buffer.buffer[letterIndex]++; // Increment to 'B'
hash.update(buffer.buffer, 0, buffer.index);
byte[] s2cCipherIV = hash.digest();
buffer.buffer[letterIndex]++; // Increment to 'C'
hash.update(buffer.buffer, 0, buffer.index);
byte[] c2sCipherKey = hash.digest();
buffer.buffer[letterIndex]++; // Increment to 'D'
hash.update(buffer.buffer, 0, buffer.index);
byte[] s2cCipherKey = hash.digest();