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KeyAgreement

public class KeyAgreement
extends Object

java.lang.Object
   ↳ javax.crypto.KeyAgreement


This class provides the functionality of a key agreement (or key exchange) protocol.

The keys involved in establishing a shared secret are created by one of the key generators (KeyPairGenerator or KeyGenerator), a KeyFactory, or as a result from an intermediate phase of the key agreement protocol.

For each of the correspondents in the key exchange, doPhase needs to be called. For example, if this key exchange is with one other party, doPhase needs to be called once, with the lastPhase flag set to true. If this key exchange is with two other parties, doPhase needs to be called twice, the first time setting the lastPhase flag to false, and the second time setting it to true. There may be any number of parties involved in a key exchange.

Android provides the following KeyAgreement algorithms:

Name Supported (API Levels)
DH 1+
ECDH 11+
This algorithm is described in the KeyAgreement section of the Java Cryptography Architecture Standard Algorithm Name Documentation.

See also:

Summary

Protected constructors

KeyAgreement(KeyAgreementSpi keyAgreeSpi, Provider provider, String algorithm)

Creates a KeyAgreement object.

Public methods

final Key doPhase(Key key, boolean lastPhase)

Executes the next phase of this key agreement with the given key that was received from one of the other parties involved in this key agreement.

final byte[] generateSecret()

Generates the shared secret and returns it in a new buffer.

final int generateSecret(byte[] sharedSecret, int offset)

Generates the shared secret, and places it into the buffer sharedSecret, beginning at offset inclusive.

final SecretKey generateSecret(String algorithm)

Creates the shared secret and returns it as a SecretKey object of the specified algorithm.

final String getAlgorithm()

Returns the algorithm name of this KeyAgreement object.

static final KeyAgreement getInstance(String algorithm)

Returns a KeyAgreement object that implements the specified key agreement algorithm.

static final KeyAgreement getInstance(String algorithm, String provider)

Returns a KeyAgreement object that implements the specified key agreement algorithm.

static final KeyAgreement getInstance(String algorithm, Provider provider)

Returns a KeyAgreement object that implements the specified key agreement algorithm.

final Provider getProvider()

Returns the provider of this KeyAgreement object.

final void init(Key key, AlgorithmParameterSpec params)

Initializes this key agreement with the given key and set of algorithm parameters.

final void init(Key key, AlgorithmParameterSpec params, SecureRandom random)

Initializes this key agreement with the given key, set of algorithm parameters, and source of randomness.

final void init(Key key, SecureRandom random)

Initializes this key agreement with the given key and source of randomness.

final void init(Key key)

Initializes this key agreement with the given key, which is required to contain all the algorithm parameters required for this key agreement.

Inherited methods

From class java.lang.Object

Protected constructors

KeyAgreement

Added in API level 1
KeyAgreement (KeyAgreementSpi keyAgreeSpi, 
                Provider provider, 
                String algorithm)

Creates a KeyAgreement object.

Parameters
keyAgreeSpi KeyAgreementSpi: the delegate
provider Provider: the provider
algorithm String: the algorithm

Public methods

doPhase

Added in API level 1
Key doPhase (Key key, 
                boolean lastPhase)

Executes the next phase of this key agreement with the given key that was received from one of the other parties involved in this key agreement.

Parameters
key Key: the key for this phase. For example, in the case of Diffie-Hellman between 2 parties, this would be the other party's Diffie-Hellman public key.
lastPhase boolean: flag which indicates whether or not this is the last phase of this key agreement.
Returns
Key the (intermediate) key resulting from this phase, or null if this phase does not yield a key
Throws
InvalidKeyException if the given key is inappropriate for this phase.
IllegalStateException if this key agreement has not been initialized.

generateSecret

Added in API level 1
byte[] generateSecret ()

Generates the shared secret and returns it in a new buffer.

This method resets this KeyAgreement object, so that it can be reused for further key agreements. Unless this key agreement is reinitialized with one of the init methods, the same private information and algorithm parameters will be used for subsequent key agreements.

Returns
byte[] the new buffer with the shared secret
Throws
IllegalStateException if this key agreement has not been completed yet

generateSecret

Added in API level 1
int generateSecret (byte[] sharedSecret, 
                int offset)

Generates the shared secret, and places it into the buffer sharedSecret, beginning at offset inclusive.

If the sharedSecret buffer is too small to hold the result, a ShortBufferException is thrown. In this case, this call should be repeated with a larger output buffer.

This method resets this KeyAgreement object, so that it can be reused for further key agreements. Unless this key agreement is reinitialized with one of the init methods, the same private information and algorithm parameters will be used for subsequent key agreements.

Parameters
sharedSecret byte: the buffer for the shared secret
offset int: the offset in sharedSecret where the shared secret will be stored
Returns
int the number of bytes placed into sharedSecret
Throws
IllegalStateException if this key agreement has not been completed yet
ShortBufferException if the given output buffer is too small to hold the secret

generateSecret

Added in API level 1
SecretKey generateSecret (String algorithm)

Creates the shared secret and returns it as a SecretKey object of the specified algorithm.

This method resets this KeyAgreement object, so that it can be reused for further key agreements. Unless this key agreement is reinitialized with one of the init methods, the same private information and algorithm parameters will be used for subsequent key agreements.

