diff --git a/x86_64/serpent-decrypt.asm b/x86_64/serpent-decrypt.asm
new file mode 100644
index 0000000000000000000000000000000000000000..6836c7bec6fd4dbc2cf6859f5cd59be641fa5258
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+++ b/x86_64/serpent-decrypt.asm
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+C nettle, low-level cryptographics library
+C 
+C Copyright (C) 2011 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.
+	
+C Register usage:
+
+C Single block serpent state, two copies
+define(<x0>, <%eax>)
+define(<x1>, <%ebx>)
+define(<x2>, <%ebp>)
+define(<x3>, <%r8d>)
+
+define(<y0>, <%r9d>)
+define(<y1>, <%r10d>)
+define(<y2>, <%r11d>)
+define(<y3>, <%r12d>)
+
+C Quadruple block serpent state, two copies
+define(<X0>, <%xmm0>)
+define(<X1>, <%xmm1>)
+define(<X2>, <%xmm2>)
+define(<X3>, <%xmm3>)
+
+define(<Y0>, <%xmm4>)
+define(<Y1>, <%xmm5>)
+define(<Y2>, <%xmm6>)
+define(<Y3>, <%xmm7>)
+
+define(<MINUS1>, <%xmm8>)
+define(<T0>, <%xmm9>)
+define(<T1>, <%xmm10>)
+define(<T2>, <%xmm11>)
+define(<T3>, <%xmm12>)
+
+C Arguments
+define(<CTX>, <%rdi>)
+define(<N>, <%rsi>)
+define(<DST>, <%rdx>)
+define(<SRC>, <%rcx>)
+
+define(<CNT>, <%r13>)
+define(<TMP32>, <%r14d>)
+
+C SBOX macros. Inputs $1 - $4 (destroyed), outputs $5 - $8
+
+define(<SBOX0I>, <
+	mov	$1, $5
+	xor	$3, $5
+	mov	$1, $7
+	or	$2, $7
+	mov	$3, $6
+	xor	$4, $6
+	xor	$6, $7
+	and	$3, $6
+	or	$2, $3
+	xor	$4, $2
+	or	$1, $6
+	and	$3, $2
+	xor	$2, $6
+	or	$7, $1
+	xor	$6, $1
+	mov	$7, $2
+	xor	$1, $2
+	not	$7
+	or	$7, $4
+	xor	$3, $4
+	mov	$1, $8
+	xor	$4, $8
+	or	$4, $2
+	xor	$2, $5
+>)
+
+define(<SBOX1I>, <
+	mov	$2, $6
+	or	$4, $6
+	xor	$6, $3
+	mov	$1, $8
+	xor	$2, $8
+	mov	$1, $5
+	or	$6, $5
+	and	$8, $5
+	xor	$5, $2
+	xor	$6, $8
+	and	$4, $2
+	mov	$1, $7
+	and	$3, $7
+	or	$7, $6
+	or	$4, $7
+	xor	$5, $7
+	not	$7
+	xor	$2, $6
+	xor	$6, $5
+	xor	$3, $5
+	or	$7, $1
+	xor	$1, $5
+>)
+
+define(<SBOX2I>, <
+	mov	$1, $5
+	xor	$4, $5
+	mov	$3, $7
+	xor	$4, $7
+	mov	$2, $6
+	or	$7, $6
+	xor	$6, $5
+	mov	$4, $6
+	or	$5, $6
+	and	$2, $6
+	not	$4
+	mov	$1, $8
+	or	$3, $8
+	and	$8, $7
+	xor	$7, $6
+	and	$2, $8
+	and	$3, $1
+	or	$4, $1
+	xor	$1, $8
+	and	$8, $3
+	xor	$1, $3
+	mov	$5, $7
+	xor	$6, $7
+	xor	$3, $7
+>)
+
+define(<SBOX3I>, <
+	mov	$3, $8
+	or	$4, $8
+	mov	$2, $5
+	and	$8, $5
+	mov	$1, $7
+	or	$4, $7
+	mov	$3, $6
+	xor	$7, $6
+	xor	$6, $5
