path: root/mcs/class/corlib/Mono.Security.Cryptography/PKCS1.cs

//
// PKCS1.cs - Implements PKCS#1 primitives.
//
// Author:
//	Sebastien Pouliot (spouliot@motus.com)
//
// (C) 2002 Motus Technologies Inc. (http://www.motus.com)
//

using System;

namespace System.Security.Cryptography { 

// References:
// a.	PKCS#1: RSA Cryptography Standard 
//	http://www.rsasecurity.com/rsalabs/pkcs/pkcs-1/index.html

internal class PKCS1 {

	private static bool Compare (byte[] array1, byte[] array2) 
	{
		bool result = (array1.Length == array2.Length);
		if (result) {
			for (int i=0; i < array1.Length; i++)
				if (array1[i] != array2[i])
					return false;
		}
		return result;
	}

	private static byte[] xor (byte[] array1, byte[] array2) 
	{
		byte[] result = new byte [array1.Length];
		for (int i=0; i < result.Length; i++)
			result[i] = (byte) (array1[i] ^ array2[i]);
		return result;
	}

	private static byte[] emptySHA1   = { 0xda, 0x39, 0xa3, 0xee, 0x5e, 0x6b, 0x4b, 0x0d, 0x32, 0x55, 0xbf, 0xef, 0x95, 0x60, 0x18, 0x90, 0xaf, 0xd8, 0x07, 0x09 };
	private static byte[] emptySHA256 = { 0xe3, 0xb0, 0xc4, 0x42, 0x98, 0xfc, 0x1c, 0x14, 0x9a, 0xfb, 0xf4, 0xc8, 0x99, 0x6f, 0xb9, 0x24, 0x27, 0xae, 0x41, 0xe4, 0x64, 0x9b, 0x93, 0x4c, 0xa4, 0x95, 0x99, 0x1b, 0x78, 0x52, 0xb8, 0x55 };
	private static byte[] emptySHA384 = { 0x38, 0xb0, 0x60, 0xa7, 0x51, 0xac, 0x96, 0x38, 0x4c, 0xd9, 0x32, 0x7e, 0xb1, 0xb1, 0xe3, 0x6a, 0x21, 0xfd, 0xb7, 0x11, 0x14, 0xbe, 0x07, 0x43, 0x4c, 0x0c, 0xc7, 0xbf, 0x63, 0xf6, 0xe1, 0xda, 0x27, 0x4e, 0xde, 0xbf, 0xe7, 0x6f, 0x65, 0xfb, 0xd5, 0x1a, 0xd2, 0xf1, 0x48, 0x98, 0xb9, 0x5b };
	private static byte[] emptySHA512 = { 0xcf, 0x83, 0xe1, 0x35, 0x7e, 0xef, 0xb8, 0xbd, 0xf1, 0x54, 0x28, 0x50, 0xd6, 0x6d, 0x80, 0x07, 0xd6, 0x20, 0xe4, 0x05, 0x0b, 0x57, 0x15, 0xdc, 0x83, 0xf4, 0xa9, 0x21, 0xd3, 0x6c, 0xe9, 0xce, 0x47, 0xd0, 0xd1, 0x3c, 0x5d, 0x85, 0xf2, 0xb0, 0xff, 0x83, 0x18, 0xd2, 0x87, 0x7e, 0xec, 0x2f, 0x63, 0xb9, 0x31, 0xbd, 0x47, 0x41, 0x7a, 0x81, 0xa5, 0x38, 0x32, 0x7a, 0xf9, 0x27, 0xda, 0x3e };

	private static byte[] GetEmptyHash (HashAlgorithm hash) 
	{
		if (hash is SHA1)
			return emptySHA1;
		else if (hash is SHA256)
			return emptySHA256;
		else if (hash is SHA384)
			return emptySHA384;
		else if (hash is SHA512)
			return emptySHA512;
		else
			return null;
	}

	// PKCS #1 v.2.1, Section 4.1
	// I2OSP converts a nonnegative integer to an octet string of a specified length.
	public static byte[] I2OSP (int x, int size) 
	{
		byte[] array = BitConverter.GetBytes (x);
		return I2OSP (array, size);
	}

	public static byte[] I2OSP (byte[] x, int size) 
	{
		byte[] result = new byte [size];
		Array.Copy (x, 0, result, (result.Length - x.Length), x.Length);
		return result;
	}

	// PKCS #1 v.2.1, Section 4.2
	// OS2IP converts an octet string to a nonnegative integer.
	public static byte[] OS2IP (byte[] x) 
	{
		int i = 0;
		while ((x[i++] == 0x00) && (i < x.Length));
		i--;
		if (i > 0) {
			byte[] result = new byte [x.Length - i];
			Array.Copy (x, i, result, 0, result.Length);
			return result;
		}
		else
			return x;
	}

	// PKCS #1 v.2.1, Section 5.1.1
	public static byte[] RSAEP (RSA rsa, byte[] m) 
	{
		// c = m^e mod n
		return rsa.EncryptValue (m);
	}

	// PKCS #1 v.2.1, Section 5.1.2
	public static byte[] RSADP (RSA rsa, byte[] c) 
	{
		// m = c^d mod n
		// Decrypt value may apply CRT optimizations
		return rsa.DecryptValue (c);
	}

