Ruby OpenSSL - RSA Public Key from modulus and exponent

November 2nd, 2007
Posted by Rodney Carvalho
Filed in:
RSA encryption rsa encryption

I am writing some code to verify an RSA signature in ruby. I have the public key in the form of an exponent and modulus. Now, the trick is for me to generate the RSA public key from those values. I haven't found any documentation on this, but have discovered the answer by playing with ruby's OpenSSL library.

Here's the code:


key = OpenSSL::PKey::RSA.new
exponent = OpenSSL::BN.new '65537'
modulus = OpenSSL::BN.new '112864421120687974159372000080760039219116461925481276352886367473487891241213943153420378504937603763046030555516582638386721662553157906521599209028584201997048923805195002300818977900203259289042008628478507712149599372498945513622899023530831288613948081523445790489877779793487480652356150164543518882963'
key.e = exponent
key.n = modulus
key

Now key is initialized with the modulus and exponent values. You can now use the public key to verify the signature.

openssl RSA signature example

October 12th, 2007
Posted by David Lowenfels
Filed in:
RSA encryption

So it seems that the openssl library is totally undocumented?? Here is an example we cooked up to demonstrate how to verify an RSA signature.



>> require 'openssl'
=> false
>> private_key = OpenSSL::PKey::RSA.new(1024)
=> -----BEGIN RSA PRIVATE KEY-----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-----END RSA PRIVATE KEY-----

>> public_key = private_key.public_key
=> -----BEGIN RSA PUBLIC KEY-----
MIGJAoGBAM74eXzeQkvmpeISkAxHX57UlHGkQoGswm7vA40SB74uMzuy+5KhJZ/v
546kj4Wvohs04uxfzH9mx1bAaOpIiNax0K886Oh0iLlIAP1Q2m3pxR4Ww3w9Bieb
L3yN2gb0HAWmYzENYpNXN+3eq8pMIwX9vQT/cQs5TvxuVmn9yDvRAgMBAAE=
-----END RSA PUBLIC KEY-----

>> XML = "abcdefg" 
=> "abcdefg" 
>> sig = private_key.sign( OpenSSL::Digest::SHA1.new, XML )
=> "Q=W\3637\275\2340\250\306k>\320\335\275\252\242\3374\364d\021U\315\273\373\322\351\347\211'\344\b\270\a\207(\216\035\b\021\200|&,Sn|\323}4\327@\343a\263Yj\227\311-&\210\245K\350*\316B'\275-\352\377\366\001]q\346F\240\211\246E\313\340\025p3\331\235w\247\351E\026N~\272\371\025&\2208\270c\252>_\246\345\272\237\226u\301\273\212J\341\213%\343\255%\b\372\245" 
>> public_key.verify( OpenSSL::Digest::SHA1.new, sig, XML )
=> true
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