nimbus-eth2/beacon_chain/spec/digest.nim

142 lines
4.4 KiB
Nim

# beacon_chain
# Copyright (c) 2018-2022 Status Research & Development GmbH
# Licensed and distributed under either of
# * MIT license (license terms in the root directory or at https://opensource.org/licenses/MIT).
# * Apache v2 license (license terms in the root directory or at https://www.apache.org/licenses/LICENSE-2.0).
# at your option. This file may not be copied, modified, or distributed except according to those terms.
# Serenity hash function / digest
#
# https://github.com/ethereum/consensus-specs/blob/v1.2.0-rc.1/specs/phase0/beacon-chain.md#hash
#
# In Phase 0 the beacon chain is deployed with SHA256 (SHA2-256).
# Note that is is different from Keccak256 (often mistakenly called SHA3-256)
# and SHA3-256.
#
# In Eth1.0, the default hash function is Keccak256 and SHA256 is available as a precompiled contract.
#
# In our code base, to enable a smooth transition
# (already did Blake2b --> Keccak256 --> SHA2-256),
# we call this function `eth2digest`, and it outputs a `Eth2Digest`. Easy to sed :)
{.push raises: [Defect].}
import
# Standard library
std/hashes,
# Status libraries
chronicles,
nimcrypto/[sha2, hash],
stew/[byteutils, endians2, objects],
json_serialization
export
# Exports from sha2 / hash are explicit to avoid exporting upper-case `$` and
# constant-time `==`
hash.fromHex, json_serialization
type
Eth2Digest* = MDigest[32 * 8] ## `hash32` from spec
const PREFER_BLST_SHA256* {.booldefine.} = true
when PREFER_BLST_SHA256:
import blscurve
when BLS_BACKEND == BLST:
const USE_BLST_SHA256 = true
else:
const USE_BLST_SHA256 = false
else:
const USE_BLST_SHA256 = false
when USE_BLST_SHA256:
export blscurve.update
type Eth2DigestCtx* = BLST_SHA256_CTX
else:
export sha2.update
type Eth2DigestCtx* = sha2.sha256
func `$`*(x: Eth2Digest): string =
x.data.toHex()
func shortLog*(x: Eth2Digest): string =
x.data.toOpenArray(0, 3).toHex()
chronicles.formatIt Eth2Digest:
shortLog(it)
# TODO: expose an in-place digest function
# when hashing in loop or into a buffer
# See: https://github.com/cheatfate/nimcrypto/blob/b90ba3abd/nimcrypto/sha2.nim#L570
func eth2digest*(v: openArray[byte]): Eth2Digest {.noinit.} =
## Apply the Eth2 Hash function
## Do NOT use for secret data.
when USE_BLST_SHA256:
# BLST has a fast assembly optimized SHA256
result.data.bls_sha256_digest(v)
else:
# We use the init-update-finish interface to avoid
# the expensive burning/clearing memory (20~30% perf)
var ctx {.noinit.}: Eth2DigestCtx
ctx.init()
ctx.update(v)
ctx.finish()
template withEth2Hash*(body: untyped): Eth2Digest =
## This little helper will init the hash function and return the sliced
## hash:
## let hashOfData = withHash: h.update(data)
when nimvm:
# In SSZ, computeZeroHashes require compile-time SHA256
block:
var h {.inject.}: sha256
init(h)
body
finish(h)
else:
when USE_BLST_SHA256:
block:
var h {.inject, noinit.}: Eth2DigestCtx
init(h)
body
var res {.noinit.}: Eth2Digest
finalize(res.data, h)
res
else:
block:
var h {.inject, noinit.}: Eth2DigestCtx
init(h)
body
finish(h)
template hash*(x: Eth2Digest): Hash =
## Hash for digests for Nim hash tables
# digests are already good hashes
cast[ptr Hash](unsafeAddr x.data[0])[]
func `==`*(a, b: Eth2Digest): bool =
when nimvm:
a.data == b.data
else:
# nimcrypto uses a constant-time comparison for all MDigest types which for
# Eth2Digest is unnecessary - the type should never hold a secret!
equalMem(unsafeAddr a.data[0], unsafeAddr b.data[0], sizeof(a.data))
func isZero*(x: Eth2Digest): bool =
x.isZeroMemory
proc writeValue*(w: var JsonWriter, a: Eth2Digest) {.raises: [Defect, IOError, SerializationError].} =
w.writeValue $a
proc readValue*(r: var JsonReader, a: var Eth2Digest) {.raises: [Defect, IOError, SerializationError].} =
try:
a = fromHex(type(a), r.readValue(string))
except ValueError:
raiseUnexpectedValue(r, "Hex string expected")
func toGaugeValue*(hash: Eth2Digest): int64 =
# Only the last 8 bytes are taken into consideration in accordance
# to the ETH2 metrics spec:
# https://github.com/ethereum/beacon-metrics/blob/6a79914cb31f7d54858c7dd57eee75b6162ec737/metrics.md#interop-metrics
cast[int64](uint64.fromBytesLE(hash.data.toOpenArray(24, 31)))