C header translation

[JK]

How would i translate this C struct (wincrypt.h) to ASM

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typedef struct _CRYPT_AES_256_KEY_STATE {
  unsigned char Key[32];
  unsigned char IV[16];
  unsigned char EncryptionState[15][16];
  unsigned char DecryptionState[15][16];
  unsigned char Feedback[16];
} CRYPT_AES_256_KEY_STATE, *PCRYPT_AES_256_KEY_STATE;


and what would be a valid syntax for reading or writing EncryptionState[2][3] or EncryptionState[i1][i2] (where i1 and i2 are local variables)?


JK

[jj2007]

Not tested:

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CRYPT_AES_256_KEY_STATE STRUCT
Key        char 32 dup(?)
IV        char 16 dup(?)
EncryptionState char 15 dup(?)
DecryptionState char 15 dup(?)
Feedback  char 16 dup(?)
CRYPT_AES_256_KEY_STATE ENDS

PCRYPT_AES_256_KEY_STATE typedef ptr CRYPT_AES_256_KEY_STATE


Gcc chokes on this one:

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#include <stdio.h> // template for a simple C console app
#include <windows.h> // needs Gcc or Visual C and the Compile plugin
#include <WinCrypt.h>
int main() {
  long long q=1234567890123456789;
  CRYPT_AES_256_KEY_STATE cstate;
}

[JK]

FreeBASIC defines it (two-dimensional) as:

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    type _CRYPT_AES_256_KEY_STATE
        Key(0 to 31) as ubyte
        IV(0 to 15) as ubyte
        EncryptionState(0 to 14, 0 to 15) as ubyte
        DecryptionState(0 to 14, 0 to 15) as ubyte
        Feedback(0 to 15) as ubyte
    end type


my point here is, it is a two-dimensional array for EncryptionState and DecryptionState so the total number of elements would be 240 (15 x 16), so one-dimensional it must be:

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... 240 dup (?)

but is there an assembler syntax supporting two dimensions as well?

And, if yes - what would be a valid syntax for reading or writing EncryptionState[2][3] or EncryptionState[i1][i2] (where i1 and i2 are local variables)?

[Greenhorn]

Members EncryptionState and DecryptionState are two-dimensional arrays.

Should be like this:

CRYPT_AES_256_KEY_STATE STRUCT
Key            byte 32 dup(?)
IV            byte 16 dup(?)
EncryptionState   byte 15 dup(16 dup(?))
DecryptionState   byte 15 dup(16 dup(?))
Feedback         byte 16 dup(?)
CRYPT_AES_256_KEY_STATE ENDS

PCRYPT_AES_256_KEY_STATE typedef ptr CRYPT_AES_256_KEY_STATE

...
LOCAL ca2ks:    CRYPT_AES_256_KEY_STATE

...
mov  al, ca2ks.EncryptionState[2  *16*sizeof(byte)]    ;// same as ca2ks.EncryptionState[2][0] in C lang
mov  al, ca2ks.EncryptionState[14*16*sizeof(byte)]    ;// same as ca2ks.EncryptionState[14][0] in C lang


The sizeof(byte) is not necessary here, it's just to show how it works with array element sizes.


Kind regards
Greenhorn

[JK]

So there is no such syntax?

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mov  al, ca2ks.EncryptionState[2, 0]

In my case i must always CALCULATE the one-dimensional index from the two indices for this two-dimensional array, i cannot let the assembler resolve it for me - is this true?


Thanks for your help!

[jj2007]

So there is no such syntax?

No, but you can use (if both are immediates)
index=rows*xsize+column
mov  al, ca2ks.EncryptionState[index]

[Greenhorn]

In my case i must always CALCULATE the one-dimensional index from the two indices for this two-dimensional array, i cannot let the assembler resolve it for me - is this true?

True.

ca2ks.EncryptionState[2, 0]
This is high level programming language. That means, the compiler is doing the calculation for you.
In Assembly language you are on the lowest (machine) level and all memory access is on a byte basis.

This is a good read for beginners in MASM: MASM Programmer's Guide

[Greenhorn]

And these books are also very good:
Write Great Code, Volume 1, 2nd Edition
Write Great Code, Volume 2, 2nd Edition

[JK]

testing with UASM this code is accepted,

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mov al, ca2ks.EncryptionState[14*16*sizeof(byte)][3*sizeof(byte)][5]

all [...] get added to a final index.

[jj2007]

you can use (if both are immediates)
index=rows*xsize+column
mov  al, ca2ks.EncryptionState[index]

Yes indeed, but only with immediates. If your rows and columns are in registers or in variables, use e.g.
imul eax, row, sizeof row
add eax, column
mov  al, ca2ks.EncryptionState[eax]

[HSE]

You can define:

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"if you are using ANSI srintrings:"
    char textequ <byte>
"elseif you are using WIDE strings:"
    char textequ <word>

CRYPT_AES_256_KEY_STATE STRUCT
  ···
EncryptionState char 15*16 dup(?)
  ···
CRYPT_AES_256_KEY_STATE ENDS


[TouEnMasm]

CRYPT_AES_256_KEY_STATE   STRUCT DEFALIGNMASM
   Key BYTE 32 dup (?)
   IV BYTE 16 dup (?)
   EncryptionState BYTE 15 dup (?)
   DecryptionState BYTE 15 dup (?)
   Feedback BYTE 16 dup (?)
CRYPT_AES_256_KEY_STATE      ENDS

it is in wincrypt.sdk here http://luce.yves.pagesperso-orange.fr/header.htm

[HSE]

Hi Yves!

CRYPT_AES_256_KEY_STATE   STRUCT DEFALIGNMASM
   Key BYTE 32 dup (?)
   IV BYTE 16 dup (?)
   EncryptionState BYTE 15 dup (?)
   DecryptionState BYTE 15 dup (?)
   Feedback BYTE 16 dup (?)
CRYPT_AES_256_KEY_STATE      ENDS

it is in wincrypt.sdk here http://luce.yves.pagesperso-orange.fr/header.htm

Your CRYPT_AES_256_KEY_STATE is wrong.
Also CRYPT_AES_128_KEY_STATE is wrong in your sdk.
For sure your translator don't understand this arrays, only take first index.

Very interesting also ObjAsm sdk is wrong but it's a different translator, and take last index!

[TouEnMasm]

Last SDK

typedef struct _CRYPT_AES_256_KEY_STATE {
    unsigned char Key[32];
    unsigned char IV[16];
    unsigned char EncryptionState[15][16];      // 14 rounds + 1
    unsigned char DecryptionState[15][16];
    unsigned char Feedback[16];
} CRYPT_AES_256_KEY_STATE, *PCRYPT_AES_256_KEY_STATE;

char EncryptionState[15][16]; is what is bad translated,not really very current
need to know exactly if it is a 15 * 16 bytes  or a 16 * 15 ,adressing is not the same
The comment  // 14 rounds + 1 seem to say it is a 15 * 16     

[HSE]

need to know exactly if it is a 15 * 16 bytes  or a 16 * 15 ,adressing is not the same

For sure say 15*16

Other vectors in structure have 16 char, then you can guess:

     y*16+x

just like Greenhorn posted before.

Regards. HSE