Added in API level 1

KeyGenerator

open class KeyGenerator
kotlin.Any
   ↳ javax.crypto.KeyGenerator

This class provides the functionality of a secret (symmetric) key generator.

Key generators are constructed using one of the getInstance class methods of this class.

KeyGenerator objects are reusable, i.e., after a key has been generated, the same KeyGenerator object can be re-used to generate further keys.

There are two ways to generate a key: in an algorithm-independent manner, and in an algorithm-specific manner. The only difference between the two is the initialization of the object:

  • Algorithm-Independent Initialization

    All key generators share the concepts of a keysize and a source of randomness. There is an init method in this KeyGenerator class that takes these two universally shared types of arguments. There is also one that takes just a keysize argument, and uses the SecureRandom implementation of the highest-priority installed provider as the source of randomness (or a system-provided source of randomness if none of the installed providers supply a SecureRandom implementation), and one that takes just a source of randomness.

    Since no other parameters are specified when you call the above algorithm-independent init methods, it is up to the provider what to do about the algorithm-specific parameters (if any) to be associated with each of the keys.

  • Algorithm-Specific Initialization

    For situations where a set of algorithm-specific parameters already exists, there are two init methods that have an AlgorithmParameterSpec argument. One also has a SecureRandom argument, while the other uses the SecureRandom implementation of the highest-priority installed provider as the source of randomness (or a system-provided source of randomness if none of the installed providers supply a SecureRandom implementation).

In case the client does not explicitly initialize the KeyGenerator (via a call to an init method), each provider must supply (and document) a default initialization.

Android provides the following KeyGenerator algorithms:

Algorithm Supported API Levels
AES 1+
AESWRAP 1-8
ARC4 14+
BLOWFISH 10+
ChaCha20 28+
DES 1+
DESede 1+
DESedeWRAP 1-8
HmacMD5 1+
HmacSHA1 11+
HmacSHA224 1-8,22+
HmacSHA256 1+
HmacSHA384 1+
HmacSHA512 1+
RC4 10-13
These algorithms are described in the KeyGenerator section of the Java Cryptography Architecture Standard Algorithm Name Documentation.

Summary

Protected constructors
KeyGenerator(keyGenSpi: KeyGeneratorSpi!, provider: Provider!, algorithm: String!)

Creates a KeyGenerator object.
Public methods
SecretKey!

Generates a secret key.
String!

Returns the algorithm name of this KeyGenerator object.
static KeyGenerator!
getInstance(algorithm: String!)

Returns a KeyGenerator object that generates secret keys for the specified algorithm.
static KeyGenerator!
getInstance(algorithm: String!, provider: String!)

Returns a KeyGenerator object that generates secret keys for the specified algorithm.
static KeyGenerator!
getInstance(algorithm: String!, provider: Provider!)

Returns a KeyGenerator object that generates secret keys for the specified algorithm.
Provider!

Returns the provider of this KeyGenerator object.
Unit
init(keysize: Int)

Initializes this key generator for a certain keysize.
Unit
init(keysize: Int, random: SecureRandom!)

Initializes this key generator for a certain keysize, using a user-provided source of randomness.
Unit
init(random: SecureRandom!)

Initializes this key generator.
Unit

Initializes this key generator with the specified parameter set.
Unit

Initializes this key generator with the specified parameter set and a user-provided source of randomness.

Protected constructors

KeyGenerator

Added in API level 1
protected KeyGenerator(
    keyGenSpi: KeyGeneratorSpi!, 
    provider: Provider!, 
    algorithm: String!)

Creates a KeyGenerator object.

Parameters
keyGenSpi KeyGeneratorSpi!: the delegate
provider Provider!: the provider
algorithm String!: the algorithm

Public methods

generateKey

Added in API level 1
fun generateKey(): SecretKey!

Generates a secret key.

Return
SecretKey! the new key

getAlgorithm

Added in API level 1
fun getAlgorithm(): String!

Returns the algorithm name of this KeyGenerator object.

This is the same name that was specified in one of the getInstance calls that created this KeyGenerator object.

Return
String! the algorithm name of this KeyGenerator object.

getInstance

Added in API level 1
static fun getInstance(algorithm: String!): KeyGenerator!

Returns a KeyGenerator object that generates secret keys for the specified algorithm.

This method traverses the list of registered security Providers, starting with the most preferred Provider. A new KeyGenerator object encapsulating the KeyGeneratorSpi 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.

