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 P. 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 L. 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

yermej wrote:

On Dec 13, 9:24 am, Shandy N. [email protected] 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 Dec 13, 9:24 am, Shandy N. [email protected] 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)

On 12/13/07, Shandy N. [email protected] 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/