FAQ
Reviewers: golang-dev_googlegroups.com,

Message:
Hello golang-dev@googlegroups.com,

I'd like you to review this change to
https://code.google.com/p/go/


Description:
crypto/sha1: Make sha-1 do block mixup in place

Please review this at http://codereview.appspot.com/6820096/

Affected files:
M src/pkg/crypto/sha1/sha1block.go


Index: src/pkg/crypto/sha1/sha1block.go
===================================================================
--- a/src/pkg/crypto/sha1/sha1block.go
+++ b/src/pkg/crypto/sha1/sha1block.go
@@ -16,7 +16,7 @@
)

func block(dig *digest, p []byte) {
- var w [80]uint32
+ var w [16]uint32

h0, h1, h2, h3, h4 := dig.h[0], dig.h[1], dig.h[2], dig.h[3], dig.h[4]
for len(p) >= chunk {
@@ -26,42 +26,54 @@
j := i * 4
w[i] = uint32(p[j])<<24 | uint32(p[j+1])<<16 | uint32(p[j+2])<<8 |
uint32(p[j+3])
}
- for i := 16; i < 80; i++ {
- tmp := w[i-3] ^ w[i-8] ^ w[i-14] ^ w[i-16]
- w[i] = tmp<<1 | tmp>>(32-1)
- }

a, b, c, d, e := h0, h1, h2, h3, h4

// Each of the four 20-iteration rounds
// differs only in the computation of f and
// the choice of K (_K0, _K1, etc).
- for i := 0; i < 20; i++ {
+ for i := 0; i < 16; i++ {
f := b&c | (^b)&d
a5 := a<<5 | a>>(32-5)
b30 := b<<30 | b>>(32-30)
t := a5 + f + e + w[i] + _K0
a, b, c, d, e = t, a, b30, c, d
}
+ for i := 16; i < 20; i++ {
+ tmp := w[(i-3)&0xf] ^ w[(i-8)&0xf] ^ w[(i-14)&0xf] ^ w[(i)&0xf]
+ w[i&0xf] = tmp<<1 | tmp>>(32-1)
+
+ f := b&c | (^b)&d
+ a5 := a<<5 | a>>(32-5)
+ b30 := b<<30 | b>>(32-30)
+ t := a5 + f + e + w[i&0xf] + _K0
+ a, b, c, d, e = t, a, b30, c, d
+ }
for i := 20; i < 40; i++ {
+ tmp := w[(i-3)&0xf] ^ w[(i-8)&0xf] ^ w[(i-14)&0xf] ^ w[(i)&0xf]
+ w[i&0xf] = tmp<<1 | tmp>>(32-1)
f := b ^ c ^ d
a5 := a<<5 | a>>(32-5)
b30 := b<<30 | b>>(32-30)
- t := a5 + f + e + w[i] + _K1
+ t := a5 + f + e + w[i&0xf] + _K1
a, b, c, d, e = t, a, b30, c, d
}
for i := 40; i < 60; i++ {
+ tmp := w[(i-3)&0xf] ^ w[(i-8)&0xf] ^ w[(i-14)&0xf] ^ w[(i)&0xf]
+ w[i&0xf] = tmp<<1 | tmp>>(32-1)
f := b&c | b&d | c&d
a5 := a<<5 | a>>(32-5)
b30 := b<<30 | b>>(32-30)
- t := a5 + f + e + w[i] + _K2
+ t := a5 + f + e + w[i&0xf] + _K2
a, b, c, d, e = t, a, b30, c, d
}
for i := 60; i < 80; i++ {
+ tmp := w[(i-3)&0xf] ^ w[(i-8)&0xf] ^ w[(i-14)&0xf] ^ w[(i)&0xf]
+ w[i&0xf] = tmp<<1 | tmp>>(32-1)
f := b ^ c ^ d
a5 := a<<5 | a>>(32-5)
b30 := b<<30 | b>>(32-30)
- t := a5 + f + e + w[i] + _K3
+ t := a5 + f + e + w[i&0xf] + _K3
a, b, c, d, e = t, a, b30, c, d
}

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