zig/lib/std/crypto/25519/ed25519.zig
2020-10-25 21:55:05 +01:00

354 lines
16 KiB
Zig

// SPDX-License-Identifier: MIT
// Copyright (c) 2015-2020 Zig Contributors
// This file is part of [zig](https://ziglang.org/), which is MIT licensed.
// The MIT license requires this copyright notice to be included in all copies
// and substantial portions of the software.
const std = @import("std");
const crypto = std.crypto;
const debug = std.debug;
const fmt = std.fmt;
const mem = std.mem;
const Sha512 = std.crypto.hash.sha2.Sha512;
/// Ed25519 (EdDSA) signatures.
pub const Ed25519 = struct {
/// The underlying elliptic curve.
pub const Curve = @import("edwards25519.zig").Edwards25519;
/// Length (in bytes) of a seed required to create a key pair.
pub const seed_length = 32;
/// Length (in bytes) of a compressed secret key.
pub const secret_length = 64;
/// Length (in bytes) of a compressed public key.
pub const public_length = 32;
/// Length (in bytes) of a signature.
pub const signature_length = 64;
/// Length (in bytes) of optional random bytes, for non-deterministic signatures.
pub const noise_length = 32;
/// An Ed25519 key pair.
pub const KeyPair = struct {
/// Public part.
public_key: [public_length]u8,
/// Secret part. What we expose as a secret key is, under the hood, the concatenation of the seed and the public key.
secret_key: [secret_length]u8,
/// Derive a key pair from an optional secret seed.
///
/// As in RFC 8032, an Ed25519 public key is generated by hashing
/// the secret key using the SHA-512 function, and interpreting the
/// bit-swapped, clamped lower-half of the output as the secret scalar.
///
/// For this reason, an EdDSA secret key is commonly called a seed,
/// from which the actual secret is derived.
pub fn create(seed: ?[seed_length]u8) !KeyPair {
const ss = seed orelse ss: {
var random_seed: [seed_length]u8 = undefined;
try crypto.randomBytes(&random_seed);
break :ss random_seed;
};
var az: [Sha512.digest_length]u8 = undefined;
var h = Sha512.init(.{});
h.update(&ss);
h.final(&az);
const p = try Curve.basePoint.clampedMul(az[0..32].*);
var sk: [secret_length]u8 = undefined;
mem.copy(u8, &sk, &ss);
const pk = p.toBytes();
mem.copy(u8, sk[seed_length..], &pk);
return KeyPair{ .public_key = pk, .secret_key = sk };
}
/// Create a KeyPair from a secret key.
pub fn fromSecretKey(secret_key: [secret_length]u8) KeyPair {
return KeyPair{
.secret_key = secret_key,
.public_key = secret_key[seed_length..].*,
};
}
};
/// Sign a message using a key pair, and optional random noise.
/// Having noise creates non-standard, non-deterministic signatures,
/// but has been proven to increase resilience against fault attacks.
pub fn sign(msg: []const u8, key_pair: KeyPair, noise: ?[noise_length]u8) ![signature_length]u8 {
const seed = key_pair.secret_key[0..seed_length];
const public_key = key_pair.secret_key[seed_length..];
if (!mem.eql(u8, public_key, &key_pair.public_key)) {
return error.KeyMismatch;
}
var az: [Sha512.digest_length]u8 = undefined;
var h = Sha512.init(.{});
h.update(seed);
h.final(&az);
h = Sha512.init(.{});
if (noise) |*z| {
h.update(z);
}
h.update(az[32..]);
h.update(msg);
var nonce64: [64]u8 = undefined;
h.final(&nonce64);
const nonce = Curve.scalar.reduce64(nonce64);
const r = try Curve.basePoint.mul(nonce);
var sig: [signature_length]u8 = undefined;
mem.copy(u8, sig[0..32], &r.toBytes());
mem.copy(u8, sig[32..], public_key);
h = Sha512.init(.{});
h.update(&sig);
h.update(msg);
var hram64: [Sha512.digest_length]u8 = undefined;
h.final(&hram64);
const hram = Curve.scalar.reduce64(hram64);
var x = az[0..32];
Curve.scalar.clamp(x);
const s = Curve.scalar.mulAdd(hram, x.*, nonce);
mem.copy(u8, sig[32..], s[0..]);
return sig;
}
/// Verify an Ed25519 signature given a message and a public key.
