Class SecureRandom
- All Implemented Interfaces:
Serializable
,RandomGenerator
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.
Thread safety
SecureRandom
objects are safe for use by multiple concurrent threads.- Implementation Requirements:
- A
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 theSecureRandomSpi
implementation: - Since:
- 1.1
- External Specifications
- See Also:
-
Nested Class Summary
Nested classes/interfaces inherited from interface java.util.random.RandomGenerator
RandomGenerator.ArbitrarilyJumpableGenerator, RandomGenerator.JumpableGenerator, RandomGenerator.LeapableGenerator, RandomGenerator.SplittableGenerator, RandomGenerator.StreamableGenerator
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Constructor Summary
ModifierConstructorDescriptionConstructs 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 aSecureRandom
object. -
Method Summary
Modifier and TypeMethodDescriptionbyte[]
generateSeed
(int numBytes) Returns the given number of seed bytes, computed using the seed generation algorithm that this class uses to seed itself.Returns the name of the algorithm implemented by thisSecureRandom
object.static SecureRandom
getInstance
(String algorithm) Returns aSecureRandom
object that implements the specified Random Number Generator (RNG) algorithm.static SecureRandom
getInstance
(String algorithm, String provider) Returns aSecureRandom
object that implements the specified Random Number Generator (RNG) algorithm.static SecureRandom
getInstance
(String algorithm, Provider provider) Returns aSecureRandom
object that implements the specified Random Number Generator (RNG) algorithm.static SecureRandom
getInstance
(String algorithm, SecureRandomParameters params) Returns aSecureRandom
object that implements the specified Random Number Generator (RNG) algorithm and supports the specifiedSecureRandomParameters
request.static SecureRandom
getInstance
(String algorithm, SecureRandomParameters params, String provider) Returns aSecureRandom
object that implements the specified Random Number Generator (RNG) algorithm and supports the specifiedSecureRandomParameters
request.static SecureRandom
getInstance
(String algorithm, SecureRandomParameters params, Provider provider) Returns aSecureRandom
object that implements the specified Random Number Generator (RNG) algorithm and supports the specifiedSecureRandomParameters
request.static SecureRandom
Returns aSecureRandom
object that was selected by using the algorithms/providers specified in thesecurerandom.strongAlgorithms
Security
property.Returns the effectiveSecureRandomParameters
for thisSecureRandom
instance.final Provider
Returns the provider of thisSecureRandom
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 final 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 thisSecureRandom
with entropy input read from its entropy source.void
reseed
(SecureRandomParameters params) Reseeds thisSecureRandom
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 givenlong seed
.toString()
Returns a Human-readable string representation of thisSecureRandom
.Methods inherited from class java.util.Random
doubles, doubles, doubles, doubles, from, ints, ints, ints, ints, longs, longs, longs, longs, nextBoolean, nextDouble, nextFloat, nextGaussian, nextInt, nextInt, nextLong
Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait
Methods inherited from interface java.util.random.RandomGenerator
equiDoubles, isDeprecated, nextDouble, nextDouble, nextExponential, nextFloat, nextFloat, nextGaussian, nextInt, nextLong, nextLong
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Constructor Details
-
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 theSecureRandomSpi
implementation from the first provider that supports aSecureRandom
(RNG) algorithm is returned. If none of the providers support an 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 Security Standard Algorithm Names Specification for information about standard RNG algorithm names. -
SecureRandom
public SecureRandom(byte[] seed) Constructs a secure random number generator (RNG) implementing the default random number algorithm. TheSecureRandom
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 theSecureRandomSpi
implementation from the first provider that supports aSecureRandom
(RNG) algorithm is returned. If none of the providers support an 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 Security Standard Algorithm Names Specification for information about standard RNG algorithm names.- Parameters:
seed
- the seed.- Throws:
NullPointerException
- ifseed
isnull
-
SecureRandom
Creates aSecureRandom
object.- Parameters:
secureRandomSpi
- theSecureRandom
implementation.provider
- the provider.
