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. However,
support for key exchanges with more than two parties is implementation
specific or as specified by the standard key agreement algorithm.
Every implementation of the Java platform is required to support the
following standard KeyAgreement
algorithm:
DiffieHellman
- Since:
- 1.4
- See Also:
-
Constructor Summary
ModifierConstructorDescriptionprotected
KeyAgreement
(KeyAgreementSpi keyAgreeSpi, Provider provider, String algorithm) Creates aKeyAgreement
object. -
Method Summary
Modifier and TypeMethodDescriptionfinal Key
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[]
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 buffersharedSecret
, beginning atoffset
inclusive.final SecretKey
generateSecret
(String algorithm) Creates the shared secret and returns it as aSecretKey
object of the specified algorithm.final String
Returns the algorithm name of thisKeyAgreement
object.static final KeyAgreement
getInstance
(String algorithm) Returns aKeyAgreement
object that implements the specified key agreement algorithm.static final KeyAgreement
getInstance
(String algorithm, String provider) Returns aKeyAgreement
object that implements the specified key agreement algorithm.static final KeyAgreement
getInstance
(String algorithm, Provider provider) Returns aKeyAgreement
object that implements the specified key agreement algorithm.final Provider
Returns the provider of thisKeyAgreement
object.final void
Initializes this key agreement with the given key, which is required to contain all the algorithm parameters required for this key agreement.final void
init
(Key key, SecureRandom random) Initializes this key agreement with the given key and source of randomness.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.
-
Constructor Details
-
KeyAgreement
Creates aKeyAgreement
object.- Parameters:
keyAgreeSpi
- the delegateprovider
- the provideralgorithm
- the algorithm
-
-
Method Details
-
getAlgorithm
Returns the algorithm name of thisKeyAgreement
object.This is the same name that was specified in one of the
getInstance
calls that created thisKeyAgreement
object.- Returns:
- the algorithm name of this
KeyAgreement
object.
-
getInstance
Returns aKeyAgreement
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 theKeyAgreementSpi
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 from the order of providers returned bySecurity.getProviders()
. - Parameters:
algorithm
- the standard name of the requested key agreement algorithm. See the KeyAgreement section in the Java Security Standard Algorithm Names Specification for information about standard algorithm names.- Returns:
- the new
KeyAgreement
object - Throws:
NoSuchAlgorithmException
- if noProvider
supports aKeyAgreementSpi
implementation for the specified algorithmNullPointerException
- ifalgorithm
isnull
- See Also:
-
getInstance
public static final KeyAgreement getInstance(String algorithm, String provider) throws NoSuchAlgorithmException, NoSuchProviderException Returns aKeyAgreement
object that implements the specified key agreement algorithm.A new
KeyAgreement
object encapsulating theKeyAgreementSpi
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
- the standard name of the requested key agreement algorithm. See the KeyAgreement section in the Java Security Standard Algorithm Names Specification for information about standard algorithm names.provider
- the name of the provider.- Returns:
- the new
KeyAgreement
object - Throws:
IllegalArgumentException
- if theprovider
isnull
or emptyNoSuchAlgorithmException
- if aKeyAgreementSpi
implementation for the specified algorithm is not available from the specified providerNoSuchProviderException
- if the specified provider is not registered in the security provider listNullPointerException
- ifalgorithm
isnull
- See Also:
-
getInstance
public static final KeyAgreement getInstance(String algorithm, Provider provider) throws NoSuchAlgorithmException Returns aKeyAgreement
object that implements the specified key agreement algorithm.A new
KeyAgreement
object encapsulating theKeyAgreementSpi
implementation from the specified provider is returned. Note that the specified provider does not have to be registered in the provider list.- Parameters:
algorithm
- the standard name of the requested key agreement algorithm. See the KeyAgreement section in the Java Security Standard Algorithm Names Specification for information about standard algorithm names.provider
- the provider.- Returns:
- the new
KeyAgreement
object - Throws:
IllegalArgumentException
- if theprovider
isnull
NoSuchAlgorithmException
- if aKeyAgreementSpi
implementation for the specified algorithm is not available from the specifiedProvider
objectNullPointerException
- ifalgorithm
isnull
- See Also:
-
getProvider
Returns the provider of thisKeyAgreement
object.- Returns:
- the provider of this
KeyAgreement
object
-
init
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 ofSecureRandom
, a system-provided source of randomness will be used.)- Parameters:
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.