/// Returns error.InvalidSignature is the signature verification failed.
pub fn verify(sig: [signature_length]u8, msg: []const u8, public_key: [public_length]u8) !void {
const r = sig[0..32];
const s = sig[32..64];
try Curve.scalar.rejectNonCanonical(s.*);
try Curve.rejectNonCanonical(public_key);
const a = try Curve.fromBytes(public_key);
try a.rejectIdentity();
try Curve.rejectNonCanonical(r.*);
const expected_r = try Curve.fromBytes(r.*);
var h = Sha512.init(.{});
h.update(r);
h.update(&public_key);
h.update(msg);
var hram64: [Sha512.digest_length]u8 = undefined;
h.final(&hram64);
const hram = Curve.scalar.reduce64(hram64);
const ah = try a.neg().mulPublic(hram);
const sb_ah = (try Curve.basePoint.mulPublic(s.*)).add(ah);
if (expected_r.sub(sb_ah).clearCofactor().rejectIdentity()) |_| {
return error.InvalidSignature;
} else |_| {}
}
/// A (signature, message, public_key) tuple for batch verification
pub const BatchElement = struct {
sig: [signature_length]u8,
msg: []const u8,
public_key: [public_length]u8,
};
/// Verify several signatures in a single operation, much faster than verifying signatures one-by-one
pub fn verifyBatch(comptime count: usize, signature_batch: [count]BatchElement) !void {
var r_batch: [count][32]u8 = undefined;
var s_batch: [count][32]u8 = undefined;
var a_batch: [count]Curve = undefined;
var expected_r_batch: [count]Curve = undefined;
for (signature_batch) |signature, i| {
const r = signature.sig[0..32];
const s = signature.sig[32..64];
try Curve.scalar.rejectNonCanonical(s.*);
try Curve.rejectNonCanonical(signature.public_key);
const a = try Curve.fromBytes(signature.public_key);
try a.rejectIdentity();
try Curve.rejectNonCanonical(r.*);
const expected_r = try Curve.fromBytes(r.*);
expected_r_batch[i] = expected_r;
r_batch[i] = r.*;
s_batch[i] = s.*;
a_batch[i] = a;
}
var hram_batch: [count]Curve.scalar.CompressedScalar = undefined;
for (signature_batch) |signature, i| {
var h = Sha512.init(.{});
h.update(&r_batch[i]);
h.update(&signature.public_key);
h.update(signature.msg);
var hram64: [Sha512.digest_length]u8 = undefined;
h.final(&hram64);
hram_batch[i] = Curve.scalar.reduce64(hram64);
}
var z_batch: [count]Curve.scalar.CompressedScalar = undefined;
for (z_batch) |*z| {
try std.crypto.randomBytes(z[0..16]);
mem.set(u8, z[16..], 0);
}
var zs_sum = Curve.scalar.zero;
for (z_batch) |z, i| {
const zs = Curve.scalar.mul(z, s_batch[i]);
zs_sum = Curve.scalar.add(zs_sum, zs);
}
zs_sum = Curve.scalar.mul8(zs_sum);
var zhs: [count]Curve.scalar.CompressedScalar = undefined;
for (z_batch) |z, i| {
zhs[i] = Curve.scalar.mul(z, hram_batch[i]);
}
const zr = (try Curve.mulMulti(count, expected_r_batch, z_batch)).clearCofactor();
const zah = (try Curve.mulMulti(count, a_batch, zhs)).clearCofactor();
const zsb = try Curve.basePoint.mulPublic(zs_sum);
if (zr.add(zah).sub(zsb).rejectIdentity()) |_| {
return error.InvalidSignature;
} else |_| {}
}
};
test "ed25519 key pair creation" {
var seed: [32]u8 = undefined;
try fmt.hexToBytes(seed[0..], "8052030376d47112be7f73ed7a019293dd12ad910b654455798b4667d73de166");
const key_pair = try Ed25519.KeyPair.create(seed);
var buf: [256]u8 = undefined;
std.testing.expectEqualStrings(try std.fmt.bufPrint(&buf, "{X}", .{key_pair.secret_key}), "8052030376D47112BE7F73ED7A019293DD12AD910B654455798B4667D73DE1662D6F7455D97B4A3A10D7293909D1A4F2058CB9A370E43FA8154BB280DB839083");
