艾伦图灵研究所 双语畅销书《艾伦图灵传》第7章:运转起来(29)

双语畅销书《艾伦图灵传》第7章:运转起来(29)  

Assuming the circuit to be 'linear'
meaning that the input of a 'spike' of say half a unit would produce exactly half of this response
the effect of feeding into it the train of 'spikes' would be to 'join the dots' in a very precise way.
The information of each 'spike' would go exactly into the amplitude of the response of this circuit one unit of time later
and nowhere else.
The transmission would then be straightforward
and could be achieved by perfectly standard means; the decipherment process did not require any further new ideas.
然后就可以直接进行传输了，接收方可以通过非常标准的方式接收，而解码过程也不需要什么特殊技术。
Apart from the question of supplying a key-system
this was all that was required for the Delilah to effect an 'adding-on' encipherment of speech

the analogy of what agents like Muggeridge
or the machines which produced the Fish signals
or the Rockex
were all alike doing for telegraph or teleprinter.
If the key were truly 'random'
or without any discernible pattern
such a speech cipher system would be as secure as the Vernam one-time cipher for telegraph tape
and on exactly the same argument.
From the enemy's point of view
if all keys were equally probable
then all messages would be equally likely. There would be nothing to go on.
The disadvantage of the simple Delilah system
as pared with the X-system
was that its output signal would be one of bandwidth 2000 Hz
rather than a stream of digits
and that it would have to be municated perfectly
or all would be lost.
In particular
any variation in time delay
or distortion in amplitudes
would ruin the decipherment process.
Sender and receiver would have to keep in time to the microsecond for the same reason. This was why it could never be used for long-range short-wave transmissions.
But it could be used for local short-wave
for VHF and for telephone munication. For tactical or domestic purposes
therefore
it held considerable potential.