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:
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Constructor Summary
ConstructorsModifierConstructorDescriptionprotectedKeyAgreement(KeyAgreementSpi keyAgreeSpi, Provider provider, String algorithm) Creates a KeyAgreement object. -
Method Summary
Modifier and TypeMethodDescriptionfinal KeyExecutes 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 intgenerateSecret(byte[] sharedSecret, int offset) Generates the shared secret, and places it into the buffersharedSecret, beginning atoffsetinclusive.final SecretKeygenerateSecret(String algorithm) Creates the shared secret and returns it as aSecretKeyobject of the specified algorithm.final StringReturns the algorithm name of thisKeyAgreementobject.static final KeyAgreementgetInstance(String algorithm) Returns aKeyAgreementobject that implements the specified key agreement algorithm.static final KeyAgreementgetInstance(String algorithm, String provider) Returns aKeyAgreementobject that implements the specified key agreement algorithm.static final KeyAgreementgetInstance(String algorithm, Provider provider) Returns aKeyAgreementobject that implements the specified key agreement algorithm.final ProviderReturns the provider of thisKeyAgreementobject.final voidInitializes this key agreement with the given key, which is required to contain all the algorithm parameters required for this key agreement.final voidinit(Key key, SecureRandom random) Initializes this key agreement with the given key and source of randomness.final voidinit(Key key, AlgorithmParameterSpec params) Initializes this key agreement with the given key and set of algorithm parameters.final voidinit(Key key, AlgorithmParameterSpec params, SecureRandom random) Initializes this key agreement with the given key, set of algorithm parameters, and source of randomness.
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Constructor Details
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KeyAgreement
Creates a KeyAgreement object.- Parameters:
keyAgreeSpi- the delegateprovider- the provideralgorithm- the algorithm
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Method Details
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getAlgorithm
Returns the algorithm name of thisKeyAgreementobject.This is the same name that was specified in one of the
getInstancecalls that created thisKeyAgreementobject.- Returns:
- the algorithm name of this
KeyAgreementobject.
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getInstance
Returns aKeyAgreementobject 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.- Implementation Note:
- The JDK Reference Implementation additionally uses the
jdk.security.provider.preferredSecurityproperty to determine the preferred provider order for the specified algorithm. This may be different than 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
KeyAgreementobject - Throws:
NoSuchAlgorithmException- if noProvidersupports aKeyAgreementSpiimplementation for the specified algorithmNullPointerException- ifalgorithmisnull- See Also:
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getInstance
public static final KeyAgreement getInstance(String algorithm, String provider) throws NoSuchAlgorithmException, NoSuchProviderException Returns aKeyAgreementobject 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- 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
KeyAgreementobject - Throws:
IllegalArgumentException- if theproviderisnullor emptyNoSuchAlgorithmException- if aKeyAgreementSpiimplementation for the specified algorithm is not available from the specified providerNoSuchProviderException- if the specified provider is not registered in the security provider listNullPointerException- ifalgorithmisnull- See Also:
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getInstance
public static final KeyAgreement getInstance(String algorithm, Provider provider) throws NoSuchAlgorithmException Returns aKeyAgreementobject 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- 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
KeyAgreementobject - Throws:
IllegalArgumentException- if theproviderisnullNoSuchAlgorithmException- if aKeyAgreementSpiimplementation for the specified algorithm is not available from the specified Provider objectNullPointerException- ifalgorithmisnull- See Also:
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getProvider
Returns the provider of thisKeyAgreementobject.- Returns:
- the provider of this
KeyAgreementobject
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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
SecureRandomimplementation 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- 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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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,randomis 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.
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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
SecureRandomimplementation 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- 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.
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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.
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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 or not 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.
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generateSecret
Generates the shared secret and returns it in a new buffer.This method resets this
KeyAgreementobject to the state that it was in after the most recent call to one of theinitmethods. After a call togenerateSecret, the object can be reused for further key agreement operations by callingdoPhaseto supply new keys, and then callinggenerateSecretto produce a new secret. In this case, the private information and algorithm parameters supplied toinitwill be used for multiple key agreement operations. Theinitmethod can be called aftergenerateSecretto 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 ifdoPhasehas not been called to supply the keys for all parties in the agreement
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generateSecret
public final int generateSecret(byte[] sharedSecret, int offset) throws IllegalStateException, ShortBufferException Generates the shared secret, and places it into the buffersharedSecret, beginning atoffsetinclusive.If the
sharedSecretbuffer is too small to hold the result, aShortBufferExceptionis thrown. In this case, this call should be repeated with a larger output buffer.This method resets this
KeyAgreementobject to the state that it was in after the most recent call to one of theinitmethods. After a call togenerateSecret, the object can be reused for further key agreement operations by callingdoPhaseto supply new keys, and then callinggenerateSecretto produce a new secret. In this case, the private information and algorithm parameters supplied toinitwill be used for multiple key agreement operations. Theinitmethod can be called aftergenerateSecretto change the private information used in subsequent operations.- Parameters:
sharedSecret- the buffer for the shared secretoffset- the offset insharedSecretwhere 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 ifdoPhasehas 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
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generateSecret
public final SecretKey generateSecret(String algorithm) throws IllegalStateException, NoSuchAlgorithmException, InvalidKeyException Creates the shared secret and returns it as aSecretKeyobject of the specified algorithm.This method resets this
KeyAgreementobject to the state that it was in after the most recent call to one of theinitmethods. After a call togenerateSecret, the object can be reused for further key agreement operations by callingdoPhaseto supply new keys, and then callinggenerateSecretto produce a new secret. In this case, the private information and algorithm parameters supplied toinitwill be used for multiple key agreement operations. Theinitmethod can be called aftergenerateSecretto 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 ifdoPhasehas 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)
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