Class DrbgParameters
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(java.lang.String)
, 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()));
- Implementation Requirements:
- By convention, a provider should name its primary DRBG implementation
with the
standard
SecureRandom
algorithm name "DRBG". - Implementation Note:
- The following notes apply to the "DRBG" implementation in the SUN provider
of the JDK reference implementation.
This implementation supports the Hash_DRBG and HMAC_DRBG mechanisms with DRBG algorithm SHA-224, SHA-512/224, SHA-256, SHA-512/256, SHA-384 and SHA-512, and CTR_DRBG (both using derivation function and not using derivation function) with DRBG algorithm AES-128, AES-192 and AES-256.
The mechanism name and DRBG algorithm name are determined by the security property
securerandom.drbg.config
. The default choice is Hash_DRBG with SHA-256.For each combination, the security strength can be requested from 112 up to the highest strength it supports. Both reseeding and prediction resistance are supported.
Personalization string is supported through the
DrbgParameters.Instantiation
class and additional input is supported through theDrbgParameters.NextBytes
andDrbgParameters.Reseed
classes.If a DRBG is not instantiated with a
DrbgParameters.Instantiation
object explicitly, this implementation instantiates it with a default requested strength of 128 bits, no prediction resistance request, and no personalization string. These default instantiation parameters can also be customized with thesecurerandom.drbg.config
security property.This implementation reads fresh entropy from the system default entropy source determined by the security property
securerandom.source
.Calling
SecureRandom.generateSeed(int)
will directly read from this system default entropy source. - Since:
- 9
- External Specifications
-
Nested Class Summary
Modifier and TypeClassDescriptionstatic enum
The reseedable and prediction resistance capabilities of a DRBG.static final class
DRBG parameters for instantiation.static final class
DRBG parameters for random bits generation.static final class
DRBG parameters for reseed. -
Method Summary
Modifier and TypeMethodDescriptionstatic DrbgParameters.Instantiation
instantiation
(int strength, DrbgParameters.Capability capability, byte[] personalizationString) Generates aDrbgParameters.Instantiation
object.static DrbgParameters.NextBytes
nextBytes
(int strength, boolean predictionResistance, byte[] additionalInput) Generates aDrbgParameters.NextBytes
object.static DrbgParameters.Reseed
reseed
(boolean predictionResistance, byte[] additionalInput) Generates aDrbgParameters.Reseed
object.
-
Method Details
-
instantiation
public static DrbgParameters.Instantiation instantiation(int strength, DrbgParameters.Capability capability, byte[] personalizationString) Generates aDrbgParameters.Instantiation
object.- Parameters:
strength
- security strength in bits, -1 for default strength if used ingetInstance
.capability
- capabilitypersonalizationString
- personalization string as a byte array, can benull
. The content of this byte array will be copied.- Returns:
- a new
Instantiation
object - Throws:
NullPointerException
- ifcapability
isnull
IllegalArgumentException
- ifstrength
is less than -1
-
nextBytes
public static DrbgParameters.NextBytes nextBytes(int strength, boolean predictionResistance, byte[] additionalInput) Generates aDrbgParameters.NextBytes
object.- Parameters:
strength
- requested security strength in bits. If set to -1, the effective strength will be used.predictionResistance
- prediction resistance requestedadditionalInput
- additional input, can benull
. The content of this byte array will be copied.- Returns:
- a new
NextBytes
object - Throws:
IllegalArgumentException
- ifstrength
is less than -1
-
reseed
Generates aDrbgParameters.Reseed
object.- Parameters:
predictionResistance
- prediction resistance requestedadditionalInput
- additional input, can benull
. The content of this byte array will be copied.- Returns:
- a new
Reseed
object
-