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package stfe
import (
"fmt"
"time"
"crypto"
"crypto/rand"
"crypto/tls"
"crypto/x509"
"github.com/system-transparency/stfe/x509util"
)
// buildChainFromDerList builds an X.509 certificate chain from a list of
// DER-encoded certificates using the log's configured trust anchors, extended
// key-usages, and maximum chain length (which includes the trust anchor).
func (lp *LogParameters) buildChainFromDerList(derChain [][]byte) ([]*x509.Certificate, error) {
certificate, intermediatePool, err := x509util.ParseDerChain(derChain)
if err != nil {
return nil, err
}
opts := x509.VerifyOptions{
Roots: lp.AnchorPool,
Intermediates: intermediatePool,
KeyUsages: lp.KeyUsage, // no extended key usage passes by default
}
chains, err := certificate.Verify(opts)
if err != nil {
return nil, fmt.Errorf("chain verification failed: %v", err)
}
if len(chains) == 0 {
return nil, fmt.Errorf("bad certificate chain length: empty")
}
// there might be several valid chains
for _, chain := range chains {
if int64(len(chain)) <= lp.MaxChain {
return chain, nil // just pick the first valid chain
}
}
return nil, fmt.Errorf("bad certificate chain length: too large")
}
// verifySignature checks if signature is valid for some serialized data. The
// only supported signature scheme is ed25519(0x0807), see ยง4.2.3 in RFC 8446.
func (lp *LogParameters) verifySignature(certificate *x509.Certificate, scheme tls.SignatureScheme, serialized, signature []byte) error {
if scheme != tls.Ed25519 {
return fmt.Errorf("unsupported signature scheme: %v", scheme)
}
if err := certificate.CheckSignature(x509.PureEd25519, serialized, signature); err != nil {
return fmt.Errorf("invalid signature: %v", err)
}
return nil
}
// genV1Sdi issues a new SignedDebugInfoV1 StItem from a serialized leaf value
func (lp *LogParameters) genV1Sdi(serialized []byte) (*StItem, error) {
sig, err := lp.Signer.Sign(rand.Reader, serialized, crypto.Hash(0)) // ed25519
if err != nil {
return nil, fmt.Errorf("ed25519 signature failed: %v", err)
}
lastSdiTimestamp.Set(float64(time.Now().Unix()), lp.id())
return NewSignedDebugInfoV1(lp.LogId, []byte("reserved"), sig), nil
}
// genV1Sth issues a new SignedTreeHeadV1 StItem from a TreeHeadV1 structure
func (lp *LogParameters) genV1Sth(th *TreeHeadV1) (*StItem, error) {
serialized, err := th.Marshal()
if err != nil {
return nil, fmt.Errorf("failed tls marshaling tree head: %v", err)
}
sig, err := lp.Signer.Sign(rand.Reader, serialized, crypto.Hash(0)) // ed25519
if err != nil {
return nil, fmt.Errorf("ed25519 signature failed: %v", err)
}
lastSthTimestamp.Set(float64(time.Now().Unix()), lp.id())
lastSthSize.Set(float64(th.TreeSize), lp.id())
return NewSignedTreeHeadV1(th, lp.LogId, sig), nil
}
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