(*key12)
-	t.Logf("aik blob: %x\naik pubkey: %x\n", k.blob, k.public)
 }
 
 func TestTPMQuote(t *testing.T) {
diff --git a/attest/key_linux.go b/attest/key_linux.go
index 14bfbf6..53f1a59 100644
--- a/attest/key_linux.go
+++ b/attest/key_linux.go
@@ -39,7 +39,7 @@ func newKey12(blob, public []byte) aik {
 
 // Marshal represents the key in a persistent format which may be
 // loaded at a later time using tpm.LoadKey().
-func (k *key12) Marshal() ([]byte, error) {
+func (k *key12) marshal() ([]byte, error) {
 	out := serializedKey{
 		Encoding:   keyEncodingEncrypted,
 		TPMVersion: TPMVersion12,
@@ -49,13 +49,11 @@ func (k *key12) Marshal() ([]byte, error) {
 	return out.Serialize()
 }
 
-func (k *key12) Close(tpm *TPM) error {
+func (k *key12) close(tpm *platformTPM) error {
 	return nil // No state for tpm 1.2.
 }
 
-// ActivateCredential decrypts the specified credential using key.
-// This operation is synonymous with TPM2_ActivateCredential.
-func (k *key12) ActivateCredential(t *TPM, in EncryptedCredential) ([]byte, error) {
+func (k *key12) activateCredential(t *platformTPM, in EncryptedCredential) ([]byte, error) {
 	cred, err := attestation.AIKChallengeResponse(t.ctx, k.blob, in.Credential, in.Secret)
 	if err != nil {
 		return nil, fmt.Errorf("failed to activate aik: %v", err)
@@ -63,8 +61,7 @@ func (k *key12) ActivateCredential(t *TPM, in EncryptedCredential) ([]byte, erro
 	return cred, nil
 }
 
-// Quote returns a quote over the platform state, signed by the key.
-func (k *key12) Quote(t *TPM, nonce []byte, alg HashAlg) (*Quote, error) {
+func (k *key12) quote(t *platformTPM, nonce []byte, alg HashAlg) (*Quote, error) {
 	if alg != HashSHA1 {
 		return nil, fmt.Errorf("only SHA1 algorithms supported on TPM 1.2, not HashAlg(%v)", alg)
 	}
@@ -81,8 +78,7 @@ func (k *key12) Quote(t *TPM, nonce []byte, alg HashAlg) (*Quote, error) {
 	}, nil
 }
 
-// AttestationParameters returns information about the AIK.
-func (k *key12) AttestationParameters() AttestationParameters {
+func (k *key12) attestationParameters() AttestationParameters {
 	return AttestationParameters{
 		Public:                  k.public,
 		UseTCSDActivationFormat: true,
@@ -111,9 +107,7 @@ func newKey20(hnd tpmutil.Handle, blob, public, createData, createAttestation, c
 	}
 }
 
-// Marshal represents the key in a persistent format which may be
-// loaded at a later time using tpm.LoadKey().
-func (k *key20) Marshal() ([]byte, error) {
+func (k *key20) marshal() ([]byte, error) {
 	return (&serializedKey{
 		Encoding:   keyEncodingEncrypted,
 		TPMVersion: TPMVersion20,
@@ -126,14 +120,11 @@ func (k *key20) Marshal() ([]byte, error) {
 	}).Serialize()
 }
 
-// Close frees any resources associated with the key.
-func (k *key20) Close(tpm *TPM) error {
+func (k *key20) close(tpm *platformTPM) error {
 	return tpm2.FlushContext(tpm.rwc, k.hnd)
 }
 
-// ActivateCredential decrypts the specified credential using key.
-// This operation is synonymous with TPM2_ActivateCredential.
-func (k *key20) ActivateCredential(t *TPM, in EncryptedCredential) ([]byte, error) {
+func (k *key20) activateCredential(t *platformTPM, in EncryptedCredential) ([]byte, error) {
 	ekHnd, _, err := t.getPrimaryKeyHandle(commonEkEquivalentHandle)
 	if err != nil {
 		return nil, err
@@ -163,13 +154,11 @@ func (k *key20) ActivateCredential(t *TPM, in EncryptedCredential) ([]byte, erro
 	}, k.hnd, ekHnd, in.Credential[2:], in.Secret[2:])
 }
 
