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SecureEq.scala
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SecureEq.scala
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/*
* Copyright 2021 Typelevel
*
* 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
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* 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 bobcats
import cats.kernel.Eq
import scodec.bits.ByteVector
trait SecureEq[A] extends Eq[A]
object SecureEq {
def apply[A](implicit eq: SecureEq[A]): eq.type = eq
/**
* A port of Java's `MessageDigest.isEqual`.
*
* All bytes in `digesta` are examined to determine equality. The calculation time depends
* only on the length of `digesta`. It does not depend on the length of `digestb` or the
* contents of `digesta` and `digestb`.
*/
implicit val secureEqForByteVector: SecureEq[ByteVector] = new SecureEq[ByteVector] {
override def eqv(digesta: ByteVector, digestb: ByteVector): Boolean =
(digesta eq digestb) || {
val lenA = digesta.intSize.get
val lenB = digestb.intSize.get
if (lenB == 0) {
lenA == 0
} else {
var result = 0
result |= lenA - lenB
var i = 0
// time-constant comparison
while (i < lenA) {
val indexB = ((i - lenB) >>> 31) * i
result |= digesta(i.toLong) ^ digestb(indexB.toLong)
i += 1
}
result == 0
}
}
}
}