private void deriveKey()

in java/src/main/java/com/alexa/awisapi/AuthenticationHelper.java [424:459]
32 lines of code
7 McCabe index (conditional complexity)

        private void deriveKey(byte[] info, int length, byte[] output, int offset)
                throws ShortBufferException {
            this.assertInitialized();
            if (length < 0) {
                throw new IllegalArgumentException("Length must be a non-negative value.");
            } else if (output.length < offset + length) {
                throw new ShortBufferException();
            } else {
                final Mac mac = this.createMac();
                if (length > MAX_KEY_SIZE * mac.getMacLength()) {
                    throw new IllegalArgumentException(
                            "Requested keys may not be longer than 255 times the underlying HMAC length.");
                } else {
                    byte[] t = EMPTY_ARRAY;

                    try {
                        int loc = 0;

                        for (byte i = 1; loc < length; ++i) {
                            mac.update(t);
                            mac.update(info);
                            mac.update(i);
                            t = mac.doFinal();

                            for (int x = 0; x < t.length && loc < length; ++loc) {
                                output[loc] = t[x];
                                ++x;
                            }
                        }
                    } finally {
                        Arrays.fill(t, (byte) 0);
                    }

                }
            }
        }