aes192: more comments & optimize key generation

1 files changed, 155 insertions, 92 deletions

diff --git a/src/aes192.asm b/src/aes192.asm
index 9695961..9cd4cfa 100644
--- a/src/aes192.asm
+++ b/src/aes192.asm
@@ -53,107 +53,170 @@ inverted_key_schedule oword 13 dup(0)
 @raw_aes192ecb_decrypt@48 endp
 
 expand_keys_192ecb proc
-    ; key = k0 k1 k2 k3 k4 k5
-    ; xmm1 = k0 k1 k2 k3
-    ; xmm2 =  0  0 k5 k4
-
-    ; w[0] = k0 k1 k2 k3
-    ; w[1] = k4 k5  -  -
-
+    ; 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 12 "regular" keys and a dumb key for
+    ; the "whitening" step.
+    ; It's stored in `key_schedule`.
+    ;
+    ; A key schedule is thus composed of 52 "words".
+    ; The FIPS standard includes an algorithm to calculate these words via
+    ; a simple loop:
+    ;
     ; i = 6
-    ; while (i < 52):
+    ; while i < 52:
     ;     temp = w[i - 1]
-    ;     if (i % 6 == 0):
-    ;         temp = SubWord(RotWord(w[i - 1])) * Rcon
-    ;     w[i] = w[i - 6] * temp
+    ;     if i % 6 == 0:
+    ;         temp = SubWord(RotWord(temp))^Rcon
+    ;     w[i] = w[i - 6]^temp
     ;     i = i + 1
+    ;
+    ; The loop above may be unrolled like this:
+    ;
+    ; w[6] = SubWord(RotWord(w[5]))^Rcon^w[0]
+    ; w[7] = w[6]^w[1]
+    ;      = SubWord(RotWord(w[5]))^Rcon^w[0]^w[1]
+    ; w[8] = w[7]^w[2]
+    ;      = SubWord(RotWord(w[5]))^Rcon^w[0]^w[1]^w[2]
+    ; w[9] = w[8]^w[3]
+    ;      = SubWord(RotWord(w[5]))^Rcon^w[0]^w[1]^w[2]^w[3]
+    ; w[10] = w[9]^w[4]
+    ;       = SubWord(RotWord(w[5]))^Rcon^w[0]^w[1]^w[2]^w[3]^w[4]
+    ; w[11] = w[10]^w[5]
+    ;       = SubWord(RotWord(w[5]))^Rcon^w[0]^w[1]^w[2]^w[3]^w[4]^w[5]
+    ; w[12] = SubWord(RotWord(w[11]))^Rcon^w[6]
+    ; w[13] = w[12]^w[7]
+    ;       = SubWord(RotWord(w[11]))^Rcon^w[6]^w[7]
+    ; w[14] = w[13]^w[8]
+    ;       = SubWord(RotWord(w[11]))^Rcon^w[6]^w[7]^w[8]
+    ; w[15] = w[14]^w[9]
+    ;       = SubWord(RotWord(w[11]))^Rcon^w[6]^w[7]^w[8]^w[9]
+    ; w[16] = w[15]^w[10]
+    ;       = SubWord(RotWord(w[11]))^Rcon^w[6]^w[7]^w[8]^w[9]^w[10]
+    ; w[17] = w[16]^w[11]
+    ;       = SubWort(RotWord(w[11]))^Rcon^w[6]^w[7]^w[8]^w[9]^w[10]^w[11]
+    ;
+    ; ... and so on.
+    ;
+    ; The Intel AES-NI instruction set facilitates calculating SubWord
+    ; and RotWord using `aeskeygenassist`, which is used in this routine.
+    ;
+    ; Preconditions:
+    ; * xmm2[63:32]  == w[5],
+    ; * xmm2[31:0]   == w[4],
+    ; * 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]
+    movdqa [key_schedule + 10h], xmm2    ; sets w[4], w[5]
 
