How do I unpack the x and y values from the BITSTRING in a DER ECDSA public key?
The first octet in a DER encoded BITSTRING is the number of unused bits (0 in this case). The remaining 65 octets are the elliptic curve point encoded as described in SEC 1 (http://www.secg.org/collateral/sec1_final.pdf) section 2.3.4. The first octet distinguishes the identity point and whether point compression is being used. Since you have 65=1+32+32 octets, this is an uncompressed point and the first octet should be 04, follows by the X and Y values encoded as described in section 2.3.6 (basically fixed length big endian).