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Copy pathimplementation.ASM
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implementation.ASM
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; Copyright © 2018 Michael Mamic
; ----------------------------------------------------
; Permission is hereby granted, free of charge,
; to any person obtaining a copy of this software
; and associated documentation files (the “Software”),
; to deal in the Software without restriction,
; including without limitation the rights to use,
; copy, modify, merge, publish, distribute, sublicense,
; and/or sell copies of the Software,
; and to permit persons to whom the Software is furnished to do so,
; subject to the following conditions:
;
; The above copyright notice and this permission notice shall be
; included in all copies or substantial portions of the Software.
; THE SOFTWARE IS PROVIDED “AS IS”, WITHOUT WARRANTY OF ANY KIND,
; EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES
; OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
; IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM,
; DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
; TORT OR OTHERWISE, ARISING FROM,
; OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
; -----------------------------------------------------
; The code below provides two functions,
; AESEncryptSector and AESDecryptSector,
; which each need a key, a buffer, and a sector LBA,
; to perform a CBC AES256 encryption or decryption on
; the given sector.
; -----------------------------------------------------
; The code was designed to use only the simplest instructions:
; mov, push, pop, xor, inc, dec, cmp, sub, rol ... etc
; In order to be easily portable for more restricted architectures.
; -----------------------------------------------------
; The block of constants used at the bottom of the code
; was generated by a C# .NET Console program based on the information
; found at https://en.wikipedia.org/wiki/Advanced_Encryption_Standard
use16
loadDX:
push di
push ds
mov di, 0x5F0
mov ds, di
xor di, di
mov dx, word [ds:di]
pop ds
pop di
ret
; AES Implementation: Clear all memory used by AES
AESClearMemory:
push di
push ds
mov di, 0x602
mov ds, di
xor di, di
AESClearMemory_ClearLoop:
mov [ds:di], byte 0
inc di
cmp di, 0x4E0
jne AESClearMemory_ClearLoop
AESClearMemory_end:
pop ds
pop di
ret
; # AES Implementation Encrypt Sector CBC (Unoptimized) #
; Input: CX = Sector, Key at 0x6000:0x0, Memory at [ds:di]. DI should be 0 to begin with.
AESEncryptSector:
; Generate IV at 0x60E0
pusha
push ds
push es
mov bx, 0x60E
mov es, bx
xor bx, bx
mov di, 0x630
mov ds, di
xor di, di
AESEncryptSector_GenerateIVLoop:
mov al, 0x5A
;xor al, al
;rdrand ax
mov [ds:di], byte al
mov [es:bx], byte al
inc di
inc bx
cmp bx, 0x10
jne AESEncryptSector_GenerateIVLoop
pop es
pop ds
popa
pusha
; Times 32 (32 * 16 = 512) Encrypt each block by the last one.
push cx
add di, 0x10
xor cx, cx
; Copy memory to 0x60E0 + 0x10 (IV is at 0x60E0)
AESEncryptSector_EncryptBlockLoop:
pusha
push es
mov bx, 0x60F
mov es, bx
xor bx, bx
xor cx, cx
AESEncryptSector_EncryptBlockLoop_LoadBlock:
mov al, byte [ds:di]
mov [es:bx], byte al
inc di
inc bx
inc cx
cmp cx, 0x10
jne AESEncryptSector_EncryptBlockLoop_LoadBlock
pop es
popa
; XOR by previous block
pusha
push ds
push es
mov bx, 0x630
mov ds, bx
mov bx, 0x60F
mov es, bx
xor cx, cx
xor bx, bx
sub di, 0x10
AESEncryptSector_EncryptBlockLoop_XORByLastBlock:
mov al, byte [es:bx]
