[erlang-questions] Crypto and public_key usage....

[Peter W. Morreale]

On Thu, 2011-04-14 at 08:49 -0700, Seth Falcon wrote:
> Hi Peter,
> 
> On Thu, Apr 14, 2011 at 7:55 AM, Peter W. Morreale <pmorreale@REDACTED> wrote:
> > I'm attempting to use the crypto and public key modules to decrypt
> > an encrypted response I get in a server.
> >
> > I found this
> > http://erlang.2086793.n4.nabble.com/rsa-encryption-decryption-example-code-doesn-t-work-td2114965.html
> >
> > example on the web, however in my case, I already have the public key as
> > a string.
> 
> If your string represents an RSA public key in SubjectPublicKeyInfo
> PEM format and you are using the latest Erlang release, I think you
> can obtain the key record that you can use in the encrypt/decrpyt
> functions in the public_key module as follows:
> 
>     {ok, RSAPubPem} = file:read_file("rsa_pub.pem"),
>     PemEntries = public_key:pem_decode(RSAPubPem),
>     RSAPubKey = public_key:pem_entry_decode(hd(PemEntries)),
>     % now use RSAPubKey to decrypt/encrypt
> 

I *think* this is what I need.  I'm new to dealing with encryption from
a programmatic sense.  Almost as new as I am to Erlang. :-)

I will try and see how far I can get. 

This is for decrypting a SAML response obtained from a SAML IdP.  I have
the key from the IdP metadata.  

Thank you for this insight.

Best,
-PWM

 
> You will have a few more hoops to jump through for older versions of
> Erlang.  Here's one way:
> 
>     read_rsa_public_key(Key) ->
>         Bin = erlang:iolist_to_binary(public_key_lines(re:split(Key,
> "\n"), [])),
>         Spki = public_key:der_decode('SubjectPublicKeyInfo',
> base64:mime_decode(Bin)),
>         {_, _, {0, KeyDer}} = Spki,
>         public_key:der_decode('RSAPublicKey', KeyDer).
> 
>     public_key_lines([<<"-----BEGIN PUBLIC KEY-----">>|Rest], Acc) ->
>         public_key_lines(Rest, Acc);
>     public_key_lines([<<"-----END PUBLIC KEY-----">>|_Rest], Acc) ->
>         lists:reverse(Acc);
>     public_key_lines([Line|Rest], Acc) ->
>         public_key_lines(Rest, [Line|Acc]).
> 
> If this isn't what you are looking for, it would be helpful to provide
> more detail on the type of key you have and what you want to do with
> it.
> 
> + seth
> 
> 
>