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RFC 3161 Timestamping Support #16

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merged 1 commit into from
Oct 13, 2022
Merged

RFC 3161 Timestamping Support #16

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14 changes: 14 additions & 0 deletions cryptoutil/util.go
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Original file line number Diff line number Diff line change
Expand Up @@ -133,3 +133,17 @@ func TryParseKeyFromReader(r io.Reader) (interface{}, error) {
pemBlock, _ := pem.Decode(bytes)
return TryParsePEMBlock(pemBlock)
}

func TryParseCertificate(data []byte) (*x509.Certificate, error) {
possibleCert, err := TryParseKeyFromReader(bytes.NewReader(data))
if err != nil {
return nil, err
}

cert, ok := possibleCert.(*x509.Certificate)
if !ok {
return nil, fmt.Errorf("data was a valid verifier but not a certificate")
}

return cert, nil
}
227 changes: 13 additions & 214 deletions dsse/dsse.go
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Expand Up @@ -15,14 +15,7 @@
package dsse

import (
"bytes"
"crypto/x509"
"encoding/pem"
"fmt"
"io"
"time"

"github.com/testifysec/go-witness/cryptoutil"
)

type ErrNoSignatures struct{}
Expand Down Expand Up @@ -61,12 +54,20 @@ type Envelope struct {
}

type Signature struct {
KeyID string `json:"keyid"`
Signature []byte `json:"sig"`
Certificate []byte `json:"certificate,omitempty"`
Intermediates [][]byte `json:"intermediates,omitempty"`
KeyID string `json:"keyid"`
Signature []byte `json:"sig"`
Certificate []byte `json:"certificate,omitempty"`
Intermediates [][]byte `json:"intermediates,omitempty"`
Timestamps []SignatureTimestamp `json:"timestamps,omitempty"`
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This looks like a timestamp signature on the signature, correct?

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Correct

}

type SignatureTimestampType string

const TimestampRFC3161 SignatureTimestampType = "tsp"

trustedTime time.Time
type SignatureTimestamp struct {
Type SignatureTimestampType `json:"type"`
Data []byte `json:"data"`
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How is this data encoded?

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@mikhailswift mikhailswift Sep 18, 2022 •
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Base64. Go json marshals all byte arrays to base64 strings.

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@mikhailswift mikhailswift Sep 18, 2022 •
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As far as what data actually is that is an implementation detail of the timestamper being used.

In the case of TSP it’s an ASN1 DER encoded Timestamp Token object.

}

// preauthEncode wraps the data to be signed or verified and it's type in the DSSE protocol's
Expand All @@ -76,205 +77,3 @@ func preauthEncode(bodyType string, body []byte) []byte {
const dsseVersion = "DSSEv1"
return []byte(fmt.Sprintf("%s %d %s %d %s", dsseVersion, len(bodyType), bodyType, len(body), body))
}

// TODO: it'd be nice to break some of this logic out of what should be a presentation layer only
func Sign(bodyType string, body io.Reader, signers ...cryptoutil.Signer) (Envelope, error) {
env := Envelope{}
bodyBytes, err := io.ReadAll(body)
if err != nil {
return env, err
}

env.PayloadType = bodyType
env.Payload = bodyBytes
env.Signatures = make([]Signature, 0)
pae := preauthEncode(bodyType, bodyBytes)
for _, signer := range signers {
sig, err := signer.Sign(bytes.NewReader(pae))
if err != nil {
return env, err
}

keyID, err := signer.KeyID()
if err != nil {
return env, err
}

dsseSig := Signature{
KeyID: keyID,
Signature: sig,
}

if trustBundler, ok := signer.(cryptoutil.TrustBundler); ok {
leaf := trustBundler.Certificate()
intermediates := trustBundler.Intermediates()
if leaf != nil {
dsseSig.Certificate = pem.EncodeToMemory(&pem.Block{Type: PemTypeCertificate, Bytes: leaf.Raw})
}

for _, intermediate := range intermediates {
dsseSig.Intermediates = append(dsseSig.Intermediates, pem.EncodeToMemory(&pem.Block{Type: PemTypeCertificate, Bytes: intermediate.Raw}))
}
}