-    ; w[6] = SubWord(RotWord(w[5])) * Rcon * w[0]
-    ; w[7] = w[6] * w[1]
-    ;      = SubWord(RotWord(w[5])) * Rcon * w[0] * w[1]
-    ; w[8] = w[7] * w[2]
-    ;      = SubWord(RotWord(w[5])) * Rcon * w[0] * w[1] * w[2]
-    ; w[9] = w[8] * w[3]
-    ;      = SubWord(RotWord(w[5])) * Rcon * w[0] * w[1] * w[2] * w[3]
-    ; w[10] = w[9] * w[4]
-    ;       = SubWord(RotWord(w[5])) * Rcon * w[0] * w[1] * w[2] * w[3] * w[4]
-    ; w[11] = w[10] * w[5]
-    ;       = SubWord(RotWord(w[5])) * Rcon * w[0] * w[1] * w[2] * w[3] * w[4] * w[5]
-
-    movdqa [key_schedule], xmm1
-    movdqa [key_schedule + 10h], xmm2
-
-    lea ecx, [key_schedule + 18h]
-    aeskeygenassist xmm7, xmm2, 1
-    call gen_round_key
-    aeskeygenassist xmm7, xmm2, 2
-    call gen_round_key
-    aeskeygenassist xmm7, xmm2, 4
-    call gen_round_key
-    aeskeygenassist xmm7, xmm2, 8
-    call gen_round_key
-    aeskeygenassist xmm7, xmm2, 10h
-    call gen_round_key
-    aeskeygenassist xmm7, xmm2, 20h
-    call gen_round_key
-    aeskeygenassist xmm7, xmm2, 40h
-    call gen_round_key
-    aeskeygenassist xmm7, xmm2, 80h
-    call gen_round_key
+    lea ecx, [key_schedule + 18h]        ; ecx = &w[6]
+    aeskeygenassist xmm7, xmm2, 1        ; xmm7[63:32] = RotWord(SubWord(w[5]))^Rcon,
+    call gen_round_key                   ; sets w[6], w[7], w[8], w[9], w[10], w[11]
+    aeskeygenassist xmm7, xmm2, 2        ; xmm7[63:32] = RotWord(SubWord(w[11]))^Rcon
+    call gen_round_key                   ; sets w[12], w[13], w[14], w[15], w[16], w[17]
+    aeskeygenassist xmm7, xmm2, 4        ; xmm7[63:32] = RotWord(SubWord(w[17]))^Rcon
+    call gen_round_key                   ; sets w[18], w[19], w[20], w[21], w[22], w[23]
+    aeskeygenassist xmm7, xmm2, 8        ; xmm7[63:32] = RotWord(SubWord(w[23]))^Rcon
+    call gen_round_key                   ; sets w[24], w[25], w[26], w[27], w[28], w[29]
+    aeskeygenassist xmm7, xmm2, 10h      ; xmm7[63:32] = RotWord(SubWord(w[29]))^Rcon
+    call gen_round_key                   ; sets w[30], w[31], w[32], w[33], w[34], w[35]
+    aeskeygenassist xmm7, xmm2, 20h      ; xmm7[63:32] = RotWord(SubWord(w[35]))^Rcon
+    call gen_round_key                   ; sets w[36], w[37], w[38], w[39], w[40], w[41]
+    aeskeygenassist xmm7, xmm2, 40h      ; xmm7[63:32] = RotWord(SubWord(w[41]))^Rcon
+    call gen_round_key                   ; sets w[42], w[43], w[44], w[45], w[46], w[47]
+    aeskeygenassist xmm7, xmm2, 80h      ; xmm7[63:32] = RotWord(SubWord(w[49]))^Rcon
+    call gen_round_key                   ; sets w[48], w[49], w[50], w[51], w[52], w[53] // FIXME
 
     call invert_key_schedule
     ret
 
 gen_round_key:
-    ; xmm1 = x3 x2 x1 x0
-    ; xmm2 =  -  - x5 x4
-    ; xmm7 = RotWord(SubWord(-)) xor Rcon
-    ;        SubWord(-)
-    ;        RotWord(SubWord(x5)) xor Rcon
-    ;        SubWord(x5)
-    movdqa xmm6, xmm1
-
-    pslldq xmm6, 4     ; xmm6 = x2 x1 x0 0
-    pxor xmm1, xmm6    ; xmm1 = (x3 * x2) (x1 * x2) (x1 * x0) x0
-    pslldq xmm6, 4     ; xmm6 = x1 x0 0 0
-    pxor xmm1, xmm6    ; xmm1 = (x3 * x2 * x1) (x1 * x2 * x0) (x1 * x0) x0
-    pslldq xmm6, 4     ; xmm6 = x0 0 0 0
-    pxor xmm1, xmm6    ; xmm1 = (x3 * x2 * x1 * x0) (x1 * x2 * x0) (x1 * x0) x0
-
-    pshufd xmm7, xmm7, 55h    ; xmm7 = RotWord(SubWord(x5)) * Rcon
-                              ;        RotWord(SubWord(x5)) * Rcon
-                              ;        RotWord(SubWord(x5)) * Rcon
-                              ;        RotWord(SubWord(x5)) * Rcon
-
-    pxor xmm1, xmm7    ; xmm1 = RotWord(SubWord(x5)) * Rcon * x3 * x2 * x1 * x0
-                       ;        RotWord(SubWord(x5)) * Rcon * x2 * x1 * x0
-                       ;        RotWord(SubWord(x5)) * Rcon * x1 * x0
-                       ;        RotWord(SubWord(x5)) * Rcon * x0
-
-    movq qword ptr [ecx], xmm1
-    add ecx, 8
-
-    pshufd xmm7, xmm1, 0FFh    ; xmm7 = -
-                               ;        -
-                               ;        RotWord(SubWord(x5)) * Rcon * x3 * x2 * x1 * x0
-                               ;        RotWord(SubWord(x5)) * Rcon * x3 * x2 * x1 * x0
-    pxor xmm7, xmm2            ; xmm7 = -
-                               ;        -
-                               ;        RotWord(SubWord(x5)) * Rcon * x5 * x3 * x2 * x1 * x0
-                               ;        RotWord(SubWord(x5)) * Rcon * x4 * x3 * x2 * x1 * x0
-    pslldq xmm2, 4             ; xmm2 = - k5 k4 0
-    pxor xmm7, xmm2            ; xmm7 = -
-                               ;        -
-                               ;        RotWord(SubWord(x5)) * Rcon * x5 * x4 * x3 * x2 * x1 * x0
-                               ;        RotWord(SubWord(x5)) * Rcon * x4 * x3 * x2 * x1 * x0
-
-    movq xmm2, xmm7
-    pslldq xmm7, 8
-    movdqa xmm6, xmm1
-    psrldq xmm6, 8
-    por xmm7, xmm6
-    movdqu [ecx], xmm7
-    add ecx, 10h
+    ; Preconditions:
+    ; * xmm2[127:96] == 0,
+    ; * xmm2[95:64]  == 0,
+    ; * xmm2[63:32]  == w[i+5],
+    ; * xmm2[31:0]   == w[i+4],
+    ; * xmm1[127:96] == w[i+3],
+    ; * xmm1[95:64]  == w[i+2],
+    ; * xmm1[63:32]  == w[i+1],
+    ; * xmm1[31:0]   == w[i],
+    ; * xmm7[63:32]  == RotWord(SubWord(w[i+5]))^Rcon,
+    ; * ecx == &w[i+6].
+    ;
+    ; Postconditions:
+    ; * xmm2[127:96] == 0,
+    ; * xmm2[95:64]  == 0,
+    ; * xmm2[63:32]  == w[i+11] == RotWord(SubWord(w[i+5]))^Rcon^w[i+5]^w[i+4]^w[i+3]^w[i+2]^w[i+1]^w[i],
+    ; * xmm2[31:0]   == w[i+10] == RotWord(SubWord(w[i+5]))^Rcon^w[i+4]^w[i+3]^w[i+2]^w[i+1]^w[i],
+    ; * xmm1[127:96] == w[i+9]  == RotWord(SubWord(w[i+5]))^Rcon^w[i+3]^w[i+2]^w[i+1]^w[i],
