In case of faiplay audio(airplay audio from mac itunes) that can not decrypt correct AESkey.

[chenhui-cvte]

In case of faiplay audio(airplay audio from mac itunes) that can not decrypt correct key.

there is the fairplay data for decrypt.

fpaeskey(decoded)=
{ 0x46, 0x50, 0x4c, 0x59, 0x01, 0x02, 0x01, 0x00, 0x00, 0x00,
0x00, 0x3c, 0x00, 0x00, 0x00, 0x00, 0xea, 0xf3, 0xe0, 0x79,
0x09, 0xb6, 0x45, 0xa2, 0x7e, 0x3f, 0x69, 0x68, 0x81, 0x30,
0x5e, 0x9c, 0x00, 0x00, 0x00, 0x10, 0xc7, 0x77, 0xac, 0x4c,
0x5d, 0x0b, 0x82, 0xe0, 0xd1, 0x44, 0x2f, 0x15, 0xc6, 0xff,
0x43, 0xd4, 0xb9, 0x41, 0xd0, 0x6a, 0xa1, 0xe3, 0x68, 0xe5,
0x27, 0x21, 0xbc, 0x79, 0x0b, 0x25, 0xee, 0xd1, 0xa5, 0x07,
0xb4, 0x8f }

challenge data=
{ 0x46, 0x50, 0x4c, 0x59, 0x02, 0x01, 0x01, 0x00, 0x00, 0x00,
0x00, 0x04, 0x02, 0x00, 0x01, 0xbb }

challenge data=
{ 0x46, 0x50, 0x4c, 0x59, 0x02, 0x01, 0x03, 0x00, 0x00, 0x00,
0x00, 0x98, 0x01, 0x8f, 0x1a, 0x9c, 0xfb, 0x2f, 0xa4, 0x81,
0x15, 0x91, 0x9d, 0xe5, 0xc6, 0x4e, 0x2e, 0x00, 0x24, 0xf3,
0x13, 0xac, 0xe8, 0x71, 0x11, 0x63, 0x6e, 0x8c, 0xfc, 0x9a,
0xe3, 0xed, 0x80, 0x5b, 0x2f, 0xb8, 0xc0, 0x04, 0x07, 0x44,
0xa1, 0x59, 0xd1, 0x1a, 0xd7, 0x15, 0x08, 0x30, 0x2f, 0xbc,
0x2e, 0x59, 0x29, 0x45, 0x08, 0x30, 0x0a, 0x70, 0x9f, 0xc9,
0x94, 0x52, 0x79, 0xc9, 0x8a, 0xd6, 0x92, 0xa6, 0x31, 0xa3,
0xf6, 0x27, 0x40, 0xdc, 0x59, 0xec, 0x03, 0x00, 0x93, 0x6b,
0x34, 0xa0, 0xf0, 0xc4, 0xe4, 0x33, 0x44, 0xfc, 0x7c, 0x00,
0x0e, 0x28, 0xca, 0x75, 0x37, 0xd9, 0x8d, 0x21, 0x2b, 0x76,
0x85, 0xcf, 0x9d, 0x5e, 0x0a, 0xd4, 0x4f, 0x0d, 0xdb, 0x31,
0x23, 0x4d, 0xb9, 0x2f, 0x6e, 0xfc, 0x0f, 0x80, 0xe5, 0x59,
0xc1, 0x90, 0x08, 0x2a, 0xc2, 0x9f, 0xc8, 0xb3, 0x7b, 0x05,
0x41, 0xe9, 0xc2, 0xcc, 0x50, 0xf1, 0x77, 0x1d, 0xb9, 0x7f,
0x1c, 0xac, 0x89, 0x94, 0x4d, 0xa9, 0xd8, 0x6b, 0x14, 0x95,
0x74, 0x59, 0xeb, 0x65 }

//Correct decrypt fpaeskey result is
fpaeskey(decrpted) aeskey =
{ 0xa8, 0xb0, 0x0c, 0xbb, 0xfb, 0xb6, 0xe0, 0x65, 0xd5, 0x0d, 0x4e, 0x15, 0x3c, 0xe1, 0xb9, 0xcb }

//But in playfair decrypt result is wrong
Dump aeskey : ,
0xD6, 0x4E, 0x48, 0xF8, 0xDD, 0xBB, 0x26, 0xCC, 0xD3, 0xFF, 0x7D, 0xF6, 0xC9, 0x0B, 0x4E, 0xA2

I think the cause is this fairplay data is FPLY(0x2)(0x46, 0x50, 0x4c, 0x59, 0x02) , and normaly in mirroring fairplay data is FPLY(0x3)(0x46, 0x50, 0x4c, 0x59, 0x03).

[EstebanKubata]

Feel free to submit a pull request if you have some insight I don’t :)