nim-libp2p/libp2p/crypto/curve25519.nim

118 lines
4.8 KiB
Nim

## Nim-Libp2p
## Copyright (c) 2020 Status Research & Development GmbH
## Licensed under either of
## * Apache License, version 2.0, ([LICENSE-APACHE](LICENSE-APACHE))
## * MIT license ([LICENSE-MIT](LICENSE-MIT))
## at your option.
## This file may not be copied, modified, or distributed except according to
## those terms.
## This module integrates BearSSL Cyrve25519 mul and mulgen
##
## This module uses unmodified parts of code from
## BearSSL library <https://bearssl.org/>
## Copyright(C) 2018 Thomas Pornin <pornin@bolet.org>.
# RFC @ https://tools.ietf.org/html/rfc7748
{.push raises: [Defect].}
import bearssl
import stew/results
export results
const
Curve25519KeySize* = 32
type
Curve25519* = object
Curve25519Key* = array[Curve25519KeySize, byte]
pcuchar = ptr cuchar
Curve25519Error* = enum
Curver25519GenError
proc intoCurve25519Key*(s: openarray[byte]): Curve25519Key =
assert s.len == Curve25519KeySize
copyMem(addr result[0], unsafeaddr s[0], Curve25519KeySize)
proc getBytes*(key: Curve25519Key): seq[byte] = @key
const
ForbiddenCurveValues: array[12, Curve25519Key] = [
[0.byte, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0],
[1.byte, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0],
[224.byte, 235, 122, 124, 59, 65, 184, 174, 22, 86, 227, 250, 241, 159, 196, 106, 218, 9, 141, 235, 156, 50, 177, 253, 134, 98, 5, 22, 95, 73, 184, 0],
[95.byte, 156, 149, 188, 163, 80, 140, 36, 177, 208, 177, 85, 156, 131, 239, 91, 4, 68, 92, 196, 88, 28, 142, 134, 216, 34, 78, 221, 208, 159, 17, 87],
[236.byte, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 127],
[237.byte, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 127],
[238.byte, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 127],
[205.byte, 235, 122, 124, 59, 65, 184, 174, 22, 86, 227, 250, 241, 159, 196, 106, 218, 9, 141, 235, 156, 50, 177, 253, 134, 98, 5, 22, 95, 73, 184, 128],
[76.byte, 156, 149, 188, 163, 80, 140, 36, 177, 208, 177, 85, 156, 131, 239, 91, 4, 68, 92, 196, 88, 28, 142, 134, 216, 34, 78, 221, 208, 159, 17, 215],
[217.byte, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255],
[218.byte, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255],
[219.byte, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 25],
]
proc byteswap(buf: var Curve25519Key) {.inline.} =
for i in 0..<16:
let
x = buf[i]
buf[i] = buf[31 - i]
buf[31 - i] = x
proc mul*(_: type[Curve25519], dst: var Curve25519Key, scalar: Curve25519Key, point: Curve25519Key) =
let defaultBrEc = brEcGetDefault()
# The source point is provided in array G (of size Glen bytes);
# the multiplication result is written over it.
dst = scalar
# point needs to be big-endian
var
rpoint = point
rpoint.byteswap()
let
res = defaultBrEc.mul(
cast[pcuchar](addr dst[0]),
Curve25519KeySize,
cast[pcuchar](addr rpoint[0]),
Curve25519KeySize,
EC_curve25519)
assert res == 1
proc mulgen*(_: type[Curve25519], dst: var Curve25519Key, point: Curve25519Key) =
let defaultBrEc = brEcGetDefault()
var
rpoint = point
rpoint.byteswap()
block iterate:
while true:
block derive:
let
size = defaultBrEc.mulgen(
cast[pcuchar](addr dst[0]),
cast[pcuchar](addr rpoint[0]),
Curve25519KeySize,
EC_curve25519)
assert size == Curve25519KeySize
for forbid in ForbiddenCurveValues:
if dst == forbid:
break derive
break iterate
proc public*(private: Curve25519Key): Curve25519Key =
Curve25519.mulgen(result, private)
proc random*(_: type[Curve25519Key], rng: var BrHmacDrbgContext): Curve25519Key =
var res: Curve25519Key
let defaultBrEc = brEcGetDefault()
let len = brEcKeygen(
addr rng.vtable, defaultBrEc, nil, addr res[0], EC_curve25519)
# Per bearssl documentation, the keygen only fails if the curve is
# unrecognised -
doAssert len == Curve25519KeySize, "Could not generate curve"
res