move to lib

cmd/discreteLog.go

@@ -17,11 +17,11 @@ along with this program. If not, see <http://www.gnu.org/licenses/>.
 package cmd
 
 import (
-	"errors"
 	"fmt"
 	"math/big"
 
 	"github.com/spf13/cobra"
+	"scm.dairydemon.net/filifa/mathtools/internal/lib"
 )
 
 var discreteLogModulus string
@@ -29,62 +29,6 @@ var discreteLogBase string
 var discreteLogElement string
 var discreteLogOrder string
 
-// whyyyy doesn't math/big have a ceil functionnnn
-func ceilSqrt(x *big.Int) *big.Int {
-	z := new(big.Int).Sqrt(x)
-	s := new(big.Int).Exp(z, big.NewInt(2), nil)
-	if s.Cmp(x) != 0 {
-		z.Add(z, big.NewInt(1))
-	}
-
-	return z
-}
-
-// TODO: this can be extended to work with n, b not coprime
-// https://cp-algorithms.com/algebra/discrete-log.html
-func babyStepGiantStep(n, b, x, order *big.Int) (*big.Int, error) {
-	z := new(big.Int).GCD(nil, nil, b, n)
-	if z.Cmp(big.NewInt(1)) != 0 {
-		return nil, fmt.Errorf("base %v and modulus %v are not coprime", b, n)
-	}
-
-	var m *big.Int
-	if order == nil {
-		// m = ceil(sqrt(n - 1))
-		z := big.NewInt(1)
-		z.Sub(n, z)
-		m = ceilSqrt(z)
-	} else {
-		m = ceilSqrt(order)
-	}
-
-	table := make(map[string]*big.Int)
-	for j := big.NewInt(1); j.Cmp(m) <= 0; j.Add(j, big.NewInt(1)) {
-		a := new(big.Int).Exp(b, j, n)
-		table[a.String()] = new(big.Int).Set(j)
-	}
-
-	// p = b^-m modulo n
-	p := new(big.Int).Neg(m)
-	p.Exp(b, p, n)
-
-	gamma := new(big.Int).Set(x)
-
-	for i := big.NewInt(0); i.Cmp(m) == -1; i.Add(i, big.NewInt(1)) {
-		j, ok := table[gamma.String()]
-		if ok {
-			i.Mul(i, m)
-			i.Add(i, j)
-			return i, nil
-		}
-
-		gamma.Mul(gamma, p)
-		gamma.Mod(gamma, n)
-	}
-
-	return nil, errors.New("no solution")
-}
-
 func discreteLog(cmd *cobra.Command, args []string) {
 	m, ok := new(big.Int).SetString(discreteLogModulus, 10)
 	if !ok {
@@ -109,7 +53,7 @@ func discreteLog(cmd *cobra.Command, args []string) {
 		}
 	}
 
-	k, err := babyStepGiantStep(m, b, x, order)
+	k, err := lib.BabyStepGiantStep(m, b, x, order)
 	if err != nil {
 		cobra.CheckErr(err)
 	}