-// Quote returns a quote over the platform state, signed by the key.
-func (k *key20) Quote(t *TPM, nonce []byte, alg HashAlg) (*Quote, error) {
+func (k *key20) quote(t *platformTPM, nonce []byte, alg HashAlg) (*Quote, error) {
 	return quote20(t.rwc, k.hnd, tpm2.Algorithm(alg), nonce)
 }
 
-// AttestationParameters returns information about the AIK.
-func (k *key20) AttestationParameters() AttestationParameters {
+func (k *key20) attestationParameters() AttestationParameters {
 	return AttestationParameters{
 		Public:            k.public,
 		CreateData:        k.createData,
diff --git a/attest/key_windows.go b/attest/key_windows.go
index 1cf5c3b..9e58242 100644
--- a/attest/key_windows.go
+++ b/attest/key_windows.go
@@ -37,9 +37,7 @@ func newKey12(hnd uintptr, pcpKeyName string, public []byte) aik {
 	}
 }
 
-// Marshal represents the key in a persistent format which may be
-// loaded at a later time using tpm.LoadKey().
-func (k *key12) Marshal() ([]byte, error) {
+func (k *key12) marshal() ([]byte, error) {
 	out := serializedKey{
 		Encoding:   keyEncodingOSManaged,
 		TPMVersion: TPMVersion12,
@@ -49,9 +47,7 @@ func (k *key12) Marshal() ([]byte, error) {
 	return out.Serialize()
 }
 
-// ActivateCredential decrypts the specified credential using key.
-// This operation is synonymous with TPM_ActivateIdentity for TPM1.2.
-func (k *key12) ActivateCredential(tpm *TPM, in EncryptedCredential) ([]byte, error) {
+func (k *key12) activateCredential(tpm *platformTPM, in EncryptedCredential) ([]byte, error) {
 	secretKey, err := tpm.pcp.ActivateCredential(k.hnd, in.Credential)
 	if err != nil {
 		return nil, err
@@ -59,8 +55,7 @@ func (k *key12) ActivateCredential(tpm *TPM, in EncryptedCredential) ([]byte, er
 	return decryptCredential(secretKey, in.Secret)
 }
 
-// Quote returns a quote over the platform state, signed by the key.
-func (k *key12) Quote(t *TPM, nonce []byte, alg HashAlg) (*Quote, error) {
+func (k *key12) quote(t *platformTPM, nonce []byte, alg HashAlg) (*Quote, error) {
 	if alg != HashSHA1 {
 		return nil, fmt.Errorf("only SHA1 algorithms supported on TPM 1.2, not HashAlg(%v)", alg)
 	}
@@ -98,13 +93,11 @@ func (k *key12) Quote(t *TPM, nonce []byte, alg HashAlg) (*Quote, error) {
 	}, nil
 }
 
-// Close frees any resources associated with the key.
-func (k *key12) Close(tpm *TPM) error {
+func (k *key12) close(tpm *platformTPM) error {
 	return closeNCryptObject(k.hnd)
 }
 
-// AttestationParameters returns information about the AIK.
-func (k *key12) AttestationParameters() AttestationParameters {
+func (k *key12) attestationParameters() AttestationParameters {
 	return AttestationParameters{
 		Public: k.public,
 	}
@@ -132,9 +125,7 @@ func newKey20(hnd uintptr, pcpKeyName string, public, createData, createAttest,
 	}
 }
 
-// Marshal represents the key in a persistent format which may be
-// loaded at a later time using tpm.LoadKey().
-func (k *key20) Marshal() ([]byte, error) {
+func (k *key20) marshal() ([]byte, error) {
 	out := serializedKey{
 		Encoding:   keyEncodingOSManaged,
 		TPMVersion: TPMVersion20,
@@ -148,14 +139,11 @@ func (k *key20) Marshal() ([]byte, error) {
 	return out.Serialize()
 }
 
-// ActivateCredential decrypts the specified credential using the key.
-// This operation is synonymous with TPM2_ActivateCredential.
-func (k *key20) ActivateCredential(tpm *TPM, in EncryptedCredential) ([]byte, error) {
+func (k *key20) activateCredential(tpm *platformTPM, in EncryptedCredential) ([]byte, error) {
 	return tpm.pcp.ActivateCredential(k.hnd, append(in.Credential, in.Secret...))
 }
 
