diff --git a/client/canonical_eventlog.go b/client/canonical_eventlog.go
new file mode 100644
index 000000000..65d6f28b8
--- /dev/null
+++ b/client/canonical_eventlog.go
@@ -0,0 +1,266 @@
+package client
+
+import (
+	"bytes"
+	"crypto"
+	"encoding/binary"
+	"fmt"
+	"io"
+
+	"github.com/google/go-tpm/tpm2"
+)
+
+var hashAlgoMapping = map[crypto.Hash]tpm2.Algorithm{
+	crypto.SHA1:   tpm2.AlgSHA1,
+	crypto.SHA256: tpm2.AlgSHA256,
+	crypto.SHA384: tpm2.AlgSHA384,
+	crypto.SHA512: tpm2.AlgSHA512,
+}
+
+const (
+	// CEL spec 5.1
+	recNumTagValue  uint8 = 0
+	pcrTagValue     uint8 = 1
+	nvIndexTagValue uint8 = 2
+	digestsTagValue uint8 = 3
+
+	tlvTagFieldLength    int = 1
+	tlvLengthFieldLength int = 4
+
+	recNumValueLength uint32 = 8 // support up to 2^64 records
+	pcrValueLength    uint32 = 1 // support up to 256 PCRs
+)
+
+// TLV definition according to CEL spec, page 16
+type TLV struct {
+	Tag    uint8
+	Length uint32 // big-endian when encoding
+	Value  []byte // with size of Length
+}
+
+// TLVMarshal marhsal a TLV to a byte slice
+func TLVMarshal(tlv TLV) []byte {
+	buf := make([]byte, tlv.Length+uint32(tlvTagFieldLength)+uint32(tlvLengthFieldLength))
+
+	buf[0] = tlv.Tag
+	binary.BigEndian.PutUint32(buf[tlvTagFieldLength:], tlv.Length)
+	copy(buf[tlvTagFieldLength+tlvLengthFieldLength:], tlv.Value)
+
+	return buf
+}
+
+// TLVUnmarshal reads and parse the first TLV from the bytes buffer.
+func TLVUnmarshal(buf *bytes.Buffer) (TLV, error) {
+	var tlv TLV
+	var err error
+
+	// read tag
+	tlv.Tag, err = buf.ReadByte()
+	if err != nil {
+		return TLV{}, err
+	}
+
+	// read length
+	b := make([]byte, tlvLengthFieldLength)
+	l, err := buf.Read(b)
+
+	if err != nil || l < tlvLengthFieldLength {
+		return TLV{}, io.EOF
+	}
+	tlv.Length = binary.BigEndian.Uint32(b)
+
+	// read value
+	tlv.Value = make([]byte, tlv.Length)
+	l, err = buf.Read(tlv.Value)
+	if err != nil || l < int(tlv.Length) {
+		return TLV{}, io.EOF
+	}
+	return tlv, nil
+}
+
+// CELR represents a Canoical Eventlog Record
+type CELR struct {
+	RecNum  TLV
+	PCR     TLV
+	Digests TLV
+	Content TLV
+}
+
+// CELREventData is a interface for the content in CELR.
+type CELREventData interface {
+	GenerateDigest(crypto.Hash) ([]byte, error)
+	GetTLV() TLV
+}
+
+// CEL represents a Canonical Eventlog, which contains a list of CELR
+type CEL struct {
+	Records []CELR
+}
+
+// AppendEvent appends a new record to the CEL.
+func (c *CEL) AppendEvent(tpm io.ReadWriteCloser, pcr int, hashAlgos []crypto.Hash, payload CELREventData) error {
+	digestsMap := make(map[tpm2.Algorithm][]byte)
+	for _, hashAlgo := range hashAlgos {
+		digest, err := payload.GenerateDigest(hashAlgo)
+		if err != nil {
+			return err
+		}
+		digestsMap[hashAlgoMapping[hashAlgo]] = digest
+
+		// TODO: extend the digest to TPM PCR
+	}
+
+	celr, err := createCELR(uint64(len(c.Records)), uint8(pcr), digestsMap, payload)
+	if err != nil {
+		return err
+	}
+
+	c.Records = append(c.Records, celr)
+	return nil
+}
+
+func createRecNumField(recNum uint64) TLV {
+	payload := make([]byte, recNumValueLength)
+	binary.BigEndian.PutUint64(payload, recNum)
+	return TLV{recNumTagValue, recNumValueLength, payload}
+}
+
+// UnmarshalRecNum takes in a TLV with its tag equals to the recnum tag value (0), and
+// return its record number.
