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|
package dsse
import (
"context"
"crypto"
"errors"
"fmt"
"golang.org/x/crypto/ssh"
)
// ErrNoSignature indicates that an envelope did not contain any signatures.
var ErrNoSignature = errors.New("no signature found")
type EnvelopeVerifier struct {
providers []Verifier
threshold int
}
type AcceptedKey struct {
Public crypto.PublicKey
KeyID string
Sig Signature
}
func (ev *EnvelopeVerifier) Verify(ctx context.Context, e *Envelope) ([]AcceptedKey, error) {
if e == nil {
return nil, errors.New("cannot verify a nil envelope")
}
if len(e.Signatures) == 0 {
return nil, ErrNoSignature
}
// Decode payload (i.e serialized body)
body, err := e.DecodeB64Payload()
if err != nil {
return nil, err
}
// Generate PAE(payloadtype, serialized body)
paeEnc := PAE(e.PayloadType, body)
// If *any* signature is found to be incorrect, it is skipped
var acceptedKeys []AcceptedKey
usedKeyids := make(map[string]string)
unverified_providers := ev.providers
for _, s := range e.Signatures {
sig, err := b64Decode(s.Sig)
if err != nil {
return nil, err
}
// Loop over the providers.
// If provider and signature include key IDs but do not match skip.
// If a provider recognizes the key, we exit
// the loop and use the result.
providers := unverified_providers
for i, v := range providers {
keyID, err := v.KeyID()
// Verifiers that do not provide a keyid will be generated one using public.
if err != nil || keyID == "" {
keyID, err = SHA256KeyID(v.Public())
if err != nil {
keyID = ""
}
}
if s.KeyID != "" && keyID != "" && err == nil && s.KeyID != keyID {
continue
}
err = v.Verify(ctx, paeEnc, sig)
if err != nil {
continue
}
acceptedKey := AcceptedKey{
Public: v.Public(),
KeyID: keyID,
Sig: s,
}
unverified_providers = removeIndex(providers, i)
// See https://github.com/in-toto/in-toto/pull/251
if _, ok := usedKeyids[keyID]; ok {
fmt.Printf("Found envelope signed by different subkeys of the same main key, Only one of them is counted towards the step threshold, KeyID=%s\n", keyID)
continue
}
usedKeyids[keyID] = ""
acceptedKeys = append(acceptedKeys, acceptedKey)
break
}
}
// Sanity if with some reflect magic this happens.
if ev.threshold <= 0 || ev.threshold > len(ev.providers) {
return nil, errors.New("invalid threshold")
}
if len(usedKeyids) < ev.threshold {
return acceptedKeys, fmt.Errorf("accepted signatures do not match threshold, Found: %d, Expected %d", len(acceptedKeys), ev.threshold)
}
return acceptedKeys, nil
}
func NewEnvelopeVerifier(v ...Verifier) (*EnvelopeVerifier, error) {
return NewMultiEnvelopeVerifier(1, v...)
}
func NewMultiEnvelopeVerifier(threshold int, p ...Verifier) (*EnvelopeVerifier, error) {
if threshold <= 0 || threshold > len(p) {
return nil, errors.New("invalid threshold")
}
ev := EnvelopeVerifier{
providers: p,
threshold: threshold,
}
return &ev, nil
}
func SHA256KeyID(pub crypto.PublicKey) (string, error) {
// Generate public key fingerprint
sshpk, err := ssh.NewPublicKey(pub)
if err != nil {
return "", err
}
fingerprint := ssh.FingerprintSHA256(sshpk)
return fingerprint, nil
}
func removeIndex(v []Verifier, index int) []Verifier {
return append(v[:index], v[index+1:]...)
}
|
