The Java Cryptography Extension (JCE) is a framework built into the JVM to allow developers to easily and securely use cryptography in their programs. It does this by providing a simple, portable interface to programmers, while using a system of JCE Providers to securely implement the underlying cryptographic operations.

While the JCE secures cryptographic operations and key generation, it is up to the developer to actually manage their keys. More information needs to be provided here.

One commonly-accepted best practice for handling keys at runtime is to store them only as byte arrays, and never as strings. This is because Java strings are immutable, and cannot be manually "cleared" or "zeroed out" in memory; while a reference to a string can be removed, the exact string will remain in memory until its segment of memory is garbage-collected and reused. An attacker would have a large window in which they could dump the program's memory and easily find the key. Contrarily, byte arrays are mutable, and can have their contents overwritten in place; it is a good idea to 'zero-out' your keys as soon as you no longer need them.

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For most applications, the java.utils.Random class is a perfectly fine source of "random" data. If you need to choose a random element from an array, or generate a random string, or create a temporary "unique" identifier, you should probably use Random.

However, many cryptographic systems rely on randomness for their security, and the randomness provided by Random simply isn't of high enough quality. For any cryptographic operation that requires a random input, you should use SecureRandom instead.

More information needed.

A cryptographic hash function is a member of a class of functions with three vital properties; consistency, uniqueness, and irreversibility.

Consistency: Given the same data, a hash function will always return the same value. That is, if X = Y, f(x) will always equal f(y) for hash function f.

Uniqueness: No two inputs to a hash function will ever result in the same output. That is, if X != Y, f(x) != f(y), for any values of X and Y.

Irreversibility: It is impractically difficult, if not impossible, to "reverse" a hash function. That is, given only f(X), there should be no way of finding the original X short of putting every possible value of X through the function f (brute-force). There should be no function f1 such that f1(f(X)) = X.

Many functions lack at least one of these attributes. For example, MD5 and SHA1 are known to have collisions, i.e. two inputs that have the same output, so they lack uniqueness. Some functions that are currently believed to be secure are SHA-256 and SHA-512.