Add textbook RSA encryption and decryption

bzip2
Graham 5 years ago
parent 808c80e896
commit 0f767c86eb
  1. 59
      common/src/main/java/dev/openrs2/common/crypto/Rsa.kt
  2. 54
      common/src/test/java/dev/openrs2/common/crypto/RsaTest.kt

@ -13,6 +13,7 @@ import org.bouncycastle.crypto.params.RSAKeyParameters
import org.bouncycastle.crypto.params.RSAPrivateCrtKeyParameters
import org.bouncycastle.crypto.util.PrivateKeyInfoFactory
import org.bouncycastle.crypto.util.SubjectPublicKeyInfoFactory
import org.bouncycastle.util.BigIntegers
import org.bouncycastle.util.io.pem.PemObject
import org.bouncycastle.util.io.pem.PemReader
import org.bouncycastle.util.io.pem.PemWriter
@ -51,6 +52,64 @@ object Rsa {
return Pair(keyPair.public as RSAKeyParameters, keyPair.private as RSAPrivateCrtKeyParameters)
}
fun encrypt(plaintext: BigInteger, key: RSAKeyParameters): BigInteger {
require(!key.isPrivate)
return plaintext.modPow(key.exponent, key.modulus)
}
private fun generateBlindingFactor(m: BigInteger): Pair<BigInteger, BigInteger> {
val max = m - BigInteger.ONE
while (true) {
val r = BigIntegers.createRandomInRange(BigInteger.ONE, max, secureRandom)
val rInv = try {
r.modInverse(m)
} catch (ex: ArithmeticException) {
continue
}
return Pair(r, rInv)
}
}
fun decrypt(ciphertext: BigInteger, key: RSAKeyParameters): BigInteger {
require(key.isPrivate)
if (key is RSAPrivateCrtKeyParameters) {
// blind the input
val e = key.publicExponent
val m = key.modulus
val (r, rInv) = generateBlindingFactor(m)
val blindCiphertext = (r.modPow(e, m) * ciphertext).mod(m)
// decrypt using the Chinese Remainder Theorem
val p = key.p
val q = key.q
val dP = key.dp
val dQ = key.dq
val qInv = key.qInv
val mP = (blindCiphertext.mod(p)).modPow(dP, p)
val mQ = (blindCiphertext.mod(q)).modPow(dQ, q)
val h = (qInv * (mP - mQ)).mod(p)
val blindPlaintext = (h * q) + mQ
// unblind output
val plaintext = (blindPlaintext * rInv).mod(m)
// defend against CRT faults (see https://people.redhat.com/~fweimer/rsa-crt-leaks.pdf)
if (plaintext.modPow(e, m) != ciphertext) {
throw IllegalStateException()
}
return plaintext
} else {
return ciphertext.modPow(key.exponent, key.modulus)
}
}
fun readPublicKey(path: Path): RSAKeyParameters {
val der = readSinglePemObject(path, PUBLIC_KEY)

@ -0,0 +1,54 @@
package dev.openrs2.common.crypto
import org.bouncycastle.crypto.params.RSAKeyParameters
import org.bouncycastle.crypto.params.RSAPrivateCrtKeyParameters
import org.bouncycastle.util.Properties
import java.math.BigInteger
import kotlin.test.Test
import kotlin.test.assertEquals
object RsaTest {
private const val ALLOW_UNSAFE_MOD = "org.bouncycastle.rsa.allow_unsafe_mod"
@Test
fun testEncrypt() {
// from https://en.wikipedia.org/wiki/RSA_(cryptosystem)#Example
val public = allowUnsafeMod { RSAKeyParameters(false, BigInteger("3233"), BigInteger("17")) }
val ciphertext = Rsa.encrypt(BigInteger("65"), public)
assertEquals(BigInteger("2790"), ciphertext)
}
@Test
fun testDecrypt() {
// from https://en.wikipedia.org/wiki/RSA_(cryptosystem)#Example
val public = allowUnsafeMod { RSAKeyParameters(true, BigInteger("3233"), BigInteger("413")) }
val ciphertext = Rsa.decrypt(BigInteger("2790"), public)
assertEquals(BigInteger("65"), ciphertext)
}
@Test
fun testDecryptCrt() {
// from https://en.wikipedia.org/wiki/RSA_(cryptosystem)#Example
val private = allowUnsafeMod { RSAPrivateCrtKeyParameters(
BigInteger("3233"), // modulus
BigInteger("17"), // public exponent
BigInteger("413"), // private exponent
BigInteger("61"), // p
BigInteger("53"), // q
BigInteger("53"), // dP
BigInteger("49"), // dQ
BigInteger("38") // qInv
) }
val ciphertext = Rsa.decrypt(BigInteger("2790"), private)
assertEquals(BigInteger("65"), ciphertext)
}
private fun <T> allowUnsafeMod(f: () -> T): T {
Properties.setThreadOverride(ALLOW_UNSAFE_MOD, true)
try {
return f()
} finally {
Properties.setThreadOverride(ALLOW_UNSAFE_MOD, false)
}
}
}
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