+func UnmarshalRecNum(tlv TLV) (uint64, error) {
+	if tlv.Tag != recNumTagValue {
+		return 0, fmt.Errorf("tag of the TLV indicates it is not a recnum field")
+	}
+	return binary.BigEndian.Uint64(tlv.Value), nil
+}
+
+func createPCRField(pcrNum uint8) TLV {
+	return TLV{pcrTagValue, pcrValueLength, []byte{pcrNum}}
+}
+
+// UnmarshalPCR takes in a TLV with its tag equals to the PCR tag value (3), and
+// return its PCR number.
+func UnmarshalPCR(tlv TLV) (pcrNum uint8, err error) {
+	if tlv.Tag != pcrTagValue {
+		return 0, fmt.Errorf("tag of the TLV indicates it is not a PCR field")
+	}
+	return tlv.Value[0], nil
+}
+
+func createDigestField(digestMap map[tpm2.Algorithm][]byte) TLV {
+	var buf bytes.Buffer
+
+	for hashAlgo, hash := range digestMap {
+		singledigest := TLV{uint8(hashAlgo), uint32(len(hash)), hash}
+		_, err := buf.Write(TLVMarshal(singledigest))
+		if err != nil {
+			panic(err)
+		}
+	}
+
+	return TLV{digestsTagValue, uint32(buf.Len()), buf.Bytes()}
+}
+
+// UnmarshalDigests takes in a TLV with its tag equals to the digests Tag value (3), and
+// return its digests content in a map, the key is its TPM hash algorithm.
+func UnmarshalDigests(tlv TLV) (digestsMap map[tpm2.Algorithm][]byte, err error) {
+	if tlv.Tag != digestsTagValue {
+		return nil, fmt.Errorf("tag of the TLV indicates it doesn't contain digests")
+	}
+
+	buf := bytes.NewBuffer(tlv.Value)
+	digestsMap = make(map[tpm2.Algorithm][]byte)
+
+	for buf.Len() > 0 {
+		digestTLV, err := TLVUnmarshal(buf)
+		if err == io.EOF {
+			return nil, fmt.Errorf("buffer ends unexpectedly")
+		}
+		digestsMap[tpm2.Algorithm(digestTLV.Tag)] = digestTLV.Value
+	}
+	return digestsMap, nil
+}
+
+func createCELR(recNum uint64, pcr uint8, digestsmap map[tpm2.Algorithm][]byte, event CELREventData) (celr CELR, err error) {
+	recnumField := createRecNumField(recNum)
+	pcrField := createPCRField(pcr)
+
+	digestField := createDigestField(digestsmap)
+	celr = CELR{recnumField, pcrField, digestField, event.GetTLV()}
+
+	return celr, nil
+}
+
+// EncodeCELR encodes the CELR to bytes according to the CEL spec and write them
+// to the byte byffer.
+func (r *CELR) EncodeCELR(buf *bytes.Buffer) error {
+	// encode CEL and write the binary eventlog to the buf
+	recnumField := TLVMarshal(TLV(r.RecNum))
+	pcrField := TLVMarshal(TLV(r.PCR))
+	digestsField := TLVMarshal(TLV(r.Digests))
+	eventField := TLVMarshal(TLV(r.Content))
+
+	buf.Write(recnumField)
+	buf.Write(pcrField)
+	buf.Write(digestsField)
+	buf.Write(eventField)
+	return nil
+}
+
+// EncodeCEL encodes the CEL to bytes according to the CEL spec and write them
+// to the byte buffer.
+func (c *CEL) EncodeCEL(buf *bytes.Buffer) error {
+	for _, record := range c.Records {
+		if err := record.EncodeCELR(buf); err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
+// DecodeToCEL will read the buf for CEL, will return err if the buffer
+// is not complete.
+func DecodeToCEL(buf *bytes.Buffer) (CEL, error) {
+	var cel CEL
+	for buf.Len() > 0 {
+		celr, err := DecodeToCELR(buf)
+		if err == io.EOF {
+			return CEL{}, fmt.Errorf("buffer ends unexpectedly")
+		}
+		cel.Records = append(cel.Records, celr)
+	}
+	return cel, nil
+}
+
+// DecodeToCELR will read the buf for the next CELR, will return err if
+// failed to unmarshal the TLV from the buffer.
+func DecodeToCELR(buf *bytes.Buffer) (CELR, error) {
+	recNum, err := TLVUnmarshal(buf)
+	if err != nil {
+		return CELR{}, err
+	}
+
+	pcr, err := TLVUnmarshal(buf)
+	if err != nil {
+		return CELR{}, err
+	}
+
+	digests, err := TLVUnmarshal(buf)
+	if err != nil {
+		return CELR{}, err
+	}
+
+	content, err := TLVUnmarshal(buf)
+	if err != nil {
+		return CELR{}, err
+	}
+
+	celr := CELR{
+		recNum,
+		pcr,
+		digests,
+		content,
+	}
+
+	return celr, nil
+}
diff --git a/client/canonical_eventlog_test.go b/client/canonical_eventlog_test.go
new file mode 100644
index 000000000..fb690a84f
--- /dev/null
+++ b/client/canonical_eventlog_test.go
@@ -0,0 +1,69 @@
+package client
+
+import (
+	"bytes"
+	"crypto"
+	"reflect"
+	"testing"
+
+	"github.com/google/go-tpm/tpm2"
+)
+
+func TestCELEncodingDecoding(t *testing.T) {
+	hashAlgoList := []crypto.Hash{crypto.SHA256, crypto.SHA1}
+	cel := &CEL{}
+
+	someEvent := make([]byte, 10)
+	cosEvent := COSTLV{COSTagValue, uint32(10), someEvent}
+	cel.AppendEvent(nil, 13, hashAlgoList, cosEvent)
+
+	someEvent2 := make([]byte, 10)
+	cosEvent2 := COSTLV{COSTagValue, uint32(10), someEvent2}
+	cel.AppendEvent(nil, 14, hashAlgoList, cosEvent2)
+
+	var buf bytes.Buffer
+	err := cel.EncodeCEL(&buf)
+	if err != nil {
+		t.Fatalf(err.Error())
+	}
+
+	decodedcel, err := DecodeToCEL(&buf)
+	if err != nil {
+		t.Fatalf(err.Error())
+	}
+
+	if len(decodedcel.Records) != 2 {
+		t.Errorf("should have two records")
+	}
+
+	if recnum, err := UnmarshalRecNum(decodedcel.Records[0].RecNum); err != nil || recnum != uint64(0) {
+		t.Errorf("recnum mismatch")
+	}
+	if recnum, err := UnmarshalRecNum(decodedcel.Records[1].RecNum); err != nil || recnum != uint64(1) {
+		t.Errorf("recnum mismatch")
+	}
+
+	if pcr, err := UnmarshalPCR(decodedcel.Records[0].PCR); err != nil || pcr != uint8(13) {
+		t.Errorf("pcr value mismatch")
+	}
+	if pcr, err := UnmarshalPCR(decodedcel.Records[1].PCR); err != nil || pcr != uint8(14) {
+		t.Errorf("pcr value mismatch")
+	}
+
+	digestsMap, err := UnmarshalDigests(decodedcel.Records[0].Digests)
+	if err != nil {
+		t.Error(err)
+	}
+
+	if len(digestsMap[tpm2.AlgSHA256]) != 32 {
+		t.Errorf("SHA256 digest length doesn't match")
+	}
+
+	if len(digestsMap[tpm2.AlgSHA1]) != 20 {
+		t.Errorf("SHA1 digest length doesn't match")
+	}
+
+	if reflect.DeepEqual(decodedcel.Records, (*cel).Records) == false {
+		t.Errorf("decoded CEL doesn't equal to the original one")
+	}
+}
diff --git a/client/costlv.go b/client/costlv.go
new file mode 100644
index 000000000..2e3654d21
--- /dev/null
+++ b/client/costlv.go
@@ -0,0 +1,29 @@
+package client
+
+import "crypto"
+
+const (
+	// COSTagValue indicate the CELR event is a COS content
+	// TODO: the value needs to be reserved in the CEL spec
+	COSTagValue uint8 = 88
+)
+
+// COSTLV is a specific event type created for the COS (Google Container-Optimized OS),
+// used as a CEL content.
+type COSTLV TLV
+
+// GetTLV returns the TLV representation of the COS TLV.
+func (c COSTLV) GetTLV() TLV {
+	return TLV(c)
+}
+
+// GenerateDigest generates the digest for the given COS TLV. The whole TLV struct will
+// be marshaled to bytes and feed into the hash algo.
+func (c COSTLV) GenerateDigest(hashAlgo crypto.Hash) ([]byte, error) {
+	hash := hashAlgo.New()
+	_, err := hash.Write(TLVMarshal(c.GetTLV()))
+	if err != nil {
+		return nil, err
+	}
+	return hash.Sum(nil), nil
+}