DrbgParameters
public
class
DrbgParameters
extends Object
java.lang.Object | |
↳ | java.security.DrbgParameters |
This class specifies the parameters used by a DRBG (Deterministic Random Bit Generator).
According to NIST Special Publication 800-90A Revision 1, Recommendation for Random Number Generation Using Deterministic Random Bit Generators (800-90Ar1),
A DRBG is based on a DRBG mechanism as specified in this Recommendation and includes a source of randomness. A DRBG mechanism uses an algorithm (i.e., a DRBG algorithm) that produces a sequence of bits from an initial value that is determined by a seed that is determined from the output of the randomness source."
The 800-90Ar1 specification allows for a variety of DRBG implementation choices, such as:
- an entropy source,
- a DRBG mechanism (for example, Hash_DRBG),
- a DRBG algorithm (for example, SHA-256 for Hash_DRBG and AES-256
for CTR_DRBG. Please note that it is not the algorithm used in
SecureRandom#getInstance
, which we will call a SecureRandom algorithm below), - optional features, including prediction resistance and reseeding supports,
- highest security strength.
These choices are set in each implementation and are not directly
managed by the SecureRandom
API. Check your DRBG provider's
documentation to find an appropriate implementation for the situation.
On the other hand, the 800-90Ar1 specification does have some configurable options, such as:
- required security strength,
- if prediction resistance is required,
- personalization string and additional input.
A DRBG instance can be instantiated with parameters from an
DrbgParameters.Instantiation
object and other information
(for example, the nonce, which is not managed by this API). This maps
to the Instantiate_function
defined in NIST SP 800-90Ar1.
A DRBG instance can be reseeded with parameters from a
DrbgParameters.Reseed
object. This maps to the
Reseed_function
defined in NIST SP 800-90Ar1. Calling
SecureRandom#reseed()
is equivalent to calling
SecureRandom#reseed(SecureRandomParameters)
with the effective
instantiated prediction resistance flag (as returned by
SecureRandom#getParameters()
) with no additional input.
A DRBG instance generates data with additional parameters from a
DrbgParameters.NextBytes
object. This maps to the
Generate_function
defined in NIST SP 800-90Ar1. Calling
SecureRandom#nextBytes(byte[])
is equivalent to calling
SecureRandom#nextBytes(byte[], SecureRandomParameters)
with the effective instantiated strength and prediction resistance flag
(as returned by SecureRandom#getParameters()
) with no
additional input.
A DRBG should be implemented as a subclass of SecureRandomSpi
.
It is recommended that the implementation contain the 1-arg
constructor
that takes a DrbgParameters.Instantiation
argument. If implemented
this way, this implementation can be chosen by any
SecureRandom.getInstance()
method. If it is chosen by a
SecureRandom.getInstance()
with a SecureRandomParameters
parameter, the parameter is passed into this constructor. If it is chosen
by a SecureRandom.getInstance()
without a
SecureRandomParameters
parameter, the constructor is called with
a null
argument and the implementation should choose its own
parameters. Its SecureRandom#getParameters()
must always return a
non-null effective DrbgParameters.Instantiation
object that reflects
how the DRBG is actually instantiated. A caller can use this information
to determine whether a SecureRandom
object is a DRBG and what
features it supports. Please note that the returned value does not
necessarily equal to the DrbgParameters.Instantiation
object passed
into the SecureRandom.getInstance()
call. For example,
the requested capability can be DrbgParameters.Capability#NONE
but the effective value can be DrbgParameters.Capability#RESEED_ONLY
if the implementation supports reseeding. The implementation must implement
the SecureRandomSpi#engineNextBytes(byte[], SecureRandomParameters)
method which takes a DrbgParameters.NextBytes
parameter. Unless
the result of SecureRandom#getParameters()
has its
capability being
NONE
, it must implement
SecureRandomSpi#engineReseed(SecureRandomParameters)
which takes
a DrbgParameters.Reseed
parameter.
On the other hand, if a DRBG implementation does not contain a constructor
that has an DrbgParameters.Instantiation
argument (not recommended),
it can only be chosen by a SecureRandom.getInstance()
without
a SecureRandomParameters
parameter, but will not be chosen if
a getInstance
method with a SecureRandomParameters
parameter
is called. If implemented this way, its SecureRandom#getParameters()
must return null
, and it does not need to implement either
SecureRandomSpi#engineNextBytes(byte[], SecureRandomParameters)
or SecureRandomSpi#engineReseed(SecureRandomParameters)
.
