Generate a random string with a specific bit size in java

Question

How do i do that? Can't seems to find a way. Securerandom doesn't seems to allow me to specify bit size anywhere

Answer 1

If your bit-count can be divded by 8, in other words, you need a full byte-count, you can use

Random random = ThreadLocalRandom.current();
byte[] r = new byte[256]; //Means 2048 bit
random.nextBytes(r);
String s = new String(r)

If you don't like the strange characters, encode the byte-array as base64:

For example, use the Apache Commons Codec and do:

Random random = ThreadLocalRandom.current();
byte[] r = new byte[256]; //Means 2048 bit
random.nextBytes(r);
String s = Base64.encodeBase64String(r);

Answer 2

Similar to the other answer with a minor detail

Random random = ThreadLocalRandom.current();
byte[] randomBytes = new byte[32];
random.nextBytes(randomBytes);
String encoded = Base64.getUrlEncoder().encodeToString(randomBytes)

Instead of simply using Base64 encoding, which can leave you with a '+' in the out, make sure it doesn't contain any characters which need to be further URL encoded.