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dsa_key_recovery.go
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/
dsa_key_recovery.go
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package set6
import (
"github.com/dbalan/cryptopals/dsa"
"github.com/dbalan/cryptopals/sha"
"math/big"
)
const (
msg = `For those that envy a MC it can be hazardous to your health
So be friendly, a matter of life and death, just like a etch-a-sketch
`
ystr = "84ad4719d044495496a3201c8ff484feb45b962e7302e56a392aee4" +
"abab3e4bdebf2955b4736012f21a08084056b19bcd7fee56048e004" +
"e44984e2f411788efdc837a0d2e5abb7b555039fd243ac01f0fb2ed" +
"1dec568280ce678e931868d23eb095fde9d3779191b8c0299d6e07b" +
"bb283e6633451e535c45513b2d33c99ea17"
rstr = "548099063082341131477253921760299949438196259240"
sstr = "857042759984254168557880549501802188789837994940"
)
func fromStr(s string, base int) *big.Int {
t := new(big.Int)
t.SetString(s, base)
return t
}
func checkKey(x *big.Int) bool {
rc, sc, err := dsa.Sign([]byte(msg), x, dsa.GetDefaultParams)
if err != nil {
panic(err)
}
y, _ := new(big.Int).SetString(ystr, 16)
return dsa.Verify([]byte(msg), rc, sc, y,
dsa.GetDefaultParams)
}
func getKey() *big.Int {
hs := new(big.Int).SetBytes(sha.SHA([]byte(msg)))
// y := fromStr(ystr)
r := fromStr(rstr, 10)
s := fromStr(sstr, 10)
for k := 0; k <= 65536; k++ {
x := dsa.ComputeKey(big.NewInt(int64(k)), r, s, hs)
if checkKey(x) {
return x
}
}
panic("no suitable keys")
}