Serializable
public class SecureRandom extends Random
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 4086: Randomness Requirements for Security.
Many SecureRandom
implementations are in the form of a
pseudo-random number generator (PRNG, also known as deterministic random
bits generator or DRBG), which means they use a deterministic algorithm
to produce a pseudo-random sequence from a random seed.
Other implementations may produce true random numbers,
and yet others may use a combination of both techniques.
A caller obtains a SecureRandom
instance via the
no-argument constructor or one of the getInstance
methods.
For example:
SecureRandom r1 = new SecureRandom(); SecureRandom r2 = SecureRandom.getInstance("NativePRNG"); SecureRandom r3 = SecureRandom.getInstance("DRBG", DrbgParameters.instantiation(128, RESEED_ONLY, null));
The third statement above returns a SecureRandom
object of the
specific algorithm supporting the specific instantiate parameters. The
implementation's effective instantiated parameters must match this minimum
request but is not necessarily the same. For example, even if the request
does not require a certain feature, the actual instantiation can provide
the feature. An implementation may lazily instantiate a SecureRandom
until it's actually used, but the effective instantiate parameters must be
determined right after it's created and getParameters()
should
always return the same result unchanged.
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(int)
method
to generate a given number of seed bytes (to seed other random number
generators, for example):
byte[] seed = random.generateSeed(20);
A newly created PRNG SecureRandom
object is not seeded (except
if it is created by SecureRandom(byte[])
). The first call to
nextBytes
will force it to seed itself from an implementation-
specific entropy source. This self-seeding will not occur if setSeed
was previously called.
A SecureRandom
can be reseeded at any time by calling the
reseed
or setSeed
method. The reseed
method
reads entropy input from its entropy source to reseed itself.
The setSeed
method requires the caller to provide the seed.
Please note that reseed
may not be supported by all
SecureRandom
implementations.
Some SecureRandom
implementations may accept a
SecureRandomParameters
parameter in its
nextBytes(byte[], SecureRandomParameters)
and
reseed(SecureRandomParameters)
methods to further
control the behavior of the methods.
Note: Depending on the implementation, the generateSeed
,
reseed
and nextBytes
methods may block as entropy is being
gathered, for example, if the entropy source is /dev/random on various
Unix-like operating systems.
SecureRandom
objects are safe for use by multiple concurrent threads.SecureRandom
service provider can advertise that it is thread-safe
by setting the service
provider attribute "ThreadSafe" to "true" when registering the provider.
Otherwise, this class will instead synchronize access to the following
methods of the SecureRandomSpi
implementation:
SecureRandomSpi
,
Random
,
Serialized FormModifier | Constructor | Description |
---|---|---|
|
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 |
SecureRandom(SecureRandomSpi secureRandomSpi,
Provider provider) |
Creates a
SecureRandom object. |
Modifier and Type | Method | Description |
---|---|---|
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 |
getInstance(String algorithm,
SecureRandomParameters params) |
Returns a
SecureRandom object that implements the specified
Random Number Generator (RNG) algorithm and supports the specified
SecureRandomParameters request. |
static SecureRandom |
getInstance(String algorithm,
SecureRandomParameters params,
String provider) |
Returns a
SecureRandom object that implements the specified
Random Number Generator (RNG) algorithm and supports the specified
SecureRandomParameters request. |
static SecureRandom |
getInstance(String algorithm,
SecureRandomParameters params,
Provider provider) |
Returns a
SecureRandom object that implements the specified
Random Number Generator (RNG) algorithm and supports the specified
SecureRandomParameters request. |
static SecureRandom |
getInstanceStrong() |
Returns a
SecureRandom object that was selected by using
the algorithms/providers specified in the
securerandom.strongAlgorithms Security property. |
SecureRandomParameters |
getParameters() |
Returns the effective
SecureRandomParameters for this
SecureRandom instance. |
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.
