Merge pull request #94 from aws/windows-tpm

Support TPM Keys on Windows

Author: 13ajay

Info.plist

@@ -7,6 +7,6 @@
     <key>CFBundleIdentifier</key>
     <string>com.amazon.aws.rolesanywhere</string>
     <key>CFBundleVersion</key>
-    <string>1.3.0</string>
+    <string>1.4.0</string>
 </dict>
 </plist>

Makefile

@@ -1,4 +1,4 @@
-VERSION=1.3.0
+VERSION=1.4.0
 
 .PHONY: release
 release: build/bin/aws_signing_helper

aws_signing_helper/tpm_signer.go

@@ -1,9 +1,20 @@
 package aws_signing_helper
 
 import (
+	"crypto"
+	"crypto/ecdsa"
+	"crypto/sha1"
+	"crypto/sha256"
+	"crypto/sha512"
 	"crypto/x509"
 	"encoding/asn1"
 	"encoding/pem"
+	"errors"
+	"fmt"
+	"io"
+	"math/big"
+	"strconv"
+	"strings"
 
 	tpm2 "github.com/google/go-tpm/tpm2"
 	tpmutil "github.com/google/go-tpm/tpmutil"
@@ -76,3 +87,358 @@ type GetTPMv2SignerOpts struct {
 	emptyAuth        bool
 	handle           string
 }
+
+// Returns the public key associated with this TPMv2Signer
+func (tpmv2Signer *TPMv2Signer) Public() crypto.PublicKey {
+	ret, _ := tpmv2Signer.public.Key()
+	return ret
+}
+
+// Closes this TPMv2Signer
+func (tpmv2Signer *TPMv2Signer) Close() {
+	tpmv2Signer.password = ""
+}
+
+func checkCapability(rw io.ReadWriter, algo tpm2.Algorithm) error {
+	descs, _, err := tpm2.GetCapability(rw, tpm2.CapabilityAlgs, 1, uint32(algo))
+	if err != nil {
+		errMsg := fmt.Sprintf("error trying to get capability from TPM for the algorithm (%s)", algo)
+		return errors.New(errMsg)
+	}
+	if tpm2.Algorithm(descs[0].(tpm2.AlgorithmDescription).ID) != algo {
+		errMsg := fmt.Sprintf("unsupported algorithm (%s) for TPM", algo)
+		return errors.New(errMsg)
+	}
+
+	return nil
+}
+
+// Implements the crypto.Signer interface and signs the passed in digest
+func (tpmv2Signer *TPMv2Signer) Sign(rand io.Reader, digest []byte, opts crypto.SignerOpts) (signature []byte, err error) {
+	var (
+		keyHandle tpmutil.Handle
+	)
+
+	rw, err := openTPM()
+	if err != nil {
+		return nil, err
+	}
+	defer rw.Close()
+
+	if tpmv2Signer.handle != 0 {
+		keyHandle = tpmv2Signer.handle
+	} else {
+		parentHandle := tpmutil.Handle(tpmv2Signer.tpmData.Parent)
+		if !handleIsPersistent(tpmv2Signer.tpmData.Parent) {
+			// Parent and owner passwords aren't supported currently when creating a primary given a persistent handle for the parent
+			parentHandle, _, err = tpm2.CreatePrimary(rw, tpmutil.Handle(tpmv2Signer.tpmData.Parent), tpm2.PCRSelection{}, "", "", primaryParams)
+			if err != nil {
+				return nil, err
+			}
+			defer tpm2.FlushContext(rw, parentHandle)
+		}
+
+		keyHandle, _, err = tpm2.Load(rw, parentHandle, "", tpmv2Signer.tpmData.Pubkey[2:], tpmv2Signer.tpmData.Privkey[2:])
+		if err != nil {
+			return nil, err
+		}
+		defer tpm2.FlushContext(rw, keyHandle)
+	}
+
+	var algo tpm2.Algorithm
+	var shadigest []byte
+
+	switch opts.HashFunc() {
+	case crypto.SHA256:
+		sha256digest := sha256.Sum256(digest)
+		shadigest = sha256digest[:]
+		algo = tpm2.AlgSHA256
+	case crypto.SHA384:
+		sha384digest := sha512.Sum384(digest)
+		shadigest = sha384digest[:]
+		algo = tpm2.AlgSHA384
+	case crypto.SHA512:
+		sha512digest := sha512.Sum512(digest)
+		shadigest = sha512digest[:]
+		algo = tpm2.AlgSHA512
+	}
+
+	if tpmv2Signer.public.Type == tpm2.AlgECC {
+		// Check to see that ECDSA is supported for signing
+		err = checkCapability(rw, tpm2.AlgECC)
+		if err != nil {
+			return nil, err
+		}
+
+		// For an EC key we lie to the TPM about what the hash is.
+		// It doesn't actually matter what the original digest was;
+		// the algo we feed to the TPM is *purely* based on the
+		// size of the curve itself. We truncate the actual digest,
+		// or pad with zeroes, to the byte size of the key.
+		pubKey, err := tpmv2Signer.public.Key()
+		if err != nil {
+			return nil, err
+		}
+		ecPubKey, ok := pubKey.(*ecdsa.PublicKey)
