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package dtls
import (
"crypto"
"crypto/ecdsa"
"crypto/ed25519"
"crypto/rand"
"crypto/rsa"
"crypto/sha256"
"crypto/x509"
"encoding/asn1"
"encoding/binary"
"math/big"
"time"
"github.com/pion/dtls/v2/pkg/crypto/elliptic"
"github.com/pion/dtls/v2/pkg/crypto/hash"
)
type ecdsaSignature struct {
R, S *big.Int
}
func valueKeyMessage(clientRandom, serverRandom, publicKey []byte, namedCurve elliptic.Curve) []byte {
serverECDHParams := make([]byte, 4)
serverECDHParams[0] = 3 // named curve
binary.BigEndian.PutUint16(serverECDHParams[1:], uint16(namedCurve))
serverECDHParams[3] = byte(len(publicKey))
plaintext := []byte{}
plaintext = append(plaintext, clientRandom...)
plaintext = append(plaintext, serverRandom...)
plaintext = append(plaintext, serverECDHParams...)
plaintext = append(plaintext, publicKey...)
return plaintext
}
// If the client provided a "signature_algorithms" extension, then all
// certificates provided by the server MUST be signed by a
// hash/signature algorithm pair that appears in that extension
//
// https://tools.ietf.org/html/rfc5246#section-7.4.2
func generateKeySignature(clientRandom, serverRandom, publicKey []byte, namedCurve elliptic.Curve, privateKey crypto.PrivateKey, hashAlgorithm hash.Algorithm) ([]byte, error) {
msg := valueKeyMessage(clientRandom, serverRandom, publicKey, namedCurve)
switch p := privateKey.(type) {
case ed25519.PrivateKey:
// https://crypto.stackexchange.com/a/55483
return p.Sign(rand.Reader, msg, crypto.Hash(0))
case *ecdsa.PrivateKey:
hashed := hashAlgorithm.Digest(msg)
return p.Sign(rand.Reader, hashed, hashAlgorithm.CryptoHash())
case *rsa.PrivateKey:
hashed := hashAlgorithm.Digest(msg)
return p.Sign(rand.Reader, hashed, hashAlgorithm.CryptoHash())
}
return nil, errKeySignatureGenerateUnimplemented
}
func verifyKeySignature(message, remoteKeySignature []byte, hashAlgorithm hash.Algorithm, rawCertificates [][]byte) error { //nolint:dupl
if len(rawCertificates) == 0 {
return errLengthMismatch
}
certificate, err := x509.ParseCertificate(rawCertificates[0])
if err != nil {
return err
}
switch p := certificate.PublicKey.(type) {
case ed25519.PublicKey:
if ok := ed25519.Verify(p, message, remoteKeySignature); !ok {
return errKeySignatureMismatch
}
return nil
case *ecdsa.PublicKey:
ecdsaSig := &ecdsaSignature{}
if _, err := asn1.Unmarshal(remoteKeySignature, ecdsaSig); err != nil {
return err
}
if ecdsaSig.R.Sign() <= 0 || ecdsaSig.S.Sign() <= 0 {
return errInvalidECDSASignature
}
hashed := hashAlgorithm.Digest(message)
if !ecdsa.Verify(p, hashed, ecdsaSig.R, ecdsaSig.S) {
return errKeySignatureMismatch
}
return nil
case *rsa.PublicKey:
switch certificate.SignatureAlgorithm {
case x509.SHA1WithRSA, x509.SHA256WithRSA, x509.SHA384WithRSA, x509.SHA512WithRSA:
hashed := hashAlgorithm.Digest(message)
return rsa.VerifyPKCS1v15(p, hashAlgorithm.CryptoHash(), hashed, remoteKeySignature)
default:
return errKeySignatureVerifyUnimplemented
}
}
return errKeySignatureVerifyUnimplemented
}
// If the server has sent a CertificateRequest message, the client MUST send the Certificate
// message. The ClientKeyExchange message is now sent, and the content
// of that message will depend on the public key algorithm selected
// between the ClientHello and the ServerHello. If the client has sent
// a certificate with signing ability, a digitally-signed
// CertificateVerify message is sent to explicitly verify possession of
// the private key in the certificate.
