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SecureRandom
public
class
SecureRandom
extends Random
| java.lang.Object | ||
| ↳ | java.util.Random | |
| ↳ | java.security.SecureRandom | |
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.
The SHA1PRNG algorithm from the Crypto provider has been deprecated as it was insecure, and also
incorrectly used by some apps as a key derivation function. See
Security "Crypto" provider deprecated in Android N for details.
See also:
Summary
Public constructors | |
|---|---|
SecureRandom()
Constructs a secure random number generator (RNG) implementing the default random number algorithm. |
|
SecureRandom(byte[] seed)
Constructs a secure random number generator (RNG) implementing the default random number algorithm. |
|
Protected constructors | |
|---|---|
SecureRandom(SecureRandomSpi secureRandomSpi, Provider provider)
Creates a SecureRandom object. |
|
Public methods | |
|---|---|
byte[]
|
generateSeed(int numBytes)
Returns the given number of seed bytes, computed using the seed generation algorithm that this class uses to seed itself. |
String
|
getAlgorithm()
Returns the name of the algorithm implemented by this SecureRandom object. |
static
SecureRandom
|
getInstance(String algorithm)
Returns a SecureRandom object that implements the specified Random Number Generator (RNG) algorithm. |
static
SecureRandom
|
getInstance(String algorithm, String provider)
Returns a SecureRandom object that implements the specified Random Number Generator (RNG) algorithm. |
static
SecureRandom
|
getInstance(String algorithm, Provider provider)
Returns a SecureRandom object that implements the specified Random Number Generator (RNG) algorithm. |
static
SecureRandom
|
getInstanceStrong()
Returns a |
final
Provider
|
getProvider()
Returns the provider of this SecureRandom object. |
static
byte[]
|
getSeed(int numBytes)
Returns the given number of seed bytes, computed using the seed generation algorithm that this class uses to seed itself. |
void
|
nextBytes(byte[] bytes)
Generates a user-specified number of random bytes. |
void
|
setSeed(long seed)
Reseeds this random object, using the eight bytes contained
in the given |
void
|
setSeed(byte[] seed)
Reseeds this random object. |
Protected methods | |
|---|---|
final
int
|
next(int numBits)
Generates an integer containing the user-specified number of pseudo-random bits (right justified, with leading zeros). |
Inherited methods | |
|---|---|
Public constructors
SecureRandom
public SecureRandom ()
Constructs a secure random number generator (RNG) implementing the default random number algorithm.
This constructor traverses the list of registered security Providers, starting with the most preferred Provider. A new SecureRandom object encapsulating the SecureRandomSpi implementation from the first Provider that supports a SecureRandom (RNG) algorithm is returned. If none of the Providers support a RNG algorithm, then an implementation-specific default is returned.
Note that the list of registered providers may be retrieved via
the Security#getProviders() method.
See the SecureRandom section in the Java Cryptography Architecture Standard Algorithm Name Documentation for information about standard RNG algorithm names.
The returned SecureRandom object has not been seeded. To seed the
returned object, call the setSeed method.
If setSeed is not called, the first call to
nextBytes will force the SecureRandom object to seed itself.
This self-seeding will not occur if setSeed was
previously called.
SecureRandom
public SecureRandom (byte[] seed)
Constructs a secure random number generator (RNG) implementing the default random number algorithm. The SecureRandom instance is seeded with the specified seed bytes.
This constructor traverses the list of registered security Providers, starting with the most preferred Provider. A new SecureRandom object encapsulating the SecureRandomSpi implementation from the first Provider that supports a SecureRandom (RNG) algorithm is returned. If none of the Providers support a RNG algorithm, then an implementation-specific default is returned.
Note that the list of registered providers may be retrieved via
the Security#getProviders() method.
See the SecureRandom section in the Java Cryptography Architecture Standard Algorithm Name Documentation for information about standard RNG algorithm names.
| Parameters | |
|---|---|
seed |
byte: the seed. |
Protected constructors
SecureRandom
protected SecureRandom (SecureRandomSpi secureRandomSpi, Provider provider)
Creates a SecureRandom object.
| Parameters | |
|---|---|
secureRandomSpi |
SecureRandomSpi: the SecureRandom implementation. |
provider |
Provider: the provider. |
Public methods
generateSeed
public byte[] generateSeed (int numBytes)
Returns the given number of seed bytes, computed using the seed generation algorithm that this class uses to seed itself. This call may be used to seed other random number generators.
| Parameters | |
|---|---|
numBytes |
int: the number of seed bytes to generate. |
| Returns | |
|---|---|
byte[] |
the seed bytes. |
getAlgorithm
public String getAlgorithm ()
Returns the name of the algorithm implemented by this SecureRandom object.
| Returns | |
|---|---|
String |
the name of the algorithm or unknown
if the algorithm name cannot be determined. |
getInstance
public static SecureRandom getInstance (String algorithm)
Returns a SecureRandom object that implements the specified Random Number Generator (RNG) algorithm.
This method traverses the list of registered security Providers, starting with the most preferred Provider. A new SecureRandom object encapsulating the SecureRandomSpi implementation from the first Provider that supports the specified algorithm is returned.
Note that the list of registered providers may be retrieved via
the Security#getProviders() method.
The returned SecureRandom object has not been seeded. To seed the
returned object, call the setSeed method.
If setSeed is not called, the first call to
nextBytes will force the SecureRandom object to seed itself.
This self-seeding will not occur if setSeed was
previously called.
| Parameters | |
|---|---|
algorithm |
String: the name of the RNG algorithm.
