RSA and DSA public keys are stored using the SubjectPublicKeyInfo format.

src/misc/pk_get_oid.c

@@ -0,0 +1,39 @@
+/* LibTomCrypt, modular cryptographic library
+ *
+ * LibTomCrypt is a library that provides various cryptographic
+ * algorithms in a highly modular and flexible manner.
+ *
+ * The library is free for all purposes without any express
+ * guarantee it works.
+ *
+ */
+#include "tomcrypt.h"
+
+static const oid_st rsa_oid = {
+   .OIDlen = 7,
+   .OID = { 1, 2, 840, 113549, 1, 1, 1  },
+};
+
+static const oid_st dsa_oid = {
+   .OIDlen = 6,
+   .OID = { 1, 2, 840, 10040, 4, 1  },
+};
+
+/*
+   Returns the OID of the public key algorithm.
+   @return CRYPT_OK if valid
+*/
+int pk_get_oid(int pk, oid_st *st)
+{
+   switch (pk) {
+      case PKA_RSA:
+         memcpy(st, &rsa_oid, sizeof(*st));
+         break;
+      case PKA_DSA:
+         memcpy(st, &dsa_oid, sizeof(*st));
+         break;
+      default:
+         return CRYPT_INVALID_ARG;
+   }
+   return CRYPT_OK;
+}