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SHARE.go
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SHARE.go
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/*
* Copyright (c) 2012-2020 MIRACL UK Ltd.
*
* This file is part of MIRACL Core
* (see https://github.com/miracl/core).
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
/* Shamir threshold secret sharing module */
/* Split any byte array into number of shares < 256 */
/* Specify number of shares required for recovery - nsr */
/* See TestMPIN.go for an example of use */
package core
var ptab = [...]byte{
1, 3, 5, 15, 17, 51, 85, 255, 26, 46, 114, 150, 161, 248, 19, 53,
95, 225, 56, 72, 216, 115, 149, 164, 247, 2, 6, 10, 30, 34, 102, 170,
229, 52, 92, 228, 55, 89, 235, 38, 106, 190, 217, 112, 144, 171, 230, 49,
83, 245, 4, 12, 20, 60, 68, 204, 79, 209, 104, 184, 211, 110, 178, 205,
76, 212, 103, 169, 224, 59, 77, 215, 98, 166, 241, 8, 24, 40, 120, 136,
131, 158, 185, 208, 107, 189, 220, 127, 129, 152, 179, 206, 73, 219, 118, 154,
181, 196, 87, 249, 16, 48, 80, 240, 11, 29, 39, 105, 187, 214, 97, 163,
254, 25, 43, 125, 135, 146, 173, 236, 47, 113, 147, 174, 233, 32, 96, 160,
251, 22, 58, 78, 210, 109, 183, 194, 93, 231, 50, 86, 250, 21, 63, 65,
195, 94, 226, 61, 71, 201, 64, 192, 91, 237, 44, 116, 156, 191, 218, 117,
159, 186, 213, 100, 172, 239, 42, 126, 130, 157, 188, 223, 122, 142, 137, 128,
155, 182, 193, 88, 232, 35, 101, 175, 234, 37, 111, 177, 200, 67, 197, 84,
252, 31, 33, 99, 165, 244, 7, 9, 27, 45, 119, 153, 176, 203, 70, 202,
69, 207, 74, 222, 121, 139, 134, 145, 168, 227, 62, 66, 198, 81, 243, 14,
18, 54, 90, 238, 41, 123, 141, 140, 143, 138, 133, 148, 167, 242, 13, 23,
57, 75, 221, 124, 132, 151, 162, 253, 28, 36, 108, 180, 199, 82, 246, 1}
var ltab = [...]byte{
0, 255, 25, 1, 50, 2, 26, 198, 75, 199, 27, 104, 51, 238, 223, 3,
100, 4, 224, 14, 52, 141, 129, 239, 76, 113, 8, 200, 248, 105, 28, 193,
125, 194, 29, 181, 249, 185, 39, 106, 77, 228, 166, 114, 154, 201, 9, 120,
101, 47, 138, 5, 33, 15, 225, 36, 18, 240, 130, 69, 53, 147, 218, 142,
150, 143, 219, 189, 54, 208, 206, 148, 19, 92, 210, 241, 64, 70, 131, 56,
102, 221, 253, 48, 191, 6, 139, 98, 179, 37, 226, 152, 34, 136, 145, 16,
126, 110, 72, 195, 163, 182, 30, 66, 58, 107, 40, 84, 250, 133, 61, 186,
43, 121, 10, 21, 155, 159, 94, 202, 78, 212, 172, 229, 243, 115, 167, 87,
175, 88, 168, 80, 244, 234, 214, 116, 79, 174, 233, 213, 231, 230, 173, 232,
44, 215, 117, 122, 235, 22, 11, 245, 89, 203, 95, 176, 156, 169, 81, 160,
127, 12, 246, 111, 23, 196, 73, 236, 216, 67, 31, 45, 164, 118, 123, 183,
204, 187, 62, 90, 251, 96, 177, 134, 59, 82, 161, 108, 170, 85, 41, 157,
151, 178, 135, 144, 97, 190, 220, 252, 188, 149, 207, 205, 55, 63, 91, 209,
83, 57, 132, 60, 65, 162, 109, 71, 20, 42, 158, 93, 86, 242, 211, 171,
68, 17, 146, 217, 35, 32, 46, 137, 180, 124, 184, 38, 119, 153, 227, 165,
103, 74, 237, 222, 197, 49, 254, 24, 13, 99, 140, 128, 192, 247, 112, 7}
type SHARE struct {
ID byte // Unique Share ID
NSR byte // Number of Shares required for recovery
B []byte // Share
}
func add(x byte, y byte) byte {
return (x ^ y)
}
func mul(x byte, y byte) byte { /* x.y= AntiLog(Log(x) + Log(y)) */
ix := int(x) & 0xff
iy := int(y) & 0xff
lx := int(ltab[ix]) & 0xff
ly := int(ltab[iy]) & 0xff
if x != 0 && y != 0 {
return ptab[(lx+ly)%255]
} else {
return byte(0)
}
}
func inv(x byte) byte {
ix := int(x) & 0xff
lx := int(ltab[ix]) & 0xff
return ptab[255-lx]
}
/* Lagrange interpolation */
func interpolate(n int, x []byte, y []byte) byte {
yp := byte(0)
for i := 0; i < n; i++ {
p := byte(1)
for j := 0; j < n; j++ {
if i != j {
p = mul(p, mul(x[j], inv(add(x[i], x[j]))))
}
}
yp = add(yp, mul(p, y[i]))
}
return yp
}
/* Return a share of M */
/* input id - Unique share ID */
/* input nsr - Number of shares required for recovery */
/* input Message M to be shared */
/* input Random seed R */
/* return share structure */
func NewSHARE(id int, nsr int, M []byte, R []byte) *SHARE {
var S = new(SHARE)
if id < 1 || id >= 256 || nsr < 2 || nsr >= 256 {
S.ID = 0
S.NSR = 0
S.B = nil
return S
}
S.ID = byte(id)
S.NSR = byte(nsr)
m := len(M)
S.B = make([]byte, m)
rng := NewRAND()
rng.Clean()
rng.Seed(len(R), R)
for j := 0; j < m; j++ {
x := byte(S.ID)
S.B[j] = M[j]
for n := 1; n < nsr; n++ {
S.B[j] = add(S.B[j], mul(rng.GetByte(), x))
x = mul(x, S.ID)
}
}
return S
}
/* recover M from shares */
func Recover(S []*SHARE) []byte {
m := len(S[0].B)
nsr := int(S[0].NSR)
if nsr != len(S) {
return nil
}
for i := 1; i < nsr; i++ {
if int(S[i].NSR) != nsr || len(S[i].B) != m {
return nil
}
}
x := make([]byte, nsr)
y := make([]byte, nsr)
M := make([]byte, m)
for j := 0; j < m; j++ {
for i := 0; i < nsr; i++ {
x[i] = S[i].ID
y[i] = S[i].B[j]
}
M[j] = interpolate(nsr, x, y)
}
return M
}