KeyAgreement
class.
All the abstract methods in this class must be implemented by each
cryptographic service provider who wishes to supply the implementation
of a particular key agreement algorithm.
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
(engineDoPhase
).
For each of the correspondents in the key exchange,
engineDoPhase
needs to be called. For example, if the key exchange is with one other
party, engineDoPhase
needs to be called once, with the
lastPhase
flag set to true
.
If the key exchange is
with two other parties, engineDoPhase
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.
- Since:
- 1.4
- See Also:
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Constructor Summary
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Method Summary
Modifier and TypeMethodDescriptionprotected abstract Key
engineDoPhase
(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.protected abstract byte[]
Generates the shared secret and returns it in a new buffer.protected abstract int
engineGenerateSecret
(byte[] sharedSecret, int offset) Generates the shared secret, and places it into the buffersharedSecret
, beginning atoffset
inclusive.protected abstract SecretKey
engineGenerateSecret
(String algorithm) Creates the shared secret and returns it as a secret key object of the requested algorithm type.protected abstract void
engineInit
(Key key, SecureRandom random) Initializes this key agreement with the given key and source of randomness.protected abstract void
engineInit
(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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KeyAgreementSpi
public KeyAgreementSpi()Constructor for subclasses to call.
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Method Details
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engineInit
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.
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engineInit
protected abstract void engineInit(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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engineDoPhase
protected abstract Key engineDoPhase(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.
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engineGenerateSecret
Generates the shared secret and returns it in a new buffer.This method resets this
KeyAgreementSpi
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
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engineGenerateSecret
protected abstract int engineGenerateSecret(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
KeyAgreementSpi
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
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engineGenerateSecret
protected abstract SecretKey engineGenerateSecret(String algorithm) throws IllegalStateException, NoSuchAlgorithmException, InvalidKeyException Creates the shared secret and returns it as a secret key object of the requested algorithm type.This method resets this
KeyAgreementSpi
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 requested secret key algorithm is not availableInvalidKeyException
- if the shared secret key material cannot be used to generate a secret key of the requested algorithm type (e.g., the key material is too short)
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