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//: ----------------------------------------------------------------------------
//: Copyright (C) 2017 Verizon. All Rights Reserved.
//: 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
//: 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.
//: ----------------------------------------------------------------------------
package nelson
package crypto
import AuthFailure._
import scodec.bits.ByteVector
import javax.crypto.Mac
import javax.crypto.spec.SecretKeySpec
final class SignatureKey private(val bytes: ByteVector) {
lazy val keySpec: =
new SecretKeySpec(bytes.toArray, Hmac.algorithm)
object SignatureKey {
val minBytes: Int = 8
def apply(bytes: ByteVector): Either[InsufficientSignatureKeyLength, SignatureKey] =
if (bytes.length >= minBytes) Right(new SignatureKey(bytes))
else Left(InsufficientSignatureKeyLength(actual = bytes.length, required = minBytes.toLong))
def unsafe(bytes: ByteVector): SignatureKey =
apply(bytes).fold(e => throw new IllegalArgumentException(e.toString), identity)
object Hmac {
val algorithm: String = "HmacSHA256"
def mkHmac(): Mac = {
// Note we want to spell out SunJCE here to prevent possible errors when apps
// using a conflicting security provider like LunaHSM.
val hmac = Mac.getInstance(algorithm, "SunJCE")
* A `Signer` computes a signature (such as a checksum) of data.
* @tparam F The context in which results are wrapped. This allows a Signer
* to return a possible failure via Option, a disjunction, etc.
abstract class Signer[F[_]] {
def signature(key: SignatureKey, data: ByteVector, signatureLengthBytes: Int): F[ByteVector]
* An HMAC-based implementation of [[Signer]] that caches `Mac` instances to
* reduce the overhead of initialization.
* Caching a per-key `Mac` instead of just a thread-local `Mac` would remove
* the need to initialize the mac on each signature, but benchmarks show that
* it doesn't make a significant performance difference.
final class SafeHolderHmac(holder: SafeHolder[Mac]) extends Signer[AuthResult] {
def signature(key: SignatureKey, data: ByteVector, signatureLengthBytes: Int): AuthResult[ByteVector] = {
try {
val hmac = holder.getOrCreate(() => Hmac.mkHmac())
val sig = hmac.doFinal
val actualLength = sig.size
// this might be able to be slightly optimized
if (actualLength >= signatureLengthBytes) Right(ByteVector.view(sig).take(signatureLengthBytes.toLong))
else Left(InsufficientSignatureLength(signatureLengthBytes.toLong, actualLength.toLong))
} catch {
case e: Exception =>
Left(SigningError(key.bytes.length, data.length, signatureLengthBytes.toLong, e))
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