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-rw-r--r--src/aes128.asm158
1 files changed, 121 insertions, 37 deletions
diff --git a/src/aes128.asm b/src/aes128.asm
index b375daf..4f50e8f 100644
--- a/src/aes128.asm
+++ b/src/aes128.asm
@@ -49,49 +49,133 @@ inverted_key_schedule oword 11 dup(0)
@raw_aes128ecb_decrypt@32 endp
expand_keys_128ecb proc
- lea ecx, [key_schedule + 10h]
- movdqa [key_schedule], xmm1
-
- aeskeygenassist xmm7, xmm1, 01h
- call gen_round_key
- aeskeygenassist xmm7, xmm1, 02h
- call gen_round_key
- aeskeygenassist xmm7, xmm1, 04h
- call gen_round_key
- aeskeygenassist xmm7, xmm1, 08h
- call gen_round_key
- aeskeygenassist xmm7, xmm1, 10h
- call gen_round_key
- aeskeygenassist xmm7, xmm1, 20h
- call gen_round_key
- aeskeygenassist xmm7, xmm1, 40h
- call gen_round_key
- aeskeygenassist xmm7, xmm1, 80h
- call gen_round_key
- aeskeygenassist xmm7, xmm1, 1Bh
- call gen_round_key
- aeskeygenassist xmm7, xmm1, 36h
- call gen_round_key
+ ; A "word" (in terms of the FIPS 187 standard) is a 32-bit block.
+ ; Words are denoted by `w[N]`.
+ ;
+ ; A key schedule is composed of 10 "regular" keys and a dumb key for
+ ; the "whitening" step.
+ ; It's stored in `key_schedule`.
+ ;
+ ; A key schedule is thus composed of 44 "words".
+ ; The FIPS standard includes an algorithm to calculate these words via
+ ; a simple loop:
+ ;
+ ; i = 4
+ ; while i < 44:
+ ; temp = w[i - 1]
+ ; if i % 4 == 0:
+ ; temp = SubWord(RotWord(temp))^Rcon
+ ; w[i] = w[i - 4]^temp
+ ; i = i + 1
+ ;
+ ; The loop above may be unrolled like this:
+ ;
+ ; w[4] = SubWord(RotWord(w[3]))^Rcon^w[0]
+ ; w[5] = w[4]^w[1]
+ ; = SubWord(RotWord(w[3]))^Rcon^w[1]^w[0]
+ ; w[6] = w[5]^w[2]
+ ; = SubWord(RotWord(w[3]))^Rcon^w[2]^w[1]^w[0]
+ ; w[7] = w[6]^w[3]
+ ; = SubWord(RotWord(w[3]))^Rcon^w[3]^w[2]^w[1]^w[0]
+ ; w[8] = SubWord(RotWord(w[7]))^Rcon^w[4]
+ ; w[9] = w[8]^w[5]
+ ; = SubWord(RotWord(w[7]))^Rcon^w[5]^w[4]
+ ; w[10] = w[9]^w[6]
+ ; = SubWord(RotWord(w[7]))^Rcon^w[6]^w[5]^w[4]
+ ; w[11] = w[10]^w[7]
+ ; = SubWord(RotWord(w[7]))^Rcon^w[7]^w[6]^w[5]^w[4]
+ ;
+ ; ... and so on.
+ ;
+ ; The Intel AES-NI instruction set facilitates calculating SubWord
+ ; and RotWord using `aeskeygenassist`, which is used in this routine.
+ ;
+ ; Preconditions:
+ ; * xmm1[127:96] == w[3],
+ ; * xmm1[95:64] == w[2],
+ ; * xmm1[63:32] == w[1],
+ ; * xmm1[31:0] == w[0].
+
+ movdqa [key_schedule], xmm1 ; sets w[0], w[1], w[2], w[3]
+
+ lea ecx, [key_schedule + 10h] ; ecx = &w[4]
+ aeskeygenassist xmm7, xmm1, 01h ; xmm7[127:96] = RotWord(SubWord(w[3]))^Rcon
+ call gen_round_key ; sets w[4], w[5], w[6], w[7]
+ aeskeygenassist xmm7, xmm1, 02h ; xmm7[127:96] = RotWord(SubWord(w[7]))^Rcon
+ call gen_round_key ; sets w[8], w[9], w[10], w[11]
+ aeskeygenassist xmm7, xmm1, 04h ; xmm7[127:96] = RotWord(SubWord(w[11]))^Rcon
+ call gen_round_key ; sets w[12], w[13], w[14], w[15]
+ aeskeygenassist xmm7, xmm1, 08h ; xmm7[127:96] = RotWord(SubWord(w[15]))^Rcon
+ call gen_round_key ; sets w[16], w[17], w[18], w[19]
+ aeskeygenassist xmm7, xmm1, 10h ; xmm7[127:96] = RotWord(SubWord(w[19]))^Rcon
+ call gen_round_key ; sets w[20], w[21], w[22], w[23]
+ aeskeygenassist xmm7, xmm1, 20h ; xmm7[127:96] = RotWord(SubWord(w[23]))^Rcon
+ call gen_round_key ; sets w[24], w[25], w[26], w[27]
+ aeskeygenassist xmm7, xmm1, 40h ; xmm7[127:96] = RotWord(SubWord(w[27]))^Rcon
+ call gen_round_key ; sets w[28], w[29], w[30], w[31]
+ aeskeygenassist xmm7, xmm1, 80h ; xmm7[127:96] = RotWord(SubWord(w[31]))^Rcon
+ call gen_round_key ; sets w[32], w[33], w[34], w[35]
+ aeskeygenassist xmm7, xmm1, 1Bh ; xmm7[127:96] = RotWord(SubWord(w[35]))^Rcon
+ call gen_round_key ; sets w[36], w[37], w[38], w[39]
+ aeskeygenassist xmm7, xmm1, 36h ; xmm7[127:96] = RotWord(SubWord(w[39]))^Rcon
+ call gen_round_key ; sets w[40], w[41], w[42], w[43]
call invert_key_schedule
ret
gen_round_key:
- movdqa xmm6, xmm1 ; xmm6 = key_schedule[i]
- ; xmm6 = x3 x2 x1 x0
+ ; Preconditions:
+ ; * xmm1[127:96] == w[i+3],
+ ; * xmm1[95:64] == w[i+2],
+ ; * xmm1[63:32] == w[i+1],
+ ; * xmm1[31:0] == w[i],
+ ; * xmm7[127:96] == RotWord(SubWord(w[i+3]))^Rcon,
+ ; * ecx == &w[i+4].