+		if !ok {
+			return nil, errors.New("failed to obtain ecdsa.PublicKey")
+		}
+		bitSize := ecPubKey.Curve.Params().BitSize
+		byteSize := (bitSize + 7) / 8
+		if byteSize > sha512.Size {
+			byteSize = sha512.Size
+		}
+		switch byteSize {
+		case sha512.Size:
+			algo = tpm2.AlgSHA512
+		case sha512.Size384:
+			algo = tpm2.AlgSHA384
+		case sha512.Size256:
+			algo = tpm2.AlgSHA256
+		case sha1.Size:
+			algo = tpm2.AlgSHA1
+		default:
+			return nil, errors.New("unsupported curve")
+		}
+
+		if len(shadigest) > byteSize {
+			shadigest = shadigest[:byteSize]
+		}
+
+		for len(shadigest) < byteSize {
+			shadigest = append([]byte{0}, shadigest...)
+		}
+
+		sig, err := tpmv2Signer.signHelper(rw, keyHandle, shadigest,
+			&tpm2.SigScheme{Alg: tpm2.AlgECDSA, Hash: algo})
+		if err != nil {
+			return nil, err
+		}
+		signature, err = asn1.Marshal(struct {
+			R *big.Int
+			S *big.Int
+		}{sig.ECC.R, sig.ECC.S})
+		if err != nil {
+			return nil, err
+		}
+	} else {
+		// Check to see that the requested hash function is supported
+		err = checkCapability(rw, algo)
+		if err != nil {
+			return nil, err
+		}
+
+		// Check to see that RSASSA is supported for signing
+		err = checkCapability(rw, tpm2.AlgRSASSA)
+		if err != nil {
+			return nil, err
+		}
+
+		sig, err := tpmv2Signer.signHelper(rw, keyHandle, shadigest,
+			&tpm2.SigScheme{Alg: tpm2.AlgRSASSA, Hash: algo})
+		if err != nil {
+			return nil, err
+		}
+		signature = sig.RSA.Signature
+	}
+	return signature, nil
+}
+
+func (tpmv2Signer *TPMv2Signer) signHelper(rw io.ReadWriter, keyHandle tpmutil.Handle, digest tpmutil.U16Bytes, sigScheme *tpm2.SigScheme) (*tpm2.Signature, error) {
+	passwordPromptInput := PasswordPromptProps{
+		InitialPassword: tpmv2Signer.password,
+		NoPassword:      tpmv2Signer.emptyAuth,
+		CheckPassword: func(password string) (interface{}, error) {
+			return tpm2.Sign(rw, keyHandle, password, digest, nil, sigScheme)
+		},
+		IncorrectPasswordMsg:               "incorrect TPM key password",
+		Prompt:                             "Please enter your TPM key password:",
+		Reprompt:                           "Incorrect TPM key password. Please try again:",
+		ParseErrMsg:                        "unable to read your TPM key password",
+		CheckPasswordAuthorizationErrorMsg: TPM_RC_AUTH_FAIL,
+	}
+
+	password, sig, err := PasswordPrompt(passwordPromptInput)
+	if err != nil {
+		return nil, err
+	}
+
+	tpmv2Signer.password = password
+	return sig.(*tpm2.Signature), err
+}
+
+// Gets the x509.Certificate associated with this TPMv2Signer
+func (tpmv2Signer *TPMv2Signer) Certificate() (*x509.Certificate, error) {
+	return tpmv2Signer.cert, nil
+}
+
+// Gets the certificate chain associated with this TPMv2Signer
+func (tpmv2Signer *TPMv2Signer) CertificateChain() (chain []*x509.Certificate, err error) {
+	return tpmv2Signer.certChain, nil
+}
+
+/*
+ * DER forbids storing a BOOLEAN as anything but 0x00 or 0xFF,
+ * 0x01, and the Go asn1 parser cannot be relaxed. But both
+ * OpenSSL ENGINEs which produce these keys have at least in
+ * the past emitted 0x01 as the value, leading to an Unmarshal
+ * failure with 'asn1: syntax error: invalid boolean'. So...
+ */
+func fixupEmptyAuth(tpmData *[]byte) {
+	var pos int = 0
+
+	// Skip the SEQUENCE tag and length
+	if len(*tpmData) < 2 || (*tpmData)[0] != 0x30 {
+		return
+	}
+
+	// Don't care what the SEQUENCE length is, just skip it
+	pos = 1
+	lenByte := (*tpmData)[pos]
+	if lenByte < 0x80 {
+		pos = pos + 1
+	} else if lenByte < 0x85 {
+		pos = pos + 1 + int(lenByte) - 0x80
+	} else {
+		return
+	}
+
+	if len(*tpmData) <= pos {
+		return
+	}
+
+	// Use asn1.Unmarshal to eat the OID; we care about 'rest'
+	var oid asn1.ObjectIdentifier
+	rest, err := asn1.Unmarshal((*tpmData)[pos:], &oid)
