Add check function to verify that pkey is usable with a sigalg.

Include check for appropriate RSA key size when used with PSS.
ok tb@

1 files changed, 17 insertions, 1 deletions

diff --git a/src/lib/libssl/ssl_sigalgs.c b/src/lib/libssl/ssl_sigalgs.c
index 5dc261810b..a6c5a4e9d8 100644
--- a/src/lib/libssl/ssl_sigalgs.c
+++ b/src/lib/libssl/ssl_sigalgs.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: ssl_sigalgs.c,v 1.6 2018/11/11 02:03:23 beck Exp $ */
+/* $OpenBSD: ssl_sigalgs.c,v 1.7 2018/11/11 21:54:47 beck Exp $ */
 /*
  * Copyright (c) 2018, Bob Beck <beck@openbsd.org>
  *
@@ -225,3 +225,19 @@ ssl_sigalgs_build(CBB *cbb, uint16_t *values, size_t len)
         }
         return 1;
 }
+
+int
+ssl_sigalg_pkey_ok(const struct ssl_sigalg *sigalg, EVP_PKEY *pkey)
+{
+        if (sigalg->key_type == pkey->type) {
+                if (!(sigalg->flags & SIGALG_FLAG_RSA_PSS))
+                        return 1;
+                /*
+                 * RSA keys for PSS need to be at least
+                 * as big as twice the size of the hash + 2
+                 */
+                if (EVP_PKEY_size(pkey) < (2 * EVP_MD_size(sigalg->md()) + 2))
+                        return 1;
+        }
+        return 0;
+}