// https://tools.ietf.org/html/rfc5246#section-7.3
func generateCertificateVerify(handshakeBodies []byte, privateKey crypto.PrivateKey, hashAlgorithm hash.Algorithm) ([]byte, error) {
h := sha256.New()
if _, err := h.Write(handshakeBodies); err != nil {
return nil, err
}
hashed := h.Sum(nil)
switch p := privateKey.(type) {
case ed25519.PrivateKey:
// https://crypto.stackexchange.com/a/55483
return p.Sign(rand.Reader, hashed, crypto.Hash(0))
case *ecdsa.PrivateKey:
return p.Sign(rand.Reader, hashed, hashAlgorithm.CryptoHash())
case *rsa.PrivateKey:
return p.Sign(rand.Reader, hashed, hashAlgorithm.CryptoHash())
}
return nil, errInvalidSignatureAlgorithm
}
func verifyCertificateVerify(handshakeBodies []byte, hashAlgorithm hash.Algorithm, remoteKeySignature []byte, rawCertificates [][]byte) error { //nolint:dupl
if len(rawCertificates) == 0 {
return errLengthMismatch
}
certificate, err := x509.ParseCertificate(rawCertificates[0])
if err != nil {
return err
}
switch p := certificate.PublicKey.(type) {
case ed25519.PublicKey:
if ok := ed25519.Verify(p, handshakeBodies, remoteKeySignature); !ok {
return errKeySignatureMismatch
}
return nil
case *ecdsa.PublicKey:
ecdsaSig := &ecdsaSignature{}
if _, err := asn1.Unmarshal(remoteKeySignature, ecdsaSig); err != nil {
return err
}
if ecdsaSig.R.Sign() <= 0 || ecdsaSig.S.Sign() <= 0 {
return errInvalidECDSASignature
}
hash := hashAlgorithm.Digest(handshakeBodies)
if !ecdsa.Verify(p, hash, ecdsaSig.R, ecdsaSig.S) {
return errKeySignatureMismatch
}
return nil
case *rsa.PublicKey:
switch certificate.SignatureAlgorithm {
case x509.SHA1WithRSA, x509.SHA256WithRSA, x509.SHA384WithRSA, x509.SHA512WithRSA:
hash := hashAlgorithm.Digest(handshakeBodies)
return rsa.VerifyPKCS1v15(p, hashAlgorithm.CryptoHash(), hash, remoteKeySignature)
default:
return errKeySignatureVerifyUnimplemented
}
}
return errKeySignatureVerifyUnimplemented
}
func loadCerts(rawCertificates [][]byte) ([]*x509.Certificate, error) {
if len(rawCertificates) == 0 {
return nil, errLengthMismatch
}
certs := make([]*x509.Certificate, 0, len(rawCertificates))
for _, rawCert := range rawCertificates {
cert, err := x509.ParseCertificate(rawCert)
if err != nil {
return nil, err
}
certs = append(certs, cert)
}
return certs, nil
}
func verifyClientCert(rawCertificates [][]byte, roots *x509.CertPool) (chains [][]*x509.Certificate, err error) {
certificate, err := loadCerts(rawCertificates)
if err != nil {
return nil, err
}
intermediateCAPool := x509.NewCertPool()
for _, cert := range certificate[1:] {
intermediateCAPool.AddCert(cert)
}
opts := x509.VerifyOptions{
Roots: roots,
CurrentTime: time.Now(),
Intermediates: intermediateCAPool,
KeyUsages: []x509.ExtKeyUsage{x509.ExtKeyUsageClientAuth},
}
return certificate[0].Verify(opts)
}
func verifyServerCert(rawCertificates [][]byte, roots *x509.CertPool, serverName string) (chains [][]*x509.Certificate, err error) {
certificate, err := loadCerts(rawCertificates)
if err != nil {
return nil, err
}
intermediateCAPool := x509.NewCertPool()
for _, cert := range certificate[1:] {
intermediateCAPool.AddCert(cert)
}
opts := x509.VerifyOptions{
Roots: roots,
CurrentTime: time.Now(),
DNSName: serverName,
Intermediates: intermediateCAPool,
}
return certificate[0].Verify(opts)
}
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