+	xor	$1, $4
+	xor	$4, $8
+	xor	$2, $7
+	and	$6, $7
+	xor	$4, $7
+	xor	$1, $6
+	or	$5, $4
+	and	$4, $6
+	xor	$2, $6
+	and	$7, $1
+	or	$2, $1
+	xor	$1, $8
+>)
+
+define(<SBOX4I>, <
+	mov	$3, $6
+	xor	$4, $6
+	mov	$3, $7
+	or	$4, $7
+	xor	$2, $7
+	or	$4, $2
+	mov	$1, $5
+	xor	$7, $5
+	xor	$7, $4
+	and	$1, $7
+	xor	$7, $6
+	xor	$1, $7
+	or	$3, $7
+	and	$2, $1
+	mov	$1, $8
+	xor	$4, $8
+	not	$1
+	or	$6, $1
+	xor	$1, $5
+	xor	$2, $1
+	xor	$1, $7
+>)
+
+define(<SBOX5I>, <
+	mov	$1, $6
+	and	$4, $6
+	mov	$3, $8
+	xor	$6, $8
+	mov	$2, $5
+	and	$8, $5
+	mov	$1, $7
+	xor	$4, $7
+	xor	$2, $4
+	xor	$7, $5
+	and	$1, $3
+	and	$5, $1
+	or	$2, $3
+	xor	$5, $6
+	xor	$3, $6
+	mov	$5, $7
+	or	$6, $7
+	xor	$8, $7
+	xor	$4, $7
+	not	$2
+	or	$1, $2
+	xor	$2, $8
+>)
+
+define(<SBOX6I>, <
+	mov	$1, $7
+	xor	$3, $7
+	not	$3
+	mov	$2, $5
+	xor	$4, $5
+	mov	$1, $6
+	or	$3, $6
+	xor	$5, $6
+	mov	$2, $8
+	and	$7, $8
+	or	$4, $8
+	or	$3, $4
+	or	$2, $3
+	and	$1, $3
+	mov	$3, $5
+	xor	$8, $5
+	not	$5
+	and	$7, $8
+	xor	$3, $8
+	xor	$6, $1
+	xor	$1, $8
+	and	$5, $2
+	xor	$2, $7
+	xor	$4, $7
+>)
+
+define(<SBOX7I>, <
+	mov	$1, $8
+	and	$2, $8
+	mov	$2, $7
+	xor	$4, $7
+	or	$8, $7
+	mov	$1, $6
+	or	$4, $6
+	and	$4, $6
+	xor	$6, $7
+	or	$3, $8
+	mov	$1, $5
+	or	$2, $5
+	and	$4, $5
+	xor	$5, $8
+	xor	$2, $5
+	mov	$4, $6
+	xor	$8, $6
+	not	$6
+	or	$5, $6
+	xor	$3, $5
+	xor	$1, $6
+	or	$6, $4
+	xor	$4, $5
+>)
+
+define(<LTI>, <
+	rol	<$>10, $3
+	rol	<$>27, $1
+	mov	$2, TMP32
+	shl	<$>7, TMP32
+	xor	$4, $3
+	xor	TMP32, $3
+	xor	$2, $1
+	xor	$4, $1
+	rol	<$>25, $4
+	rol	<$>31, $2
+	mov	$1, TMP32
+	shl	<$>3, TMP32
+	xor	$3, $4
+	xor	TMP32, $4
+	xor	$1, $2
+	xor	$3, $2
+	rol	<$>29, $3
+	rol	<$>19, $1
+>)
+
+	.file "serpent-decrypt.asm"
+	
+	C serpent_decrypt(struct serpent_context *ctx, 
+	C	          unsigned length, uint8_t *dst,
+	C	          const uint8_t *src)
+	.text
+	ALIGN(4)
+PROLOGUE(nettle_serpent_decrypt)
+        C save all registers that need to be saved
+	push	%rbx
+	push	%rbp
+	push	%r12
+	push	%r13
+	push	%r14
+
+	lea	(SRC, N), SRC
+	lea	(DST, N), DST
+	neg	N
+	jz	.Lend
+
+.Lblock_loop:
+	movl	(SRC, N), x0
+	movl	4(SRC, N), x1
+	movl	8(SRC, N), x2
+	movl	12(SRC, N), x3
+
+	
+	movl	x0, (DST, N)
+	movl	x1, 4(DST, N)
+	movl	x2, 8(DST, N)
+	movl	x3, 12(DST, N)
+	add	$16, N
+	jnc	.Lblock_loop
+	
+.Lend:
+	pop	%r14
+	pop	%r13
+	pop	%r12
+	pop	%rbp
+	pop	%rbx
+	ret