In Java, we can use SecureRandom.nextBytes(byte[] bytes) to generate a user-specified number of random bytes. This SecureRandom is a cryptographically secure random number generator (RNG).
1. Random 12 bytes (96 bits)
1.1 Generates a random 12 bytes (96 bits) nonce.
HelloCryptoApp.java
package com.mkyong.crypto;
import java.security.SecureRandom;
public class HelloCryptoApp {
public static void main(String[] args) {
byte[] nonce = new byte[12];
new SecureRandom().nextBytes(nonce);
System.out.println(convertBytesToHex(nonce));
}
// util to print bytes in hex
private static String convertBytesToHex(byte[] bytes) {
StringBuilder result = new StringBuilder();
for (byte temp : bytes) {
result.append(String.format("%02x", temp));
}
return result.toString();
}
}
Output
Terminal
0747a9ad467d4dc29ce70344
1.2 Generates a random 20 bytes (160 bits)
byte[] nonce = new byte[20];
new SecureRandom().nextBytes(nonce);
System.out.println(convertBytesToHex(nonce));
Output
Terminal
e2ac8893b23ef174461e4ec37598080ec910b87b
2. Random 32 bytes (256 bits) + DRBG algorithm
2.1 Generates a random 32 bytes (256 bits) with the DRBG algorithm defined in NIST SP 800-90Ar1. By default, SecureRandom uses the SHA1PRNG algorithm to generate a random number.
HelloCryptoApp2.java
package com.mkyong.java11;
import java.security.NoSuchAlgorithmException;
import java.security.SecureRandom;
public class HelloCryptoApp2 {
public static void main(String[] args) throws NoSuchAlgorithmException {
byte[] nonce = new byte[32];
SecureRandom rand = SecureRandom.getInstance("DRBG");
rand.nextBytes(nonce);
System.out.println(convertBytesToHex(nonce));
}
private static String convertBytesToHex(byte[] bytes) {
StringBuilder result = new StringBuilder();
for (byte temp : bytes) {
result.append(String.format("%02x", temp));
}
return result.toString();
}
}
Output
Terminal
7d5bca7a4cfab6abec28da5cc899c32a0c36f17128f242a3df20301b3812b881
Further Reading
For all supported random algorithm, refer to this SecureRandom Number Generation Algorithms