-// Quote returns a quote over the platform state, signed by the key.
-func (k *key20) Quote(t *TPM, nonce []byte, alg HashAlg) (*Quote, error) {
+func (k *key20) quote(t *platformTPM, nonce []byte, alg HashAlg) (*Quote, error) {
 	tpmKeyHnd, err := t.pcp.TPMKeyHandle(k.hnd)
 	if err != nil {
 		return nil, fmt.Errorf("TPMKeyHandle() failed: %v", err)
@@ -168,19 +156,11 @@ func (k *key20) Quote(t *TPM, nonce []byte, alg HashAlg) (*Quote, error) {
 	return quote20(tpm, tpmKeyHnd, alg.goTPMAlg(), nonce)
 }
 
-// Close frees any resources associated with the key.
-func (k *key20) Close(tpm *TPM) error {
+func (k *key20) close(tpm *platformTPM) error {
 	return closeNCryptObject(k.hnd)
 }
 
-// Delete permenantly removes the key from the system. This method
-// invalidates Key and any further method invocations are invalid.
-func (k *key20) Delete(tpm *TPM) error {
-	return tpm.pcp.DeleteKey(k.hnd)
-}
-
-// AttestationParameters returns information about the AIK.
-func (k *key20) AttestationParameters() AttestationParameters {
+func (k *key20) attestationParameters() AttestationParameters {
 	return AttestationParameters{
 		Public:            k.public,
 		CreateData:        k.createData,
diff --git a/attest/tpm.go b/attest/tpm.go
index 196e48c..2cca3d8 100644
--- a/attest/tpm.go
+++ b/attest/tpm.go
@@ -267,10 +267,52 @@ func readAllPCRs20(tpm io.ReadWriter, alg tpm2.Algorithm) (map[uint32][]byte, er
 	return out, nil
 }
 
+//TPM interfaces with a TPM device on the system.
+type TPM struct {
+	// tpm holds a platform specific implementation of TPM logic: Windows or Linux.
+	// see *_linux.go and *_windows.go files for definitions of these structs.
+	tpm *platformTPM
+}
+
+// Close shuts down the connection to the TPM.
+func (t *TPM) Close() error {
+	return t.tpm.close()
+}
+
+// EKs returns the endorsement keys burned-in to the platform.
+func (t *TPM) EKs() ([]EK, error) {
+	return t.tpm.eks()
+}
+
+// Info returns information about the TPM.
+func (t *TPM) Info() (*TPMInfo, error) {
+	return t.tpm.info()
+}
+
 // LoadAIK loads a previously-created aik into the TPM for use.
 // A key loaded via this function needs to be closed with .Close().
 // Only blobs generated by calling AIK.Serialize() are valid parameters
 // to this function.
 func (t *TPM) LoadAIK(opaqueBlob []byte) (*AIK, error) {
-	return t.loadAIK(opaqueBlob)
+	return t.tpm.loadAIK(opaqueBlob)
+}
+
+// MeasurementLog returns the present value of the System Measurement Log.
+func (t *TPM) MeasurementLog() ([]byte, error) {
+	return t.tpm.measurementLog()
+}
+
+// NewAIK creates an attestation key.
+func (t *TPM) NewAIK(opts *AIKConfig) (*AIK, error) {
+	return t.tpm.newAIK(opts)
+}
+
+// PCRs returns the present value of Platform Configuration Registers with the given digest algorithm.
+func (t *TPM) PCRs(alg HashAlg) ([]PCR, error) {
+	return t.tpm.pcrs(alg)
+}
+
+// Version returns the version of the TPM.
+func (t *TPM) Version() TPMVersion {
+	return t.tpm.tpmVersion()
 }
diff --git a/attest/tpm_linux.go b/attest/tpm_linux.go
index 0218fb1..9dec895 100644
--- a/attest/tpm_linux.go
+++ b/attest/tpm_linux.go
@@ -42,8 +42,8 @@ const (
 	tpmRoot = "/sys/class/tpm"
 )
 
-// TPM interfaces with a TPM device on the system.
-type TPM struct {
+// platformTPM interfaces with a TPM device on the system.
+type platformTPM struct {
 	version TPMVersion
 	interf  TPMInterface
 
@@ -122,22 +122,20 @@ func openTPM(tpm probedTPM) (*TPM, error) {
 		}
 	}
 
-	return &TPM{
+	return &TPM{&platformTPM{
 		version: tpm.Version,
 		interf:  interf,
 		sysPath: tpm.Path,
 		rwc:     rwc,
 		ctx:     ctx,
-	}, nil
+	}}, nil
 }
 
-// Version returns the version of the TPM.
-func (t *TPM) Version() TPMVersion {
+func (t *platformTPM) tpmVersion() TPMVersion {
 	return t.version
 }
 
-// Close shuts down the connection to the TPM.
-func (t *TPM) Close() error {
+func (t *platformTPM) close() error {
 	switch t.version {
 	case TPMVersion12:
 		return t.ctx.Close()
@@ -162,7 +160,7 @@ func readTPM12VendorAttributes(context *tspi.Context) (TCGVendorID, string, erro
 }
 
 // Info returns information about the TPM.
-func (t *TPM) Info() (*TPMInfo, error) {
+func (t *platformTPM) info() (*TPMInfo, error) {
 	tInfo := TPMInfo{
 		Version:   t.version,
 		Interface: t.interf,
@@ -190,7 +188,7 @@ func (t *TPM) Info() (*TPMInfo, error) {
 }
 
 // Return value: handle, whether we generated a new one, error
-func (t *TPM) getPrimaryKeyHandle(pHnd tpmutil.Handle) (tpmutil.Handle, bool, error) {
+func (t *platformTPM) getPrimaryKeyHandle(pHnd tpmutil.Handle) (tpmutil.Handle, bool, error) {
 	_, _, _, err := tpm2.ReadPublic(t.rwc, pHnd)
 	if err == nil {
 		// Found the persistent handle, assume it's the key we want.
@@ -225,8 +223,7 @@ func readEKCertFromNVRAM12(ctx *tspi.Context) (*x509.Certificate, error) {
 	return ParseEKCertificate(ekCert)
 }
 
-// EKs returns the endorsement keys burned-in to the platform.
-func (t *TPM) EKs() ([]EK, error) {
+func (t *platformTPM) eks() ([]EK, error) {
 	switch t.version {
 	case TPMVersion12:
 		cert, err := readEKCertFromNVRAM12(t.ctx)
@@ -270,8 +267,7 @@ func (t *TPM) EKs() ([]EK, error) {
 	}
 }
 
-// NewAIK creates an attestation key.
-func (t *TPM) NewAIK(opts *AIKConfig) (*AIK, error) {
+func (t *platformTPM) newAIK(opts *AIKConfig) (*AIK, error) {
 	switch t.version {
 	case TPMVersion12:
 		pub, blob, err := attestation.CreateAIK(t.ctx)
@@ -317,7 +313,7 @@ func (t *TPM) NewAIK(opts *AIKConfig) (*AIK, error) {
 	}
 }
 
-func (t *TPM) loadAIK(opaqueBlob []byte) (*AIK, error) {
+func (t *platformTPM) loadAIK(opaqueBlob []byte) (*AIK, error) {
 	sKey, err := deserializeKey(opaqueBlob, t.version)
 	if err != nil {
 		return nil, fmt.Errorf("deserializeKey() failed: %v", err)
@@ -359,12 +355,7 @@ func allPCRs12(ctx *tspi.Context) (map[uint32][]byte, error) {
 	return PCRs, nil
 }
 
-// TODO: Refactor PCRs() into a file not subject to build tags, and implement
-// platform-specific logic in private methods.
-
-// PCRs returns the present value of Platform Configuration Registers with the
-// given digest algorithm.
-func (t *TPM) PCRs(alg HashAlg) ([]PCR, error) {
+func (t *platformTPM) pcrs(alg HashAlg) ([]PCR, error) {
 	var PCRs map[uint32][]byte
 	var err error
 
@@ -400,7 +391,6 @@ func (t *TPM) PCRs(alg HashAlg) ([]PCR, error) {
 	return out, nil
 }
 
-// MeasurementLog returns the present value of the System Measurement Log.
-func (t *TPM) MeasurementLog() ([]byte, error) {
+func (t *platformTPM) measurementLog() ([]byte, error) {
 	return ioutil.ReadFile("/sys/kernel/security/tpm0/binary_bios_measurements")
 }
diff --git a/attest/tpm_windows.go b/attest/tpm_windows.go
index 9470bee..bdad5de 100644
--- a/attest/tpm_windows.go
+++ b/attest/tpm_windows.go
@@ -34,8 +34,7 @@ import (
 
 var wellKnownAuth [20]byte
 
-// TPM interfaces with a TPM device on the system.
-type TPM struct {
+type platformTPM struct {
 	version TPMVersion
 	pcp     *winPCP
 }
@@ -90,19 +89,17 @@ func openTPM(tpm probedTPM) (*TPM, error) {
 		return nil, fmt.Errorf("tbsConvertVersion(%v) failed: %v", info.TBSInfo.TPMVersion, err)
 	}
 
