bytebuffer.kt

fun ByteBuffer.rsadec(exponent: BigInteger, modulus: BigInteger) {
    val length = g1
    val dec = BigInteger(gdata(length)).modPow(exponent, modulus).toByteArray()
    position(0)
    pdata(dec)
    position(0)
}

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fun ByteBuffer.rsadec(pem: RSAPrivateCrtKey) {
    val p = pem.primeP
    val q = pem.primeQ
    val dP = pem.primeExponentP
    val dQ = pem.primeExponentQ
    val qInv = pem.crtCoefficient

    val length = g1
    val bytes = gdata(length)
    val data = BigInteger(1, bytes)

    val m1 = data.mod(p).modPow(dP, p)
    val m2 = data.mod(q).modPow(dQ, q)

    val h = qInv * (m1 - m2) % p
    val dec = (m2 + h * q).toByteArray()

    position(0)
    pdata(dec)
    position(0)
}