mov ah, byte [ds:di]
xor al, ah
mov [es:bx], byte al
;mov [ds:di], byte al
inc bx
inc di
inc cx
cmp cx, 0x10
jne AESEncryptSector_EncryptBlockLoop_XORByLastBlock
pop es
pop ds
popa
; Copy 0x60F0 to 0x60E0
pusha
push ds
mov di, 0x600
mov ds, di
mov di, 0xE0
mov si, 0xF0
AESEncryptSector_EncryptBlockLoop_CopyToEncryptBufferLoop:
mov al, byte [ds:si]
mov [ds:di], byte al
inc si
inc di
cmp di, 0xF0
jne AESEncryptSector_EncryptBlockLoop_CopyToEncryptBufferLoop
pop ds
popa
; Call AESEncryptBlock
call AESEncryptBlock
; Copy 0x60E0 to 0x60F0
pusha
push ds
mov di, 0x600
mov ds, di
mov di, 0xE0
mov si, 0xF0
AESEncryptSector_EncryptBlockLoop_CopyFromEncryptBufferLoop:
mov al, byte [ds:di]
mov [ds:si], byte al
inc si
inc di
cmp di, 0xF0
jne AESEncryptSector_EncryptBlockLoop_CopyFromEncryptBufferLoop
pop ds
popa
; Copy memory to 0x6300
pusha
push es
push ds
mov bx, 0x60F
mov es, bx
mov bx, 0x630
mov ds, bx
xor bx, bx
xor cx, cx
AESEncryptSector_EncryptBlockLoop_UnloadBlock:
mov al, byte [es:bx]
mov [ds:di], byte al
inc di
inc bx
inc cx
cmp cx, 0x10
jne AESEncryptSector_EncryptBlockLoop_UnloadBlock
pop ds
pop es
popa
add di, 0x10
inc cx
cmp cx, 31
jne AESEncryptSector_EncryptBlockLoop
pop cx
; Write Sector
call loadDX
call convertCXToTrackSector
mov bx, 0x630
mov es, bx
mov bx, 0x0
AESEncryptSector_checkSectorWrite:
mov ah, 0x3
mov al, 0x1
int 0x13
jc AESEncryptSector_checkSectorWrite
AESEncryptSector_end:
popa
ret
; # AES Implementation Decrypt Sector CBC (Unoptimized) #
; Input: CX = Sector, Key at 0x6000:0x0, Memory at [ds:di]. DI should be 0 to begin with.
AESDecryptSector:
; Load Sector
call loadDX
call convertCXToTrackSector
mov bx, 0x630
mov es, bx
mov bx, 0x0
AESDecryptSector_checkSectorRead:
mov ah, 0x2
mov al, 0x1
int 0x13
jc AESDecryptSector_checkSectorRead
pusha
push ds
; Times 32 (32 * 16 = 512) Encrypt each block by the last one.
push cx
mov di, 0x630
mov ds, di
mov di, 0x200
xor cx, cx
; Decrypt:
; Copy memory from block.
; Decrypt.
; XOR block by previous one.
; Copy memory to 0x60E0
AESDecryptSector_DecryptBlockLoop:
pusha
push es
mov bx, 0x60E
mov es, bx
mov bx, 0x630
mov ds, bx
xor bx, bx
xor cx, cx
AESDecryptSector_DecryptBlockLoop_LoadBlock:
mov al, byte [ds:di]
mov [es:bx], byte al
inc di
inc bx
inc cx
cmp cx, 0x10
jne AESDecryptSector_DecryptBlockLoop_LoadBlock
xor bx, bx
pop es
popa
; Call AESDecryptBlock
call AESDecryptBlock
; XOR block by previous one.
pusha
push ds
push es
mov bx, 0x630
mov ds, bx
mov bx, 0x60E
mov es, bx
xor cx, cx
xor bx, bx
sub di, 0x10
AESDecryptSector_DecryptBlockLoop_XORByLastBlock:
mov al, byte [es:bx]
mov ah, byte [ds:di]
xor al, ah
mov [es:bx], byte al
inc bx
inc di
inc cx
cmp cx, 0x10
jne AESDecryptSector_DecryptBlockLoop_XORByLastBlock
pop es
pop ds
popa
; Copy memory to 0x6300
pusha
push es
push ds
mov bx, 0x60E
mov es, bx
xor bx, bx
xor cx, cx
AESDecryptSector_DecryptBlockLoop_UnloadBlock:
mov al, byte [es:bx]
mov [ds:di], byte al
inc di
inc bx
inc cx
cmp cx, 0x10
jne AESDecryptSector_DecryptBlockLoop_UnloadBlock
pop ds
pop es
popa
sub di, 0x10
inc cx
cmp cx, 32
jne AESDecryptSector_DecryptBlockLoop
; Memory decrypted at 0x6300. Copy it to [DS:DI]
pop cx
pop ds
popa
pusha
push es
mov bx, 0x631
mov es, bx
xor bx, bx
xor cx, cx
AESDecryptSector_CopyMemoryToDSDI:
mov al, byte [es:bx]
mov [ds:di], byte al
inc bx
inc di
inc cx
cmp cx, 0x1F0
jne AESDecryptSector_CopyMemoryToDSDI
AESDecryptSector_end:
pop es
popa
ret
; AES Implementation Encrypt Block (Unoptimized)
; Input: Plaintext at 0x60E0, Key at 0x6000.
