x509: implement RSA-PSS signature scheme

This patch enables RSA-PSS signature scheme in the X.509 functions and
certtool.

When creating RSA-PSS signature, there are 3 different scenarios:

a. both a private key and a certificate are RSA-PSS
b. the private key is RSA, while the certificate is RSA-PSS
c. both the private key and the certificate are RSA

For (a) and (b), the RSA-PSS parameters are read from the certificate.
Any conflicts in parameters between the private key and the certificate
are reported as an error.

For (c), the sign functions, such as gnutls_x509_crt_privkey_sign() or
gnutls_privkey_sign_data(), shall be instructed to generate an RSA-PSS
signature.  This can be done with the new flag
GNUTLS_PRIVKEY_SIGN_FLAG_RSA_PSS.

Verification is similar to signing, except for the case (c), use the
flag GNUTLS_VERIFY_USE_RSA_PSS instead of
GNUTLS_PRIVKEY_SIGN_FLAG_RSA_PSS.

From the command line, certtool has a couple of new options: --rsa-pss
and --rsa-pss-sign.  The --rsa-pss option indicates that the generated
private key or certificate is restricted to RSA-PSS, while the
--rsa-pss-sign option indicates that the generated certificate is signed
with RSA-PSS.

For simplicity, there is no means of choosing arbitrary salt length.
When it is not given by a private key or a certificate, it is
automatically calculated from the underlying hash algorithm and the
RSA modulus bits.

[minor naming changes by nmav]

Signed-off-by: Daiki Ueno <dueno@redhat.com>
Signed-off-by: Nikos Mavrogiannopoulos <nmav@redhat.com>

1 files changed, 12 insertions, 0 deletions

diff --git a/src/certtool-args.def b/src/certtool-args.def
index f7889ccde6..ba5a7f0eeb 100644
--- a/src/certtool-args.def
+++ b/src/certtool-args.def
@@ -458,6 +458,18 @@ flag = {
 };
 
 flag = {
+    name      = rsa-pss;
+    descrip   = "Generate RSA-PSS key or certificate";
+    doc = "This option can be combined with --generate-privkey or --generate-certificate, to generate private key or certificate restricted to the use with the RSA-PSS padding scheme.";
+};
+
+flag = {
+    name      = rsa-pss-sign;
+    descrip   = "Sign certificate with RSA-PSS";
+    doc = "This option can be combined with --generate-certificate, to sign the certificate with the RSA-PSS padding scheme.";
+};
+
+flag = {
     name      = hash;
     arg-type  = string;
     descrip   = "Hash algorithm to use for signing";