Allow rsa.PSSSaltLengthEqualsHash as option

This commit adds support to the salt length set to rsa.PSSSaltLengthEqualsHash when signing with an RSA key. This is currently supported, but the user must sspecify the length to the digest size. Adding rsa.PSSSaltLengthEqualsHash allows using a key generated by the TPM for TLS client authentication, Go will set this option by default if an RSA key is used. Signed-off-by: Mariano Cano <[email protected]>
google · Jan 11, 2024 · dca66cd · dca66cd
1 parent 02cf9e2
commit dca66cd
Show file tree

Hide file tree

Showing 2 changed files with 14 additions and 2 deletions.
diff --git a/attest/application_key_test.go b/attest/application_key_test.go
@@ -288,6 +288,18 @@ func testKeySign(t *testing.T, tpm *TPM) {
 			},
 			digest: []byte("1234567890123456789012345678901212345678901234567890123456789012"),
 		},
+		{
+			name: "RSA2048-PSS-SHA256, PSSSaltLengthEqualsHash",
+			keyOpts: &KeyConfig{
+				Algorithm: RSA,
+				Size:      2048,
+			},
+			signOpts: &rsa.PSSOptions{
+				SaltLength: rsa.PSSSaltLengthEqualsHash,
+				Hash:       crypto.SHA256,
+			},
+			digest: []byte("12345678901234567890123456789012"),
+		},
 		{
 			name: "RSA2048-PSS-SHA256, explicit salt len",
 			keyOpts: &KeyConfig{

diff --git a/attest/wrapped_tpm20.go b/attest/wrapped_tpm20.go
@@ -652,8 +652,8 @@ func signRSA(rw io.ReadWriter, key tpmutil.Handle, digest []byte, opts crypto.Si
 	}
 
 	if pss, ok := opts.(*rsa.PSSOptions); ok {
-		if pss.SaltLength != rsa.PSSSaltLengthAuto && pss.SaltLength != len(digest) {
-			return nil, fmt.Errorf("PSS salt length %d is incorrect, expected rsa.PSSSaltLengthAuto or %d", pss.SaltLength, len(digest))
+		if pss.SaltLength != rsa.PSSSaltLengthAuto && pss.SaltLength != rsa.PSSSaltLengthEqualsHash && pss.SaltLength != len(digest) {
+			return nil, fmt.Errorf("PSS salt length %d is incorrect, expected rsa.PSSSaltLengthAuto, rsa.PSSSaltLengthEqualsHash or %d", pss.SaltLength, len(digest))
 		}
 		scheme.Alg = tpm2.AlgRSAPSS
 	}