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crypto/tls: refactor certificate and signature algorithm logic

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This refactors a lot of the certificate support logic to make it cleaner
and reusable where possible. These changes will make the following CLs
much simpler.

In particular, the heavily overloaded pickSignatureAlgorithm is gone.
That function used to cover both signing and verifying side, would work
both for pre-signature_algorithms TLS 1.0/1.1 and TLS 1.2, and returned
sigalg, type and hash.

Now, TLS 1.0/1.1 and 1.2 are differentiated at the caller, as they have
effectively completely different logic. TLS 1.0/1.1 simply use
legacyTypeAndHashFromPublicKey as they employ a fixed hash function and
signature algorithm for each public key type. TLS 1.2 is instead routed
through selectSignatureScheme (on the signing side) or
isSupportedSignatureAlgorithm (on the verifying side) and
typeAndHashFromSignatureScheme, like TLS 1.3.

On the signing side, signatureSchemesForCertificate was already version
aware (for PKCS#1 v1.5 vs PSS support), so selectSignatureScheme just
had to learn the Section 7.4.1.4.1 defaults for a missing
signature_algorithms to replace pickSignatureAlgorithm.

On the verifying side, pickSignatureAlgorithm was also checking the
public key type, while isSupportedSignatureAlgorithm +
typeAndHashFromSignatureScheme are not, but that check was redundant
with the one in verifyHandshakeSignature.

There should be no major change in behavior so far. A few minor changes
came from the refactor: we now correctly require signature_algorithms in
TLS 1.3 when using a certificate; we won't use Ed25519 in TLS 1.2 if the
client didn't send signature_algorithms; and we don't send
ec_points_format in the ServerHello (a compatibility measure) if we are
not doing ECDHE anyway because there are no mutually supported curves.

The tests also got simpler because they test simpler functions. The
caller logic switching between TLS 1.0/1.1 and 1.2 is tested by the
transcript tests.

Updates #32426

Change-Id: Ice9dcaea78d204718f661f8d60efdb408ba41577
Reviewed-on: https://go-review.googlesource.com/c/go/+/205061
Reviewed-by: Katie Hockman <katie@golang.org>
This commit is contained in:
Filippo Valsorda 2019-11-01 19:00:33 -04:00
parent edbdd2848e
commit 0c490ab182
11 changed files with 398 additions and 348 deletions
Download patch file Download diff file Expand all files Collapse all files

