This class provides a cryptographically strong random number generator (RNG).
A cryptographically strong random number minimally complies with the statistical random number generator tests specified in FIPS 140-2, Security Requirements for Cryptographic Modules, section 4.9.1. Additionally, SecureRandom must produce non-deterministic output. Therefore any seed material passed to a SecureRandom object must be unpredictable, and all SecureRandom output sequences must be cryptographically strong, as described in RFC 1750: Randomness Recommendations for Security.
A caller obtains a SecureRandom instance via the no-argument constructor or one of the getInstance methods:
SecureRandom random = new SecureRandom();
Many SecureRandom implementations are in the form of a pseudo-random number generator (PRNG), which means they use a deterministic algorithm to produce a pseudo-random sequence from a true random seed. Other implementations may produce true random numbers, and yet others may use a combination of both techniques.
Typical callers of SecureRandom invoke the following methods to retrieve random bytes:
SecureRandom random = new SecureRandom();
byte bytes[] = new byte[20];
random.nextBytes(bytes);
Callers may also invoke the generateSeed method to generate a given number of seed bytes (to seed other random number generators, for example):
byte seed[] = random.generateSeed(20);
Note: Depending on the implementation, the
generateSeed
and
nextBytes
methods may block as entropy is being gathered, for example, if they need to read from /dev/random on various Unix-like operating systems.
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