A DRBG might reseed itself automatically if the seed period is bigger than the maximum seed life defined by the DRBG mechanism.
A DRBG implementation should support serialization and deserialization by retaining the configuration and effective parameters, but the internal state must not be serialized and the deserialized object must be reinstantiated.
Examples:
SecureRandom drbg; byte[] buffer = new byte[32]; // Any DRBG is OK drbg = SecureRandom.getInstance("DRBG"); drbg.nextBytes(buffer); SecureRandomParameters params = drbg.getParameters(); if (params instanceof DrbgParameters.Instantiation) { DrbgParameters.Instantiation ins = (DrbgParameters.Instantiation) params; if (ins.getCapability().supportsReseeding()) { drbg.reseed(); } } // The following call requests a weak DRBG instance. It is only // guaranteed to support 112 bits of security strength. drbg = SecureRandom.getInstance("DRBG", DrbgParameters.instantiation(112, NONE, null)); // Both the next two calls will likely fail, because drbg could be // instantiated with a smaller strength with no prediction resistance // support. drbg.nextBytes(buffer, DrbgParameters.nextBytes(256, false, "more".getBytes())); drbg.nextBytes(buffer, DrbgParameters.nextBytes(112, true, "more".getBytes())); // The following call requests a strong DRBG instance, with a // personalization string. If it successfully returns an instance, // that instance is guaranteed to support 256 bits of security strength // with prediction resistance available. drbg = SecureRandom.getInstance("DRBG", DrbgParameters.instantiation( 256, PR_AND_RESEED, "hello".getBytes())); // Prediction resistance is not requested in this single call, // but an additional input is used. drbg.nextBytes(buffer, DrbgParameters.nextBytes(-1, false, "more".getBytes())); // Same for this call. drbg.reseed(DrbgParameters.reseed(false, "extra".getBytes()));
Summary
Nested classes | |
---|---|
class |
DrbgParameters.Instantiation
DRBG parameters for instantiation. |
class |
DrbgParameters.NextBytes
DRBG parameters for random bits generation. |
class |
DrbgParameters.Reseed
DRBG parameters for reseed. |
Public methods | |
---|---|
static
DrbgParameters.Instantiation
|
instantiation(int strength, DrbgParameters.Capability capability, byte[] personalizationString)
Generates a |
static
DrbgParameters.NextBytes
|
nextBytes(int strength, boolean predictionResistance, byte[] additionalInput)
Generates a |
static
DrbgParameters.Reseed
|
reseed(boolean predictionResistance, byte[] additionalInput)
Generates a |
Inherited methods | |
---|---|
Public methods
instantiation
public static DrbgParameters.Instantiation instantiation (int strength, DrbgParameters.Capability capability, byte[] personalizationString)
Generates a DrbgParameters.Instantiation
object.
Parameters | |
---|---|
strength |
int : security strength in bits, -1 for default strength
if used in getInstance . |
capability |
DrbgParameters.Capability : capability |
personalizationString |
byte : personalization string as a byte array,
can be null . The content of this
byte array will be copied. |
Returns | |
---|---|
DrbgParameters.Instantiation |
a new Instantiation object |
Throws | |
---|---|
NullPointerException |
if capability is null |
IllegalArgumentException |
if strength is less than -1 |
nextBytes
public static DrbgParameters.NextBytes nextBytes (int strength, boolean predictionResistance, byte[] additionalInput)
Generates a NextBytes
object.
Parameters | |
---|---|
strength |
int : requested security strength in bits. If set to -1, the
effective strength will be used. |
predictionResistance |
boolean : prediction resistance requested |
additionalInput |
byte : additional input, can be null .
The content of this byte array will be copied. |
Returns | |
---|---|
DrbgParameters.NextBytes |
a new NextBytes object |
Throws | |
---|---|
IllegalArgumentException |
if strength is less than -1 |
reseed
public static DrbgParameters.Reseed reseed (boolean predictionResistance, byte[] additionalInput)
Generates a Reseed
object.
Parameters | |
---|---|
predictionResistance |
boolean : prediction resistance requested |
additionalInput |
byte : additional input, can be null .
The content of this byte array will be copied. |
Returns | |
---|---|
DrbgParameters.Reseed |
a new Reseed object |
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Last updated 2024-06-18 UTC.