tpm2: Implement TPM2_Import

[Foxboron]

This is an attempt from me to try and implement TPM2_Import, but I suspect I picked a non-obvious thing to implement.

Useage I have is to take a pre-existing EC key and import it into the TPM. But I suspect there is a bunch of wrapping with the duplicate argument I just don't understand. The legacy/tpm2 implementation seemed to just do things with the Private struct, but transferring that to the tpmdirect API is very non-obvious.

The outline for the test I have been trying to write for the implementation>

Any help our guidance would be appreicated.

package tpm2test

import (
	"crypto/ecdsa"
	"crypto/elliptic"
	"crypto/rand"
	"crypto/x509"
	"testing"

	. "github.com/google/go-tpm/tpm2"
	"github.com/google/go-tpm/tpm2/transport/simulator"
)

func TestImport(t *testing.T) {
	thetpm, err := simulator.OpenSimulator()
	if err != nil {
		t.Fatalf("could not connect to TPM simulator: %v", err)
	}
	defer thetpm.Close()

	srkCreate := CreatePrimary{
		PrimaryHandle: TPMRHOwner,
		InPublic:      New2B(ECCSRKTemplate),
	}

	srkCreateRsp, err := srkCreate.Execute(thetpm)
	if err != nil {
		t.Fatalf("could not generate SRK: %v", err)
	}
	defer func() {
		flush := FlushContext{
			FlushHandle: srkCreateRsp.ObjectHandle,
		}
		_, err := flush.Execute(thetpm)
		if err != nil {
			t.Fatalf("could not flush SRK: %v", err)
		}
	}()

	pk, err := ecdsa.GenerateKey(elliptic.P256(), rand.Reader)
	if err != nil {
		t.Fatalf("something")
	}
	b, err := x509.MarshalECPrivateKey(pk)
	if err != nil {
		t.Fatalf("failed DER encoding")
	}

	tpmdata := TPM2BPrivate{
		Buffer: b,
	}
	m := Marshal(tpmdata)

	_, err = Import{
		ParentHandle: &AuthHandle{
			Handle: srkCreateRsp.ObjectHandle,
			Name:   srkCreateRsp.Name,
			Auth:   PasswordAuth(nil),
		},
		Duplicate: TPM2BPrivate{Buffer: m},
		ObjectPublic: New2B(TPMTPublic{
			Type:    TPMAlgECC,
			NameAlg: TPMAlgSHA256,
			ObjectAttributes: TPMAObject{
				SignEncrypt:         true,
				SensitiveDataOrigin: true,
			},
			Parameters: NewTPMUPublicParms(
				TPMAlgECC,
				&TPMSECCParms{
					CurveID: TPMECCNistP256,
					Scheme: TPMTECCScheme{
						Scheme: TPMAlgECDSA,
						Details: NewTPMUAsymScheme(
							TPMAlgECDSA,
							&TPMSSigSchemeECDSA{
								HashAlg: TPMAlgSHA256,
							},
						),
					},
				},
			),
		}),
	}.Execute(thetpm)
	if err != nil {
		t.Fatalf("could not import: %v", err)
	}
}

[chrisfenner]

pk, err := ecdsa.GenerateKey(elliptic.P256(), rand.Reader)
	if err != nil {
		t.Fatalf("something")
	}
	b, err := x509.MarshalECPrivateKey(pk)
	if err != nil {
		t.Fatalf("failed DER encoding")
	}

	tpmdata := TPM2BPrivate{
		Buffer: b,
	}
	m := Marshal(tpmdata)

This might cause a problem, because TPMs don't deal in DER-encoded data. Instead, you probably want to create a TPMT_SENSITIVE and then encrypt it (using the parent's public key) using a similar method to how go-tpm-tools does it. Heck, I'd probably just use go-tpm-tools for the test: let somebody else take up the separate work of dealing with import blobs.

[chrisfenner]

TPM2_Import might be the hardest possible command to build a test for. So once you've cracked this, you should feel prepared to deal with anything. 😎

[Foxboron]

This might cause a problem, because TPMs don't deal in DER-encoded data.

I might have been tricked by the tpm2_tools implementation as they said it could be DER and I never found a place in the C code where they did anything with the bytes at all and assumed as a result it would be fine.

