chore: vendor

vendor/github.com/cloudflare/circl/math/mlsbset/mlsbset.go

@@ -0,0 +1,122 @@
+// Package mlsbset provides a constant-time exponentiation method with precomputation.
+//
+// References: "Efficient and secure algorithms for GLV-based scalar
+// multiplication and their implementation on GLV–GLS curves" by (Faz-Hernandez et al.)
+//   - https://doi.org/10.1007/s13389-014-0085-7
+//   - https://eprint.iacr.org/2013/158
+package mlsbset
+
+import (
+	"errors"
+	"fmt"
+	"math/big"
+
+	"github.com/cloudflare/circl/internal/conv"
+)
+
+// EltG is a group element.
+type EltG interface{}
+
+// EltP is a precomputed group element.
+type EltP interface{}
+
+// Group defines the operations required by MLSBSet exponentiation method.
+type Group interface {
+	Identity() EltG                    // Returns the identity of the group.
+	Sqr(x EltG)                        // Calculates x = x^2.
+	Mul(x EltG, y EltP)                // Calculates x = x*y.
+	NewEltP() EltP                     // Returns an arbitrary precomputed element.
+	ExtendedEltP() EltP                // Returns the precomputed element x^(2^(w*d)).
+	Lookup(a EltP, v uint, s, u int32) // Sets a = s*T[v][u].
+}
+
+// Params contains the parameters of the encoding.
+type Params struct {
+	T uint // T is the maximum size (in bits) of exponents.
+	V uint // V is the number of tables.
+	W uint // W is the window size.
+	E uint // E is the number of digits per table.
+	D uint // D is the number of digits in total.
+	L uint // L is the length of the code.
+}
+
+// Encoder allows to convert integers into valid powers.
+type Encoder struct{ p Params }
+
+// New produces an encoder of the MLSBSet algorithm.
+func New(t, v, w uint) (Encoder, error) {
+	if !(t > 1 && v >= 1 && w >= 2) {
+		return Encoder{}, errors.New("t>1, v>=1, w>=2")
+	}
+	e := (t + w*v - 1) / (w * v)
+	d := e * v
+	l := d * w
+	return Encoder{Params{t, v, w, e, d, l}}, nil
+}
+
+// Encode converts an odd integer k into a valid power for exponentiation.
+func (m Encoder) Encode(k []byte) (*Power, error) {
+	if len(k) == 0 {
+		return nil, errors.New("empty slice")
+	}
+	if !(len(k) <= int(m.p.L+7)>>3) {
+		return nil, errors.New("k too big")
+	}
+	if k[0]%2 == 0 {
+		return nil, errors.New("k must be odd")
+	}
+	ap := int((m.p.L+7)/8) - len(k)
+	k = append(k, make([]byte, ap)...)
+	s := m.signs(k)
+	b := make([]int32, m.p.L-m.p.D)
+	c := conv.BytesLe2BigInt(k)
+	c.Rsh(c, m.p.D)
+	var bi big.Int
+	for i := m.p.D; i < m.p.L; i++ {
+		c0 := int32(c.Bit(0))
+		b[i-m.p.D] = s[i%m.p.D] * c0
+		bi.SetInt64(int64(b[i-m.p.D] >> 1))
+		c.Rsh(c, 1)
+		c.Sub(c, &bi)
+	}
+	carry := int(c.Int64())
+	return &Power{m, s, b, carry}, nil
+}
+
+// signs calculates the set of signs.
+func (m Encoder) signs(k []byte) []int32 {
+	s := make([]int32, m.p.D)
+	s[m.p.D-1] = 1
+	for i := uint(1); i < m.p.D; i++ {
+		ki := int32((k[i>>3] >> (i & 0x7)) & 0x1)
+		s[i-1] = 2*ki - 1
+	}
+	return s
+}
+
+// GetParams returns the complementary parameters of the encoding.
+func (m Encoder) GetParams() Params { return m.p }
+
+// tableSize returns the size of each table.
+func (m Encoder) tableSize() uint { return 1 << (m.p.W - 1) }
+
+// Elts returns the total number of elements that must be precomputed.
+func (m Encoder) Elts() uint { return m.p.V * m.tableSize() }
+
+// IsExtended returns true if the element x^(2^(wd)) must be calculated.
+func (m Encoder) IsExtended() bool { q := m.p.T / (m.p.V * m.p.W); return m.p.T == q*m.p.V*m.p.W }
+
+// Ops returns the number of squares and multiplications executed during an exponentiation.
+func (m Encoder) Ops() (S uint, M uint) {
+	S = m.p.E
+	M = m.p.E * m.p.V
+	if m.IsExtended() {
+		M++
+	}
+	return
+}
+
+func (m Encoder) String() string {
+	return fmt.Sprintf("T: %v W: %v V: %v e: %v d: %v l: %v wv|t: %v",
+		m.p.T, m.p.W, m.p.V, m.p.E, m.p.D, m.p.L, m.IsExtended())
+}