On Thu, Jan 24, 2013 at 05:25:48PM +0000, Tovey, Dwight (LaserJet R&D FW Eng.)
wrote:
> On Jan 23, 2013, at 4:18 PM, kap...@mizera.cz wrote:
>
> > I have build the whole pub-key (in DER) from yours pubkey.bin by adding
> > public key header - as wrote w...@omnigroup.com
> >
> > If I did not make error, it could work now - try it.
> > It is in attachment.
> >
> > openssl asn1parse -in pub-key.der -inform der -strparse 18
> >
> > and you will see the same as by parsing yours pubkey.bin.
> >
> > To see whole public key structure:
> > openssl asn1parse -in pub-key.der -inform der
> >
> > --kapetr
> >
>
> This worked. I translated the .der key into PEM format, which I was then
> able to load into my python script with M2Crypto.RSA.load_pub_key(). I could
> then use the resulting RSA_pub object to encrypt my data and send it to the
> device.
>
> So, my next question is, how did you add the public key header? What does
> this header look like? If I know that then I should be able to add it within
> my script and handle it all directly.
Here's a hex dump of a complete public key:
0000000 30 81 9f 30 0d 06 09 2a 86 48 86 f7 0d 01 01 01
0000020 05 00 03 81 8d 00 30 81 89 02 81 81 00 9a a7 8d
0000040 3f 46 10 6e 1c 5d 90 ac 43 e7 49 d7 ca 15 62 f3
0000060 0c d3 af 8b 28 74 c7 49 fe aa 3d 51 9c 7f 14 70
0000100 88 9f 94 24 29 33 6f e6 88 29 c0 57 35 d1 92 b3
0000120 4c de 48 79 8e 94 e0 d8 7a 16 94 57 57 35 ba 4f
0000140 de b7 44 37 c1 56 2e e3 41 14 54 9f b3 c5 9a a5
0000160 4a a9 8e 00 67 1c e2 35 ee cb f9 fc f0 53 d7 f8
0000200 1d 73 95 26 36 c1 1f c8 2c 29 3e 7f 36 e5 31 0a
0000220 8d 5b c9 aa 35 c5 21 28 51 80 ba e8 9b 02 03 01
0000240 00 01
This is an ASN.1 structure:
0:d=0 hl=3 l= 159 cons: SEQUENCE
3:d=1 hl=2 l= 13 cons: SEQUENCE
5:d=2 hl=2 l= 9 prim: OBJECT :rsaEncryption
16:d=2 hl=2 l= 0 prim: NULL
18:d=1 hl=3 l= 141 prim: BIT STRING
The tag "30" means "SEQUENCE". The bytes "81 9f" encode the sequence
length, in this case 144 + 15 = 159 bytes (excluding the tag and the
length).
The first element of the sequece is also a sequence which encodes
the algorithm and parameters (RSA and no parameters). This sequence
is of length 0d == 13. Its first element (tag == 06 == Object ID)
is an OID of length 9:
2a 86 48 86 f7 0d 01 01 01
which decodes to:
1.2.840.113549.1.1.1 RSA Encryption
What followis is a tag of 05 (NULL) with a length of 0.
Finally, the key is encoded as a BITSTRING: (type == 03) (length
== 81 8d = 128 + 13 = 141). Since the bit string's length is a
multiple of 8, the firstr octet encodes 0 padding bits, the remaining
octets are the ASN.1 sequence encoding a sequence of the modulus
and exponent, which is the public key you started with.
--
Viktor.
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