case AES_CTR:
        {
            size_t bytes_to_copy = ctx->mode.ctr.last_block_stop;
            size_t bytes_offset = AES_BLOCK_SIZE - bytes_to_copy;

            // xor remaining bytes from last encrypt operation into new plaintext
            if(bytes_to_copy){
                memcpy(out, in, bytes_offset);
                xor_buf(&ctx->mode.ctr.last_block[bytes_to_copy], out, bytes_offset);
                blocks = ((in_len - bytes_offset) / AES_BLOCK_SIZE);
            }
            // encrypt message in CTR mode
            for(idx = 0; idx <= blocks; idx++){
                bytes_to_copy = MIN(AES_BLOCK_SIZE, in_len - (idx * AES_BLOCK_SIZE));
                //bytes_to_pad = AES_BLOCK_SIZE-bytes_to_copy;
                memcpy(&out[idx*AES_BLOCK_SIZE], &in[idx*AES_BLOCK_SIZE], bytes_to_copy);
                // memset(&buf[bytes_to_copy], 0, bytes_to_pad);        // if bytes_to_copy is less than blocksize, do nothing, since msg is truncated anyway
                aes_encrypt_block(iv, buf, ctx);
                xor_buf(buf, &out[idx*AES_BLOCK_SIZE], bytes_to_copy);
                increment_iv(iv, ctx->mode.ctr.counter_len);        // increment iv for continued use
                if(idx==blocks){
                    memcpy(ctx->mode.ctr.last_block, buf, AES_BLOCK_SIZE);
                    ctx->mode.ctr.last_block_stop = bytes_to_copy;
                }
            }
            break;
        }