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// Copyright (c) 2016 Thomas Pornin <pornin@bolet.org>
// All rights reserved.
//
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions
// are met:
//
// 1. Redistributions of source code must retain the above copyright
// notice, this list of conditions and the following disclaimer.
//
// THIS SOFTWARE IS PROVIDED BY THE AUTHORS “AS IS” AND ANY EXPRESS OR
// IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
// WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
// ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHORS BE LIABLE FOR ANY
// DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
// DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE
// GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
// INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
// WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
// NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
// THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
package aes_ct64
inv_sub_bytes :: proc "contextless" (q: ^[8]u64) {
// AES S-box is:
// S(x) = A(I(x)) ^ 0x63
// where I() is inversion in GF(256), and A() is a linear
// transform (0 is formally defined to be its own inverse).
// Since inversion is an involution, the inverse S-box can be
// computed from the S-box as:
// iS(x) = B(S(B(x ^ 0x63)) ^ 0x63)
// where B() is the inverse of A(). Indeed, for any y in GF(256):
// iS(S(y)) = B(A(I(B(A(I(y)) ^ 0x63 ^ 0x63))) ^ 0x63 ^ 0x63) = y
//
// Note: we reuse the implementation of the forward S-box,
// instead of duplicating it here, so that total code size is
// lower. By merging the B() transforms into the S-box circuit
// we could make faster CBC decryption, but CBC decryption is
// already quite faster than CBC encryption because we can
// process four blocks in parallel.
q0 := ~q[0]
q1 := ~q[1]
q2 := q[2]
q3 := q[3]
q4 := q[4]
q5 := ~q[5]
q6 := ~q[6]
q7 := q[7]
q[7] = q1 ~ q4 ~ q6
q[6] = q0 ~ q3 ~ q5
q[5] = q7 ~ q2 ~ q4
q[4] = q6 ~ q1 ~ q3
q[3] = q5 ~ q0 ~ q2
q[2] = q4 ~ q7 ~ q1
q[1] = q3 ~ q6 ~ q0
q[0] = q2 ~ q5 ~ q7
sub_bytes(q)
q0 = ~q[0]
q1 = ~q[1]
q2 = q[2]
q3 = q[3]
q4 = q[4]
q5 = ~q[5]
q6 = ~q[6]
q7 = q[7]
q[7] = q1 ~ q4 ~ q6
q[6] = q0 ~ q3 ~ q5
q[5] = q7 ~ q2 ~ q4
q[4] = q6 ~ q1 ~ q3
q[3] = q5 ~ q0 ~ q2
q[2] = q4 ~ q7 ~ q1
q[1] = q3 ~ q6 ~ q0
q[0] = q2 ~ q5 ~ q7
}
inv_shift_rows :: proc "contextless" (q: ^[8]u64) {
for x, i in q {
q[i] =
(x & 0x000000000000FFFF) |
((x & 0x000000000FFF0000) << 4) |
((x & 0x00000000F0000000) >> 12) |
((x & 0x000000FF00000000) << 8) |
((x & 0x0000FF0000000000) >> 8) |
((x & 0x000F000000000000) << 12) |
((x & 0xFFF0000000000000) >> 4)
}
}
inv_mix_columns :: proc "contextless" (q: ^[8]u64) {
q0 := q[0]
q1 := q[1]
q2 := q[2]
q3 := q[3]
q4 := q[4]
q5 := q[5]
q6 := q[6]
q7 := q[7]
r0 := (q0 >> 16) | (q0 << 48)
r1 := (q1 >> 16) | (q1 << 48)
r2 := (q2 >> 16) | (q2 << 48)
r3 := (q3 >> 16) | (q3 << 48)
r4 := (q4 >> 16) | (q4 << 48)
r5 := (q5 >> 16) | (q5 << 48)
r6 := (q6 >> 16) | (q6 << 48)
r7 := (q7 >> 16) | (q7 << 48)
q[0] = q5 ~ q6 ~ q7 ~ r0 ~ r5 ~ r7 ~ rotr32(q0 ~ q5 ~ q6 ~ r0 ~ r5)
q[1] = q0 ~ q5 ~ r0 ~ r1 ~ r5 ~ r6 ~ r7 ~ rotr32(q1 ~ q5 ~ q7 ~ r1 ~ r5 ~ r6)
q[2] = q0 ~ q1 ~ q6 ~ r1 ~ r2 ~ r6 ~ r7 ~ rotr32(q0 ~ q2 ~ q6 ~ r2 ~ r6 ~ r7)
q[3] = q0 ~ q1 ~ q2 ~ q5 ~ q6 ~ r0 ~ r2 ~ r3 ~ r5 ~ rotr32(q0 ~ q1 ~ q3 ~ q5 ~ q6 ~ q7 ~ r0 ~ r3 ~ r5 ~ r7)
q[4] = q1 ~ q2 ~ q3 ~ q5 ~ r1 ~ r3 ~ r4 ~ r5 ~ r6 ~ r7 ~ rotr32(q1 ~ q2 ~ q4 ~ q5 ~ q7 ~ r1 ~ r4 ~ r5 ~ r6)
q[5] = q2 ~ q3 ~ q4 ~ q6 ~ r2 ~ r4 ~ r5 ~ r6 ~ r7 ~ rotr32(q2 ~ q3 ~ q5 ~ q6 ~ r2 ~ r5 ~ r6 ~ r7)
q[6] = q3 ~ q4 ~ q5 ~ q7 ~ r3 ~ r5 ~ r6 ~ r7 ~ rotr32(q3 ~ q4 ~ q6 ~ q7 ~ r3 ~ r6 ~ r7)
q[7] = q4 ~ q5 ~ q6 ~ r4 ~ r6 ~ r7 ~ rotr32(q4 ~ q5 ~ q7 ~ r4 ~ r7)
}
@(private)
_decrypt :: proc "contextless" (q: ^[8]u64, skey: []u64, num_rounds: int) {
add_round_key(q, skey[num_rounds << 3:])
for u := num_rounds - 1; u > 0; u -= 1 {
inv_shift_rows(q)
inv_sub_bytes(q)
add_round_key(q, skey[u << 3:])
inv_mix_columns(q)
}
inv_shift_rows(q)
inv_sub_bytes(q)
add_round_key(q, skey)
}
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