/
certinfo.go
282 lines (248 loc) · 7.12 KB
/
certinfo.go
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package googletpm
import (
"bytes"
"crypto/sha1"
"crypto/sha256"
"crypto/sha512"
"fmt"
"hash"
)
// DecodeAttestationData decode a TPMS_ATTEST message. No error is returned if
// the input has extra trailing data.
func DecodeAttestationData(in []byte) (*AttestationData, error) {
buf := bytes.NewBuffer(in)
var ad AttestationData
if err := UnpackBuf(buf, &ad.Magic, &ad.Type); err != nil {
return nil, fmt.Errorf("decoding Magic/Type: %v", err)
}
n, err := decodeName(buf)
if err != nil {
return nil, fmt.Errorf("decoding QualifiedSigner: %v", err)
}
ad.QualifiedSigner = *n
if err := UnpackBuf(buf, &ad.ExtraData, &ad.ClockInfo, &ad.FirmwareVersion); err != nil {
return nil, fmt.Errorf("decoding ExtraData/ClockInfo/FirmwareVersion: %v", err)
}
// The spec specifies several other types of attestation data. We only need
// parsing of Certify & Creation attestation data for now. If you need
// support for other attestation types, add them here.
switch ad.Type {
case TagAttestCertify:
if ad.AttestedCertifyInfo, err = decodeCertifyInfo(buf); err != nil {
return nil, fmt.Errorf("decoding AttestedCertifyInfo: %v", err)
}
case TagAttestCreation:
if ad.AttestedCreationInfo, err = decodeCreationInfo(buf); err != nil {
return nil, fmt.Errorf("decoding AttestedCreationInfo: %v", err)
}
case TagAttestQuote:
if ad.AttestedQuoteInfo, err = decodeQuoteInfo(buf); err != nil {
return nil, fmt.Errorf("decoding AttestedQuoteInfo: %v", err)
}
default:
return nil, fmt.Errorf("only Certify & Creation attestation structures are supported, got type 0x%x", ad.Type)
}
return &ad, nil
}
// AttestationData contains data attested by TPM commands (like Certify).
type AttestationData struct {
Magic uint32
Type Tag
QualifiedSigner Name
ExtraData []byte
ClockInfo ClockInfo
FirmwareVersion uint64
AttestedCertifyInfo *CertifyInfo
AttestedQuoteInfo *QuoteInfo
AttestedCreationInfo *CreationInfo
}
// Tag is a command tag.
type Tag uint16
type Name struct {
Handle *Handle
Digest *HashValue
}
// A Handle is a reference to a TPM object.
type Handle uint32
type HashValue struct {
Alg Algorithm
Value []byte
}
// ClockInfo contains TPM state info included in AttestationData.
type ClockInfo struct {
Clock uint64
ResetCount uint32
RestartCount uint32
Safe byte
}
// CertifyInfo contains Certify-specific data for TPMS_ATTEST.
type CertifyInfo struct {
Name Name
QualifiedName Name
}
// QuoteInfo represents a TPMS_QUOTE_INFO structure.
type QuoteInfo struct {
PCRSelection PCRSelection
PCRDigest []byte
}
// PCRSelection contains a slice of PCR indexes and a hash algorithm used in
// them.
type PCRSelection struct {
Hash Algorithm
PCRs []int
}
// CreationInfo contains Creation-specific data for TPMS_ATTEST.
type CreationInfo struct {
Name Name
// Most TPM2B_Digest structures contain a TPMU_HA structure
// and get parsed to HashValue. This is never the case for the
// digest in TPMS_CREATION_INFO.
OpaqueDigest []byte
}
func decodeName(in *bytes.Buffer) (*Name, error) {
var nameBuf []byte
if err := UnpackBuf(in, &nameBuf); err != nil {
return nil, err
}
name := new(Name)
switch len(nameBuf) {
case 0:
// No name is present.
case 4:
name.Handle = new(Handle)
if err := UnpackBuf(bytes.NewBuffer(nameBuf), name.Handle); err != nil {
return nil, fmt.Errorf("decoding Handle: %v", err)
}
default:
var err error
name.Digest, err = decodeHashValue(bytes.NewBuffer(nameBuf))
if err != nil {
return nil, fmt.Errorf("decoding Digest: %v", err)
}
}
return name, nil
}
func decodeHashValue(in *bytes.Buffer) (*HashValue, error) {
var hv HashValue
if err := UnpackBuf(in, &hv.Alg); err != nil {
return nil, fmt.Errorf("decoding Alg: %v", err)
}
hfn, ok := hashConstructors[hv.Alg]
if !ok {
return nil, fmt.Errorf("unsupported hash algorithm type 0x%x", hv.Alg)
}
hv.Value = make([]byte, hfn().Size())
if _, err := in.Read(hv.Value); err != nil {
return nil, fmt.Errorf("decoding Value: %v", err)
}
return &hv, nil
}
// HashConstructor returns a function that can be used to make a
// hash.Hash using the specified algorithm. An error is returned
// if the algorithm is not a hash algorithm.
func (a Algorithm) HashConstructor() (func() hash.Hash, error) {
c, ok := hashConstructors[a]
if !ok {
return nil, fmt.Errorf("algorithm not supported: 0x%x", a)
}
return c, nil
}
var hashConstructors = map[Algorithm]func() hash.Hash{
AlgSHA1: sha1.New,
AlgSHA256: sha256.New,
AlgSHA384: sha512.New384,
AlgSHA512: sha512.New,
}
// TPM Structure Tags. Tags are used to disambiguate structures, similar to Alg
// values: tag value defines what kind of data lives in a nested field.
const (
TagNull Tag = 0x8000
TagNoSessions Tag = 0x8001
TagSessions Tag = 0x8002
TagAttestCertify Tag = 0x8017
TagAttestQuote Tag = 0x8018
TagAttestCreation Tag = 0x801a
TagHashCheck Tag = 0x8024
)
func decodeCertifyInfo(in *bytes.Buffer) (*CertifyInfo, error) {
var ci CertifyInfo
n, err := decodeName(in)
if err != nil {
return nil, fmt.Errorf("decoding Name: %v", err)
}
ci.Name = *n
n, err = decodeName(in)
if err != nil {
return nil, fmt.Errorf("decoding QualifiedName: %v", err)
}
ci.QualifiedName = *n
return &ci, nil
}
func decodeCreationInfo(in *bytes.Buffer) (*CreationInfo, error) {
var ci CreationInfo
n, err := decodeName(in)
if err != nil {
return nil, fmt.Errorf("decoding Name: %v", err)
}
ci.Name = *n
if err := UnpackBuf(in, &ci.OpaqueDigest); err != nil {
return nil, fmt.Errorf("decoding Digest: %v", err)
}
return &ci, nil
}
func decodeQuoteInfo(in *bytes.Buffer) (*QuoteInfo, error) {
var out QuoteInfo
sel, err := decodeTPMLPCRSelection(in)
if err != nil {
return nil, fmt.Errorf("decoding PCRSelection: %v", err)
}
out.PCRSelection = sel
if err := UnpackBuf(in, &out.PCRDigest); err != nil {
return nil, fmt.Errorf("decoding PCRDigest: %v", err)
}
return &out, nil
}
func decodeTPMLPCRSelection(buf *bytes.Buffer) (PCRSelection, error) {
var count uint32
var sel PCRSelection
if err := UnpackBuf(buf, &count); err != nil {
return sel, err
}
switch count {
case 0:
sel.Hash = AlgUnknown
return sel, nil
case 1: // We only support decoding of a single PCRSelection.
default:
return sel, fmt.Errorf("decoding TPML_PCR_SELECTION list longer than 1 is not supported (got length %d)", count)
}
// See comment in encodeTPMLPCRSelection for details on this format.
var ts tpmsPCRSelection
if err := UnpackBuf(buf, &ts.Hash, &ts.Size); err != nil {
return sel, err
}
ts.PCRs = make([]byte, ts.Size)
if _, err := buf.Read(ts.PCRs); err != nil {
return sel, err
}
sel.Hash = ts.Hash
for i := 0; i < int(ts.Size); i++ {
for j := 0; j < 8; j++ {
set := ts.PCRs[i] & byte(1<<byte(j))
if set == 0 {
continue
}
sel.PCRs = append(sel.PCRs, 8*i+j)
}
}
return sel, nil
}
type tpmsPCRSelection struct {
Hash Algorithm
Size byte
PCRs RawBytes
}
// RawBytes is for Pack and RunCommand arguments that are already encoded.
// Compared to []byte, RawBytes will not be prepended with slice length during
// encoding.
type RawBytes []byte