; Output: Ciphertext at 0x60E0
AESEncryptBlock:
pusha
push ds
push es
; Generate Key Schedule
call GenerateKeySchedule
; Move plaintext to memory after the keys
mov bx, 0x50 ; Move pointer to the plaintext.
mov es, bx
xor bx, bx
mov di, 0x600
mov ds, di
mov di, 0xE0
xor si, si
xor cx, cx
AESEncryptBlock_XORPlaintextByFirstKeyLoop: ; XOR the plaintext by the first key.
mov ax, word [ds:si]
mov bx, word [ds:di]
xor ax, bx
mov [ds:di], word ax
add si, 0x2
add di, 0x2
inc cx
cmp cx, 0x8
jne AESEncryptBlock_XORPlaintextByFirstKeyLoop
mov di, 0xE0
mov si, 0x20
xor cx, cx
AESEncryptBlock_EncryptBlockRoundLoop: ; Loop to encrypt the block.
; A B C D Row 0
; B C D A Row 1
; C D A B Row 2
; D A B C Row 3
push cx
push di
push si
; Shift the plaintext
mov di, 0xE0
add di, 0x4 ; Second Row
mov ah, byte [ds:di]
inc di
mov al, byte [ds:di]
inc di
mov bh, byte [ds:di]
inc di
mov bl, byte [ds:di]
mov [ds:di], byte ah
dec di
mov [ds:di], byte bl
dec di
mov [ds:di], byte bh
dec di
mov [ds:di], byte al
add di, 0x4 ; Third Row
mov ah, byte [ds:di]
inc di
mov al, byte [ds:di]
inc di
mov bh, byte [ds:di]
inc di
mov bl, byte [ds:di]
mov [ds:di], byte al
dec di
mov [ds:di], byte ah
dec di
mov [ds:di], byte bl
dec di
mov [ds:di], byte bh
add di, 0x4 ; Fourth Row
mov ah, byte [ds:di]
inc di
mov al, byte [ds:di]
inc di
mov bh, byte [ds:di]
inc di
mov bl, byte [ds:di]
mov [ds:di], byte bh
dec di
mov [ds:di], byte al
dec di
mov [ds:di], byte ah
dec di
mov [ds:di], byte bl
; Run the plaintext through the S-Box
sub di, 12
xor cx, cx
xor ah, ah
AESEncryptBlock_EncryptBlockRoundLoop_RunThroughSBoxLoop: ; Run each column through the S-Box
mov al, byte [ds:di]
xor ah, ah
rol al, 4
mov bx, SBox
add bx, ax
mov al, byte [es:bx]
mov [ds:di], byte al
inc cx
inc di
cmp cx, 0x10
jne AESEncryptBlock_EncryptBlockRoundLoop_RunThroughSBoxLoop
; MixColumns on the plaintext
call MixColumns
pop si
; XOR plaintext by the current key
pusha
mov di, 0xE0
xor cx, cx
AESEncryptBlock_EncryptBlockRoundLoop_XORPlaintextByCurrentKeyLoop: ; XOR the plaintext by the current key.
mov ax, word [ds:si]
mov bx, word [ds:di]
xor ax, bx
mov [ds:di], word ax
add si, 0x2
add di, 0x2
inc cx
cmp cx, 0x8
jne AESEncryptBlock_EncryptBlockRoundLoop_XORPlaintextByCurrentKeyLoop
popa
pop di
pop cx
mov di, 0xE0
inc cx
add si, 0x10
cmp cx, 12
jne AESEncryptBlock_EncryptBlockRoundLoop
; The loop is now done. Now do the final step, which is everything minus the MixColumns function
; Shift the plaintext
mov di, 0xE0
add di, 0x4 ; Second Row
mov ah, byte [ds:di]
inc di
mov al, byte [ds:di]
inc di
mov bh, byte [ds:di]
inc di
mov bl, byte [ds:di]
mov [ds:di], byte ah
dec di
mov [ds:di], byte bl
dec di
mov [ds:di], byte bh
dec di
mov [ds:di], byte al
add di, 0x4 ; Third Row
mov ah, byte [ds:di]
inc di
mov al, byte [ds:di]
inc di
mov bh, byte [ds:di]
inc di
mov bl, byte [ds:di]
mov [ds:di], byte al
dec di
mov [ds:di], byte ah
dec di
mov [ds:di], byte bl
dec di
mov [ds:di], byte bh
add di, 0x4 ; Fourth Row
mov ah, byte [ds:di]
inc di
mov al, byte [ds:di]
inc di
mov bh, byte [ds:di]
inc di
mov bl, byte [ds:di]
mov [ds:di], byte bh
dec di
mov [ds:di], byte al
dec di
mov [ds:di], byte ah
dec di
mov [ds:di], byte bl
; Run the plaintext through the S-Box
sub di, 12
xor cx, cx
xor ah, ah
AESEncryptBlock_RunThroughSBoxLoop: ; Run each column through the S-Box
mov al, byte [ds:di]
xor ah, ah
rol al, 4
mov bx, SBox
add bx, ax
mov al, byte [es:bx]
mov [ds:di], byte al
inc cx
inc di
cmp cx, 0x10
jne AESEncryptBlock_RunThroughSBoxLoop
; XOR plaintext by the last key
mov di, 0xE0
mov si, 0xD0
xor cx, cx
AESEncryptBlock_XORPlaintextByLastKeyLoop: ; XOR the plaintext by the last key.