Parameters
algorithm String!: the standard name of the requested key algorithm. See the KeyGenerator section in the Java Cryptography Architecture Standard Algorithm Name Documentation for information about standard algorithm names.
Return
KeyGenerator! the new KeyGenerator object.
Exceptions
java.lang.NullPointerException if the specified algorithm is null.
java.security.NoSuchAlgorithmException if no Provider supports a KeyGeneratorSpi implementation for the specified algorithm.

getInstance

Added in API level 1
static fun getInstance(
    algorithm: String!, 
    provider: String!
): KeyGenerator!

Returns a KeyGenerator object that generates secret keys for the specified algorithm.

A new KeyGenerator object encapsulating the KeyGeneratorSpi 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 standard name of the requested key algorithm. See the KeyGenerator section in the Java Cryptography Architecture Standard Algorithm Name Documentation for information about standard algorithm names.
provider String!: the name of the provider.
Return
KeyGenerator! the new KeyGenerator object.
Exceptions
java.lang.NullPointerException if the specified algorithm is null.
java.security.NoSuchAlgorithmException if a KeyGeneratorSpi implementation for the specified algorithm is not available from the specified provider.
java.security.NoSuchProviderException if the specified provider is not registered in the security provider list.
java.lang.IllegalArgumentException if the provider is null or empty.

getInstance

Added in API level 1
static fun getInstance(
    algorithm: String!, 
    provider: Provider!
): KeyGenerator!

Returns a KeyGenerator object that generates secret keys for the specified algorithm.

A new KeyGenerator object encapsulating the KeyGeneratorSpi 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 standard name of the requested key algorithm. See the KeyGenerator section in the Java Cryptography Architecture Standard Algorithm Name Documentation for information about standard algorithm names.
provider Provider!: the provider.
Return
KeyGenerator! the new KeyGenerator object.
Exceptions
java.lang.NullPointerException if the specified algorithm is null.
java.security.NoSuchAlgorithmException if a KeyGeneratorSpi implementation for the specified algorithm is not available from the specified Provider object.
java.lang.IllegalArgumentException if the provider is null.

getProvider

Added in API level 1
fun getProvider(): Provider!

Returns the provider of this KeyGenerator object.

Return
Provider! the provider of this KeyGenerator object

init

Added in API level 1
fun init(keysize: Int): Unit

Initializes this key generator for a certain keysize.

If this key generator requires any random bytes, it will get them using the java.security.SecureRandom implementation of the highest-priority installed provider as the source of randomness. (If none of the installed providers supply an implementation of SecureRandom, a system-provided source of randomness will be used.)

Parameters
keysize Int: the keysize. This is an algorithm-specific metric, specified in number of bits.
Exceptions
java.security.InvalidParameterException if the keysize is wrong or not supported.

init

Added in API level 1
fun init(
    keysize: Int, 
    random: SecureRandom!
): Unit

Initializes this key generator for a certain keysize, using a user-provided source of randomness.

Parameters
keysize Int: the keysize. This is an algorithm-specific metric, specified in number of bits.
random SecureRandom!: the source of randomness for this key generator
Exceptions
java.security.InvalidParameterException if the keysize is wrong or not supported.

init

Added in API level 1
fun init(random: SecureRandom!): Unit

Initializes this key generator.

Parameters
random SecureRandom!: the source of randomness for this generator

init

Added in API level 1
fun init(params: AlgorithmParameterSpec!): Unit

Initializes this key generator with the specified parameter set.

If this key generator requires any random bytes, it will get them using the java.security.SecureRandom implementation of the highest-priority installed provider as the source of randomness. (If none of the installed providers supply an implementation of SecureRandom, a system-provided source of randomness will be used.)

Parameters
params AlgorithmParameterSpec!: the key generation parameters
Exceptions
java.security.InvalidAlgorithmParameterException if the given parameters are inappropriate for this key generator

init

Added in API level 1
fun init(
    params: AlgorithmParameterSpec!, 
    random: SecureRandom!
): Unit

Initializes this key generator with the specified parameter set and a user-provided source of randomness.

Parameters
params AlgorithmParameterSpec!: the key generation parameters
random SecureRandom!: the source of randomness for this key generator
Exceptions
java.security.InvalidAlgorithmParameterException if params is inappropriate for this key generator