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package stfe
import (
"fmt"
"crypto"
"crypto/ecdsa"
"crypto/ed25519"
"crypto/rand"
"crypto/rsa"
stdtls "crypto/tls"
"crypto/x509"
"encoding/base64"
"encoding/pem"
"io/ioutil"
"github.com/google/certificate-transparency-go/tls"
)
// LoadTrustAnchors loads a list of PEM-encoded certificates from file
func LoadTrustAnchors(path string) ([]*x509.Certificate, *x509.CertPool, error) {
rest, err := ioutil.ReadFile(path)
if err != nil {
return nil, nil, fmt.Errorf("failed reading trust anchors: %v", err)
}
pool := x509.NewCertPool()
var anchors []*x509.Certificate
for len(rest) > 0 {
var block *pem.Block
block, rest = pem.Decode(rest)
if block == nil {
break
}
if block.Type != "CERTIFICATE" {
return nil, nil, fmt.Errorf("unexpected PEM block type: %s", block.Type)
}
certificate, err := x509.ParseCertificate(block.Bytes)
if err != nil {
return nil, nil, fmt.Errorf("invalid trust anchor before rest(%s): %v", rest, err)
}
anchors = append(anchors, certificate)
pool.AddCert(certificate)
}
if len(anchors) == 0 {
return nil, nil, fmt.Errorf("found no valid trust anchor in: %s", path)
}
return anchors, pool, nil
}
func LoadEd25519SigningKey(path string) (ed25519.PrivateKey, error) {
data, err := ioutil.ReadFile(path)
if err != nil {
return nil, fmt.Errorf("failed reading private key: %v", err)
}
var block *pem.Block
block, data = pem.Decode(data)
if block == nil {
return nil, fmt.Errorf("private key not loaded")
}
if block.Type != "PRIVATE KEY" {
return nil, fmt.Errorf("unexpected PEM block type: %s", block.Type)
}
if len(data) != 0 {
return nil, fmt.Errorf("trailing data found after key: %v", data)
}
key, err := x509.ParsePKCS8PrivateKey(block.Bytes)
if err != nil {
return nil, fmt.Errorf("failed parsing signing key: %v", err)
}
switch t := key.(type) {
case ed25519.PrivateKey:
return key.(ed25519.PrivateKey), nil
default:
return nil, fmt.Errorf("unexpected signing key type: %v", t)
}
}
func VerifyChain(ld *LogParameters, certificate *x509.Certificate) ([]*x509.Certificate, error) {
opts := x509.VerifyOptions{
Roots: ld.AnchorPool,
KeyUsages: []x509.ExtKeyUsage{x509.ExtKeyUsageAny}, // TODO: move to ld
} // TODO: add intermediates
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("chain verification failed: no chain")
}
return chains[0], nil // if we found multiple paths just pick the first one
}
func VerifySignature(leaf, signature []byte, certificate *x509.Certificate) error {
var algo x509.SignatureAlgorithm
switch t := certificate.PublicKey.(type) {
case *rsa.PublicKey:
algo = x509.SHA256WithRSA
case *ecdsa.PublicKey:
algo = x509.ECDSAWithSHA256
default:
return fmt.Errorf("unsupported public key algorithm: %v", t)
}
if err := certificate.CheckSignature(algo, leaf, signature); err != nil {
return fmt.Errorf("invalid signature: %v", err)
}
return nil
}
func GenV1SDI(ld *LogParameters, leaf []byte) (StItem, error) {
// Note that ed25519 does not use the passed io.Reader
sig, err := ld.Signer.Sign(rand.Reader, leaf, crypto.Hash(0))
if err != nil {
return StItem{}, fmt.Errorf("ed25519 signature failed: %v", err)
}
return NewSignedDebugInfoV1(ld.LogId, []byte("reserved"), sig), nil
}
func GenV1STH(ld *LogParameters, th TreeHeadV1) (StItem, error) {
serialized, err := tls.Marshal(th)
if err != nil {
return StItem{}, fmt.Errorf("failed tls marshaling tree head: %v", err)
}
// Note that ed25519 does not use the passed io.Reader
sig, err := ld.Signer.Sign(rand.Reader, serialized, crypto.Hash(0))
if err != nil {
return StItem{}, fmt.Errorf("ed25519 signature failed: %v", err)
}
return NewSignedTreeHeadV1(th, ld.LogId, sig), nil
}
// ParseB64Chain parses a list of base64 DER-encoded X.509 certificates, such
// that the first (zero-index) string is interpretted as an end-entity
// certificate and the remaining ones as the an intermediate CertPool.
func ParseB64Chain(chain []string) (*x509.Certificate, *x509.CertPool, error) {
var certificate *x509.Certificate
intermediatePool := x509.NewCertPool()
for index, cert := range chain {
der, err := base64.StdEncoding.DecodeString(cert)
if err != nil {
return nil, nil, fmt.Errorf("certificate decoding failed: %v", err)
}
c, err := x509.ParseCertificate(der)
if err != nil {
return nil, nil, fmt.Errorf("certificate decoding failed: %v", err)
}
if index == 0 {
certificate = c
} else {
intermediatePool.AddCert(c)
}
}
if certificate == nil {
return nil, nil, fmt.Errorf("certificate chain is empty")
}
return certificate, intermediatePool, nil
}
func buildChainFromB64List(lp *LogParameters, b64chain []string) ([]*x509.Certificate, error) {
certificate, _, err := ParseB64Chain(b64chain) // TODO: use intermediatePool
if err != nil {
return nil, err
}
opts := x509.VerifyOptions{
Roots: lp.AnchorPool,
KeyUsages: []x509.ExtKeyUsage{x509.ExtKeyUsageAny}, // TODO: move to ld
}
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("chain verification failed: no chain")
}
chain := chains[0] // if we found multiple paths just pick the first one
// TODO: check that len(chain) is OK
return chain, nil
}
// verifySignature checks if signature is valid for some serialized data. The
// only supported signature scheme is ecdsa_secp256r1_sha256(0x0403), see ยง4.3.2
// in RFC 8446. TODO: replace ECDSA with ed25519(0x0807)
func verifySignature(_ *LogParameters, certificate *x509.Certificate, scheme stdtls.SignatureScheme, serialized, signature []byte) error {
if scheme != stdtls.ECDSAWithP256AndSHA256 {
return fmt.Errorf("unsupported signature scheme: %v", scheme)
}
if err := certificate.CheckSignature(x509.ECDSAWithSHA256, serialized, signature); err != nil {
return fmt.Errorf("invalid signature: %v", err)
}
return nil
}
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