mov ax, word [ds:si]
mov bx, word [ds:di]
xor ax, bx
mov [ds:di], word ax
add si, 0x2
add di, 0x2
inc cx
cmp cx, 0x8
jne AESEncryptBlock_XORPlaintextByLastKeyLoop
AESEncryptBlock_end:
pop es
pop ds
popa
ret
; AES Implementation Decrypt Block (Unoptimized)
AESDecryptBlock:
pusha
push ds
push es
; Generate Key Schedule
call GenerateKeySchedule
; Move plaintext to memory after the keys
mov bx, 0x50 ; Move pointer to the plaintext.
mov es, bx
xor bx, bx
mov di, 0x600
mov ds, di
mov di, 0xE0
mov si, 0xD0
xor cx, cx
AESDecryptBlock_XORPlaintextByLastKeyLoop: ; XOR the plaintext by the last key.
mov ax, word [ds:si]
mov bx, word [ds:di]
xor ax, bx
mov [ds:di], word ax
add si, 0x2
add di, 0x2
inc cx
cmp cx, 0x8
jne AESDecryptBlock_XORPlaintextByLastKeyLoop
mov bx, 0x50
mov es, bx
mov di, 0xE0
; Run the plaintext through the S-Box
xor cx, cx
xor ah, ah
AESDecryptBlock_RunThroughSBoxLoop: ; Run each column through the S-Box
mov al, byte [ds:di]
xor ah, ah
rol al, 4
mov bx, InverseSBox
add bx, ax
mov al, byte [es:bx]
mov [ds:di], byte al
inc cx
inc di
cmp cx, 0x10
jne AESDecryptBlock_RunThroughSBoxLoop
; Shift the plaintext
; A B C D Row 0
; D A B C Row 1
; C D A B Row 2
; B C D A Row 3
mov di, 0xE0
add di, 0x4 ; Second Row
mov ah, byte [ds:di]
inc di
mov al, byte [ds:di]
inc di
mov bh, byte [ds:di]
inc di
mov bl, byte [ds:di]
mov [ds:di], byte bh
dec di
mov [ds:di], byte al
dec di
mov [ds:di], byte ah
dec di
mov [ds:di], byte bl
add di, 0x4 ; Third Row
mov ah, byte [ds:di]
inc di
mov al, byte [ds:di]
inc di
mov bh, byte [ds:di]
inc di
mov bl, byte [ds:di]
mov [ds:di], byte al
dec di
mov [ds:di], byte ah
dec di
mov [ds:di], byte bl
dec di
mov [ds:di], byte bh
add di, 0x4 ; Fourth Row
mov ah, byte [ds:di]
inc di
mov al, byte [ds:di]
inc di
mov bh, byte [ds:di]
inc di
mov bl, byte [ds:di]
mov [ds:di], byte ah
dec di
mov [ds:di], byte bl
dec di
mov [ds:di], byte bh
dec di
mov [ds:di], byte al
; Loop 12 times
mov di, 0xE0
mov si, 0xD0
xor cx, cx
AESDecryptBlock_DecryptBlockRoundLoop: ; Loop to encrypt the block.
push di
push si
push cx
pusha
mov di, 0xE0
xor cx, cx
AESDecryptBlock_DecryptBlockRoundLoop_XORPlaintextByCurrentKeyLoop: ; XOR the plaintext by the first key.
mov ax, word [ds:si]
mov bx, word [ds:di]
xor ax, bx
mov [ds:di], word ax
add si, 0x2
add di, 0x2
inc cx
cmp cx, 0x8
jne AESDecryptBlock_DecryptBlockRoundLoop_XORPlaintextByCurrentKeyLoop
popa
; MixColumns on the plaintext
call MixColumnsInverse
; Run the plaintext through the S-Box
xor cx, cx
xor ah, ah
AESDecryptBlock_DecryptBlockRoundLoop_RunThroughSBoxLoop: ; Run each column through the S-Box
mov al, byte [ds:di]
xor ah, ah
rol al, 4
mov bx, InverseSBox
add bx, ax
mov al, byte [es:bx]
mov [ds:di], byte al
inc cx
inc di
cmp cx, 0x10
jne AESDecryptBlock_DecryptBlockRoundLoop_RunThroughSBoxLoop
; Shift the plaintext
; A B C D Row 0
; D A B C Row 1
; C D A B Row 2
; B C D A Row 3
mov di, 0xE0
add di, 0x4 ; Second Row
mov ah, byte [ds:di]
inc di
mov al, byte [ds:di]
inc di
mov bh, byte [ds:di]
inc di
mov bl, byte [ds:di]
mov [ds:di], byte bh
dec di
mov [ds:di], byte al
dec di
mov [ds:di], byte ah
dec di
mov [ds:di], byte bl
add di, 0x4 ; Third Row
mov ah, byte [ds:di]
inc di
mov al, byte [ds:di]
inc di
mov bh, byte [ds:di]
inc di
mov bl, byte [ds:di]
mov [ds:di], byte al
dec di
mov [ds:di], byte ah
dec di
mov [ds:di], byte bl
dec di
mov [ds:di], byte bh
add di, 0x4 ; Fourth Row
mov ah, byte [ds:di]
inc di
mov al, byte [ds:di]
inc di
mov bh, byte [ds:di]
inc di
mov bl, byte [ds:di]
mov [ds:di], byte ah
dec di
mov [ds:di], byte bl
dec di
mov [ds:di], byte bh
dec di
mov [ds:di], byte al
pop cx
pop si
pop di
mov di, 0xE0
sub si, 0x10
inc cx
cmp cx, 12
jne AESDecryptBlock_DecryptBlockRoundLoop
; XOR plaintext by the first key
mov di, 0x600
mov ds, di
mov di, 0xE0
xor si, si
xor cx, cx
AESDecryptBlock_XORPlaintextByFirstKeyLoop: ; XOR the plaintext by the first key.
mov ax, word [ds:si]
mov bx, word [ds:di]
xor ax, bx
mov [ds:di], word ax
add si, 0x2
add di, 0x2
inc cx
cmp cx, 0x8
jne AESDecryptBlock_XORPlaintextByFirstKeyLoop
AESDecryptBlock_end:
pop es
pop ds
popa
ret
; Runs the MixColumns operation on the plaintext at 0xD0
MixColumns:
pusha
push es
; Copy plaintext to give us something to work with
mov di, 0xE0
mov si, di
mov di, 0xF0
xor cx, cx
MixColumns_CopyPlaintextLoop:
mov ax, word [ds:si]
mov [ds:di], word ax
add si, 0x2
add di, 0x2
mov ax, word [ds:si]
mov [ds:di], word ax
add si, 0x2
add di, 0x2
add cx, 0x4
cmp cx, 0x10
jne MixColumns_CopyPlaintextLoop
; Actual algorithm
mov di, 0xE0
mov si, di
mov di, 0xF0
mov bx, 0x50
mov es, bx
mov bx, MixColumnEncryptMatrix
xor cx, cx
MixColumns_MixColumnLoop:
push di
push si
push cx
push bx
xor cx, cx
MixColumns_MixRowLoop:
push di
push cx
push bx
xor ax, ax
xor dx, dx
xor cx, cx
; Add each row to ah and set the row/column to it.
