Signature verification error during SSL enabling

Hi Team,

We are getting below error during the process of Enabling SSL for OHS 11g Web Server.

openssl genrsa -out oracle_privkey.pem

openssl req -new -x509 -keyout oracle_privkey.pem -out oracle_root_cert.pem -days 3650

---during the below step running we are getting error message as "Signature verification failed"

openssl x509 -req -in oracle.req -CA oracle_root_cert.pem -CAkey oracle_privkey.pem -CAcreateserial -out oracle.pem

ERROR Message:

sslcerts]$ openssl x509 -req -in oracle.req -CA oracle_root_cert.pem -CAkey oracle_privkey.pem -CAcreateserial -out oracle.pem

Signature verification error

140204876679056:error:0D0C50A1:asn1 encoding routines:ASN1_item_verify:unknown message digest algorithm:a_verify.c:206