+ ;
+ ; Postconditions:
+ ; * xmm1[127:96] == w[i+7] == RotWord(SubWord(w[i+3]))^Rcon^w[i+3]^w[i+2]^w[i+1]^w[i],
+ ; * xmm1[95:64] == w[i+6] == RotWord(SubWord(w[i+3]))^Rcon^w[i+2]^w[i+1]^w[i],
+ ; * xmm1[63:32] == w[i+5] == RotWord(SubWord(w[i+3]))^Rcon^w[i+1]^w[i],
+ ; * xmm1[31:0] == w[i+4] == RotWord(SubWord(w[i+3]))^Rcon^w[i],
+ ; * ecx == &w[i+8],
+ ; * the value in xmm6 is also modified.
+
+ ; Calculate
+ ; w[i+3]^w[i+2]^w[i+1]^w[i],
+ ; w[i+2]^w[i+1]^w[i],
+ ; w[i+1]^w[i] and
+ ; w[i].
+ movdqa xmm6, xmm1 ; xmm6 = xmm1
+ pslldq xmm6, 4 ; xmm6 <<= 32
+ pxor xmm1, xmm6 ; xmm1 ^= xmm6
+ pslldq xmm6, 4 ; xmm6 <<= 32
+ pxor xmm1, xmm6 ; xmm1 ^= xmm6
+ pslldq xmm6, 4 ; xmm6 <<= 32
+ pxor xmm1, xmm6 ; xmm1 ^= xmm6
+ ; xmm1[127:96] == w[i+3]^w[i+2]^w[i+1]^w[i]
+ ; xmm1[95:64] == w[i+2]^w[i+1]^w[i]
+ ; xmm1[63:32] == w[i+1]^w[i]
+ ; xmm1[31:0] == w[i]
+
+ ; Calculate
+ ; w[i+7] == RotWord(SubWord(w[i+3]))^Rcon^w[i+3]^w[i+2]^w[i+1]^w[i],
+ ; w[i+6] == RotWord(SubWord(w[i+3]))^Rcon^w[i+2]^w[i+1]^w[i],
+ ; w[i+5] == RotWord(SubWord(w[i+3]))^Rcon^w[i+1]^w[i] and
+ ; w[i+4] == RotWord(SubWord(w[i+3]))^Rcon^w[i].
+ pshufd xmm6, xmm7, 0FFh ; xmm6[127:96] = xmm6[95:64] = xmm6[63:32] = xmm6[31:0] = xmm7[127:96]
+ pxor xmm1, xmm6 ; xmm1 ^= xmm6
+ ; xmm1[127:96] == w[i+7] == RotWord(SubWord(w[i+3]))^Rcon^w[i+3]^w[i+2]^w[i+1]^w[i]
+ ; xmm1[95:64] == w[i+6] == RotWord(SubWord(w[i+3]))^Rcon^w[i+2]^w[i+1]^w[i]
+ ; xmm1[63:32] == w[i+5] == RotWord(SubWord(w[i+3]))^Rcon^w[i+1]^w[i]
+ ; xmm1[31:0] == w[i+4] == RotWord(SubWord(w[i+3]))^Rcon^w[i]
+
+ ; Set w[i+4], w[i+5], w[i+6] and w[i+7].
+ movdqa [ecx], xmm1 ; w[i+7] = RotWord(SubWord(w[i+3]))^Rcon^w[i+3]^w[i+2]^w[i+1]^w[i]
+ ; w[i+6] = RotWord(SubWord(w[i+3]))^Rcon^w[i+2]^w[i+1]^w[i]
+ ; w[i+5] = RotWord(SubWord(w[i+3]))^Rcon^w[i+1]^w[i]
+ ; w[i+4] = RotWord(SubWord(w[i+3]))^Rcon^w[i]
+ add ecx, 10h ; ecx = &w[i+8]
- pslldq xmm6, 4 ; xmm6 = x2 x1 x0 0
- pxor xmm1, xmm6 ; xmm1 = (x3 x2) (x2 x1) (x1 x0) x0
- pslldq xmm6, 4 ; xmm6 = x1 x0 0 0
- pxor xmm1, xmm6 ; xmm1 = (x3 x2 x1) (x2 x1 x0) (x1 x0) x0
- pslldq xmm6, 4 ; xmm6 = x0 0 0 0
- pxor xmm1, xmm6 ; xmm1 = (x3 x2 x1 x0) (x2 x1 x0) (x1 x0) x0
-
- pshufd xmm7, xmm7, 0FFh
- pxor xmm1, xmm7
-
- movdqa [ecx], xmm1
- add ecx, 10h
ret
invert_key_schedule: