109 lines
3.7 KiB
C#
109 lines
3.7 KiB
C#
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/*
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* Secucore
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*
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* Copyright (C) 2023 Trevor Hall
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* All rights reserved.
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*
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* This software may be modified and distributed under the terms
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* of the MIT license.
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*
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*/
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using System;
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using System.Numerics;
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namespace SecuCore.Security
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{
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public class RSAPublicKey
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{
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public int keysize;
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public byte[] keydat;
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public byte[] modulusbytes;
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public byte[] exponentbytes;
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public RSAPublicKey(byte[] dat, int offset = 0)
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{
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keydat = dat;
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int dp = offset;
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Asn1Info ai = DerDecoder.GetAsn1Data(dat, ref dp);
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if (ai.type != Asn1Type.SEQUENCE) throw new AsnException("Malformed RSA key");
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ai = DerDecoder.GetAsn1Data(dat, ref dp);
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if (ai.type != Asn1Type.INTEGER) throw new AsnException("Malformed RSA key");
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modulusbytes = new byte[ai.length - 1];
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Buffer.BlockCopy(dat, ai.contentOffset + 1, modulusbytes, 0, ai.length - 1);
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keysize = modulusbytes.Length;
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dp += ai.length;
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ai = DerDecoder.GetAsn1Data(dat, ref dp);
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if (ai.type != Asn1Type.INTEGER) throw new AsnException("Malformed RSA key");
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exponentbytes = new byte[ai.length];
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Buffer.BlockCopy(dat, ai.contentOffset, exponentbytes, 0, ai.length);
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}
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public byte[] EncryptData(byte[] data)
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{
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SecRNG sr = new SecRNG();
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BigInteger modulus = new BigInteger(modulusbytes, true, true);
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BigInteger exponent = new BigInteger(exponentbytes, true, true);
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byte[] block = new byte[keysize];
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byte[] brng = new byte[keysize];
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int bp = 0;
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while (bp < keysize)
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{
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sr.GetRandomBytes(brng, 0, brng.Length);
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for(int i = 0; i < brng.Length; i++)
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{
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if (brng[i] > 2) block[bp++] = brng[i];
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if (bp >= keysize) break;
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}
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}
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block[0] = 0x00;
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block[1] = 0x02;
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block[block.Length - data.Length - 1] = 0x00;
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Buffer.BlockCopy(data, 0, block, block.Length - data.Length, data.Length);
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BigInteger B = new BigInteger(block, true, true);
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BigInteger D = ModPow(B, exponent, modulus);
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byte[] bigendian = D.ToByteArray(true, true);
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return bigendian;
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}
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public byte[] DecryptSignature(byte[] signature)
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{
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BigInteger modulus = new BigInteger(modulusbytes, true, true);
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BigInteger exponent = new BigInteger(exponentbytes, true, true);
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BigInteger B = new BigInteger(signature, true, true);
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BigInteger D = ModPow(B, exponent, modulus);
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byte[] bigendian = D.ToByteArray(false, true);
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int start = 0;
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for(int i = 0; i < bigendian.Length; i++)
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{
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if(bigendian[i] == 0)
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{
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start = i + 1;
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break;
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}
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}
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byte[] cropped = new byte[bigendian.Length - start];
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Buffer.BlockCopy(bigendian, start, cropped, 0, bigendian.Length - start);
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return cropped;
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}
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private static BigInteger ModPow(BigInteger basenum, BigInteger exponent, BigInteger modulus)
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{
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if (modulus == 1) return 0;
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BigInteger curPow = basenum % modulus;
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BigInteger res = 1;
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while (exponent > 0)
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{
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if ((exponent & 0x01) == 1) res = (res * curPow) % modulus;
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exponent >>= 1;
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curPow = (curPow * curPow) % modulus;
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}
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return res;
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}
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}
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}
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