-
init
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
- 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
- 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
public final void init(Key key, AlgorithmParameterSpec params) throws InvalidKeyException, InvalidAlgorithmParameterException 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 ofSecureRandom
, a system-provided source of randomness will be used.)- Parameters:
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
- 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
public final void init(Key key, AlgorithmParameterSpec params, SecureRandom random) throws InvalidKeyException, InvalidAlgorithmParameterException Initializes this key agreement with the given key, set of algorithm parameters, and source of randomness.- Parameters:
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
- the key agreement parametersrandom
- 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.
-
doPhase
public final Key doPhase(Key key, boolean lastPhase) throws InvalidKeyException, IllegalStateException 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
- 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
- flag which indicates whether this is the last phase of this key agreement.- Returns:
- 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
Generates the shared secret and returns it in a new buffer.This method resets this
KeyAgreement
object to the state that it was in after the most recent call to one of theinit
methods. After a call togenerateSecret
, the object can be reused for further key agreement operations by callingdoPhase
to supply new keys, and then callinggenerateSecret
to produce a new secret. In this case, the private information and algorithm parameters supplied toinit
will be used for multiple key agreement operations. Theinit
method can be called aftergenerateSecret
to change the private information used in subsequent operations.- Returns:
- the new buffer with the shared secret
- Throws:
IllegalStateException
- if this key agreement has not been initialized or ifdoPhase
has not been called to supply the keys for all parties in the agreement
-
generateSecret
public final int generateSecret(byte[] sharedSecret, int offset) throws IllegalStateException, ShortBufferException Generates the shared secret, and places it into the buffersharedSecret
, beginning atoffset
inclusive.If the
sharedSecret
buffer is too small to hold the result, aShortBufferException
is thrown. In this case, this call should be repeated with a larger output buffer.This method resets this
KeyAgreement
object to the state that it was in after the most recent call to one of theinit
methods. After a call togenerateSecret
, the object can be reused for further key agreement operations by callingdoPhase
to supply new keys, and then callinggenerateSecret
to produce a new secret. In this case, the private information and algorithm parameters supplied toinit
will be used for multiple key agreement operations. Theinit
method can be called aftergenerateSecret
to change the private information used in subsequent operations.- Parameters:
sharedSecret
- the buffer for the shared secretoffset
- the offset insharedSecret
where the shared secret will be stored- Returns:
- the number of bytes placed into
sharedSecret
- Throws:
IllegalStateException
- if this key agreement has not been initialized or ifdoPhase
has not been called to supply the keys for all parties in the agreementShortBufferException
- if the given output buffer is too small to hold the secret
-
generateSecret
public final SecretKey generateSecret(String algorithm) throws IllegalStateException, NoSuchAlgorithmException, InvalidKeyException Creates the shared secret and returns it as aSecretKey
object of the specified algorithm.This method resets this
KeyAgreement
object to the state that it was in after the most recent call to one of theinit
methods. After a call togenerateSecret
, the object can be reused for further key agreement operations by callingdoPhase
to supply new keys, and then callinggenerateSecret
to produce a new secret. In this case, the private information and algorithm parameters supplied toinit
will be used for multiple key agreement operations. Theinit
method can be called aftergenerateSecret
to change the private information used in subsequent operations.- Parameters:
algorithm
- the requested secret-key algorithm- Returns:
- the shared secret key
- Throws:
IllegalStateException
- if this key agreement has not been initialized or ifdoPhase
has not been called to supply the keys for all parties in the agreementNoSuchAlgorithmException
- if the specified secret-key algorithm is not availableInvalidKeyException
- 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)
-