See the SecureRandom section in the
Java Cryptography Architecture Standard Algorithm Name Documentation
for information about standard RNG algorithm names. |
| Returns | |
|---|---|
SecureRandom |
the new SecureRandom object. |
| Throws | |
|---|---|
NoSuchAlgorithmException |
if no Provider supports a SecureRandomSpi implementation for the specified algorithm. |
See also:
getInstance
public static SecureRandom getInstance (String algorithm, String provider)
Returns a SecureRandom object that implements the specified Random Number Generator (RNG) algorithm.
A new SecureRandom object encapsulating the SecureRandomSpi implementation from the specified provider is returned. The specified provider must be registered in the security provider list.
Note that the list of registered providers may be retrieved via
the Security#getProviders() method.
The returned SecureRandom object has not been seeded. To seed the
returned object, call the setSeed method.
If setSeed is not called, the first call to
nextBytes will force the SecureRandom object to seed itself.
This self-seeding will not occur if setSeed was
previously called.
| Parameters | |
|---|---|
algorithm |
String: the name of the RNG algorithm.
See the SecureRandom section in the
Java Cryptography Architecture Standard Algorithm Name Documentation
for information about standard RNG algorithm names. |
provider |
String: the name of the provider. |
| Returns | |
|---|---|
SecureRandom |
the new SecureRandom object. |
| Throws | |
|---|---|
NoSuchAlgorithmException |
if a SecureRandomSpi implementation for the specified algorithm is not available from the specified provider. |
NoSuchProviderException |
if the specified provider is not registered in the security provider list. |
IllegalArgumentException |
if the provider name is null or empty. |
See also:
getInstance
public static SecureRandom getInstance (String algorithm, Provider provider)
Returns a SecureRandom object that implements the specified Random Number Generator (RNG) algorithm.
A new SecureRandom object encapsulating the SecureRandomSpi implementation from the specified Provider object is returned. Note that the specified Provider object does not have to be registered in the provider list.
The returned SecureRandom object has not been seeded. To seed the
returned object, call the setSeed method.
If setSeed is not called, the first call to
nextBytes will force the SecureRandom object to seed itself.
This self-seeding will not occur if setSeed was
previously called.
| Parameters | |
|---|---|
algorithm |
String: the name of the RNG algorithm.
See the SecureRandom section in the
Java Cryptography Architecture Standard Algorithm Name Documentation
for information about standard RNG algorithm names. |
provider |
Provider: the provider. |
| Returns | |
|---|---|
SecureRandom |
the new SecureRandom object. |
| Throws | |
|---|---|
NoSuchAlgorithmException |
if a SecureRandomSpi implementation for the specified algorithm is not available from the specified Provider object. |
IllegalArgumentException |
if the specified provider is null. |
See also:
getInstanceStrong
public static SecureRandom getInstanceStrong ()
Returns a SecureRandom object.
In Android this is equivalent to get a SHA1PRNG from AndroidOpenSSL.
Some situations require strong random values, such as when
creating high-value/long-lived secrets like RSA public/private
keys. To help guide applications in selecting a suitable strong
SecureRandom implementation, Java distributions
include a list of known strong SecureRandom
implementations in the securerandom.strongAlgorithms
Security property.
Every implementation of the Java platform is required to
support at least one strong SecureRandom implementation.
| Returns | |
|---|---|
SecureRandom |
a strong SecureRandom implementation |
| Throws | |
|---|---|
NoSuchAlgorithmException |
if no algorithm is available |
See also:
getProvider
public final Provider getProvider ()
Returns the provider of this SecureRandom object.
| Returns | |
|---|---|
Provider |
the provider of this SecureRandom object. |
getSeed
public static byte[] getSeed (int numBytes)
Returns the given number of seed bytes, computed using the seed generation algorithm that this class uses to seed itself. This call may be used to seed other random number generators.
This method is only included for backwards compatibility.
The caller is encouraged to use one of the alternative
getInstance methods to obtain a SecureRandom object, and
then call the generateSeed method to obtain seed bytes
from that object.
| Parameters | |
|---|---|
numBytes |
int: the number of seed bytes to generate. |
| Returns | |
|---|---|
byte[] |
the seed bytes. |
See also:
nextBytes
public void nextBytes (byte[] bytes)
Generates a user-specified number of random bytes.
If a call to setSeed had not occurred previously,
the first call to this method forces this SecureRandom object
to seed itself. This self-seeding will not occur if
setSeed was previously called.
| Parameters | |
|---|---|
bytes |
byte: the array to be filled in with random bytes. |
setSeed
public void setSeed (long seed)
Reseeds this random object, using the eight bytes contained
in the given long seed. The given seed supplements,
rather than replaces, the existing seed. Thus, repeated calls
are guaranteed never to reduce randomness.
This method is defined for compatibility with
java.util.Random.
| Parameters | |
|---|---|
seed |
long: the seed. |
See also:
setSeed
public void setSeed (byte[] seed)
Reseeds this random object. The given seed supplements, rather than replaces, the existing seed. Thus, repeated calls are guaranteed never to reduce randomness.
| Parameters | |
|---|---|
seed |
byte: the seed. |
See also:
Protected methods
next
protected final int next (int numBits)
Generates an integer containing the user-specified number of
pseudo-random bits (right justified, with leading zeros). This
method overrides a java.util.Random method, and serves
to provide a source of random bits to all of the methods inherited
from that class (for example, nextInt,
nextLong, and nextFloat).
| Parameters | |
|---|---|
numBits |
int: number of pseudo-random bits to be generated, where
0 <= numBits <= 32. |
| Returns | |
|---|---|
int |
an int containing the user-specified number
of pseudo-random bits (right justified, with leading zeros). |