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.
*
* @param 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.
* @param random the source of randomness
*
* @exception InvalidKeyException if the given key is
* inappropriate for this key agreement, e.g., is of the wrong type or
* has an incompatible algorithm type.
*/
protected void engineInit(Key key, SecureRandom random)
throws InvalidKeyException
{
try {
engineInit(key, null, random);
} catch (InvalidAlgorithmParameterException e) {
// never happens, because we did not pass any parameters
}
}
/**
* Initializes this key agreement with the given key, set of
* algorithm parameters, and source of randomness.
*
* @param 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.
* @param params the key agreement parameters
* @param random the source of randomness
*
* @exception InvalidKeyException if the given key is
* inappropriate for this key agreement, e.g., is of the wrong type or
* has an incompatible algorithm type.
* @exception InvalidAlgorithmParameterException if the given parameters
* are inappropriate for this key agreement.
*/
protected void engineInit(Key key, AlgorithmParameterSpec params,
SecureRandom random)
throws InvalidKeyException, InvalidAlgorithmParameterException
{
// ignore "random" parameter, because our implementation does not
// require any source of randomness
generateSecret = false;
init_p = null;
init_g = null;
if ((params != null) && !(params instanceof DHParameterSpec)) {
throw new InvalidAlgorithmParameterException
("Diffie-Hellman parameters expected");
}
if (!(key instanceof javax.crypto.interfaces.DHPrivateKey)) {
throw new InvalidKeyException("Diffie-Hellman private key "
+ "expected");
}
javax.crypto.interfaces.DHPrivateKey dhPrivKey;
dhPrivKey = (javax.crypto.interfaces.DHPrivateKey)key;
// check if private key parameters are compatible with
// initialized ones
if (params != null) {
init_p = ((DHParameterSpec)params).getP();
init_g = ((DHParameterSpec)params).getG();
}
BigInteger priv_p = dhPrivKey.getParams().getP();
BigInteger priv_g = dhPrivKey.getParams().getG();
if (init_p != null && priv_p != null && !(init_p.equals(priv_p))) {
throw new InvalidKeyException("Incompatible parameters");
}
if (init_g != null && priv_g != null && !(init_g.equals(priv_g))) {
throw new InvalidKeyException("Incompatible parameters");
}
if ((init_p == null && priv_p == null)
|| (init_g == null && priv_g == null)) {
throw new InvalidKeyException("Missing parameters");
}
init_p = priv_p;
init_g = priv_g;
// store the x value
this.x = dhPrivKey.getX();
}
/**
* 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.
*
* @param 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.
* @param lastPhase flag which indicates whether or not this is the last
* phase of this key agreement.
*
* @return the (intermediate) key resulting from this phase, or null if
* this phase does not yield a key
*
* @exception InvalidKeyException if the given key is inappropriate for
* this phase.
* @exception IllegalStateException if this key agreement has not been
* initialized.
*/
protected Key engineDoPhase(Key key, boolean lastPhase)
throws InvalidKeyException, IllegalStateException
{
if (!(key instanceof javax.crypto.interfaces.DHPublicKey)) {
throw new InvalidKeyException("Diffie-Hellman public key "
+ "expected");
}
javax.crypto.interfaces.DHPublicKey dhPubKey;
dhPubKey = (javax.crypto.interfaces.DHPublicKey)key;
if (init_p == null || init_g == null) {
throw new IllegalStateException("Not initialized");
}
// check if public key parameters are compatible with
// initialized ones
BigInteger pub_p = dhPubKey.getParams().getP();
BigInteger pub_g = dhPubKey.getParams().getG();
if (pub_p != null && !(init_p.equals(pub_p))) {
throw new InvalidKeyException("Incompatible parameters");
}
if (pub_g != null && !(init_g.equals(pub_g))) {
throw new InvalidKeyException("Incompatible parameters");
}
// validate the Diffie-Hellman public key
KeyUtil.validate(dhPubKey);
// store the y value
this.y = dhPubKey.getY();
// we've received a public key (from one of the other parties),
// so we are ready to create the secret, which may be an
// intermediate secret, in which case we wrap it into a
// Diffie-Hellman public key object and return it.
generateSecret = true;
if (lastPhase == false) {
byte[] intermediate = engineGenerateSecret();
return new DHPublicKey(new BigInteger(1, intermediate),
init_p, init_g);
} else {
return null;
}
}
/**
* Generates the shared secret and returns it in a new buffer.
*
*
This method resets this KeyAgreementSpi object,
* so that it
* can be reused for further key agreements. Unless this key agreement is
* reinitialized with one of the engineInit methods, the same
* private information and algorithm parameters will be used for
* subsequent key agreements.
*
* @return the new buffer with the shared secret
*
* @exception IllegalStateException if this key agreement has not been
* completed yet
*/
protected byte[] engineGenerateSecret()
throws IllegalStateException
{
int expectedLen = (init_p.bitLength() + 7) >>> 3;
byte[] result = new byte[expectedLen];
try {
engineGenerateSecret(result, 0);
} catch (ShortBufferException sbe) {
// should never happen since secret lengths in the two
// methods are identical
}
return result;
}
/**
* Generates the shared secret, and places it into the buffer
* sharedSecret, beginning at offset.
