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 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[], java.security.SecureRandomParameters)
and
reseed(java.security.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.
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 |
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
|
static
SecureRandom
|
getInstance(String algorithm)
Returns a |
static
SecureRandom
|
getInstance(String algorithm, String provider)
Returns a |
static
SecureRandom
|
getInstance(String algorithm, SecureRandomParameters params)
Returns a |
static
SecureRandom
|
getInstance(String algorithm, Provider provider)
Returns a |
static
SecureRandom
|
getInstance(String algorithm, SecureRandomParameters params, String provider)
Returns a |
static
SecureRandom
|
getInstance(String algorithm, SecureRandomParameters params, Provider provider)
Returns a |
static
SecureRandom
|
getInstanceStrong()
Returns a |
SecureRandomParameters
|
getParameters()
Returns the effective |
final
Provider
|
getProvider()
Returns the provider of this |
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, SecureRandomParameters params)
Generates a user-specified number of random bytes with additional parameters. |
void
|
nextBytes(byte[] bytes)
Generates a user-specified number of random bytes. |
void
|
reseed(SecureRandomParameters params)
Reseeds this |
void
|
reseed()
Reseeds this |
void
|
setSeed(long seed)
Reseeds this random object, using the eight bytes contained
in the given |
void
|
setSeed(byte[] seed)
Reseeds this random object with the given seed. |
String
|
toString()
Returns a Human-readable string representation of this
|
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 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.
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 Security Standard Algorithm Names Specification
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. |
Throws | |
---|---|
IllegalArgumentException |
if numBytes is negative |
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.
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 than the order of providers returned bySecurity.getProviders()
.
Parameters | |
---|---|
algorithm |
String : the name of the RNG algorithm.
See the SecureRandom section in the
Java Security Standard Algorithm Names Specification
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 |
NullPointerException |
if algorithm is null |
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.
Parameters | |
---|---|
algorithm |
String : the name of the RNG algorithm.
See the SecureRandom section in the
Java Security Standard Algorithm Names Specification
for information about standard RNG algorithm names. |
provider |
String : the name of the provider. |
Returns | |
---|---|
SecureRandom |
the new SecureRandom object |
Throws | |
---|---|
IllegalArgumentException |
if the provider name is null
or empty |
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 |
NullPointerException |
if algorithm is null |
See also:
getInstance
public 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.
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.
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 than the order of providers returned bySecurity.getProviders()
.
Parameters | |
---|---|
algorithm |
String : the name of the RNG algorithm.
See the SecureRandom section in the
Java Security Standard Algorithm Names Specification
for information about standard RNG algorithm names. |
params |
SecureRandomParameters : the SecureRandomParameters
the newly created SecureRandom object must support. |
Returns | |
---|---|
SecureRandom |
the new SecureRandom object |
Throws | |
---|---|
IllegalArgumentException |
if the specified params is
null |
NoSuchAlgorithmException |
if no Provider supports a
SecureRandomSpi implementation for the specified
algorithm and parameters |
NullPointerException |
if algorithm is null |
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.
Parameters | |
---|---|
algorithm |
String : the name of the RNG algorithm.
See the SecureRandom section in the
Java Security Standard Algorithm Names Specification
for information about standard RNG algorithm names. |
provider |
Provider : the provider. |
Returns | |
---|---|
SecureRandom |
the new SecureRandom object |
Throws | |
---|---|
IllegalArgumentException |
if the specified provider is
null |
NoSuchAlgorithmException |
if a SecureRandomSpi
implementation for the specified algorithm is not available
from the specified Provider object |
NullPointerException |
if algorithm is null |
See also:
getInstance
public 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.
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.
Parameters | |
---|---|
algorithm |
String : the name of the RNG algorithm.
See the SecureRandom section in the
Java Security Standard Algorithm Names Specification
for information about standard RNG algorithm names. |
params |
SecureRandomParameters : the SecureRandomParameters
the newly created SecureRandom object must support. |
provider |
String : the name of the provider. |
Returns | |
---|---|
SecureRandom |
the new SecureRandom object |
Throws | |
---|---|
IllegalArgumentException |
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 parameters |
NoSuchProviderException |
if the specified provider is not registered in the security provider list |
NullPointerException |
if algorithm is null |
See also:
getInstance
public 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.
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.
Parameters | |
---|---|
algorithm |
String : the name of the RNG algorithm.
See the SecureRandom section in the
Java Security Standard Algorithm Names Specification
for information about standard RNG algorithm names. |
params |
SecureRandomParameters : the SecureRandomParameters
the newly created SecureRandom object must support. |
provider |
Provider : the provider. |
Returns | |
---|---|
SecureRandom |
the new SecureRandom object |
Throws | |
---|---|
IllegalArgumentException |
if the specified provider or params
is null |
NoSuchAlgorithmException |
if the specified provider does not
support a SecureRandomSpi implementation for the
specified algorithm and parameters |
NullPointerException |
if algorithm 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:
getParameters
public SecureRandomParameters getParameters ()
Returns the effective 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.
Returns | |
---|---|
SecureRandomParameters |
the effective SecureRandomParameters parameters,
or null if no parameters were used. |
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. |
Throws | |
---|---|
IllegalArgumentException |
if numBytes is negative |
See also:
nextBytes
public void nextBytes (byte[] bytes, SecureRandomParameters params)
Generates a user-specified number of random bytes with additional parameters.
Parameters | |
---|---|
bytes |
byte : the array to be filled in with random bytes |
params |
SecureRandomParameters : additional parameters |
Throws | |
---|---|
NullPointerException |
if bytes is null |
UnsupportedOperationException |
if the underlying provider implementation has not overridden this method |
IllegalArgumentException |
if params is null ,
illegal or unsupported by this SecureRandom |
nextBytes
public void nextBytes (byte[] bytes)
Generates a user-specified number of random bytes.
Parameters | |
---|---|
bytes |
byte : the array to be filled in with random bytes. |
reseed
public void reseed (SecureRandomParameters params)
Reseeds this 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.
Parameters | |
---|---|
params |
SecureRandomParameters : extra parameters |
Throws | |
---|---|
UnsupportedOperationException |
if the underlying provider implementation has not overridden this method. |
IllegalArgumentException |
if params is null ,
illegal or unsupported by this SecureRandom |
reseed
public void reseed ()
Reseeds this SecureRandom
with entropy input read from its
entropy source.
Throws | |
---|---|
UnsupportedOperationException |
if the underlying provider implementation has not overridden this method. |
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 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 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
.
Parameters | |
---|---|
seed |
byte : the seed. |
See also:
toString
public String toString ()
Returns a Human-readable string representation of this
SecureRandom
.
Returns | |
---|---|
String |
the string representation |
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). |