91
key_agreement.go
View file

@ -11,6 +11,7 @@ import (
"crypto/sha1"
"crypto/x509"
"errors"
"fmt"
"io"
)
@ -142,16 +143,11 @@ type ecdheKeyAgreement struct {
}
func (ka *ecdheKeyAgreement) generateServerKeyExchange(config *Config, cert *Certificate, clientHello *clientHelloMsg, hello *serverHelloMsg) (*serverKeyExchangeMsg, error) {
preferredCurves := config.curvePreferences()
var curveID CurveID
NextCandidate:
for _, candidate := range preferredCurves {
for _, c := range clientHello.supportedCurves {
if candidate == c {
curveID = c
break NextCandidate
}
for _, c := range clientHello.supportedCurves {
if config.supportsCurve(c) {
curveID = c
break
}
}
@ -170,31 +166,45 @@ NextCandidate:
// See RFC 4492, Section 5.4.
ecdhePublic := params.PublicKey()
serverECDHParams := make([]byte, 1+2+1+len(ecdhePublic))
serverECDHParams[0] = 3 // named curve
serverECDHParams[1] = byte(curveID >> 8)
serverECDHParams[2] = byte(curveID)
serverECDHParams[3] = byte(len(ecdhePublic))
copy(serverECDHParams[4:], ecdhePublic)
serverECDHEParams := make([]byte, 1+2+1+len(ecdhePublic))
serverECDHEParams[0] = 3 // named curve
serverECDHEParams[1] = byte(curveID >> 8)
serverECDHEParams[2] = byte(curveID)
serverECDHEParams[3] = byte(len(ecdhePublic))
copy(serverECDHEParams[4:], ecdhePublic)
priv, ok := cert.PrivateKey.(crypto.Signer)
if !ok {
return nil, errors.New("tls: certificate private key does not implement crypto.Signer")
return nil, fmt.Errorf("tls: certificate private key of type %T does not implement crypto.Signer", cert.PrivateKey)
}
signatureAlgorithm, sigType, hashFunc, err := pickSignatureAlgorithm(priv.Public(), clientHello.supportedSignatureAlgorithms, supportedSignatureAlgorithmsTLS12, ka.version)
if err != nil {
return nil, err
var signatureAlgorithm SignatureScheme
var sigType uint8
var sigHash crypto.Hash
if ka.version >= VersionTLS12 {
signatureAlgorithm, err = selectSignatureScheme(ka.version, cert, clientHello.supportedSignatureAlgorithms)
if err != nil {
return nil, err
}
sigType, sigHash, err = typeAndHashFromSignatureScheme(signatureAlgorithm)
if err != nil {
return nil, err
}
} else {
sigType, sigHash, err = legacyTypeAndHashFromPublicKey(priv.Public())
if err != nil {
return nil, err
}
}
if (sigType == signaturePKCS1v15 || sigType == signatureRSAPSS) != ka.isRSA {
return nil, errors.New("tls: certificate cannot be used with the selected cipher suite")
}
signed := hashForServerKeyExchange(sigType, hashFunc, ka.version, clientHello.random, hello.random, serverECDHParams)
signed := hashForServerKeyExchange(sigType, sigHash, ka.version, clientHello.random, hello.random, serverECDHEParams)
signOpts := crypto.SignerOpts(hashFunc)
signOpts := crypto.SignerOpts(sigHash)
if sigType == signatureRSAPSS {
signOpts = &rsa.PSSOptions{SaltLength: rsa.PSSSaltLengthEqualsHash, Hash: hashFunc}
signOpts = &rsa.PSSOptions{SaltLength: rsa.PSSSaltLengthEqualsHash, Hash: sigHash}
}
sig, err := priv.Sign(config.rand(), signed, signOpts)
if err != nil {
@ -206,9 +216,9 @@ NextCandidate:
if ka.version >= VersionTLS12 {
sigAndHashLen = 2
}
skx.key = make([]byte, len(serverECDHParams)+sigAndHashLen+2+len(sig))
copy(skx.key, serverECDHParams)
k := skx.key[len(serverECDHParams):]
skx.key = make([]byte, len(serverECDHEParams)+sigAndHashLen+2+len(sig))
copy(skx.key, serverECDHEParams)
k := skx.key[len(serverECDHEParams):]
if ka.version >= VersionTLS12 {
k[0] = byte(signatureAlgorithm >> 8)
k[1] = byte(signatureAlgorithm)
@ -247,8 +257,8 @@ func (ka *ecdheKeyAgreement) processServerKeyExchange(config *Config, clientHell
if publicLen+4 > len(skx.key) {
return errServerKeyExchange
}
serverECDHParams := skx.key[:4+publicLen]
publicKey := serverECDHParams[4:]
serverECDHEParams := skx.key[:4+publicLen]
publicKey := serverECDHEParams[4:]
sig := skx.key[4+publicLen:]
if len(sig) < 2 {
@ -276,18 +286,27 @@ func (ka *ecdheKeyAgreement) processServerKeyExchange(config *Config, clientHell
ka.ckx.ciphertext[0] = byte(len(ourPublicKey))
copy(ka.ckx.ciphertext[1:], ourPublicKey)
var signatureAlgorithm SignatureScheme
var sigType uint8
var sigHash crypto.Hash
if ka.version >= VersionTLS12 {
// handle SignatureAndHashAlgorithm
signatureAlgorithm = SignatureScheme(sig[0])<<8 | SignatureScheme(sig[1])
signatureAlgorithm := SignatureScheme(sig[0])<<8 | SignatureScheme(sig[1])
sig = sig[2:]
if len(sig) < 2 {
return errServerKeyExchange
}
}
_, sigType, hashFunc, err := pickSignatureAlgorithm(cert.PublicKey, []SignatureScheme{signatureAlgorithm}, clientHello.supportedSignatureAlgorithms, ka.version)
if err != nil {
return err
if !isSupportedSignatureAlgorithm(signatureAlgorithm, clientHello.supportedSignatureAlgorithms) {
return errors.New("tls: certificate used with invalid signature algorithm")
}
sigType, sigHash, err = typeAndHashFromSignatureScheme(signatureAlgorithm)
if err != nil {
return err
}
} else {
sigType, sigHash, err = legacyTypeAndHashFromPublicKey(cert.PublicKey)
if err != nil {
return err
}
}
if (sigType == signaturePKCS1v15 || sigType == signatureRSAPSS) != ka.isRSA {
return errServerKeyExchange
@ -299,8 +318,8 @@ func (ka *ecdheKeyAgreement) processServerKeyExchange(config *Config, clientHell
}
sig = sig[2:]
signed := hashForServerKeyExchange(sigType, hashFunc, ka.version, clientHello.random, serverHello.random, serverECDHParams)
if err := verifyHandshakeSignature(sigType, cert.PublicKey, hashFunc, signed, sig); err != nil {
signed := hashForServerKeyExchange(sigType, sigHash, ka.version, clientHello.random, serverHello.random, serverECDHEParams)
if err := verifyHandshakeSignature(sigType, cert.PublicKey, sigHash, signed, sig); err != nil {
return errors.New("tls: invalid signature by the server certificate: " + err.Error())
}
return nil