| author |  Frank Denis <124872+jedisct1@users.noreply.github.com> 2020-10-19 22:24:09+02:00 |
| committer | Frank Denis <124872+jedisct1@users.noreply.github.com> 2020-10-22 09:58:26+02:00 |
| log | 2d9befe9bfbd333d411c1d38062e5d117da4e508 |
| tree | b4d1f7bcc301eef352863ab938333e2f25fd4da4 |
| parent | 0fb6fdd7eb8c9ec7057e2ecb2d0d4506cddc6dd1 |
Implement multiscalar edwards25519 point multiplication
2 files changed, 33 insertions(+), 9 deletions(-)
lib- std
- crypto
lib/std/crypto/25519/ed25519.zig+4-9
| ... | @@ -168,18 +168,13 @@ pub const Ed25519 = struct { | ... | @@ -168,18 +168,13 @@ pub const Ed25519 = struct { |
| 168 | } | 168 | } |
| 169 | zs_sum = Curve.scalar.mul8(zs_sum); | 169 | zs_sum = Curve.scalar.mul8(zs_sum); |
| 170 | 170 | ||
| 171 | var zr = Curve.neutralElement; | 171 | var zhs: [count]Curve.scalar.CompressedScalar = undefined; |
| 172 | for (z_batch) |z, i| { | 172 | for (z_batch) |z, i| { |
| 173 | zr = zr.add(try expected_r_batch[i].mulPublic(z)); | 173 | zhs[i] = Curve.scalar.mul(z, hram_batch[i]); |
| 174 | } | 174 | } |
| 175 | zr = zr.clearCofactor(); | ||
| 176 | 175 | ||
| 177 | var zah = Curve.neutralElement; | 176 | const zr = (try Curve.mulMulti(count, expected_r_batch, z_batch)).clearCofactor(); |
| 178 | for (z_batch) |z, i| { | 177 | const zah = (try Curve.mulMulti(count, a_batch, zhs)).clearCofactor(); |
| 179 | const zh = Curve.scalar.mul(z, hram_batch[i]); | ||
| 180 | zah = zah.add(try a_batch[i].mulPublic(zh)); | ||
| 181 | } | ||
| 182 | zah = zah.clearCofactor(); | ||
| 183 | 178 | ||
| 184 | const zsb = try Curve.basePoint.mulPublic(zs_sum); | 179 | const zsb = try Curve.basePoint.mulPublic(zs_sum); |
| 185 | if (zr.add(zah).sub(zsb).rejectIdentity()) |_| { | 180 | if (zr.add(zah).sub(zsb).rejectIdentity()) |_| { |
lib/std/crypto/25519/edwards25519.zig+29
| ... | @@ -208,6 +208,35 @@ pub const Edwards25519 = struct { | ... | @@ -208,6 +208,35 @@ pub const Edwards25519 = struct { |
| 208 | return pcMul(pc, s, true); | 208 | return pcMul(pc, s, true); |
| 209 | } | 209 | } |
| 210 | 210 | ||
| 211 | /// Multiscalar multiplication *IN VARIABLE TIME* for public data | ||
| 212 | /// Computes ps0*ss0 + ps1*ss1 + ps2*ss2... faster than doing many of these operations individually | ||
| 213 | pub fn mulMulti(comptime count: usize, ps: [count]Edwards25519, ss: [count][32]u8) !Edwards25519 { | ||
| 214 | var pcs: [count][16]Edwards25519 = undefined; | ||
| 215 | for (ps) |p, i| { | ||
| 216 | if (p.is_base) { | ||
| 217 | @setEvalBranchQuota(10000); | ||
| 218 | pcs[i] = comptime precompute(Edwards25519.basePoint); | ||
| 219 | } else { | ||
| 220 | pcs[i] = precompute(p); | ||
| 221 | pcs[i][4].rejectIdentity() catch |_| return error.WeakPublicKey; | ||
| 222 | } | ||
| 223 | } | ||
| 224 | var q = Edwards25519.identityElement; | ||
| 225 | var pos: usize = 252; | ||
| 226 | while (true) : (pos -= 4) { | ||
| 227 | q = q.dbl().dbl().dbl().dbl(); | ||
| 228 | for (ss) |s, i| { | ||
| 229 | const bit = (s[pos >> 3] >> @truncate(u3, pos)) & 0xf; | ||
| 230 | if (bit != 0) { | ||
| 231 | q = q.add(pcs[i][bit]); | ||
| 232 | } | ||
| 233 | } | ||
| 234 | if (pos == 0) break; | ||
| 235 | } | ||
| 236 | try q.rejectIdentity(); | ||
| 237 | return q; | ||
| 238 | } | ||
| 239 | |||
| 211 | /// Multiply an Edwards25519 point by a scalar after "clamping" it. | 240 | /// Multiply an Edwards25519 point by a scalar after "clamping" it. |
| 212 | /// Clamping forces the scalar to be a multiple of the cofactor in | 241 | /// Clamping forces the scalar to be a multiple of the cofactor in |
| 213 | /// order to prevent small subgroups attacks. | 242 | /// order to prevent small subgroups attacks. |