mirror of
https://github.com/cheat/cheat.git
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268 lines
7.2 KiB
Go
268 lines
7.2 KiB
Go
// Copyright 2009 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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// Originally from: https://github.com/go/blob/master/src/crypto/sha1/sha1block.go
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// It has been modified to support collision detection.
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package sha1cd
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import (
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"fmt"
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"math/bits"
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shared "github.com/pjbgf/sha1cd/internal"
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"github.com/pjbgf/sha1cd/ubc"
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)
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// blockGeneric is a portable, pure Go version of the SHA-1 block step.
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// It's used by sha1block_generic.go and tests.
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func blockGeneric(dig *digest, p []byte) {
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var w [16]uint32
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// cs stores the pre-step compression state for only the steps required for the
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// collision detection, which are 0, 58 and 65.
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// Refer to ubc/const.go for more details.
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cs := [shared.PreStepState][shared.WordBuffers]uint32{}
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h0, h1, h2, h3, h4 := dig.h[0], dig.h[1], dig.h[2], dig.h[3], dig.h[4]
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for len(p) >= shared.Chunk {
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m1 := [shared.Rounds]uint32{}
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hi := 1
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// Collision attacks are thwarted by hashing a detected near-collision block 3 times.
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// Think of it as extending SHA-1 from 80-steps to 240-steps for such blocks:
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// The best collision attacks against SHA-1 have complexity about 2^60,
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// thus for 240-steps an immediate lower-bound for the best cryptanalytic attacks would be 2^180.
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// An attacker would be better off using a generic birthday search of complexity 2^80.
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rehash:
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a, b, c, d, e := h0, h1, h2, h3, h4
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// Each of the four 20-iteration rounds
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// differs only in the computation of f and
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// the choice of K (K0, K1, etc).
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i := 0
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// Store pre-step compression state for the collision detection.
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cs[0] = [shared.WordBuffers]uint32{a, b, c, d, e}
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for ; i < 16; i++ {
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// load step
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j := i * 4
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w[i] = uint32(p[j])<<24 | uint32(p[j+1])<<16 | uint32(p[j+2])<<8 | uint32(p[j+3])
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f := b&c | (^b)&d
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t := bits.RotateLeft32(a, 5) + f + e + w[i&0xf] + shared.K0
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a, b, c, d, e = t, a, bits.RotateLeft32(b, 30), c, d
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// Store compression state for the collision detection.
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m1[i] = w[i&0xf]
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}
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for ; i < 20; i++ {
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tmp := w[(i-3)&0xf] ^ w[(i-8)&0xf] ^ w[(i-14)&0xf] ^ w[(i)&0xf]
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w[i&0xf] = tmp<<1 | tmp>>(32-1)
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f := b&c | (^b)&d
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t := bits.RotateLeft32(a, 5) + f + e + w[i&0xf] + shared.K0
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a, b, c, d, e = t, a, bits.RotateLeft32(b, 30), c, d
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// Store compression state for the collision detection.
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m1[i] = w[i&0xf]
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}
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for ; i < 40; i++ {
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tmp := w[(i-3)&0xf] ^ w[(i-8)&0xf] ^ w[(i-14)&0xf] ^ w[(i)&0xf]
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w[i&0xf] = tmp<<1 | tmp>>(32-1)
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f := b ^ c ^ d
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t := bits.RotateLeft32(a, 5) + f + e + w[i&0xf] + shared.K1
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a, b, c, d, e = t, a, bits.RotateLeft32(b, 30), c, d
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// Store compression state for the collision detection.
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m1[i] = w[i&0xf]
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}
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for ; i < 60; i++ {
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if i == 58 {
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// Store pre-step compression state for the collision detection.
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cs[1] = [shared.WordBuffers]uint32{a, b, c, d, e}
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}
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tmp := w[(i-3)&0xf] ^ w[(i-8)&0xf] ^ w[(i-14)&0xf] ^ w[(i)&0xf]
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w[i&0xf] = tmp<<1 | tmp>>(32-1)
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f := ((b | c) & d) | (b & c)
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t := bits.RotateLeft32(a, 5) + f + e + w[i&0xf] + shared.K2
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a, b, c, d, e = t, a, bits.RotateLeft32(b, 30), c, d
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// Store compression state for the collision detection.
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m1[i] = w[i&0xf]
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}
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for ; i < 80; i++ {
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if i == 65 {
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// Store pre-step compression state for the collision detection.
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cs[2] = [shared.WordBuffers]uint32{a, b, c, d, e}
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}
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tmp := w[(i-3)&0xf] ^ w[(i-8)&0xf] ^ w[(i-14)&0xf] ^ w[(i)&0xf]
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w[i&0xf] = tmp<<1 | tmp>>(32-1)
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f := b ^ c ^ d
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t := bits.RotateLeft32(a, 5) + f + e + w[i&0xf] + shared.K3
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a, b, c, d, e = t, a, bits.RotateLeft32(b, 30), c, d
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// Store compression state for the collision detection.
