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(I-a) Using the password, initializing three 32bit keys


Void CRYPT: : InitKeys ()
{
Key [ 0 ] = 0x12345678L;
Key [ 1 ] = 0x23456789L;
Key [ 2 ] = 0x34567890L;

For (int i=0; &pwd [ i ] < &pwd[48]; i++){
UpdateKeys (&pwd [ i ]);
}
}


(I-b) (I-a) Details. The algorithm of crc32 is jointly used


Void CRYPT: : UpdateKeys (unsigned
char* c)
{
Key [ 0 ] = crc_table [ (key [ 0 ] ^ *c) & 0xff ] ^ (key
[ 0 ] >> 8);
Key [ 1 ] += key [ 0 ] & 0xff;
Key [ 1 ] = key [ 1 ] * 0x8088405L + 1;
Key [ 2 ] = crc_table [ (key [ 2 ] ^ (key [ 1 ] >> 24)) & 0xff ]
^ (key [ 2 ] >> 8);
}


(II) (I-b) So using the false random number which is renewed, forming the xor key


Int CRYPT: : DecryptByte ()
{
Int tmp = (key [ 2 ] & 0x0fffd) | 2;
Return (tmp * (tmp ^ 1)) >> 8;
}


(III) The filename length minute loop doing.


For (int i=0; I < len; i++){
Buf [ i ] ^= crypt.decryptByte ();
Crypt.updateKeys (&buf [ i ]);
}



Above filename (n) series of decoding.
When 1byte it decodes, using that 1byte, because it forms false random number, xor-key yes changing in such sense, thing ・・

Therefore the encoding algorithm of well old PKZIP, it is certain to be fragility.