/**
* Creates a new {@code HKDF} instance.
*
* @param algorithm the MAC algorithm to use.
* @param info optional context and application specific information, may be {@code null} or
* empty.
* @param dkLen the desired length for derived keys, in bytes.
* @throws NullPointerException if {@code algorithm} is {@code null}.
* @throws IllegalArgumentException if {@code dkLen} is negative, or if the MAC algorithm is
* unknown, or if {@code dkLen} is greater than 255 * MAC algorithm's output length.
*/
HKDF(Algorithm<MAC> algorithm, byte[] info, int dkLen) {
Parameters.checkCondition(dkLen > 0);
MAC mac = Factory.newMAC(algorithm, new byte[0]);
Parameters.checkCondition(dkLen <= 255 * mac.length());
this.algorithm = algorithm;
this.dkLen = dkLen;
this.info = info == null ? new byte[0] : XArrays.copyOf(info);
}
@Override
public long skip(long n) {
Parameters.checkCondition(n >= 0);
if (finished()) {
return 0;
}
long skipped = n;
if (n > in.length() - index) {
skipped = in.length() - index;
}
index += skipped;
return skipped;
}
/**
* Marks the current position in the stream. Subsequent calls to reset() will reposition the
* stream to this point.
*
* @param readLimit limit on the number of characters that may be read while still preserving the
* mark. Because the stream's input comes from {@code String}s, there is no actual limit, so
* this argument must not be negative, but is otherwise ignored.
* @throws IllegalArgumentException if {@code readLimit} is negative.
*/
@Override
public void mark(int readLimit) {
Parameters.checkCondition(readLimit >= 0);
mark = index;
}