|
protected int |
next(int numBits) |
Generates an integer containing the user-specified number of
pseudo-random bits (right justified, with leading zeros).
|
void |
nextBytes(byte[] bytes) |
Generates a user-specified number of random bytes.
|
void |
nextBytes(byte[] bytes,
SecureRandomParameters params) |
Generates a user-specified number of random bytes with
additional parameters.
|
void |
reseed() |
Reseeds this
SecureRandom with entropy input read from its
entropy source. |
void |
reseed(SecureRandomParameters params) |
Reseeds this
SecureRandom with entropy input read from its
entropy source with additional parameters. |
void |
setSeed(byte[] seed) |
Reseeds this random object with the given seed.
|
void |
setSeed(long seed) |
Reseeds this random object, using the eight bytes contained
in the given
long seed . |
String |
toString() |
Returns a Human-readable string representation of this
SecureRandom . |
public SecureRandom()
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.
public SecureRandom(byte[] seed)
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.
seed
- the seed.protected SecureRandom(SecureRandomSpi secureRandomSpi, Provider provider)
SecureRandom
object.secureRandomSpi
- the SecureRandom
implementation.provider
- the provider.public static SecureRandom getInstance(String algorithm) throws NoSuchAlgorithmException
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.
jdk.security.provider.preferred
Security
property to determine
the preferred provider order for the specified algorithm. This
may be different than the order of providers returned by
Security.getProviders()
.algorithm
- 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.SecureRandom
objectNoSuchAlgorithmException
- if no Provider
supports a
SecureRandomSpi
implementation for the
specified algorithmNullPointerException
- if algorithm
is null
Provider
public static SecureRandom getInstance(String algorithm, String provider) throws NoSuchAlgorithmException, NoSuchProviderException
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.
algorithm
- 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
- the name of the provider.SecureRandom
objectIllegalArgumentException
- if the provider name is null
or emptyNoSuchAlgorithmException
- if a SecureRandomSpi
implementation for the specified algorithm is not
available from the specified providerNoSuchProviderException
- if the specified provider is not
registered in the security provider listNullPointerException
- if algorithm
is null
Provider
public static SecureRandom getInstance(String algorithm, Provider provider) throws NoSuchAlgorithmException
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.
algorithm
- 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
- the provider.SecureRandom
objectIllegalArgumentException
- if the specified provider is
null
NoSuchAlgorithmException
- if a SecureRandomSpi
implementation for the specified algorithm is not available
from the specified Provider
objectNullPointerException
- if algorithm
is null
Provider
public static SecureRandom getInstance(String algorithm, SecureRandomParameters params) throws NoSuchAlgorithmException
SecureRandom
object that implements the specified
Random Number Generator (RNG) algorithm and supports the specified
SecureRandomParameters
request.
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 and the specified
SecureRandomParameters
is returned.
Note that the list of registered providers may be retrieved via
the Security.getProviders()
method.
jdk.security.provider.preferred
property to determine
the preferred provider order for the specified algorithm. This
may be different than the order of providers returned by
Security.getProviders()
.algorithm
- 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.params
- the SecureRandomParameters
the newly created SecureRandom
object must support.SecureRandom
objectIllegalArgumentException
- if the specified params is
null
NoSuchAlgorithmException
- if no Provider supports a
SecureRandomSpi
implementation for the specified
algorithm and parametersNullPointerException
- if algorithm
is null
Provider
public static SecureRandom getInstance(String algorithm, SecureRandomParameters params, String provider) throws NoSuchAlgorithmException, NoSuchProviderException
SecureRandom
object that implements the specified
Random Number Generator (RNG) algorithm and supports the specified
SecureRandomParameters
request.
