start TPM support

shared/management/certposture/certposture_test.go

@@ -2,6 +2,9 @@ package certposture
 
 import (
 	"crypto"
+	"crypto/rand"
+	"crypto/rsa"
+	"crypto/sha256"
 	"crypto/x509"
 	"testing"
 	"time"
@@ -138,6 +141,22 @@ func TestChainPEM_RoundTrip(t *testing.T) {
 	assert.Equal(t, ca.Cert.Raw, chain[1].Raw)
 }
 
+func TestVerify_AcceptsMaximumPSSSalt(t *testing.T) {
+	// A TPM chooses the PSS salt itself and older firmware uses the largest salt that
+	// fits, so a proof from such a key carries more salt than Sign asks a software key for.
+	ca := certtest.NewCA(t, "root")
+	key := certtest.RSAKey(t).(*rsa.PrivateKey)
+	leaf := ca.Issue(t, key, "device")
+	c := NewChallenger(secret)
+	nonce := c.Nonce(peerKey, now)
+	digest := sha256.Sum256(proofMessage(nonce, peerKey))
+	sig, err := rsa.SignPSS(rand.Reader, key, crypto.SHA256, digest[:], &rsa.PSSOptions{SaltLength: rsa.PSSSaltLengthAuto})
+	require.NoError(t, err)
+
+	_, err = c.Verify(Proof{Nonce: nonce, Chain: [][]byte{leaf.Raw}, SigAlg: SigAlgRSAPSSSHA256, Signature: sig}, peerKey, now)
+	assert.NoError(t, err, "a valid PSS signature must verify regardless of salt length")
+}
+
 func signedProof(t *testing.T, c *Challenger, ca *certtest.CA, key crypto.Signer) Proof {
 	t.Helper()
 	leaf := ca.Issue(t, key, "device")

shared/management/certposture/proof.go

@@ -131,7 +131,7 @@ func verifySignature(pub crypto.PublicKey, sigAlg string, msg, sig []byte) bool
 		return ecdsa.VerifyASN1(pub.(*ecdsa.PublicKey), d[:], sig)
 	case SigAlgRSAPSSSHA256:
 		d := sha256.Sum256(msg)
-		return rsa.VerifyPSS(pub.(*rsa.PublicKey), crypto.SHA256, d[:], sig, &rsa.PSSOptions{SaltLength: rsa.PSSSaltLengthEqualsHash}) == nil
+		return rsa.VerifyPSS(pub.(*rsa.PublicKey), crypto.SHA256, d[:], sig, &rsa.PSSOptions{SaltLength: rsa.PSSSaltLengthAuto}) == nil
 	case SigAlgEd25519:
 		return ed25519.Verify(pub.(ed25519.PublicKey), msg, sig)
 	}