RSA - Does knowledge of part of the ciphertext decrease encryption security for the rest of the ciphertext? There is a language called SystemVerilog that can be protected via encryption to allow sharing/licensing code for others to use, but prevents them from seeing the code contents. This is done based on the recommendations of IEEE 1735 (paywall) and through support through the Compiler/Simulation software. If the correct keys are used, the compiler/simulator is able to read the 'shared' IP, compile, and run the protected IP.

Within IEEE 1735, it recommends RSA >=2048 for Asymmetric encryption.

I can have some code, protected by this encryption scheme, that prints text out to a log file. If the text it prints out is static text, will I need to worry about the encryption security of my file?

module my_encrypted_module;
 initial begin
    $display ("This text will be printed to log file");
 end
endmodule



The encrypted file is 1000 characters long
500 characters is a text message that will be printed to the log when running
Does knowledge from seeing the resulting print message decrease the security of the other portions of this same file, allowing someone to more easily decrypt the file?


Thanks.
No known, modern cipher should be vulnerable against known plaintext attacks. Now just RSA 2048 is not likely to be used on all the text, and RSA encryption can be implemented in different ways, but it is unlikely to the extreme that the protocol is vulnerable against known plaintext attacks. It may of course well be vulnerable against other attacks, such as padding oracle attacks on PKCS#1 v1.5 padding, if that is used.

So you can create a string as large as you want and still be secure against known plaintext attacks, no matter how much of it is guessed or gets known otherwise.



Hah, and I looked up the standard after I wrote this answer and got this in return. It doesn't contain known plaintext attacks of course, that would be too easy. But it does use PKCS#1 v1.5 - which may be vulnerable and AES-CBC without authentication which is even more likely to be vulnerable (ugh).

The paper by the way has been "withdrawn for non scientific reasons" - probably to hide it under the carpet, but you can still download it if you know how to retrieve old internet content (deliberately not linked). Here is the security advisory that links to the missing paper.