-
-
Method Details
-
getInstance
Returns aSecureRandom
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 theSecureRandomSpi
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.- Implementation Note:
- The JDK Reference Implementation additionally uses the
jdk.security.provider.preferred
Security
property to determine the preferred provider order for the specified algorithm. This may be different from the order of providers returned bySecurity.getProviders()
. - Parameters:
algorithm
- the name of the RNG algorithm. See theSecureRandom
section in the Java Security Standard Algorithm Names Specification for information about standard RNG algorithm names.- Returns:
- the new
SecureRandom
object - Throws:
NoSuchAlgorithmException
- if noProvider
supports aSecureRandomSpi
implementation for the specified algorithmNullPointerException
- ifalgorithm
isnull
- Since:
- 1.2
- See Also:
-
getInstance
public static SecureRandom getInstance(String algorithm, String provider) throws NoSuchAlgorithmException, NoSuchProviderException Returns aSecureRandom
object that implements the specified Random Number Generator (RNG) algorithm.A new
SecureRandom
object encapsulating theSecureRandomSpi
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.- Parameters:
algorithm
- the name of the RNG algorithm. See theSecureRandom
section in the Java Security Standard Algorithm Names Specification for information about standard RNG algorithm names.provider
- the name of the provider.- Returns:
- the new
SecureRandom
object - Throws:
IllegalArgumentException
- if the provider name isnull
or emptyNoSuchAlgorithmException
- if aSecureRandomSpi
implementation for the specified algorithm is not available from the specified providerNoSuchProviderException
- if the specified provider is not registered in the security provider listNullPointerException
- ifalgorithm
isnull
- Since:
- 1.2
- See Also:
-
getInstance
public static SecureRandom getInstance(String algorithm, Provider provider) throws NoSuchAlgorithmException Returns aSecureRandom
object that implements the specified Random Number Generator (RNG) algorithm.A new
SecureRandom
object encapsulating theSecureRandomSpi
implementation from the specified provider is returned. Note that the specified provider does not have to be registered in the provider list.- Parameters:
algorithm
- the name of the RNG algorithm. See theSecureRandom
section in the Java Security Standard Algorithm Names Specification for information about standard RNG algorithm names.provider
- the provider.- Returns:
- the new
SecureRandom
object - Throws:
IllegalArgumentException
- if the specified provider isnull
NoSuchAlgorithmException
- if aSecureRandomSpi
implementation for the specified algorithm is not available from the specifiedProvider
objectNullPointerException
- ifalgorithm
isnull
- Since:
- 1.4
- See Also:
-
getInstance
public static SecureRandom getInstance(String algorithm, SecureRandomParameters params) throws NoSuchAlgorithmException Returns aSecureRandom
object that implements the specified Random Number Generator (RNG) algorithm and supports the specifiedSecureRandomParameters
request.This method traverses the list of registered security providers, starting with the most preferred provider. A new
SecureRandom
object encapsulating theSecureRandomSpi
implementation from the first provider that supports the specified algorithm and the specifiedSecureRandomParameters
is returned.Note that the list of registered providers may be retrieved via the
Security.getProviders()
method.- Implementation Note:
- The JDK Reference Implementation additionally uses the
jdk.security.provider.preferred
property to determine the preferred provider order for the specified algorithm. This may be different from the order of providers returned bySecurity.getProviders()
. - Parameters:
algorithm
- the name of the RNG algorithm. See theSecureRandom
section in the Java Security Standard Algorithm Names Specification for information about standard RNG algorithm names.params
- theSecureRandomParameters
the newly createdSecureRandom
object must support.- Returns:
- the new
SecureRandom
object - Throws:
IllegalArgumentException
- if the specified params isnull
NoSuchAlgorithmException
- if no Provider supports aSecureRandomSpi
implementation for the specified algorithm and parametersNullPointerException
- ifalgorithm
isnull
- Since:
- 9
- See Also:
-
getInstance
public static SecureRandom getInstance(String algorithm, SecureRandomParameters params, String provider) throws NoSuchAlgorithmException, NoSuchProviderException Returns aSecureRandom
object that implements the specified Random Number Generator (RNG) algorithm and supports the specifiedSecureRandomParameters
request.A new
SecureRandom
object encapsulating theSecureRandomSpi
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.- Parameters:
algorithm
- the name of the RNG algorithm. See theSecureRandom
section in the Java Security Standard Algorithm Names Specification for information about standard RNG algorithm names.params
- theSecureRandomParameters
the newly createdSecureRandom
object must support.provider
- the name of the provider.- Returns:
- the new
SecureRandom
object - Throws:
IllegalArgumentException
- if the provider name isnull
or empty, or params isnull
NoSuchAlgorithmException
- if the specified provider does not support aSecureRandomSpi
implementation for the specified algorithm and parametersNoSuchProviderException
- if the specified provider is not registered in the security provider listNullPointerException
- ifalgorithm
isnull
- Since:
- 9
- See Also:
-
getInstance
public static SecureRandom getInstance(String algorithm, SecureRandomParameters params, Provider provider) throws NoSuchAlgorithmException Returns aSecureRandom
object that implements the specified Random Number Generator (RNG) algorithm and supports the specifiedSecureRandomParameters
request.A new
SecureRandom
object encapsulating theSecureRandomSpi
implementation from the specified provider is returned. Note that the specified provider does not have to be registered in the provider list.- Parameters:
algorithm
- the name of the RNG algorithm. See theSecureRandom
section in the Java Security Standard Algorithm Names Specification for information about standard RNG algorithm names.params
- theSecureRandomParameters
the newly createdSecureRandom
object must support.provider
- the provider.- Returns:
- the new
SecureRandom
object - Throws:
IllegalArgumentException
- if the specified provider or params isnull
NoSuchAlgorithmException
- if the specified provider does not support aSecureRandomSpi
implementation for the specified algorithm and parametersNullPointerException
- ifalgorithm
isnull
- Since:
- 9
- See Also:
-
getProvider
Returns the provider of thisSecureRandom
object.- Returns:
- the provider of this
SecureRandom
object.
