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@kortschak
Created Apr 12, 2012
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hash collision
package main
import (
"crypto/sha256"
"fmt"
"math/rand"
"os"
"time"
)
var s = sha256.New().Size() - 7
func sha(m [8]byte) []byte {
h := sha256.New()
h.Write(m[:])
return h.Sum(nil)
}
func shaTrunc(m int64) (ma [8]byte, r [7]byte) {
ma[0] = byte(m >> 56)
ma[1] = byte(m >> 48)
ma[2] = byte(m >> 40)
ma[3] = byte(m >> 32)
ma[4] = byte(m >> 24)
ma[5] = byte(m >> 16)
ma[6] = byte(m >> 8)
ma[7] = byte(m)
h := sha256.New()
h.Write(ma[:])
copy(r[:], h.Sum(nil)[s:])
r[0] &= 0x3
return
}
func main() {
rand.Seed(time.Now().Unix())
for j := 0; j < 10; j++ {
fmt.Printf("Run %d:\n", j)
t := make(map[[7]byte][8]byte, 1<<25)
for i := 0; i < 1<<25; i++ {
m := rand.Int63()
bm, s := shaTrunc(m)
if i%(1<<20) == 0 {
fmt.Printf(" %0x...\n", i)
}
if h, ok := t[s]; ok && h != bm {
fmt.Printf("Found collision: %x == %x, %x != %x\n%x\n%x\n", s, s, h, bm, sha(h), sha(bm))
os.Exit(0)
} else {
t[s] = bm
}
}
}
fmt.Println("Failed to find collision.")
}
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