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m1[i] = w[i&0xf]
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}
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h0 += a
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h1 += b
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h2 += c
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h3 += d
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h4 += e
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if hi == 2 {
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hi++
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goto rehash
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}
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if hi == 1 {
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col := checkCollision(m1, cs, [shared.WordBuffers]uint32{h0, h1, h2, h3, h4})
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if col {
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dig.col = true
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hi++
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goto rehash
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}
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}
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p = p[shared.Chunk:]
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}
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dig.h[0], dig.h[1], dig.h[2], dig.h[3], dig.h[4] = h0, h1, h2, h3, h4
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}
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func checkCollision(
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m1 [shared.Rounds]uint32,
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cs [shared.PreStepState][shared.WordBuffers]uint32,
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state [shared.WordBuffers]uint32) bool {
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if mask := ubc.CalculateDvMask(m1); mask != 0 {
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dvs := ubc.SHA1_dvs()
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for i := 0; dvs[i].DvType != 0; i++ {
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if (mask & ((uint32)(1) << uint32(dvs[i].MaskB))) != 0 {
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var csState [shared.WordBuffers]uint32
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switch dvs[i].TestT {
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case 58:
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csState = cs[1]
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case 65:
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csState = cs[2]
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case 0:
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csState = cs[0]
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default:
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panic(fmt.Sprintf("dvs data is trying to use a testT that isn't available: %d", dvs[i].TestT))
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}
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col := hasCollided(
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dvs[i].TestT, // testT is the step number
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// m2 is a secondary message created XORing with
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// ubc's DM prior to the SHA recompression step.
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m1, dvs[i].Dm,
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csState,
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state)
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if col {
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return true
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}
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}
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}
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}
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return false
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}
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func hasCollided(step uint32, m1, dm [shared.Rounds]uint32,
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state [shared.WordBuffers]uint32, h [shared.WordBuffers]uint32) bool {
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// Intermediary Hash Value.
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ihv := [shared.WordBuffers]uint32{}
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a, b, c, d, e := state[0], state[1], state[2], state[3], state[4]
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// Walk backwards from current step to undo previous compression.
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// The existing collision detection does not have dvs higher than 65,
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// start value of i accordingly.
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for i := uint32(64); i >= 60; i-- {
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a, b, c, d, e = b, c, d, e, a
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if step > i {
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b = bits.RotateLeft32(b, -30)
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f := b ^ c ^ d
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e -= bits.RotateLeft32(a, 5) + f + shared.K3 + (m1[i] ^ dm[i]) // m2 = m1 ^ dm.
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}
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}
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for i := uint32(59); i >= 40; i-- {
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a, b, c, d, e = b, c, d, e, a
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if step > i {
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b = bits.RotateLeft32(b, -30)
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f := ((b | c) & d) | (b & c)
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e -= bits.RotateLeft32(a, 5) + f + shared.K2 + (m1[i] ^ dm[i])
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}
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}
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for i := uint32(39); i >= 20; i-- {
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a, b, c, d, e = b, c, d, e, a
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if step > i {
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b = bits.RotateLeft32(b, -30)
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f := b ^ c ^ d
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e -= bits.RotateLeft32(a, 5) + f + shared.K1 + (m1[i] ^ dm[i])
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}
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}
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for i := uint32(20); i > 0; i-- {
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j := i - 1
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a, b, c, d, e = b, c, d, e, a
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if step > j {
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b = bits.RotateLeft32(b, -30) // undo the rotate left
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f := b&c | (^b)&d
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// subtract from e
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e -= bits.RotateLeft32(a, 5) + f + shared.K0 + (m1[j] ^ dm[j])
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}
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}
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ihv[0] = a
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ihv[1] = b
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ihv[2] = c
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ihv[3] = d
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ihv[4] = e
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a = state[0]
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b = state[1]
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c = state[2]
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d = state[3]
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e = state[4]
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// Recompress blocks based on the current step.
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// The existing collision detection does not have dvs below 58, so they have been removed
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// from the source code. If new dvs are added which target rounds below 40, that logic
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// will need to be readded here.
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for i := uint32(40); i < 60; i++ {
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if step <= i {
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f := ((b | c) & d) | (b & c)
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t := bits.RotateLeft32(a, 5) + f + e + shared.K2 + (m1[i] ^ dm[i])
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a, b, c, d, e = t, a, bits.RotateLeft32(b, 30), c, d
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}
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}
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for i := uint32(60); i < 80; i++ {
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if step <= i {
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f := b ^ c ^ d
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t := bits.RotateLeft32(a, 5) + f + e + shared.K3 + (m1[i] ^ dm[i])
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a, b, c, d, e = t, a, bits.RotateLeft32(b, 30), c, d
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}
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}
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ihv[0] += a
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ihv[1] += b
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ihv[2] += c
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ihv[3] += d
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ihv[4] += e
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if ((ihv[0] ^ h[0]) | (ihv[1] ^ h[1]) |
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(ihv[2] ^ h[2]) | (ihv[3] ^ h[3]) | (ihv[4] ^ h[4])) == 0 {
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return true
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}
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return false
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}
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