-
getAlgorithm
Returns the name of the algorithm implemented by thisSecureRandom
object.- Returns:
- the name of the algorithm or
unknown
if the algorithm name cannot be determined. - Since:
- 1.5
-
toString
-
getParameters
Returns the effectiveSecureRandomParameters
for thisSecureRandom
instance.The returned value can be different from the
SecureRandomParameters
object passed into agetInstance
method, but it cannot change during the lifetime of thisSecureRandom
object.A caller can use the returned value to find out what features this
SecureRandom
supports.- Returns:
- the effective
SecureRandomParameters
parameters, ornull
if no parameters were used. - Since:
- 9
- See Also:
-
setSeed
public void setSeed(byte[] seed) Reseeds this random object with the given seed. The seed supplements, rather than replaces, the existing seed. Thus, repeated calls are guaranteed never to reduce randomness.A PRNG
SecureRandom
will not seed itself automatically ifsetSeed
is called before anynextBytes
orreseed
calls. The caller should make sure that theseed
argument contains enough entropy for the security of thisSecureRandom
.- Parameters:
seed
- the seed.- Throws:
NullPointerException
- ifseed
isnull
- See Also:
-
setSeed
public void setSeed(long seed) Reseeds this random object, using the eight bytes contained in the givenlong seed
. The given seed supplements, rather than replaces, the existing seed. Thus, repeated calls are guaranteed never to reduce randomness.A PRNG
SecureRandom
will not seed itself automatically ifsetSeed
is called before anynextBytes
orreseed
calls. The caller should make sure that theseed
argument contains enough entropy for the security of thisSecureRandom
.This method is defined for compatibility with
java.util.Random
. -
nextBytes
public void nextBytes(byte[] bytes) Generates a user-specified number of random bytes.- Specified by:
nextBytes
in interfaceRandomGenerator
- Overrides:
nextBytes
in classRandom
- Parameters:
bytes
- the array to be filled in with random bytes.- Throws:
NullPointerException
- ifbytes
isnull
-
nextBytes
Generates a user-specified number of random bytes with additional parameters.- Parameters:
bytes
- the array to be filled in with random bytesparams
- additional parameters- Throws:
NullPointerException
- ifbytes
isnull
UnsupportedOperationException
- if the underlying provider implementation has not overridden this methodIllegalArgumentException
- ifparams
isnull
, illegal or unsupported by thisSecureRandom
- Since:
- 9
-
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 ajava.util.Random
method, and serves to provide a source of random bits to all the methods inherited from that class (for example,nextInt
,nextLong
, andnextFloat
). -
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 aSecureRandom
object, and then call thegenerateSeed
method to obtain seed bytes from that object.- Parameters:
numBytes
- the number of seed bytes to generate.- Returns:
- the seed bytes.
- Throws:
IllegalArgumentException
- ifnumBytes
is negative- See Also:
-
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
- the number of seed bytes to generate.- Returns:
- the seed bytes.
- Throws:
IllegalArgumentException
- ifnumBytes
is negative
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getInstanceStrong
Returns aSecureRandom
object that was selected by using the algorithms/providers specified in thesecurerandom.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 strongSecureRandom
implementations in thesecurerandom.strongAlgorithms
Security property.Every implementation of the Java platform is required to support at least one strong
SecureRandom
implementation.- Returns:
- a strong
SecureRandom
implementation as indicated by thesecurerandom.strongAlgorithms
Security property - Throws:
NoSuchAlgorithmException
- if no algorithm is available- Since:
- 1.8
- See Also:
-
reseed
public void reseed()Reseeds thisSecureRandom
with entropy input read from its entropy source.- Throws:
UnsupportedOperationException
- if the underlying provider implementation has not overridden this method.- Since:
- 9
-
reseed
Reseeds thisSecureRandom
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.- Parameters:
params
- extra parameters- Throws:
UnsupportedOperationException
- if the underlying provider implementation has not overridden this method.IllegalArgumentException
- ifparams
isnull
, illegal or unsupported by thisSecureRandom
- Since:
- 9
-