+	if err != nil || rest == nil || !oid.Equal(oidLoadableKey) || len(rest) < 5 {
+		return
+	}
+
+	// If the OPTIONAL EXPLICIT BOOLEAN [0] exists, it'll be here
+	pos = len(*tpmData) - len(rest)
+
+	if (*tpmData)[pos] == 0xa0 && // Tag
+		(*tpmData)[pos+1] == 0x03 && // length
+		(*tpmData)[pos+2] == 0x01 &&
+		(*tpmData)[pos+3] == 0x01 &&
+		(*tpmData)[pos+4] == 0x01 {
+		(*tpmData)[pos+4] = 0xff
+	}
+}
+
+// Returns a TPMv2Signer, that can be used to sign a payload through a TPMv2-compatible
+// cryptographic device
+func GetTPMv2Signer(opts GetTPMv2SignerOpts) (signer Signer, signingAlgorithm string, err error) {
+	var (
+		certificate      *x509.Certificate
+		certificateChain []*x509.Certificate
+		keyPem           *pem.Block
+		password         string
+		emptyAuth        bool
+		tpmData          tpm2_TPMKey
+		handle           tpmutil.Handle
+		public           tpm2.Public
+		private          []byte
+	)
+
+	certificate = opts.certificate
+	certificateChain = opts.certificateChain
+	keyPem = opts.keyPem
+	password = opts.password
+	emptyAuth = opts.emptyAuth
+
+	// If a handle is provided instead of a TPM key file
+	if opts.handle != "" {
+		handleParts := strings.Split(opts.handle, ":")
+		if len(handleParts) != 2 {
+			return nil, "", errors.New("invalid TPM handle format")
+		}
+		hexHandleStr := handleParts[1]
+		if strings.HasPrefix(hexHandleStr, "0x") {
+			hexHandleStr = hexHandleStr[2:]
+		}
+		handleValue, err := strconv.ParseUint(hexHandleStr, 16, 32)
+		if err != nil {
+			return nil, "", errors.New("invalid hex TPM handle value")
+		}
+		handle = tpmutil.Handle(handleValue)
+
+		// Read the public key from the loaded key within the TPM
+		rw, err := openTPM()
+		if err != nil {
+			return nil, "", err
+		}
+		defer rw.Close()
+
+		public, _, _, err = tpm2.ReadPublic(rw, handle)
+		if err != nil {
+			return nil, "", err
+		}
+	} else {
+		fixupEmptyAuth(&keyPem.Bytes)
+		_, err = asn1.Unmarshal(keyPem.Bytes, &tpmData)
+		if err != nil {
+			return nil, "", err
+		}
+
+		emptyAuth = tpmData.EmptyAuth
+		if emptyAuth && password != "" {
+			return nil, "", errors.New("password is provided but TPM key file indicates that one isn't required")
+		}
+
+		if !tpmData.Oid.Equal(oidLoadableKey) {
+			return nil, "", errors.New("invalid OID for TPMv2 key:" + tpmData.Oid.String())
+		}
+
+		if tpmData.Policy != nil || tpmData.AuthPolicy != nil {
+			return nil, "", errors.New("TPMv2 policy not implemented yet")
+		}
+		if tpmData.Secret != nil {
+			return nil, "", errors.New("TPMv2 key has 'secret' field which should not be set")
+		}
+
+		if !handleIsPersistent(tpmData.Parent) &&
+			tpmData.Parent != int(tpm2.HandleOwner) &&
+			tpmData.Parent != int(tpm2.HandleNull) &&
+			tpmData.Parent != int(tpm2.HandleEndorsement) &&
+			tpmData.Parent != int(tpm2.HandlePlatform) {
+			return nil, "", errors.New("invalid parent for TPMv2 key")
+		}
+		if len(tpmData.Pubkey) < 2 ||
+			len(tpmData.Pubkey)-2 != (int(tpmData.Pubkey[0])<<8)+int(tpmData.Pubkey[1]) {
+			return nil, "", errors.New("invalid length for TPMv2 PUBLIC blob")
+		}
+
+		public, err = tpm2.DecodePublic(tpmData.Pubkey[2:])
+		if err != nil {
+			return nil, "", err
+		}
+
+		if len(tpmData.Privkey) < 2 ||
+			len(tpmData.Privkey)-2 != (int(tpmData.Privkey[0])<<8)+int(tpmData.Privkey[1]) {
+			return nil, "", errors.New("invalid length for TPMv2 PRIVATE blob")
+		}
+		private = tpmData.Privkey[2:]
+	}
+
+	switch public.Type {
+	case tpm2.AlgRSA:
+		signingAlgorithm = aws4_x509_rsa_sha256
+	case tpm2.AlgECC:
+		signingAlgorithm = aws4_x509_ecdsa_sha256
+	default:
+		return nil, "", errors.New("unsupported TPMv2 key type")
+	}
+
+	return &TPMv2Signer{
+			certificate,
+			certificateChain,
+			tpmData,
+			public,
+			private,
+			password,
+			emptyAuth,
+			handle,
+		},
+		signingAlgorithm, nil
+}