Parameters
algorithm String: the requested secret-key algorithm
Returns
SecretKey the shared secret key
Throws
IllegalStateException if this key agreement has not been completed yet
NoSuchAlgorithmException if the specified secret-key algorithm is not available
InvalidKeyException if the shared secret-key material cannot be used to generate a secret key of the specified algorithm (e.g., the key material is too short)

getAlgorithm

Added in API level 1
String getAlgorithm ()

Returns the algorithm name of this KeyAgreement object.

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

Returns
String the algorithm name of this KeyAgreement object.

getInstance

Added in API level 1
KeyAgreement getInstance (String algorithm)

Returns a KeyAgreement object that implements the specified key agreement algorithm.

This method traverses the list of registered security Providers, starting with the most preferred Provider. A new KeyAgreement object encapsulating the KeyAgreementSpi 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 agreement algorithm. See the KeyAgreement section in the Java Cryptography Architecture Standard Algorithm Name Documentation for information about standard algorithm names.
Returns
KeyAgreement the new KeyAgreement object.
Throws
NullPointerException if the specified algorithm is null.
NoSuchAlgorithmException if no Provider supports a KeyAgreementSpi implementation for the specified algorithm.

See also:

getInstance

Added in API level 1
KeyAgreement getInstance (String algorithm, 
                String provider)

Returns a KeyAgreement object that implements the specified key agreement algorithm.

A new KeyAgreement object encapsulating the KeyAgreementSpi 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 agreement algorithm. See the KeyAgreement section in the Java Cryptography Architecture Standard Algorithm Name Documentation for information about standard algorithm names.
provider String: the name of the provider.
Returns
KeyAgreement the new KeyAgreement object.
Throws
NullPointerException if the specified algorithm is null.
NoSuchAlgorithmException if a KeyAgreementSpi 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.
IllegalArgumentException if the provider is null or empty.

See also:

getInstance

Added in API level 1
KeyAgreement getInstance (String algorithm, 
                Provider provider)

Returns a KeyAgreement object that implements the specified key agreement algorithm.

A new KeyAgreement object encapsulating the KeyAgreementSpi 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 agreement algorithm. See the KeyAgreement section in the Java Cryptography Architecture Standard Algorithm Name Documentation for information about standard algorithm names.
provider Provider: the provider.
Returns
KeyAgreement the new KeyAgreement object.
Throws
NullPointerException if the specified algorithm is null.
NoSuchAlgorithmException if a KeyAgreementSpi implementation for the specified algorithm is not available from the specified Provider object.
IllegalArgumentException if the provider is null.

See also:

getProvider

Added in API level 1
Provider getProvider ()

Returns the provider of this KeyAgreement object.

Returns
Provider the provider of this KeyAgreement object

init

Added in API level 1
void init (Key key, 
                AlgorithmParameterSpec params)

Initializes this key agreement with the given key and set of algorithm parameters.

If this key agreement requires any random bytes, it will get them using the 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
key Key: the party's private information. For example, in the case of the Diffie-Hellman key agreement, this would be the party's own Diffie-Hellman private key.
params AlgorithmParameterSpec: the key agreement parameters
Throws
InvalidKeyException if the given key is inappropriate for this key agreement, e.g., is of the wrong type or has an incompatible algorithm type.
InvalidAlgorithmParameterException if the given parameters are inappropriate for this key agreement.

init

Added in API level 1
void init (Key key, 
                AlgorithmParameterSpec params, 
                SecureRandom random)

Initializes this key agreement with the given key, set of algorithm parameters, and source of randomness.

Parameters
key Key: the party's private information. For example, in the case of the Diffie-Hellman key agreement, this would be the party's own Diffie-Hellman private key.
params AlgorithmParameterSpec: the key agreement parameters
random SecureRandom: the source of randomness
Throws
InvalidKeyException if the given key is inappropriate for this key agreement, e.g., is of the wrong type or has an incompatible algorithm type.
InvalidAlgorithmParameterException if the given parameters are inappropriate for this key agreement.

init

Added in API level 1
void init (Key key, 
                SecureRandom random)

Initializes this key agreement with the given key and source of randomness. The given key is required to contain all the algorithm parameters required for this key agreement.

If the key agreement algorithm requires random bytes, it gets them from the given source of randomness, random. However, if the underlying algorithm implementation does not require any random bytes, random is ignored.

Parameters
key Key: the party's private information. For example, in the case of the Diffie-Hellman key agreement, this would be the party's own Diffie-Hellman private key.
random SecureRandom: the source of randomness
Throws
InvalidKeyException if the given key is inappropriate for this key agreement, e.g., is of the wrong type or has an incompatible algorithm type.

init

Added in API level 1
void init (Key key)

Initializes this key agreement with the given key, which is required to contain all the algorithm parameters required for this key agreement.

If this key agreement requires any random bytes, it will get them using the 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
key Key: the party's private information. For example, in the case of the Diffie-Hellman key agreement, this would be the party's own Diffie-Hellman private key.
Throws
InvalidKeyException if the given key is inappropriate for this key agreement, e.g., is of the wrong type or has an incompatible algorithm type.
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