-	return &TPM{
+	return &TPM{&platformTPM{
 		pcp:     pcp,
 		version: vers,
-	}, nil
+	}}, nil
 }
 
-// Version returns the version of the TPM.
-func (t *TPM) Version() TPMVersion {
+func (t *platformTPM) tpmVersion() TPMVersion {
 	return t.version
 }
 
-// Close shuts down the connection to the TPM.
-func (t *TPM) Close() error {
+func (t *platformTPM) close() error {
 	return t.pcp.Close()
 }
 
@@ -115,8 +112,7 @@ func readTPM12VendorAttributes(tpm io.ReadWriter) (TCGVendorID, string, error) {
 	return vendorID, vendorID.String(), nil
 }
 
-// Info returns information about the TPM.
-func (t *TPM) Info() (*TPMInfo, error) {
+func (t *platformTPM) info() (*TPMInfo, error) {
 	tInfo := TPMInfo{
 		Version:   t.version,
 		Interface: TPMInterfaceKernelManaged,
@@ -146,8 +142,7 @@ func (t *TPM) Info() (*TPMInfo, error) {
 	return &tInfo, nil
 }
 
-// EKs returns the Endorsement Keys burned-in to the platform.
-func (t *TPM) EKs() ([]EK, error) {
+func (t *platformTPM) eks() ([]EK, error) {
 	ekCerts, err := t.pcp.EKCerts()
 	if err != nil {
 		return nil, fmt.Errorf("could not read EKCerts: %v", err)
@@ -166,7 +161,7 @@ func (t *TPM) EKs() ([]EK, error) {
 	}
 	ek := EK{Public: pub}
 
-	i, err := t.Info()
+	i, err := t.info()
 	if err != nil {
 		return nil, err
 	}
@@ -176,7 +171,7 @@ func (t *TPM) EKs() ([]EK, error) {
 	return []EK{ek}, nil
 }
 
-func (t *TPM) ekPub() (*rsa.PublicKey, error) {
+func (t *platformTPM) ekPub() (*rsa.PublicKey, error) {
 	p, err := t.pcp.EKPub()
 	if err != nil {
 		return nil, fmt.Errorf("could not read ekpub: %v", err)
@@ -269,9 +264,7 @@ func decryptCredential(secretKey, blob []byte) ([]byte, error) {
 	return secret, nil
 }
 
-// NewAIK creates a persistent attestation key. The returned key must be
-// closed with a call to key.Close() when the caller has finished using it.
-func (t *TPM) NewAIK(opts *AIKConfig) (*AIK, error) {
+func (t *platformTPM) newAIK(opts *AIKConfig) (*AIK, error) {
 	nameHex := make([]byte, 5)
 	if n, err := rand.Read(nameHex); err != nil || n != len(nameHex) {
 		return nil, fmt.Errorf("rand.Read() failed with %d/%d bytes read and error: %v", n, len(nameHex), err)
@@ -298,7 +291,7 @@ func (t *TPM) NewAIK(opts *AIKConfig) (*AIK, error) {
 	}
 }
 
-func (t *TPM) loadAIK(opaqueBlob []byte) (*AIK, error) {
+func (t *platformTPM) loadAIK(opaqueBlob []byte) (*AIK, error) {
 	sKey, err := deserializeKey(opaqueBlob, t.version)
 	if err != nil {
 		return nil, fmt.Errorf("deserializeKey() failed: %v", err)
@@ -341,9 +334,7 @@ func allPCRs12(tpm io.ReadWriter) (map[uint32][]byte, error) {
 	return out, nil
 }
 
-// PCRs returns the present value of Platform Configuration Registers with the
-// given digest algorithm.
-func (t *TPM) PCRs(alg HashAlg) ([]PCR, error) {
+func (t *platformTPM) pcrs(alg HashAlg) ([]PCR, error) {
 	var PCRs map[uint32][]byte
 
 	switch t.version {
@@ -386,8 +377,7 @@ func (t *TPM) PCRs(alg HashAlg) ([]PCR, error) {
 	return out, nil
 }
 
-// MeasurementLog returns the present value of the System Measurement Log.
-func (t *TPM) MeasurementLog() ([]byte, error) {
+func (t *platformTPM) measurementLog() ([]byte, error) {
 	context, err := tpmtbs.CreateContext(tpmtbs.TPMVersion20, tpmtbs.IncludeTPM20|tpmtbs.IncludeTPM12)
 	if err != nil {
 		return nil, err