TPM2_Import might be the hardest possible command to build a test for. So once you've cracked this, you should feel prepared to deal with anything. sunglasses

I'm glad to see I involuntarily stumbled into the worst of them 🙃

[Foxboron]

Actually, with the links I was able to figure out how to pass the duplicate blob unencrypted.

I forgot filling out Unique with the public key parts and filling out TPM2BPrivate{} in the struct had me take a loop through Marshal() which seems a bit awkward.

If the outline for the test looks sane'ish I'll clean up this PR to undraft it.

Thanks for the help :)

package tpm2test

import (
	"crypto/ecdsa"
	"crypto/elliptic"
	"crypto/rand"
	"testing"

	. "github.com/google/go-tpm/tpm2"
	"github.com/google/go-tpm/tpm2/transport/simulator"
)

func TestImport(t *testing.T) {
	thetpm, err := simulator.OpenSimulator()
	if err != nil {
		t.Fatalf("could not connect to TPM simulator: %v", err)
	}
	defer thetpm.Close()

	srkCreate := CreatePrimary{
		PrimaryHandle: TPMRHOwner,
		InPublic:      New2B(ECCSRKTemplate),
	}

	srkCreateRsp, err := srkCreate.Execute(thetpm)
	if err != nil {
		t.Fatalf("could not generate SRK: %v", err)
	}
	defer func() {
		flush := FlushContext{
			FlushHandle: srkCreateRsp.ObjectHandle,
		}
		_, err := flush.Execute(thetpm)
		if err != nil {
			t.Fatalf("could not flush SRK: %v", err)
		}
	}()

	pk, err := ecdsa.GenerateKey(elliptic.P256(), rand.Reader)
	if err != nil {
		t.Fatalf("something")
	}

	sens2B := New2B(TPMTSensitive{
		SensitiveType: TPMAlgECC,
		Sensitive: NewTPMUSensitiveComposite(
			TPMAlgECC,
			&TPM2BECCParameter{Buffer: pk.D.FillBytes(make([]byte, 32))},
		),
	})

	l := Marshal(TPM2BPrivate{Buffer: sens2B.Bytes()})

	_, err = Import{
		ParentHandle: &AuthHandle{
			Handle: srkCreateRsp.ObjectHandle,
			Name:   srkCreateRsp.Name,
			Auth:   PasswordAuth(nil),
		},
		Duplicate: TPM2BPrivate{Buffer: l},
		ObjectPublic: New2B(TPMTPublic{
			Type:    TPMAlgECC,
			NameAlg: TPMAlgSHA256,
			ObjectAttributes: TPMAObject{
				SignEncrypt:          true,
				SensitiveDataOrigin:  false,
				EncryptedDuplication: false,
			},
			Parameters: NewTPMUPublicParms(
				TPMAlgECC,
				&TPMSECCParms{
					CurveID: TPMECCNistP256,
					Scheme: TPMTECCScheme{
						Scheme: TPMAlgECDSA,
						Details: NewTPMUAsymScheme(
							TPMAlgECDSA,
							&TPMSSigSchemeECDSA{
								HashAlg: TPMAlgSHA256,
							},
						),
					},
				},
			),
			Unique: NewTPMUPublicID(
				TPMAlgECC,
				&TPMSECCPoint{
					X: TPM2BECCParameter{
						Buffer: pk.X.FillBytes(make([]byte, 32)),
					},
					Y: TPM2BECCParameter{
						Buffer: pk.Y.FillBytes(make([]byte, 32)),
					},
				},
			),
		}),
	}.Execute(thetpm)
	if err != nil {
		t.Fatalf("could not import: %v", err)
	}
}

[chrisfenner]

Feel free to test only based on unencrypted import; I have a hard time seeing a bug you could introduce here that would succeed for unencrypted import but fail for encrypted.

[chrisfenner]

If your current plan for testing looks like the draft above (minus the DERification), seems totally reasonable!

[Foxboron]

I've implemented a feature using this into ssh-tpm-agent with a integration test suite, and it seems to work :)

Foxboron/ssh-tpm-agent#16

[chrisfenner]

Thank you @Foxboron !!