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creating byte[] with subfields

 
 
Arne Vajh°j
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      01-19-2013
On 1/18/2013 6:16 PM, Daniel Pitts wrote:
> FWIW, XOR encryption is more like XOR obfuscation. It doesn't actually
> encrypt, at least not the naive approach to it.


Not today. 200 years ago it would (1 byte XOR is really
a special case of 1 replacement alphabet and N byte XOR
of N replacements alphabets).

Arne


 
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Daniel Pitts
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      01-20-2013
On 1/18/13 11:24 PM, Roedy Green wrote:
> On Fri, 18 Jan 2013 15:16:45 -0800, Daniel Pitts
> <(E-Mail Removed)> wrote, quoted or indirectly
> quoted someone who said :
>
>> FWIW, XOR encryption is more like XOR obfuscation. It doesn't actually
>> encrypt, at least not the naive approach to it.

>
> It depends. I just finished a project which I will be permitted to
> release into the public domain in a year which uses one time pads,
> which XOR messages with strings of truly random bits.
>
> The only way you can crack it is to crack the machine at either end or
> intercept the key transfer. You can't do it just by studying
> messages.
>

It really does depend.

If the plain-text are formed poorly (eg. plain ascii text, or contains
any well known substrings), and the key is sufficiently small (needs to
be repeated several times) one could easily figure out the key, or at
least part of it. That could be enough to turn it into a simple word
game, which will eventually reveal the entire plain-text.


 
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Joshua Cranmer
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      01-20-2013
On 1/19/2013 11:46 PM, Daniel Pitts wrote:
> On 1/18/13 11:24 PM, Roedy Green wrote:
>> On Fri, 18 Jan 2013 15:16:45 -0800, Daniel Pitts
>> <(E-Mail Removed)> wrote, quoted or indirectly
>> quoted someone who said :
>>
>>> FWIW, XOR encryption is more like XOR obfuscation. It doesn't actually
>>> encrypt, at least not the naive approach to it.

>>
>> It depends. I just finished a project which I will be permitted to
>> release into the public domain in a year which uses one time pads,
>> which XOR messages with strings of truly random bits.
>>
>> The only way you can crack it is to crack the machine at either end or
>> intercept the key transfer. You can't do it just by studying
>> messages.
>>

> It really does depend.


No, it doesn't. A one-time pad is provably 100% perfectly secure, and is
the only cryptographic method to be so proven. The requirements is that
you have a string of random bits as long as the message you send and you
never reuse those random bits ever again.

--
Beware of bugs in the above code; I have only proved it correct, not
tried it. -- Donald E. Knuth
 
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Arne Vajh°j
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      01-20-2013
On 1/20/2013 12:46 AM, Daniel Pitts wrote:
> On 1/18/13 11:24 PM, Roedy Green wrote:
>> On Fri, 18 Jan 2013 15:16:45 -0800, Daniel Pitts
>> <(E-Mail Removed)> wrote, quoted or indirectly
>> quoted someone who said :
>>
>>> FWIW, XOR encryption is more like XOR obfuscation. It doesn't actually
>>> encrypt, at least not the naive approach to it.

>>
>> It depends. I just finished a project which I will be permitted to
>> release into the public domain in a year which uses one time pads,
>> which XOR messages with strings of truly random bits.
>>
>> The only way you can crack it is to crack the machine at either end or
>> intercept the key transfer. You can't do it just by studying
>> messages.
>>

> It really does depend.
>
> If the plain-text are formed poorly (eg. plain ascii text, or contains
> any well known substrings), and the key is sufficiently small (needs to
> be repeated several times)


A one time pad by definition has a key size equal to message
size so the key does not repeat.

Arne

 
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Arne Vajh├Şj
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      01-20-2013
On 1/20/2013 12:01 PM, Joshua Cranmer wrote:
> On 1/19/2013 11:46 PM, Daniel Pitts wrote:
>> On 1/18/13 11:24 PM, Roedy Green wrote:
>>> On Fri, 18 Jan 2013 15:16:45 -0800, Daniel Pitts
>>> <(E-Mail Removed)> wrote, quoted or indirectly
>>> quoted someone who said :
>>>
>>>> FWIW, XOR encryption is more like XOR obfuscation. It doesn't actually
>>>> encrypt, at least not the naive approach to it.
>>>
>>> It depends. I just finished a project which I will be permitted to
>>> release into the public domain in a year which uses one time pads,
>>> which XOR messages with strings of truly random bits.
>>>
>>> The only way you can crack it is to crack the machine at either end or
>>> intercept the key transfer. You can't do it just by studying
>>> messages.
>>>

>> It really does depend.

>
> No, it doesn't. A one-time pad is provably 100% perfectly secure, and is
> the only cryptographic method to be so proven. The requirements is that
> you have a string of random bits as long as the message you send and you
> never reuse those random bits ever again.


And there is a good reason why it is not called two times pad.

In the late forties the Russians had a shortage of one time pads
and started using twice - once for military stuff and one for
civilian stuff. In the sixties the British and Americans discovered
that and started cracking it.

Arne


 
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