aes-decrypt-internal.asm 3.05 KB
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C nettle, low-level cryptographics library
C 
C Copyright (C) 2001, 2002, 2005, 2008 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.

include_src(<x86_64/aes.m4>)

C Register usage:

C AES state, use two of them
define(<SA>,<%eax>)
define(<SB>,<%ebx>)
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define(<SC>,<%ecx>)
define(<SD>,<%edx>)
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define(<TA>,<%r10d>)
define(<TB>,<%r11d>)
define(<TC>,<%r12d>)

define(<CTX>,	<%rdi>)
define(<TABLE>,	<%rsi>)
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define(<PARAM_LENGTH>,<%edx>)		C Length is only 32 bits
define(<PARAM_DST>,	<%rcx>)
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define(<SRC>,	<%r8>)

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define(<DST>, <%r9>) 
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define(<KEY>,<%r14>)
define(<COUNT>,	<%r15d>)
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define(<BLOCK_COUNT>, <%r13d>)
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C Must correspond to an old-style register, for movzb from %ah--%dh to
C work.
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define(<TMP>,<%rbp>)
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	.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(4)
PROLOGUE(_nettle_aes_decrypt)
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	test	PARAM_LENGTH, PARAM_LENGTH
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	jz	.Lend

        C save all registers that need to be saved
	push	%rbx
	push	%rbp
	push	%r12
	push	%r13
	push	%r14
	push	%r15	

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	mov	PARAM_DST, DST
	movl	PARAM_LENGTH, BLOCK_COUNT
	shrl	$4, BLOCK_COUNT
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.Lblock_loop:
	mov	CTX,KEY
	
	AES_LOAD(SA, SB, SC, SD, SRC, KEY)
	add	$16, SRC	C Increment src pointer

	C  get number of rounds to do from ctx struct	
	movl	AES_NROUNDS (CTX), COUNT
	subl	$1, COUNT

	add	$16,KEY		C  point to next key
	ALIGN(4)
.Lround_loop:
	AES_ROUND(TABLE, SA,SD,SC,SB, TA, TMP)
	AES_ROUND(TABLE, SB,SA,SD,SC, TB, TMP)
	AES_ROUND(TABLE, SC,SB,SA,SD, TC, TMP)
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	AES_ROUND(TABLE, SD,SC,SB,SA, SD, TMP)
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	movl	TA, SA
	movl	TB, SB
	movl	TC, SC
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	xorl	(KEY),SA	C  add current session key to plaintext
	xorl	4(KEY),SB
	xorl	8(KEY),SC
	xorl	12(KEY),SD
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	add	$16,KEY	C  point to next key
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	decl	COUNT
	jnz	.Lround_loop

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	C last round
	AES_FINAL_ROUND(SA,SD,SC,SB, TABLE, TA, TMP)
	AES_FINAL_ROUND(SB,SA,SD,SC, TABLE, TB, TMP)
	AES_FINAL_ROUND(SC,SB,SA,SD, TABLE, TC, TMP)
	AES_FINAL_ROUND(SD,SC,SB,SA, TABLE, SD, TMP)
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	C Inverse S-box substitution
	mov	$3, COUNT
.Lsubst:
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	AES_SUBST_BYTE(TA,TB,TC,SD, TABLE, TMP)
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	decl	COUNT
	jnz	.Lsubst

	C Add last subkey, and store decrypted data
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	AES_STORE(TA,TB,TC,SD, KEY, DST)
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	add	$16, DST
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	decl	BLOCK_COUNT
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	jnz	.Lblock_loop

	pop	%r15	
	pop	%r14
	pop	%r13
	pop	%r12
	pop	%rbp
	pop	%rbx
.Lend:
	ret
EPILOGUE(_nettle_aes_decrypt)