MixColumns_MixRowLoop_XORAddition:
; Move ah to the matrix's cooresponding value
push bx
mov ah, byte [es:bx]
cmp ah, 1
jne MixColumns_MixRowLoop_XORAddition_MultiplyGreaterThanOne
mov ah, byte [ds:di]
jmp MixColumns_MixRowLoop_XORAddition_MultiplyByOneSkip
MixColumns_MixRowLoop_XORAddition_MultiplyGreaterThanOne:
push cx
mov cx, MultiplicationLookup3
mov bx, MultiplicationLookup2
cmp ah, 3
cmove bx, cx
mov dl, byte [ds:di]
add bx, dx
mov ah, byte [es:bx]
pop cx
MixColumns_MixRowLoop_XORAddition_MultiplyByOneSkip:
pop bx
xor al, ah
inc bx
inc cx
add di, 4
cmp cx, 4
jne MixColumns_MixRowLoop_XORAddition
mov [ds:si], byte al
; Set row-column of key to al
pop bx
pop cx
pop di
add si, 4
add bx, 4
inc cx
cmp cx, 4
jne MixColumns_MixRowLoop
pop bx
pop cx
pop si
pop di
inc di
inc si
inc cx
cmp cx, 4
jne MixColumns_MixColumnLoop
MixColumns_End:
pop es
popa
ret
; Runs the MixColumnsDecrypt operation on the plaintext at 0xE0
MixColumnsInverse:
pusha
; Copy plaintext to give us something to work with
mov di, 0xE0
mov si, di
mov di, 0xF0
xor cx, cx
MixColumnsInverse_CopyPlaintextLoop:
mov ax, word [ds:si]
mov [ds:di], word ax
add si, 0x2
add di, 0x2
mov ax, word [ds:si]
mov [ds:di], word ax
add si, 0x2
add di, 0x2
add cx, 0x4
cmp cx, 0x10
jne MixColumnsInverse_CopyPlaintextLoop
; Actual algorithm
mov di, 0xE0
mov si, di
mov di, 0xF0
mov bx, 0x50
mov es, bx
mov bx, MixColumnInverseMatrix
xor cx, cx
MixColumnsInverse_MixColumnLoop:
push di
push si
push cx
push bx
xor cx, cx
MixColumnsInverse_MixRowLoop:
push di
push cx
push bx
xor ax, ax
xor dx, dx
xor cx, cx
; Add each row to ah and set the row/column to it.
MixColumnsInverse_MixRowLoop_XORAddition:
; Move ah to the matrix's cooresponding value
push bx
push cx
mov ah, byte [es:bx]
mov bx, MultiplicationLookup9
mov cx, MultiplicationLookup11
cmp ah, 11
cmove bx, cx
mov cx, MultiplicationLookup13
cmp ah, 13
cmove bx, cx
mov cx, MultiplicationLookup14
cmp ah, 14
cmove bx, cx
mov dl, byte [ds:di]
add bx, dx
mov ah, byte [es:bx]
pop cx
pop bx
xor al, ah
inc bx
inc cx
add di, 4
cmp cx, 4
jne MixColumnsInverse_MixRowLoop_XORAddition
; Set row-column of key to al
mov [ds:si], byte al
pop bx
pop cx
pop di
add si, 4
add bx, 4
inc cx
cmp cx, 4
jne MixColumnsInverse_MixRowLoop
pop bx
pop cx
pop si
pop di
inc di
inc si
inc cx
cmp cx, 4
jne MixColumnsInverse_MixColumnLoop
MixColumnsInverse_End:
popa
ret
; Generates the Key Schedule
GenerateKeySchedule:
pusha
push es
push ds
mov bx, 0x50 ; Move pointer to the key.
mov es, bx
mov bx, 0x600
mov ds, bx
xor bx, bx
mov di, 0x20
xor cx, cx
GenerateKeySchedule_ExtendKeyLoop: ; Extend all the keys.
push di
push cx
GenerateKeySchedule_ExtendSingularKey:
; Do first column uniquely
; Copy last column to current column and shift it
; 0 0 0 A D 0 0 0
; 0 0 0 B A 0 0 0
; 0 0 0 C B 0 0 0
; 0 0 0 D C 0 0 0
sub di, 9 ; First column
mov ah, byte [ds:di]
add di, 9
mov [ds:di], byte ah
add di, 0x4 ; Second column
sub di, 9
mov ah, byte [ds:di]
add di, 9
mov [ds:di], byte ah
add di, 0x4 ; Third column
sub di, 9
mov ah, byte [ds:di]
add di, 9
mov [ds:di], byte ah
add di, 0x4 ; Fourth column
sub di, 25
mov ah, byte [ds:di]
add di, 25
mov [ds:di], byte ah
; Run each column through the S-Box
sub di, 12 ; Begin at first column
xor ah, ah
xor cx, cx
GenerateKeySchedule_ExtendSingularKey_RunThroughSBoxLoop: ; Run each column through the S-Box
mov al, byte [ds:di]
xor ah, ah
rol al, 4
mov bx, SBox