Decrypt file using original unecrypted file

[Shadow Walker]

Hi guys I'm new to all of this and was needing the help of some one that knows what they where doing...

I have the Encrypted File and the original file before it was encrypted..

Is there a way that i could use the original file to find the key needed to decrypt the other file... some how i lost all key files..


Thanks for your help

[Disch]

Just one pair of files?

Then no, it's not possible*. Not without knowing the method of encryption (or is that something you know?)

_{* brute force is always an option, so I suppose it is possible in the strictest sense of the word}

EDIT: To further clarify...

There are 4 parts to the puzzle:
- original file
- method of encryption
- key
- encrypted file

Generally speaking.... with any 3 parts and enough work, you can create the 4th part (except for the method of encryption, as there could be multiple different methods that produce the same encrypted file with the same key).

If you're talking about something like a .zip file or something, where the encryption method is well known and docuemented... then yes this is certainly possible. But if you have no idea how the file is encrypted (and you can't find out), then the only way to break the password is by brute force.

Anyway -- I don't suppose you could be more specific about your situation. Like what kind of file is this?

[smilodon]

I am going to assume that XOR encryption was used. If that is the case then xor the unencrypted file and the encrypted file, then looking for a pattern.

[Shadow Walker]

Thanks guys for jumping and helping out like that....

This is my worst headache i have had yet...

the files used are MIF files taken off of Linux mobile efs file system.. they get encrypted automatically and i have the original files.. I can get as many as are needed...

the encryption method used is RSA 1024

the key is what i need so i can decrypted BIN file that contains full efs files..

If any one is up for it then please let me know ... My brian just isn't smart enough for this... but I would love to learn methods ...


Thanks again guys...

I'm great full of any help that you can give..

[Disch]

Well I did a little bit of searching and didn't find anything that screamed "this is the solution!"

I came across this link though, which seems to explain the encryption algorithm:
http://www.di-mgt.com.au/rsa_alg.html

And it had a link near the bottom that mentioned C source to an example application:
http://www.di-mgt.com.au/bigdigits.html

As for writing a program to find the password... good luck. It doesn't look like it will be easy unless you're very familiar with the algorithm -- which I am not. Maybe someone has done it already and you can find such a program by searching (though I wasn't able to). Or perhaps you're just SOL. It doesn't look like there's a simple solution.

[Shadow Walker]

Yea i know if i have to do the programing/decrypting that i will be SOL...

that's just not in my bag of tricks ...

Thanks for information... anything is better then nothing...

Maybe someone that likes a challenge and would like to take on something like this that has the skills needed.. could jump on in and help... this i know is alot to ask for but i know this is the only way i will ever get the key..

Disch again thanks for your help..


Best Regards

[Shadow Walker]

I have a question ... could some one explain this for me..

<LIMITS>
<MAXCHAINDEPTH>2</MAXCHAINDEPTH>
<MAXLICENSESIZE>10240</MAXLICENSESIZE>
<MAXHEADERSIZE>5120</MAXHEADERSIZE>
</LIMITS><PUBLICKEY>5l8NH83CsSpIx6g42Aiq5CYmBVqQ5afb5uEh+4+3Ms3oNyfx2dCLBw==</PUBLICKEY></DATA><MSDRM_SIGNATURE_VALUE>K6RpC6FgEWVKWaN7ODEU7Pe/CUnoc1UE4qZpa9Cs43mA+v6bIQGdVw==</MSDRM_SIGNATURE_VALUE></CERTIFICATE><CERTIFICATE type="AUTHORIZATION"><DATA><SECURITYLEVEL>2000</SECURITYLEVEL><AUTH_ID>2485</AUTH_ID><PUBLICKEY>IV846jMJkAXXrcyi6OmgqjOGT1+P8Rt+cVqP7niXtjqcWdpFej6VIw==</PUBLICKEY></DATA><MSDRM_SIGNATURE_VALUE>vKHerGT1757WdirVUBeRn2QL6SyO6iYyAsQou51CO4lqWYQsIRRiRw==</MSDRM_SIGNATURE_VALUE></CERTIFICATE><CERTIFICATE type="AUTHORIZATION_ROOT"><DATA><AUTH_ID>1</AUTH_ID><PUBLICKEY>a1t3hxrg!qbOgktnbYaEEi4teCse!gz6RvTPuC!zizKJlpU7xoduSw==</PUBLICKEY></DATA><MSDRM_SIGNATURE_VALUE>4J5cuXn+vCeD+4ZDlRT95tO5N1QqtJkteQDrXLrWLRFE7+D+05DKaw==</MSDRM_SIGNATURE_VALUE></CERTIFICATE></DEVCERT>


any info would be great... I am having to do this blind


Thanks

best regards