Why do I get different RSA encrypted files between Ruby and command-line OpenSSL?

Question

I'm trying to test the interoperability of openssl when used in Ruby on one side, and on the command line on the other side.

I generated a RSA certificate and extracted its public key this way:

openssl req -x509 -nodes -days 1825 -newkey rsa:1024 -keyout mycert.pem -out mycert.pem
openssl rsa -in mycert.pem -pubout > mycert.pub

I wrote a Ruby script that does 2 things:

it encodes/decodes a test file with the public key first and then with the private key (using Base64 encoding on top of the RSA encoding to make network communication easier)
it runs system commands to encrypt the same test file with the openssl command line tool

You can find the code of this Ruby script in the following Gist: https://gist.github.com/dirtyhenry/4673331 (cf. the poc-openssl-rsa.rb file)

My question is: how come my Ruby-generated public-encrypted.txt file is different from the public-encrypted-cl64.txt? Is it caused by some file-system side effects? (ie. one is a string when the other is a file or something?)

Thanks.

Mick F · Accepted Answer · 2013-03-15 16:42:27Z

2

I've found out that the two are indeed interoperable. It's just that paddings bring some randomness which leads to the fact that 2 successive encodings will result in 2 different encoded data.

cf. http://en.wikipedia.org/wiki/RSA_%28algorithm%29#Padding_schemes :

practical RSA implementations typically embed some form of structured, randomized padding into the value m before encrypting it.

edited Mar 15, 2013 at 16:42

answered Mar 14, 2013 at 16:53

Mick F

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