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.
algorithm
- 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.params
- the SecureRandomParameters
the newly created SecureRandom
object must support.provider
- the name of the provider.SecureRandom
objectIllegalArgumentException
- if the provider name is null
or empty, or params is null
NoSuchAlgorithmException
- if the specified provider does not
support a SecureRandomSpi
implementation for the
specified algorithm and parametersNoSuchProviderException
- if the specified provider is not
registered in the security provider listNullPointerException
- if algorithm
is null
Provider
public static SecureRandom getInstance(String algorithm, SecureRandomParameters params, Provider provider) throws NoSuchAlgorithmException
SecureRandom
object that implements the specified
Random Number Generator (RNG) algorithm and supports the specified
SecureRandomParameters
request.
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.
algorithm
- 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.params
- the SecureRandomParameters
the newly created SecureRandom
object must support.provider
- the provider.SecureRandom
objectIllegalArgumentException
- if the specified provider or params
is null
NoSuchAlgorithmException
- if the specified provider does not
support a SecureRandomSpi
implementation for the
specified algorithm and parametersNullPointerException
- if algorithm
is null
Provider
public final Provider getProvider()
SecureRandom
object.SecureRandom
object.public String getAlgorithm()
SecureRandom
object.unknown
if the algorithm name cannot be determined.public String toString()
SecureRandom
.public SecureRandomParameters getParameters()
SecureRandomParameters
for this
SecureRandom
instance.
The returned value can be different from the
SecureRandomParameters
object passed into a getInstance
method, but it cannot change during the lifetime of this
SecureRandom
object.
A caller can use the returned value to find out what features this
SecureRandom
supports.
SecureRandomParameters
parameters,
or null
if no parameters were used.SecureRandomSpi
public void setSeed(byte[] seed)
A PRNG SecureRandom
will not seed itself automatically if
setSeed
is called before any nextBytes
or reseed
calls. The caller should make sure that the seed
argument
contains enough entropy for the security of this SecureRandom
.
seed
- the seed.getSeed(int)
public void setSeed(long seed)
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
.
setSeed
in class Random
seed
- the seed.getSeed(int)
public void nextBytes(byte[] bytes)
public void nextBytes(byte[] bytes, SecureRandomParameters params)
bytes
- the array to be filled in with random bytesparams
- additional parametersNullPointerException
- if bytes
is nullUnsupportedOperationException
- if the underlying provider
implementation has not overridden this methodIllegalArgumentException
- if params
is null
,
illegal or unsupported by this SecureRandom
protected final int next(int numBits)
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
).public static byte[] getSeed(int numBytes)
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.
numBytes
- the number of seed bytes to generate.IllegalArgumentException
- if numBytes
is negativesetSeed(byte[])
public byte[] generateSeed(int numBytes)
numBytes
- the number of seed bytes to generate.IllegalArgumentException
- if numBytes
is negativepublic static SecureRandom getInstanceStrong() throws NoSuchAlgorithmException
SecureRandom
object that was selected by using
the algorithms/providers specified in the
securerandom.strongAlgorithms
Security
property.
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.
SecureRandom
implementation as indicated
by the securerandom.strongAlgorithms
Security propertyNoSuchAlgorithmException
- if no algorithm is availableSecurity.getProperty(String)
public void reseed()
SecureRandom
with entropy input read from its
entropy source.UnsupportedOperationException
- if the underlying provider
implementation has not overridden this method.public void reseed(SecureRandomParameters params)
SecureRandom
with entropy input read from its
entropy source with additional parameters.
Note that entropy is obtained from an entropy source. While
some data in params
may contain entropy, its main usage is to
provide diversity.
params
- extra parametersUnsupportedOperationException
- if the underlying provider
implementation has not overridden this method.IllegalArgumentException
- if params
is null
,
illegal or unsupported by this SecureRandom
Submit a bug or feature
For further API reference and developer documentation, see Java SE Documentation. That documentation contains more detailed, developer-targeted descriptions, with conceptual overviews, definitions of terms, workarounds, and working code examples.
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DRAFT 9-internal+0-adhoc.mlchung.jdk9-jdeps