Thread Subject:

video encryption

I want to encrypt MPEG video,so i need encryption code.

On 10-12-03 01:55 AM, Sheraz ahmad wrote:
> I want to encrypt MPEG video,so i need encryption code.

Supposing I is the 2D image and it is in uint8 format, then:

encryption_key = 'Now is the time for the proles to rise up and seize the
means of chocolate production!'

encrypting_bytes = ...
encryption_key(1 + mod(1:length(numel(I)),length(encryption_key));

encrypted_I = bitxor(I, encrypting_bytes');


To decrypt, pass the encrypted data through exactly the same routine.

Walter Roberson <roberson@hushmail.com> wrote in message <idbk16$t7d$1@canopus.cc.umanitoba.ca>...
> On 10-12-03 01:55 AM, Sheraz ahmad wrote:
> > I want to encrypt MPEG video,so i need encryption code.
>
> Supposing I is the 2D image and it is in uint8 format, then:
>
> encryption_key = 'Now is the time for the proles to rise up and seize the
> means of chocolate production!'
>
> encrypting_bytes = ...
> encryption_key(1 + mod(1:length(numel(I)),length(encryption_key));
>
> encrypted_I = bitxor(I, encrypting_bytes');
>
>
> To decrypt, pass the encrypted data through exactly the same routine.

i have a question, when i run the code, Matlab notifies:
??? Error using ==> bitxor
Operands to BIT Ops must be numeric.
what's the problem and how to fix it ???

On 06/12/10 12:45 AM, Thanh wrote:
> Walter Roberson <roberson@hushmail.com> wrote in message
> <idbk16$t7d$1@canopus.cc.umanitoba.ca>...
>> On 10-12-03 01:55 AM, Sheraz ahmad wrote:
>> > I want to encrypt MPEG video,so i need encryption code.
>>
>> Supposing I is the 2D image and it is in uint8 format, then:
>>
>> encryption_key = 'Now is the time for the proles to rise up and seize
>> the means of chocolate production!'
>>
>> encrypting_bytes = ...
>> encryption_key(1 + mod(1:length(numel(I)),length(encryption_key));
>>
>> encrypted_I = bitxor(I, encrypting_bytes');
>>
>>
>> To decrypt, pass the encrypted data through exactly the same routine.
>
> i have a question, when i run the code, Matlab notifies:
> ??? Error using ==> bitxor
> Operands to BIT Ops must be numeric.
> what's the problem and how to fix it ???

Sorry, I had some typos there and missed a step.

encryption_key = 'Now is the time for the proles to rise up and seize
the means of chocolate production!';

encrypting_bytes = ...
reshape(uint8(encryption_key(1+mod(0:numel(I)-1,length(encryption_key)))),size(I));

encrypted_I = bitxor(I, encrypting_bytes);

Walter Roberson <roberson@hushmail.com> wrote in message <h80Lo.34$zh.0@newsfe13.iad>...
> On 06/12/10 12:45 AM, Thanh wrote:
> > Walter Roberson <roberson@hushmail.com> wrote in message
> > <idbk16$t7d$1@canopus.cc.umanitoba.ca>...
> >> On 10-12-03 01:55 AM, Sheraz ahmad wrote:
> >> > I want to encrypt MPEG video,so i need encryption code.
> >>
> >> Supposing I is the 2D image and it is in uint8 format, then:
> >>
> >> encryption_key = 'Now is the time for the proles to rise up and seize
> >> the means of chocolate production!'
> >>
> >> encrypting_bytes = ...
> >> encryption_key(1 + mod(1:length(numel(I)),length(encryption_key));
> >>
> >> encrypted_I = bitxor(I, encrypting_bytes');
> >>
> >>
> >> To decrypt, pass the encrypted data through exactly the same routine.
> >
> > i have a question, when i run the code, Matlab notifies:
> > ??? Error using ==> bitxor
> > Operands to BIT Ops must be numeric.
> > what's the problem and how to fix it ???
>
> Sorry, I had some typos there and missed a step.
>
> encryption_key = 'Now is the time for the proles to rise up and seize
> the means of chocolate production!';
>
> encrypting_bytes = ...
> reshape(uint8(encryption_key(1+mod(0:numel(I)-1,length(encryption_key)))),size(I));
>
> encrypted_I = bitxor(I, encrypting_bytes);
>
That's alright. Thank you a lot, i've already run this code. But please explain for me what's the purpose of the function " reshape" ?