env.Signatures = append(env.Signatures, dsseSig)
}

return env, nil
}

type VerificationOption func(*verificationOptions)

type verificationOptions struct {
roots []*x509.Certificate
intermediates []*x509.Certificate
verifiers []cryptoutil.Verifier
threshold int
}

func WithRoots(roots []*x509.Certificate) VerificationOption {
return func(vo *verificationOptions) {
vo.roots = roots
}
}

func WithIntermediates(intermediates []*x509.Certificate) VerificationOption {
return func(vo *verificationOptions) {
vo.intermediates = intermediates
}
}

func WithVerifiers(verifiers []cryptoutil.Verifier) VerificationOption {
return func(vo *verificationOptions) {
vo.verifiers = verifiers
}
}

func WithThreshold(threshold int) VerificationOption {
return func(vo *verificationOptions) {
vo.threshold = threshold
}
}

func (e Envelope) Verify(opts ...VerificationOption) ([]cryptoutil.Verifier, error) {
options := &verificationOptions{
threshold: 1,
}

for _, opt := range opts {
opt(options)
}

if options.threshold <= 0 {
return nil, ErrInvalidThreshold(options.threshold)
}

pae := preauthEncode(e.PayloadType, e.Payload)
if len(e.Signatures) == 0 {
return nil, ErrNoSignatures{}
}

matchingSigFound := false
passedVerifiers := make([]cryptoutil.Verifier, 0)
for _, sig := range e.Signatures {
if sig.Certificate != nil && len(sig.Certificate) > 0 {
cert, err := TryParseCertificate(sig.Certificate)
if err != nil {
continue
}

sigIntermediates := make([]*x509.Certificate, 0)
for _, int := range sig.Intermediates {
intCert, err := TryParseCertificate(int)
if err != nil {
continue
}

sigIntermediates = append(sigIntermediates, intCert)
}

sigIntermediates = append(sigIntermediates, options.intermediates...)
verifier, err := cryptoutil.NewX509Verifier(cert, sigIntermediates, options.roots, sig.trustedTime)
if err != nil {
return nil, err
}

if err := verifier.Verify(bytes.NewReader(pae), sig.Signature); err == nil {
passedVerifiers = append(passedVerifiers, verifier)
matchingSigFound = true
}
}

for _, verifier := range options.verifiers {
if verifier != nil {
if err := verifier.Verify(bytes.NewReader(pae), sig.Signature); err == nil {
passedVerifiers = append(passedVerifiers, verifier)
matchingSigFound = true
}
}
}
}

if !matchingSigFound {
return nil, ErrNoMatchingSigs{}
}

if len(passedVerifiers) < options.threshold {
return passedVerifiers, ErrThresholdNotMet{Theshold: options.threshold, Acutal: len(passedVerifiers)}
}

return passedVerifiers, nil
}

func TryParseCertificate(data []byte) (*x509.Certificate, error) {
possibleCert, err := cryptoutil.TryParseKeyFromReader(bytes.NewReader(data))
if err != nil {
return nil, err
}

cert, ok := possibleCert.(*x509.Certificate)
if !ok {
return nil, fmt.Errorf("data was a valid verifier but not a certificate")
}

return cert, nil
}

type SignatureOption func(so *signatureOptions)

type signatureOptions struct {
cert []byte
intermediates [][]byte
trustedTime time.Time
}

func SignatureWithCertificate(certBytes []byte) SignatureOption {
return func(so *signatureOptions) {
so.cert = certBytes
}
}

func SignatureWithIntermediates(intermediates [][]byte) SignatureOption {
return func(so *signatureOptions) {
so.intermediates = intermediates
}
}
func SignatureWithTrustedTime(trustedTime time.Time) SignatureOption {
return func(so *signatureOptions) {
so.trustedTime = trustedTime
}
}
func NewSignature(keyID string, sig []byte, opts ...SignatureOption) Signature {
so := signatureOptions{}
for _, opt := range opts {
opt(&so)
}

return Signature{
KeyID: keyID,
Signature: sig,
Certificate: so.cert,
Intermediates: so.intermediates,
trustedTime: so.trustedTime,
}
}
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