If you want to generate signing certificate for your android app with OpenSSL, you can use library in this way:

Create a key:

  $ openssl genrsa -out android_distribution.key 2048

Generate a request:

  $ openssl req -new -key android_distribution.key -out android_distribution.csr

Self-signing:

  $ openssl x509 -req -days 10950 -in android_distribution.csr \
  > -signkey android_distribution.key -out android_distribution.crt

Transform .crt в .p12:

  $ openssl pkcs12 -export -in android_distribution.crt \
  > -inkey android_distribution.key -out android_distribution.p12

Don't forget to store your data somewhere safe.

UPDATE:

If you need keystore for example for phonegap build you can canvert your certificate:

  $ keytool -importkeystore -srckeystore android_distribution.p12 \
  > -srcstoretype PKCS12 -destkeystore android_distribution.jks -deststoretype JKS

The end.