client checksum algorithm :(

http://s005.radikal.ru/i212/1010/0b/9c26a14bacf1t.jpg


0x07, // opcode
0xe4, 0x78, 0x86, 0x5f, //session id
0x00, 0x00, 0x00, 0x00, // data1 (not use)
0x00, 0x00, 0x00, 0x00, // data2 (not use)
0x00, 0x00, 0x00, 0x00, // data3 (not use)
0x00, 0x00, 0x00, 0x00, // data4 (not use)
0x7C, // what is it?
0x90, 0x1C, 0x58, 0x98, 0xE8, 0x9A,// what is it?
0x00, 0x00, 0x00, 0x00 // checksum

hello2all.
Help please, who knows.
What is 0x7c and how i can calculate this bytes: 0x90 0x1C 0x58 0x98 0xE8 0x9A
Sorry for my bad english (use PROMT _http://translate.ru)