std.testing.expectEqualStrings(try std.fmt.bufPrint(&buf, "{X}", .{key_pair.public_key}), "2D6F7455D97B4A3A10D7293909D1A4F2058CB9A370E43FA8154BB280DB839083");
}
test "ed25519 signature" {
var seed: [32]u8 = undefined;
try fmt.hexToBytes(seed[0..], "8052030376d47112be7f73ed7a019293dd12ad910b654455798b4667d73de166");
const key_pair = try Ed25519.KeyPair.create(seed);
const sig = try Ed25519.sign("test", key_pair, null);
var buf: [128]u8 = undefined;
std.testing.expectEqualStrings(try std.fmt.bufPrint(&buf, "{X}", .{sig}), "10A442B4A80CC4225B154F43BEF28D2472CA80221951262EB8E0DF9091575E2687CC486E77263C3418C757522D54F84B0359236ABBBD4ACD20DC297FDCA66808");
try Ed25519.verify(sig, "test", key_pair.public_key);
std.testing.expectError(error.InvalidSignature, Ed25519.verify(sig, "TEST", key_pair.public_key));
}
test "ed25519 batch verification" {
var i: usize = 0;
while (i < 100) : (i += 1) {
const key_pair = try Ed25519.KeyPair.create(null);
var msg1: [32]u8 = undefined;
var msg2: [32]u8 = undefined;
try std.crypto.randomBytes(&msg1);
try std.crypto.randomBytes(&msg2);
const sig1 = try Ed25519.sign(&msg1, key_pair, null);
const sig2 = try Ed25519.sign(&msg2, key_pair, null);
var signature_batch = [_]Ed25519.BatchElement{
Ed25519.BatchElement{
.sig = sig1,
.msg = &msg1,
.public_key = key_pair.public_key,
},
Ed25519.BatchElement{
.sig = sig2,
.msg = &msg2,
.public_key = key_pair.public_key,
},
};
try Ed25519.verifyBatch(2, signature_batch);
signature_batch[1].sig = sig1;
std.testing.expectError(error.InvalidSignature, Ed25519.verifyBatch(signature_batch.len, signature_batch));
}
}
test "ed25519 test vectors" {
const Vec = struct {
msg_hex: *const [64:0]u8,
public_key_hex: *const [64:0]u8,
sig_hex: *const [128:0]u8,
expected: ?anyerror,
};
const entries = [_]Vec{
Vec{
.msg_hex = "8c93255d71dcab10e8f379c26200f3c7bd5f09d9bc3068d3ef4edeb4853022b6",
.public_key_hex = "c7176a703d4dd84fba3c0b760d10670f2a2053fa2c39ccc64ec7fd7792ac03fa",
.sig_hex = "c7176a703d4dd84fba3c0b760d10670f2a2053fa2c39ccc64ec7fd7792ac037a0000000000000000000000000000000000000000000000000000000000000000",
.expected = error.WeakPublicKey, // 0
},
Vec{
.msg_hex = "9bd9f44f4dcc75bd531b56b2cd280b0bb38fc1cd6d1230e14861d861de092e79",
.public_key_hex = "c7176a703d4dd84fba3c0b760d10670f2a2053fa2c39ccc64ec7fd7792ac03fa",
.sig_hex = "f7badec5b8abeaf699583992219b7b223f1df3fbbea919844e3f7c554a43dd43a5bb704786be79fc476f91d3f3f89b03984d8068dcf1bb7dfc6637b45450ac04",
.expected = error.WeakPublicKey, // 1
},
Vec{
.msg_hex = "aebf3f2601a0c8c5d39cc7d8911642f740b78168218da8471772b35f9d35b9ab",
.public_key_hex = "f7badec5b8abeaf699583992219b7b223f1df3fbbea919844e3f7c554a43dd43",
.sig_hex = "c7176a703d4dd84fba3c0b760d10670f2a2053fa2c39ccc64ec7fd7792ac03fa8c4bd45aecaca5b24fb97bc10ac27ac8751a7dfe1baff8b953ec9f5833ca260e",
.expected = null, // 2 - small order R is acceptable
},
Vec{
.msg_hex = "9bd9f44f4dcc75bd531b56b2cd280b0bb38fc1cd6d1230e14861d861de092e79",
.public_key_hex = "cdb267ce40c5cd45306fa5d2f29731459387dbf9eb933b7bd5aed9a765b88d4d",
.sig_hex = "9046a64750444938de19f227bb80485e92b83fdb4b6506c160484c016cc1852f87909e14428a7a1d62e9f22f3d3ad7802db02eb2e688b6c52fcd6648a98bd009",
.expected = null, // 3 - mixed orders
},
Vec{
