How can I obtain the exponent and modulus from a PEM

Question

In order to perform asymmetric encryption Common's Lisp Ironclad library requires the key to be initialized with the exponent and modulus. Given that I probably don't want to generate the keys myself, so standing on the shoulder of the giants of OpenSSL for key generation I do

ssh-keygen -t rsa -C "foo@bar.com"

Inspecting the fils generated file I see it is a in the PEM format.

file ~/.id_rsa
=> ~/.ssh/id_rsa: PEM RSA private key

Following some other SO questions I get this

openssl asn1parse -i -in ~/.ssh/id_rsa
    0:d=0  hl=4 l=1187 cons: SEQUENCE          
    4:d=1  hl=2 l=   1 prim:  INTEGER           :00
    7:d=1  hl=4 l= 257 prim:  INTEGER           :BBFB9E...
  268:d=1  hl=2 l=   3 prim:  INTEGER           :010001
  273:d=1  hl=4 l= 256 prim:  INTEGER           :769BE9...
  533:d=1  hl=3 l= 129 prim:  INTEGER           :ECCB14004...
  665:d=1  hl=3 l= 129 prim:  INTEGER           :CB3B02...
  797:d=1  hl=3 l= 128 prim:  INTEGER           :78054EF...
  928:d=1  hl=3 l= 128 prim:  INTEGER           :0D474BC43....
 1059:d=1  hl=3 l= 129 prim:  INTEGER           :D71D75FF....

Now from there some posts say do add the option -strparse 19 (others 18) to get the exponent and modulus. That is where I get an error in the following lines:

openssl asn1parse -i -in ~/.ssh/id_rsa -strparse 19
Error parsing structure
140334635108032:error:0D07209B:asn1 encoding routines:ASN1_get_object:too long:asn1_lib.c:142:
140334635108032:error:0D068066:asn1 encoding routines:ASN1_CHECK_TLEN:bad object header:tasn_dec.c:1306:
140334635108032:error:0D06A03A:asn1 encoding routines:ASN1_COLLECT:nested asn1 error:tasn_dec.c:1190:

So it may be that the PEM is not in an asn1parse format. I've also tried with -inform DER. So the question is how do I go from generating a key to obtaining the modulus and exponent from the PEM Certificate.

Answer 1

Maybe this works?

% openssl rsa -text -noout < id_rsa
Private-Key: (2048 bit)
modulus:
00:ad:03: ...
...
publicExponent: 35 (0x23)
privateExponent:
94:12:aa: ...