Forum: Ruby Help with OpenSSL RSA

Hi,
I'm writing a little code to do some RSA stuff and I need to extract the
public exponent and modulus for passing to a browser that will use them
in Javascript.

I've done considerable digging but have drawn a blank as I can't find
any complete documentation of the full RSA class definition.

What I am trying right now is to do:

key = RSA.new(1024)
private_key = key.to_pem
public_modulus = key.public_key.n
public_exponent = key.public_key.e

This generates a new key and assigns the private key to a variable. I'd
like to get the public exponent and modulus returned as a hex encoded
string, similar to the output of "openssl rsa -noout -modulus"

However, I can't find suitable documentation so I don't know what method
(if any) I can use. I'd hoped for "key.public_key.n.to_h" but that does
not seem to work.

So, If anyone can give advice I'd appreciate it!

Also, A general question: how do I look up class definitions of
"standard" classes that are not documented in RDoc? Is there something
similar to a C header file? (sorry, I'm quite new to Ruby).

Many thanks for your help.

On Wed, Aug 08, 2007 at 07:05:22AM +0900, Starfry Starfry wrote:
> key = RSA.new(1024)
> not seem to work.
How about Base64 ecoding?

  [key.public_key.n.to_s].pack('m')

Aaron Patterson wrote:
> On Wed, Aug 08, 2007 at 07:05:22AM +0900, Starfry Starfry wrote:
>> key = RSA.new(1024)
>> not seem to work.
> How about Base64 ecoding?
> 
>   [key.public_key.n.to_s].pack('m')

I could not get pack to work as you described. My code is below. I have 
taken a different tack, to get my Javaption side to work with the 
modulus and exponent in decimal.

def generate_keys
    unless session[:private_key]
      k = RSA.new(128)
      session[:private_key]     = k.to_pem
      session[:public_modulus]  = k.public_key.n.to_s
      session[:public_exponent] = k.public_key.e.to_s

    end
    @private_key     = session[:private_key]
    @public_modulus  = session[:public_modulus]
    @public_exponent = session[:public_exponent]
end

I'd still like to be able to get this out of Ruby in Hex

If only I could find out the available methods in the RSA class (as I 
said before the RDoc does not include anything about this class).

Thanks!

John Lane wrote:
> def generate_keys
>     unless session[:private_key]
>       k = RSA.new(128)
>       session[:private_key]     = k.to_pem
>       session[:public_modulus]  = k.public_key.n.to_s
>       session[:public_exponent] = k.public_key.e.to_s
> 
>     end
>     @private_key     = session[:private_key]
>     @public_modulus  = session[:public_modulus]
>     @public_exponent = session[:public_exponent]
> end
> 
> I'd still like to be able to get this out of Ruby in Hex
> 
> If only I could find out the available methods in the RSA class (as I 
> said before the RDoc does not include anything about this class).
> 
> Thanks!

Did this ever get resolved? This is the exact problem that I am trying 
to solve. Thanks,

-S

On Dec 13, 9:24 am, Shandy Nantz <shandyb...@yahoo.com> wrote:
> >     @public_modulus  = session[:public_modulus]
> Did this ever get resolved? This is the exact problem that I am trying
> to solve. Thanks,
>
> -S
> --
> Posted viahttp://www.ruby-forum.com/.

This seems to work if you want it as a hex string:

key = OpenSSL::PKey::RSA.new(1024)
private_key = key.to_pem
public_modulus = key.public_key.n.to_s(16)
public_exponent = key.public_key.e.to_s(16)

yermej wrote:
> On Dec 13, 9:24 am, Shandy Nantz <shandyb...@yahoo.com> wrote:
>> >     @public_modulus  = session[:public_modulus]
>> Did this ever get resolved? This is the exact problem that I am trying
>> to solve. Thanks,
>>
>> -S
>> --
>> Posted viahttp://www.ruby-forum.com/.
> 
> This seems to work if you want it as a hex string:
> 
> key = OpenSSL::PKey::RSA.new(1024)
> private_key = key.to_pem
> public_modulus = key.public_key.n.to_s(16)
> public_exponent = key.public_key.e.to_s(16)

This does work thank you. Does anyone know how to get at all the parts 
that make up a public key such as the inverse? Thanks

On 12/13/07, Shandy Nantz <shandybleu@yahoo.com> wrote:
> > This seems to work if you want it as a hex string:
> >
> > key = OpenSSL::PKey::RSA.new(1024)
> > private_key = key.to_pem
> > public_modulus = key.public_key.n.to_s(16)
> > public_exponent = key.public_key.e.to_s(16)
>
> This does work thank you. Does anyone know how to get at all the parts
> that make up a public key such as the inverse? Thanks

I'm pretty sure that you can't extract the inverse from a public key.

The whole point of a public/private key pair is that it's extremely
difficult to compute the private key from the public key.


--
Rick DeNatale

My blog on Ruby
http://talklikeaduck.denhaven2.com/