On 06/12/10 1:48 AM, Thanh wrote:
> Walter Roberson <roberson@hushmail.com> wrote in message

>> encrypting_bytes = ...
>> reshape(uint8(encryption_key(1+mod(0:numel(I)-1,length(encryption_key)))),size(I));

> explain for me what's the purpose of the function " reshape" ?

0:numel(I)-1 is a vector of values, and the mod() and matrix lookup and
uint8() steps applied keep that form as a vector of values. However, for
the bitxor() to work against the entire image, the second argument for
bitxor needs to be a matrix the same dimensions as the first -- the same
number of rows, columns, and color channels. reshape() takes the vector
of input and reorganizes it as a matrix of appropriate size.

For information as to where the various parts of the vector end up in
the reshaped matrix, please read the documentation about reshape and
about how arrays are stored.

Walter Roberson <roberson@hushmail.com> wrote in message <wa1Lo.6457$3D2.5368@newsfe20.iad>...
> On 06/12/10 1:48 AM, Thanh wrote:
> > Walter Roberson <roberson@hushmail.com> wrote in message
>
> >> encrypting_bytes = ...
> >> reshape(uint8(encryption_key(1+mod(0:numel(I)-1,length(encryption_key)))),size(I));
>
> > explain for me what's the purpose of the function " reshape" ?
>
> 0:numel(I)-1 is a vector of values, and the mod() and matrix lookup and
> uint8() steps applied keep that form as a vector of values. However, for
> the bitxor() to work against the entire image, the second argument for
> bitxor needs to be a matrix the same dimensions as the first -- the same
> number of rows, columns, and color channels. reshape() takes the vector
> of input and reorganizes it as a matrix of appropriate size.
>
> For information as to where the various parts of the vector end up in
> the reshaped matrix, please read the documentation about reshape and
> about how arrays are stored.

thank you a lot , your answer is very helpful.

"Thanh" wrote in message <idk81h$1sh$1@fred.mathworks.com>...
> Walter Roberson <roberson@hushmail.com> wrote in message <wa1Lo.6457$3D2.5368@newsfe20.iad>...
> > On 06/12/10 1:48 AM, Thanh wrote:
> > > Walter Roberson <roberson@hushmail.com> wrote in message
> >
> > >> encrypting_bytes = ...
> > >> reshape(uint8(encryption_key(1+mod(0:numel(I)-1,length(encryption_key)))),size(I));
> >
> > > explain for me what's the purpose of the function " reshape" ?
> >
> > 0:numel(I)-1 is a vector of values, and the mod() and matrix lookup and
> > uint8() steps applied keep that form as a vector of values. However, for
> > the bitxor() to work against the entire image, the second argument for
> > bitxor needs to be a matrix the same dimensions as the first -- the same
> > number of rows, columns, and color channels. reshape() takes the vector
> > of input and reorganizes it as a matrix of appropriate size.
> >
> > For information as to where the various parts of the vector end up in
> > the reshaped matrix, please read the documentation about reshape and
> > about how arrays are stored.
>
> thank you a lot , your answer is very helpful.





Can you give me please the matlab encryption source code, cause i have to make an encryption for a video file... thanks a lot...

Florin

"Florin " <just_flow87@yahoo.com> wrote in message
news:jrioej$72b$1@newscl01ah.mathworks.com...

*snip*

> Can you give me please the matlab encryption source code, cause i have to
> make an encryption for a video file... thanks a lot...

No for several reasons including:

http://en.wikipedia.org/wiki/Export_of_cryptography_in_the_United_States

--
Steve Lord
slord@mathworks.com
To contact Technical Support use the Contact Us link on
http://www.mathworks.com