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147 lines
3.5 KiB
Go
147 lines
3.5 KiB
Go
package dsse
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import (
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"crypto"
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"errors"
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"fmt"
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"golang.org/x/crypto/ssh"
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)
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/*
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Verifier verifies a complete message against a signature and key.
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If the message was hashed prior to signature generation, the verifier
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must perform the same steps.
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If KeyID returns successfully, only signature matching the key ID will be verified.
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*/
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type Verifier interface {
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Verify(data, sig []byte) error
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KeyID() (string, error)
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Public() crypto.PublicKey
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}
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type EnvelopeVerifier struct {
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providers []Verifier
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threshold int
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}
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type AcceptedKey struct {
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Public crypto.PublicKey
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KeyID string
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Sig Signature
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}
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func (ev *EnvelopeVerifier) Verify(e *Envelope) ([]AcceptedKey, error) {
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if e == nil {
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return nil, errors.New("cannot verify a nil envelope")
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}
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if len(e.Signatures) == 0 {
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return nil, ErrNoSignature
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}
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// Decode payload (i.e serialized body)
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body, err := e.DecodeB64Payload()
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if err != nil {
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return nil, err
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}
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// Generate PAE(payloadtype, serialized body)
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paeEnc := PAE(e.PayloadType, body)
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// If *any* signature is found to be incorrect, it is skipped
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var acceptedKeys []AcceptedKey
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usedKeyids := make(map[string]string)
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unverified_providers := ev.providers
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for _, s := range e.Signatures {
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sig, err := b64Decode(s.Sig)
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if err != nil {
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return nil, err
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}
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// Loop over the providers.
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// If provider and signature include key IDs but do not match skip.
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// If a provider recognizes the key, we exit
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// the loop and use the result.
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providers := unverified_providers
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for i, v := range providers {
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keyID, err := v.KeyID()
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// Verifiers that do not provide a keyid will be generated one using public.
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if err != nil || keyID == "" {
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keyID, err = SHA256KeyID(v.Public())
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if err != nil {
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keyID = ""
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}
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}
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if s.KeyID != "" && keyID != "" && err == nil && s.KeyID != keyID {
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continue
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}
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err = v.Verify(paeEnc, sig)
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if err != nil {
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continue
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}
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acceptedKey := AcceptedKey{
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Public: v.Public(),
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KeyID: keyID,
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Sig: s,
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}
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unverified_providers = removeIndex(providers, i)
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// See https://github.com/in-toto/in-toto/pull/251
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if _, ok := usedKeyids[keyID]; ok {
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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)
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continue
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}
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usedKeyids[keyID] = ""
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acceptedKeys = append(acceptedKeys, acceptedKey)
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break
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}
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}
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// Sanity if with some reflect magic this happens.
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if ev.threshold <= 0 || ev.threshold > len(ev.providers) {
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return nil, errors.New("Invalid threshold")
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}
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if len(usedKeyids) < ev.threshold {
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return acceptedKeys, errors.New(fmt.Sprintf("Accepted signatures do not match threshold, Found: %d, Expected %d", len(acceptedKeys), ev.threshold))
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}
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return acceptedKeys, nil
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}
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func NewEnvelopeVerifier(v ...Verifier) (*EnvelopeVerifier, error) {
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return NewMultiEnvelopeVerifier(1, v...)
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}
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func NewMultiEnvelopeVerifier(threshold int, p ...Verifier) (*EnvelopeVerifier, error) {
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if threshold <= 0 || threshold > len(p) {
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return nil, errors.New("Invalid threshold")
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}
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ev := EnvelopeVerifier{
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providers: p,
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threshold: threshold,
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}
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return &ev, nil
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}
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func SHA256KeyID(pub crypto.PublicKey) (string, error) {
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// Generate public key fingerprint
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sshpk, err := ssh.NewPublicKey(pub)
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if err != nil {
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return "", err
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}
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fingerprint := ssh.FingerprintSHA256(sshpk)
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return fingerprint, nil
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}
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func removeIndex(v []Verifier, index int) []Verifier {
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return append(v[:index], v[index+1:]...)
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}
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