Help with OpenSSL RSA

ruby-talk
1

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.

···

--
Posted via http://www.ruby-forum.com/.

2

How about Base64 ecoding?

  [key.public_key.n.to_s].pack('m')

···

On Wed, Aug 08, 2007 at 07:05:22AM +0900, Starfry Starfry wrote:

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.

--
Aaron Patterson
http://tenderlovemaking.com/

3

Aaron Patterson 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!

···

On Wed, Aug 08, 2007 at 07:05:22AM +0900, Starfry Starfry wrote:

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4

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

···

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Posted via http://www.ruby-forum.com/\.

5

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)

···

On Dec 13, 9:24 am, Shandy Nantz <shandyb...@yahoo.com> wrote:

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
--
Posted viahttp://www.ruby-forum.com/.

6

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

--
Posted via http://www.ruby-forum.com/\.

7

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.

···

On 12/13/07, Shandy Nantz <shandybleu@yahoo.com> wrote:

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

--
Rick DeNatale

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