.msg_hex = "e47d62c63f830dc7a6851a0b1f33ae4bb2f507fb6cffec4011eaccd55b53f56c",
.public_key_hex = "cdb267ce40c5cd45306fa5d2f29731459387dbf9eb933b7bd5aed9a765b88d4d",
.sig_hex = "160a1cb0dc9c0258cd0a7d23e94d8fa878bcb1925f2c64246b2dee1796bed5125ec6bc982a269b723e0668e540911a9a6a58921d6925e434ab10aa7940551a09",
.expected = null, // 4 - cofactored verification
},
Vec{
.msg_hex = "e47d62c63f830dc7a6851a0b1f33ae4bb2f507fb6cffec4011eaccd55b53f56c",
.public_key_hex = "cdb267ce40c5cd45306fa5d2f29731459387dbf9eb933b7bd5aed9a765b88d4d",
.sig_hex = "21122a84e0b5fca4052f5b1235c80a537878b38f3142356b2c2384ebad4668b7e40bc836dac0f71076f9abe3a53f9c03c1ceeeddb658d0030494ace586687405",
.expected = null, // 5 - cofactored verification
},
Vec{
.msg_hex = "85e241a07d148b41e47d62c63f830dc7a6851a0b1f33ae4bb2f507fb6cffec40",
.public_key_hex = "442aad9f089ad9e14647b1ef9099a1ff4798d78589e66f28eca69c11f582a623",
.sig_hex = "e96f66be976d82e60150baecff9906684aebb1ef181f67a7189ac78ea23b6c0e547f7690a0e2ddcd04d87dbc3490dc19b3b3052f7ff0538cb68afb369ba3a514",
.expected = error.NonCanonical, // 6 - S > L
},
Vec{
.msg_hex = "85e241a07d148b41e47d62c63f830dc7a6851a0b1f33ae4bb2f507fb6cffec40",
.public_key_hex = "442aad9f089ad9e14647b1ef9099a1ff4798d78589e66f28eca69c11f582a623",
.sig_hex = "8ce5b96c8f26d0ab6c47958c9e68b937104cd36e13c33566acd2fe8d38aa19427e71f98a4734e74f2f13f06f97c20d58cc3f54b8bd0d272f42b695dd7e89a8c2",
.expected = error.NonCanonical, // 7 - S >> L
},
Vec{
.msg_hex = "9bedc267423725d473888631ebf45988bad3db83851ee85c85e241a07d148b41",
.public_key_hex = "f7badec5b8abeaf699583992219b7b223f1df3fbbea919844e3f7c554a43dd43",
.sig_hex = "ecffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff03be9678ac102edcd92b0210bb34d7428d12ffc5df5f37e359941266a4e35f0f",
.expected = error.InvalidSignature, // 8 - non-canonical R
},
Vec{
.msg_hex = "9bedc267423725d473888631ebf45988bad3db83851ee85c85e241a07d148b41",
.public_key_hex = "f7badec5b8abeaf699583992219b7b223f1df3fbbea919844e3f7c554a43dd43",
.sig_hex = "ecffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffca8c5b64cd208982aa38d4936621a4775aa233aa0505711d8fdcfdaa943d4908",
.expected = null, // 9 - non-canonical R
},
Vec{
.msg_hex = "e96b7021eb39c1a163b6da4e3093dcd3f21387da4cc4572be588fafae23c155b",
.public_key_hex = "ecffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff",
.sig_hex = "a9d55260f765261eb9b84e106f665e00b867287a761990d7135963ee0a7d59dca5bb704786be79fc476f91d3f3f89b03984d8068dcf1bb7dfc6637b45450ac04",
.expected = error.IdentityElement, // 10 - small-order A
},
Vec{
.msg_hex = "39a591f5321bbe07fd5a23dc2f39d025d74526615746727ceefd6e82ae65c06f",
.public_key_hex = "ecffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff",
.sig_hex = "a9d55260f765261eb9b84e106f665e00b867287a761990d7135963ee0a7d59dca5bb704786be79fc476f91d3f3f89b03984d8068dcf1bb7dfc6637b45450ac04",
.expected = error.IdentityElement, // 11 - small-order A
},
};
for (entries) |entry, i| {
var msg: [entry.msg_hex.len / 2]u8 = undefined;
try fmt.hexToBytes(&msg, entry.msg_hex);
var public_key: [32]u8 = undefined;
try fmt.hexToBytes(&public_key, entry.public_key_hex);
var sig: [64]u8 = undefined;
try fmt.hexToBytes(&sig, entry.sig_hex);
if (entry.expected) |error_type| {
std.testing.expectError(error_type, Ed25519.verify(sig, &msg, public_key));
} else {
try Ed25519.verify(sig, &msg, public_key);
}
}
}