PRNG (Pseudorandom number generator) 사용하기
1. Openssl 인 경우 cryptographic software needs a source of unpredictable data to work correctly. Many open source operating systems provide a "randomness device" (/dev/urandom or /dev/random) that serves this purpose. All OpenSSL versions try to use /dev/urandom by default; starting with version 0.9.7, OpenSSL also tries /dev/random if /dev/urandom is not available. 참고: https://www.openssl.org/docs/faq.html
