Extracting modulus and exponent from public key using Openssl and C++

Question

So I'm currently studying how networking works. I've got a bunch of packets from wireshark which I have already copied in buffers(only the content, without header. Wireshark->Follow TPC Stream->C arrays). I can understand the protocol but in the 3rd packet it requires a key exchange. After some googling I found that I need RSA encryption. It sends me a public key + token. And I shoud return encrypted shared key(just generated) and encrypted token which I received earlier.

RSA_key needs exponent and modulus, So my question is: How can I create RSA_key object from single char[] buffer(the public key).

NOTE:I'm posting here after long time googling. I may not be using the right keywords because I'm not english speaker. I could find threads asking this with php only. The most useful (I think) link I found is http://www.techper.net/2012/06/01/converting-rsa-public-key-modulus-and-exponent-into-pem-file/

Thanks.

PS I'm sniffing minecraft and simulating client side(I choosed it because its popular game and I knew I will find resources on the web if I get stuck). However my question is exacly how to get modulus and exponent from a public key with format: http://pastebin.com/J9ddhgW5 (thats the bytes representing the public key)

Ohh I forgot, first column is the byte position, second column is the byte value typecasted to int, 3th column is again value but (int)(unsigned char) so I can see if its +127, 4th colums is the hex representation of the value and the last column is character based on ascii table(if its visible character).

Answer 1

The data you posted is an ASN.1 encoded (DER) RSA public key:

$ openssl ssl rsa -inform der -pubin -text < 12120862.key 
Public-Key: (1024 bit)
Modulus:
    00:81:1f:1d:00:7e:d0:c7:e2:2f:31:3d:0d:f0:a8:
    ab:c1:ea:66:ba:af:1d:a4:eb:b3:fd:51:58:1c:1d:
    81:ae:f0:99:9e:5c:26:67:b5:41:14:28:79:c0:29:
    e5:56:96:06:b7:4b:a0:c9:7f:41:46:9a:7e:85:10:
    a0:91:ea:58:bd:78:78:6d:3c:07:2a:3d:61:f3:ed:
    42:8b:1e:dc:6d:2d:21:41:7a:e8:15:51:0d:75:84:
    be:20:8c:76:43:8b:4b:67:6b:49:09:e9:20:a1:11:
    53:a0:d9:30:b1:c2:27:a6:09:e1:56:36:ed:7e:9b:
    23:e2:df:5b:bd:c5:66:ca:c5
Exponent: 65537 (0x10001)
writing RSA key
-----BEGIN PUBLIC KEY-----
MIGfMA0GCSqGSIb3DQEBAQUAA4GNADCBiQKBgQCBHx0AftDH4i8xPQ3wqKvB6ma6
rx2k67P9UVgcHYGu8JmeXCZntUEUKHnAKeVWlga3S6DJf0FGmn6FEKCR6li9eHht
PAcqPWHz7UKLHtxtLSFBeugVUQ11hL4gjHZDi0tna0kJ6SChEVOg2TCxwiemCeFW
Nu1+myPi31u9xWbKxQIDAQAB
-----END PUBLIC KEY-----

In OpenSSL, you can use the d2i_RSA_PUBKEY function to get a public key from an ASN.1-encoded file (like this one).