*
*
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 KeyAgreementSpi object,
* so that it
* can be reused for further key agreements. Unless this key agreement is
* reinitialized with one of the engineInit methods, the same
* private information and algorithm parameters will be used for
* subsequent key agreements.
*
* @param sharedSecret the buffer for the shared secret
* @param offset the offset in sharedSecret where the
* shared secret will be stored
*
* @return the number of bytes placed into sharedSecret
*
* @exception IllegalStateException if this key agreement has not been
* completed yet
* @exception ShortBufferException if the given output buffer is too small
* to hold the secret
*/
protected int engineGenerateSecret(byte[] sharedSecret, int offset)
throws IllegalStateException, ShortBufferException
{
if (generateSecret == false) {
throw new IllegalStateException
("Key agreement has not been completed yet");
}
if (sharedSecret == null) {
throw new ShortBufferException
("No buffer provided for shared secret");
}
BigInteger modulus = init_p;
int expectedLen = (modulus.bitLength() + 7) >>> 3;
if ((sharedSecret.length - offset) < expectedLen) {
throw new ShortBufferException
("Buffer too short for shared secret");
}
// Reset the key agreement after checking for ShortBufferException
// above, so user can recover w/o losing internal state
generateSecret = false;
/*
* NOTE: BigInteger.toByteArray() returns a byte array containing
* the two's-complement representation of this BigInteger with
* the most significant byte is in the zeroth element. This
* contains the minimum number of bytes required to represent
* this BigInteger, including at least one sign bit whose value
* is always 0.
*
* Keys are always positive, and the above sign bit isn't
* actually used when representing keys. (i.e. key = new
* BigInteger(1, byteArray)) To obtain an array containing
* exactly expectedLen bytes of magnitude, we strip any extra
* leading 0's, or pad with 0's in case of a "short" secret.
*/
byte[] secret = this.y.modPow(this.x, modulus).toByteArray();
if (secret.length == expectedLen) {
System.arraycopy(secret, 0, sharedSecret, offset,
secret.length);
} else {
// Array too short, pad it w/ leading 0s
if (secret.length < expectedLen) {
System.arraycopy(secret, 0, sharedSecret,
offset + (expectedLen - secret.length),
secret.length);
} else {
// Array too long, check and trim off the excess
if ((secret.length == (expectedLen+1)) && secret[0] == 0) {
// ignore the leading sign byte
System.arraycopy(secret, 1, sharedSecret, offset, expectedLen);
} else {
throw new ProviderException("Generated secret is out-of-range");
}
}
}
return expectedLen;
}
/**
* Creates the shared secret and returns it as a secret key object
* of the requested algorithm type.
*
*
This method resets this KeyAgreementSpi object,
* so that it
* can be reused for further key agreements. Unless this key agreement is
* reinitialized with one of the engineInit methods, the same
* private information and algorithm parameters will be used for
* subsequent key agreements.
*
* @param algorithm the requested secret key algorithm
*
* @return the shared secret key
*
* @exception IllegalStateException if this key agreement has not been
* completed yet
* @exception NoSuchAlgorithmException if the requested secret key
* algorithm is not available
* @exception InvalidKeyException 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)
*/
protected SecretKey engineGenerateSecret(String algorithm)
throws IllegalStateException, NoSuchAlgorithmException,
InvalidKeyException
{
if (algorithm == null) {
throw new NoSuchAlgorithmException("null algorithm");
}
byte[] secret = engineGenerateSecret();
if (algorithm.equalsIgnoreCase("DES")) {
// DES
return new DESKey(secret);
} else if (algorithm.equalsIgnoreCase("DESede")
|| algorithm.equalsIgnoreCase("TripleDES")) {
// Triple DES
return new DESedeKey(secret);
} else if (algorithm.equalsIgnoreCase("Blowfish")) {
// Blowfish
int keysize = secret.length;
if (keysize >= BlowfishConstants.BLOWFISH_MAX_KEYSIZE)
keysize = BlowfishConstants.BLOWFISH_MAX_KEYSIZE;
SecretKeySpec skey = new SecretKeySpec(secret, 0, keysize,
"Blowfish");
return skey;
} else if (algorithm.equalsIgnoreCase("AES")) {
// AES
int keysize = secret.length;
SecretKeySpec skey = null;
int idx = AESConstants.AES_KEYSIZES.length - 1;
while (skey == null && idx >= 0) {
// Generate the strongest key using the shared secret
// assuming the key sizes in AESConstants class are
// in ascending order
if (keysize >= AESConstants.AES_KEYSIZES[idx]) {
keysize = AESConstants.AES_KEYSIZES[idx];
skey = new SecretKeySpec(secret, 0, keysize, "AES");
}
idx--;
}
if (skey == null) {
throw new InvalidKeyException("Key material is too short");
}
return skey;
} else if (algorithm.equals("TlsPremasterSecret")) {
// return entire secret
return new SecretKeySpec(secret, "TlsPremasterSecret");
} else {
throw new NoSuchAlgorithmException("Unsupported secret key "
+ "algorithm: "+ algorithm);
}
}
}