examples/keygen: align keygen SRK default with keyload/seal

keygen defaulted srkAlg = TPM_ALG_ECC and only switched to RSA for
RSA keys, so SYMCIPHER and KEYEDHASH blobs were created under the
ECC SRK. After the prior keyload fix made keyload default to RSA
(matching seal.c), a sym/keyedhash blob produced by keygen could
not round-trip through keyload without a parent mismatch.

Invert the default to RSA (matching seal.c and keyload.c) and only
switch to the ECC SRK when the stored key itself is ECC. Keeps all
three tools aligned so any blob round-trips without callers having
to specify a parent.

Author: aidangarske

examples/keygen/keygen.c

@@ -132,7 +132,7 @@ int TPM2_Keygen_Example(void* userCtx, int argc, char *argv[])
     WOLFTPM2_KEYBLOB primaryBlob; /* Primary key as WOLFTPM2_KEYBLOB */
     TPMT_PUBLIC publicTemplate;
     TPMI_ALG_PUBLIC alg = TPM_ALG_RSA; /* default, see usage() for options */
-    TPMI_ALG_PUBLIC srkAlg = TPM_ALG_ECC; /* prefer ECC, but allow RSA */
+    TPMI_ALG_PUBLIC srkAlg = TPM_ALG_RSA; /* default matches seal.c / keyload.c */
     TPM_ALG_ID algSym = TPM_ALG_CTR; /* default Symmetric Cipher, see usage */
     TPM_ALG_ID paramEncAlg = TPM_ALG_NULL;
     WOLFTPM2_SESSION tpmSession;
@@ -222,8 +222,10 @@ int TPM2_Keygen_Example(void* userCtx, int argc, char *argv[])
     XMEMSET(&tpmSession, 0, sizeof(tpmSession));
     XMEMSET(&auth, 0, sizeof(auth));
 
-    if (alg == TPM_ALG_RSA)
-        srkAlg = TPM_ALG_RSA;
+    /* Only use the ECC SRK for ECC child keys; RSA, SYMCIPHER, KEYEDHASH
+     * all stay on the RSA SRK so that keyload/seal can round-trip them. */
+    if (alg == TPM_ALG_ECC)
+        srkAlg = TPM_ALG_ECC;
     if (alg == TPM_ALG_SYMCIPHER) {
         rc = symChoice(symMode, &algSym, &keyBits);
         if (rc != TPM_RC_SUCCESS) {