public static byte[]
        ctrHMac(byte[] keyDerivationKey, byte[] label, Supplier<Digest> digestSupplier, int keyLengthBytes) {

    logger.trace("<< ctrHMac() - keyDerivationKey: 0x{} label: {} digestSupplier: {} length: {}",
            Hex.toHexString(keyDerivationKey), Hex.toHexString(label), digestSupplier, keyLengthBytes);

    byte[] derivedKey = new byte[keyLengthBytes];

    // fixedInputData = label || 0x00 || dkLen in bits as 4 bytes big endian
    ByteBuffer buffer = ByteBuffer.allocate(label.length + 5);
    buffer.put(label);
    buffer.put((byte) 0);
    buffer.putInt(keyLengthBytes * 8);
    byte[] fixedInputData = buffer.array();
    logger.debug("-- ctrHMac() - fixed input data: 0x{}", Hex.toHexString(fixedInputData));

    HMac hMac = new HMac(digestSupplier.get());
    KDFCounterBytesGenerator generator = new KDFCounterBytesGenerator(hMac);
    generator.init(new KDFCounterParameters(keyDerivationKey, fixedInputData, R));
    generator.generateBytes(derivedKey, 0, derivedKey.length);

    logger.trace(">> ctrHMac() - derivedKey: 0x{}", Hex.toHexString(derivedKey));
    return derivedKey;
}
 

private static byte[] scp03_kdf(byte[] key, byte[] a, byte[] b, int bytes) {
    BlockCipher cipher = new AESEngine();
    CMac cmac = new CMac(cipher);
    KDFCounterBytesGenerator kdf = new KDFCounterBytesGenerator(cmac);
    kdf.init(new KDFCounterParameters(key, a, b, 8));
    byte[] cgram = new byte[bytes];
    kdf.generateBytes(cgram, 0, cgram.length);
    return cgram;
}
 

/**
 * @param sessionKey
 * @param label
 * @param context
 */
private static byte[] derive ( byte[] sessionKey, byte[] label, byte[] context ) {
    KDFCounterBytesGenerator gen = new KDFCounterBytesGenerator(new HMac(new SHA256Digest()));

    int r = 32;
    byte[] suffix = new byte[label.length + context.length + 5];
    // per bouncycastle
    // <li>1: K(i) := PRF( KI, [i]_2 || Label || 0x00 || Context || [L]_2 ) with the counter at the very beginning
    // of the fixedInputData (The default implementation has this format)</li>
    // with the parameters
    // <li>1. KDFCounterParameters(ki, null, "Label || 0x00 || Context || [L]_2]", 8);

    // all fixed inputs go into the suffix:
    // + label
    System.arraycopy(label, 0, suffix, 0, label.length);
    // + 1 byte 0x00
    // + context
    System.arraycopy(context, 0, suffix, label.length + 1, context.length);
    // + 4 byte (== r bits) big endian encoding of L
    suffix[ suffix.length - 1 ] = (byte) 128;

    DerivationParameters param = new KDFCounterParameters(sessionKey, null /* prefix */, suffix /* suffix */, r /* r */);
    gen.init(param);

    byte[] derived = new byte[16];
    gen.generateBytes(derived, 0, 16);
    return derived;
}
 

/**
 * @param sessionKey
 * @param label
 * @param context
 */
private static byte[] derive ( byte[] sessionKey, byte[] label, byte[] context ) {
    KDFCounterBytesGenerator gen = new KDFCounterBytesGenerator(new HMac(new SHA256Digest()));

    int r = 32;
    byte[] suffix = new byte[label.length + context.length + 5];
    // per bouncycastle
    // <li>1: K(i) := PRF( KI, [i]_2 || Label || 0x00 || Context || [L]_2 ) with the counter at the very beginning
    // of the fixedInputData (The default implementation has this format)</li>
    // with the parameters
    // <li>1. KDFCounterParameters(ki, null, "Label || 0x00 || Context || [L]_2]", 8);

    // all fixed inputs go into the suffix:
    // + label
    System.arraycopy(label, 0, suffix, 0, label.length);
    // + 1 byte 0x00
    // + context
    System.arraycopy(context, 0, suffix, label.length + 1, context.length);
    // + 4 byte (== r bits) big endian encoding of L
    suffix[ suffix.length - 1 ] = (byte) 128;

    DerivationParameters param = new KDFCounterParameters(sessionKey, null /* prefix */, suffix /* suffix */, r /* r */);
    gen.init(param);

    byte[] derived = new byte[16];
    gen.generateBytes(derived, 0, 16);
    return derived;
}
 

public static byte[] scp03_kdf(byte[] key, byte[] a, byte[] b, int bytes) {
    BlockCipher cipher = new AESEngine();
    CMac cmac = new CMac(cipher);
    KDFCounterBytesGenerator kdf = new KDFCounterBytesGenerator(cmac);
    kdf.init(new KDFCounterParameters(key, a, b, 8)); // counter size is in bits
    byte[] cgram = new byte[bytes];
    kdf.generateBytes(cgram, 0, cgram.length);
    return cgram;
}