+    ; * xmm1[95:64]  == w[i+8]  == RotWord(SubWord(w[i+5]))^Rcon^w[i+2]^w[i+1]^w[i],
+    ; * xmm1[63:32]  == w[i+7]  == RotWord(SubWord(w[i+5]))^Rcon^w[i+1]^w[i],
+    ; * xmm1[31:0]   == w[i+6]  == RotWord(SubWord(w[i+5]))^Rcon^w[i],
+    ; * ecx == &w[i+12],
+    ; * 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 <<= 4
+    pxor xmm1, xmm6      ; xmm1 ^= xmm6
+    pslldq xmm6, 4       ; xmm6 <<= 4
+    pxor xmm1, xmm6      ; xmm1 ^= xmm6
+    pslldq xmm6, 4       ; xmm6 <<= 4
+    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+9] == RotWord(SubWord(w[i+5]))^Rcon^w[i+3]^w[i+2]^w[i+1]^w[i],
+    ;     w[i+8] == RotWord(SubWord(w[i+5]))^Rcon^w[i+2]^w[i+1]^w[i],
+    ;     w[i+7] == RotWord(SubWord(w[i+5]))^Rcon^w[i+1]^w[i] and
+    ;     w[i+6] == RotWord(SubWord(w[i+5]))^Rcon^w[i].
+    pshufd xmm6, xmm7, 55h    ; xmm6[127:96] = xmm6[95:64] = xmm6[63:32] = xmm6[31:0] = xmm7[63:32]
+    pxor xmm1, xmm6           ; xmm1 ^= xmm6
+                              ; xmm1[127:96] == w[i+9] == RotWord(SubWord(w[i+5]))^Rcon^w[i+3]^w[i+2]^w[i+1]^w[i]
+                              ; xmm1[95:64]  == w[i+8] == RotWord(SubWord(w[i+5]))^Rcon^w[i+2]^w[i+1]^w[i]
+                              ; xmm1[63:32]  == w[i+7] == RotWord(SubWord(w[i+5]))^Rcon^w[i+1]^w[i]
+                              ; xmm1[31:0]   == w[i+6] == RotWord(SubWord(w[i+5]))^Rcon^w[i]
+
+    ; Set w[i+6], w[i+7], w[i+8] and w[i+9].
+    movdqu [ecx], xmm1    ; w[i+6] = RotWord(SubWord(w[i+5]))^Rcon^w[i]
+                          ; w[i+7] = RotWord(SubWord(w[i+5]))^Rcon^w[i+1]^w[i]
+                          ; w[i+8] = RotWord(SubWord(w[i+5]))^Rcon^w[i+2]^w[i+1]^w[i]
+                          ; w[i+9] = RotWord(SubWord(w[i+5]))^Rcon^w[i+3]^w[i+2]^w[i+1]^w[i]
+    add ecx, 10h          ; ecx = &w[i+10]
+
+    ; Calculate
+    ;     w[i+5]^w[i+4],
+    ;     w[i+4].
+    pshufd xmm6, xmm2, 0F3h    ; xmm6 = xmm2[31:0] << 4
+    pxor xmm2, xmm6            ; xmm2 ^= xmm7
+                               ; xmm2[63:32] == w[i+5]^w[i+4]
+                               ; xmm2[31:0]  == w[i+4]
+
+    ; Calculate
+    ;     w[i+10] == RotWord(SubWord(w[i+5]))^Rcon^w[i+5]^w[i+4]^w[i+3]^w[i+2]^w[i+1]^w[i],
+    ;     w[i+11] == RotWord(SubWord(w[i+5]))^Rcon^w[i+4]^w[i+3]^w[i+2]^w[i+1]^w[i].
+    pshufd xmm6, xmm1, 0FFh    ; xmm6[127:96] = xmm6[95:64] = xmm6[63:32] = xmm6[31:0] = xmm1[127:96]
+    psrldq xmm6, 8             ; xmm6 >>= 8
+    pxor xmm2, xmm6            ; xmm2 ^= xmm6
+                               ; xmm2[63:32] == w[i+11] == RotWord(SubWord(w[i+5]))^Rcon^w[i+5]^w[i+4]^w[i+3]^w[i+2]^w[i+1]^w[i]
+                               ; xmm2[31:0]  == w[i+10] == RotWord(SubWord(w[i+5]))^Rcon^w[i+4]^w[i+3]^w[i+2]^w[i+1]^w[i]
+
+    ; Set w[i+10] and w[i+11].
+    movq qword ptr [ecx], xmm2    ; w[i+10] = RotWord(SubWord(w[i+5]))^Rcon^w[i+4]^w[i+3]^w[i+2]^w[i+1]^w[i]
+                                  ; w[i+11] = RotWord(SubWord(w[i+5]))^Rcon^w[i+5]^w[i+4]^w[i+3]^w[i+2]^w[i+1]^w[i]
+    add ecx, 8                    ; ecx = &w[i+12]
+
     ret
 
 invert_key_schedule: