* x86/aes-decrypt-internal.asm: New file.

Rev: src/nettle/x86/aes-decrypt-internal.asm:1.1

x86/aes-decrypt-internal.asm

+C -*- mode: asm; asm-comment-char: ?C; -*-  
+C nettle, low-level cryptographics library
+C 
+C Copyright (C) 2001, 2002, 2005 Rafael R. Sevilla, Niels Mller
+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.
+
+C Register usage:
+
+C AES state
+define(<SA>,<%eax>)
+define(<SB>,<%ebx>)
+define(<SC>,<%ecx>)
+define(<SD>,<%edx>)
+
+C Primary use of these registers. They're also used temporarily for other things.
+define(<T>,<%ebp>)
+define(<TMP>,<%edi>)
+define(<KEY>,<%esi>)
+
+define(<FRAME_CTX>,	<28(%esp)>)
+define(<FRAME_TABLE>,	<32(%esp)>)
+define(<FRAME_LENGTH>,	<36(%esp)>)
+define(<FRAME_DST>,	<40(%esp)>)
+define(<FRAME_SRC>,	<44(%esp)>)
+
+define(<FRAME_KEY>,	<4(%esp)>)
+define(<FRAME_COUNT>,	<(%esp)>)
+
+C The aes state is kept in %eax, %ebx, %ecx and %edx
+C
+C %esi is used as temporary, to point to the input, and to the
+C subkeys, etc.
+C
+C %ebp is used as the round counter, and as a temporary in the final round.
+C
+C %edi is a temporary, often used as an accumulator.
+
+	.file "aes-decrypt-internal.asm"
+	
+	C _aes_decrypt(struct aes_context *ctx, 
+	C	       const struct aes_table *T,
+	C	       unsigned length, uint8_t *dst,
+	C	       uint8_t *src)
+	.text
+	.align 16
+PROLOGUE(_nettle_aes_decrypt)
+	C save all registers that need to be saved
+	pushl	%ebx		C  20(%esp)
+	pushl	%ebp		C  16(%esp)
+	pushl	%esi		C  12(%esp)
+	pushl	%edi		C  8(%esp)
+
+	subl	$8, %esp	C  loop counter and save area for the key pointer
+
+	movl	FRAME_LENGTH, %ebp
+	testl	%ebp,%ebp
+	jz	.Lend
+
+.Lblock_loop:
+	movl	FRAME_CTX,KEY	C  address of context struct ctx
+	C  get number of rounds to do from ctx struct	
+	
+	movl	FRAME_SRC,TMP	C  address of plaintext
+	AES_LOAD(SA, SB, SC, SD, TMP, KEY)
+	addl	$16, FRAME_SRC	C Increment src pointer
+	movl	FRAME_TABLE, T
+
+	C  get number of rounds to do from ctx struct	
+	movl	AES_NROUNDS (KEY),TMP
+	subl	$1,TMP
+
+	C Loop counter on stack
+	movl	TMP, FRAME_COUNT
+
+	addl	$16,KEY		C  point to next key
+	movl	KEY,FRAME_KEY
+	.align 16
+.Lround_loop:
+	AES_ROUND(T, SA,SD,SC,SB, TMP, KEY)
+	pushl	TMP
+
+	AES_ROUND(T, SB,SA,SD,SC, TMP, KEY)
+	pushl	TMP
+
+	AES_ROUND(T, SC,SB,SA,SD, TMP, KEY)
+	pushl	TMP
+
+	AES_ROUND(T, SD,SC,SB,SA, TMP, KEY)
+	
+	movl	TMP,SD
+	popl	SC
+	popl	SB
+	popl	SA
+	
+	movl	FRAME_KEY, KEY
+
+	xorl	(KEY),SA	C  add current session key to plaintext
+	xorl	4(KEY),SB
+	xorl	8(KEY),SC
+	xorl	12(KEY),SD
+	addl	$16,FRAME_KEY	C  point to next key
+	decl	FRAME_COUNT
+	jnz	.Lround_loop
+
+	C last round
+
+	AES_FINAL_ROUND(SA,SD,SC,SB, TMP, KEY)
+	pushl	TMP
+
+	AES_FINAL_ROUND(SB,SA,SD,SC, TMP, KEY)
+	pushl	TMP
+
+	AES_FINAL_ROUND(SC,SB,SA,SD, TMP, KEY)
+	pushl	TMP
+
+	AES_FINAL_ROUND(SD,SC,SB,SA, TMP, KEY)
+
+	movl	TMP,SD
+	popl	SC
+	popl	SB
+	popl	SA
+
+	C Inverse S-box substitution
+	mov	$4,TMP
+.Lsubst:
+	AES_SUBST_BYTE(T, KEY)
+
+	decl	TMP
+	jnz	.Lsubst
+
+	C Add last subkey, and store decrypted data
+	movl	FRAME_DST,TMP
+	movl	FRAME_KEY, KEY
+	AES_STORE(SA,SB,SC,SD, KEY, TMP)
+	
+	addl	$16, FRAME_DST		C Increment destination pointer
+	subl	$16, FRAME_LENGTH	C Length
+
+	C NOTE: Will loop forever if input data is not an
+	C integer number of blocks.
+	jnz	.Lblock_loop
+
+.Lend:
+	addl	$8, %esp
+	popl	%edi
+	popl	%esi
+	popl	%ebp
+	popl	%ebx
+	ret
+EPILOGUE(_nettle_aes_decrypt)