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C nettle, low-level cryptographics library
C
C Copyright (C) 2001, 2002 Rafael R. Sevilla, Niels Möller
C
C The nettle library is free software; you can redistribute it and/or modify
C it under the terms of the GNU Lesser General Public License as published by
C the Free Software Foundation; either version 2.1 of the License, or (at your
C option) any later version.
C
C The nettle library is distributed in the hope that it will be useful, but
C WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
C or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public
C License for more details.
C
C You should have received a copy of the GNU Lesser General Public License
C along with the nettle library; see the file COPYING.LIB. If not, write to
C the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
C MA 02111-1307, USA.
.file "aes-decrypt.asm"
C aes_decrypt(struct aes_context *ctx,
C unsigned length, uint8_t *dst,
C uint8_t *src)
.text
.align 16
.globl C_NAME(nettle_aes_decrypt)
.type C_NAME(nettle_aes_decrypt),@function
C_NAME(nettle_aes_decrypt):
C save all registers that need to be saved
pushl %ebx C 16(%esp)
pushl %ebp C 12(%esp)
pushl %esi C 8(%esp)
pushl %edi C 4(%esp)
C ctx = 20(%esp)
C length = 24(%esp)
C dst = 28(%esp)
C src = 32(%esp)
movl 24(%esp), %ebp
testl %ebp,%ebp
jz .Lend
.Lblock_loop:
movl 20(%esp),%esi C address of context struct ctx
movl 32(%esp),%ebp C address of plaintext
AES_LOAD(%esi, %ebp)
addl $16, 32(%esp) C Increment src pointer
C get number of rounds to do from struct
movl AES_NROUNDS (%esi),%ebp
subl $1,%ebp C one round is complete
addl $16,%esi C point to next key
.Lround_loop:
pushl %esi C save this first: we'll clobber it later
C In these patterns, note that each row, like
C "a,d,c,b" corresponds to one *column* of the
C array _aes_decrypt_table.idx.
AES_ROUND(C_NAME(_nettle_aes_decrypt_table),a,d,c,b)
pushl %edi C save first on stack
AES_ROUND(C_NAME(_nettle_aes_decrypt_table),b,a,d,c)
pushl %edi
AES_ROUND(C_NAME(_nettle_aes_decrypt_table),c,b,a,d)
pushl %edi C save first on stack
AES_ROUND(C_NAME(_nettle_aes_decrypt_table),d,c,b,a)
movl %edi,%edx
popl %ecx
popl %ebx
popl %eax
popl %esi
xorl (%esi),%eax C add current session key to plaintext
xorl 4(%esi),%ebx
xorl 8(%esi),%ecx
xorl 12(%esi),%edx
addl $16,%esi C point to next key
decl %ebp
jnz .Lround_loop
C last round
AES_FINAL_ROUND(a,d,c,b)
pushl %edi
AES_FINAL_ROUND(b,a,d,c)
pushl %edi
AES_FINAL_ROUND(c,b,a,d)
pushl %edi
AES_FINAL_ROUND(d,c,b,a)
movl %edi,%edx
popl %ecx
popl %ebx
popl %eax
C inverse S-box substitution
mov $4,%edi
.Lsubst:
AES_SUBST_BYTE(_nettle_aes_decrypt_table)
decl %edi
jnz .Lsubst
C Add last subkey, and store encrypted data
movl 28(%esp),%edi
AES_STORE(%esi, %edi)
addl $16, 28(%esp) C Increment destination pointer
subl $16, 24(%esp) C Length
C NOTE: Will loop forever if input data is not an
C integer number of blocks.
jnz .Lblock_loop
.Lend:
popl %edi
popl %esi
popl %ebp
popl %ebx
ret
.Leord:
.size C_NAME(nettle_aes_decrypt),.Leord-C_NAME(nettle_aes_decrypt)
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