Re: Convert::ASN1: RSA Public Keys

[Lars U. <la...@kn...>]

On Mon, Feb 24, 2003 at 07:22:34AM +0000, Chris Ridd wrote:
> On 23/2/03 9:20 pm, Lars Uffmann <la...@kn...> wrote:

Hello Chris,

thanks for your help. The following ASN1 worked:

AlgorithmIdentifier ::= SEQUENCE {
  algorithm OBJECT IDENTIFIER,
  parameters ANY
}
SubjectPublicKeyInfo ::= SEQUENCE  {
  algorithm AlgorithmIdentifier,
  subjectPublicKey BIT STRING
}
-- from ftp://ftp.rsasecurity.com/pub/pkcs/pkcs-1/pkcs-1v2.asn
RSAPublicKey ::= SEQUENCE {
   modulus          INTEGER,  -- (Usually large) n = p*q
   publicExponent   INTEGER  -- (Usually small) e
}

I attached an updated version of my script, this one only decodes the
publick key in DER, but support for Convert::PEM schould be trivial.

> I don't think the ASN.1 of the public key looks like that. Using dumpasn1
> (grab from http://www.cs.auckland.ac.nz/~pgut001/) on the public.der file I
> get something like:
> 
>    0   92: SEQUENCE {
>    2   13:   SEQUENCE {
>    4    9:     OBJECT IDENTIFIER '1 2 840 113549 1 1 1'
>   15    0:     NULL
>          :     }
>   17   75:   BIT STRING, encapsulates {
>   20   72:     SEQUENCE {
>   22   65:       INTEGER
>          :         00 B9 79 14 11 64 33 67 A2 2D 8F 7A E0 F4 DD BD
>          :         1E 4E 3F 88 73 19 A5 FD D2 24 17 4F 0C 68 D8 52
>          :         A2 EA BB B5 00 ED 32 1A AF AA C2 B8 A1 97 1D 6D
>          :         99 4E C5 58 80 CE 8D 6A AC 7E 9C 6F D4 B5 49 E4
>          :         71
>   89    3:       INTEGER 65537
>          :       }
>          :     }
>          :   }
> 
> In other words there's some extra wrapper, and your encoded public key SEQ
> is actually inside a BIT STRING.
> 
> I'd be inclined to try telling Convert::ASN1 that the BIT STRING is actually
> a [UNIVERSAL 3 IMPLICIT] OCTET STRING so you can get the raw bytes of the
> bit string out, and then do a second parse using your original ASN.1 on that
> octet string.

Actually BIT STRING worked fine.

> But you can't have too many ASN.1 decoders as far as I'm concerned ;-)

I'll try dumpasn1, seems to be _really_ usefull.

regards,
	Lars