	// PKCS #1 v.2.1, Section 5.2.1
	public static byte[] RSASP1 (RSA rsa, byte[] m) 
	{
		// first form: s = m^d mod n
		// Decrypt value may apply CRT optimizations
		return rsa.DecryptValue (m);
	}

	// PKCS #1 v.2.1, Section 5.2.2
	public static byte[] RSAVP1 (RSA rsa, byte[] s) 
	{
		// m = s^e mod n
		return rsa.EncryptValue (s);
	}

	// PKCS #1 v.2.1, Section 7.1.1
	// RSAES-OAEP-ENCRYPT ((n, e), M, L)
	public static byte[] Encrypt_OAEP (RSA rsa, HashAlgorithm hash, RandomNumberGenerator rng, byte[] M) 
	{
		int size = rsa.KeySize / 8;
		int hLen = hash.HashSize / 8;
		if (M.Length > size - 2 * hLen - 2)
			throw new CryptographicException ("message too long");
		// empty label L SHA1 hash
		byte[] lHash = GetEmptyHash (hash);
		int PSLength = (size - M.Length - 2 * hLen - 2);
		// DB = lHash || PS || 0x01 || M
		byte[] DB = new byte [lHash.Length + PSLength + 1 + M.Length];
		Array.Copy (lHash, 0, DB, 0, lHash.Length);
		DB [(lHash.Length + PSLength)] = 0x01;
		Array.Copy (M, 0, DB, (DB.Length - M.Length), M.Length);

		byte[] seed = new byte [hLen];
		rng.GetBytes (seed);

		byte[] dbMask = MGF1 (hash, seed, size - hLen - 1);
		byte[] maskedDB = xor (DB, dbMask);
		byte[] seedMask = MGF1 (hash, maskedDB, hLen);
		byte[] maskedSeed = xor (seed, seedMask);
		// EM = 0x00 || maskedSeed || maskedDB
		byte[] EM = new byte [maskedSeed.Length + maskedDB.Length + 1];
		Array.Copy (maskedSeed, 0, EM, 1, maskedSeed.Length);
		Array.Copy (maskedDB, 0, EM, maskedSeed.Length + 1, maskedDB.Length);

		byte[] m = OS2IP (EM);
		byte[] c = RSAEP (rsa, m);
		return I2OSP (c, size);
	}

	// PKCS #1 v.2.1, Section 7.1.2
	// RSAES-OAEP-DECRYPT (K, C, L)
	public static byte[] Decrypt_OAEP (RSA rsa, HashAlgorithm hash, byte[] C) 
	{
		int size = rsa.KeySize / 8;
		int hLen = hash.HashSize / 8;
		if ((size < (2 * hLen + 2)) || (C.Length != size))
			throw new CryptographicException ("decryption error");

		byte[] c = OS2IP (C);
		byte[] m = RSADP (rsa, c);
		byte[] EM = I2OSP (m, size);

		// split EM = Y || maskedSeed || maskedDB
		byte[] maskedSeed = new byte [hLen];
		Array.Copy (EM, 1, maskedSeed, 0, maskedSeed.Length);
		byte[] maskedDB = new byte [size - hLen - 1];
		Array.Copy (EM, (EM.Length - maskedDB.Length), maskedDB, 0, maskedDB.Length);

		byte[] seedMask = MGF1 (hash, maskedDB, hLen);
		byte[] seed = xor (maskedSeed, seedMask);
		byte[] dbMask = MGF1 (hash, seed, size - hLen - 1);
		byte[] DB = xor (maskedDB, dbMask);

		byte[] lHash = GetEmptyHash (hash);
		// split DB = lHash’ || PS || 0x01 || M
		byte[] dbHash = new byte [lHash.Length];
		Array.Copy (DB, 0, dbHash, 0, dbHash.Length);
		bool h = Compare (lHash, dbHash);

		// find separator 0x01
		int nPos = lHash.Length;
		while (DB[nPos] == 0)
			nPos++;

		int Msize = DB.Length - nPos - 1;
		byte[] M = new byte [Msize];
		Array.Copy (DB, (nPos + 1), M, 0, Msize);

		// we could have returned EM[0] sooner but would be helping a timing attack
		if ((EM[0] != 0) || (!h) || (DB[nPos] != 0x01))
			return null;
		return M;
	}

	// PKCS #1 v.2.1, Section 7.2.1
	// RSAES-PKCS1-V1_5-ENCRYPT ((n, e), M)
	public static byte[] Encrypt_v15 (RSA rsa, RandomNumberGenerator rng, byte[] M) 
	{
		int size = rsa.KeySize / 8;
		if (M.Length > size - 11)
			throw new CryptographicException ("message too long");
		int PSLength = Math.Max (8, (size - M.Length - 3));
		byte[] PS = new byte [PSLength];
		rng.GetNonZeroBytes (PS);
		byte[] EM = new byte [size];
		EM [1] = 0x02;
		Array.Copy (PS, 0, EM, 2, PSLength);
		Array.Copy (M, 0, EM, (size - M.Length), M.Length);

		byte[] m = OS2IP (EM);
		byte[] c = RSAEP (rsa, m);
		byte[] C = I2OSP (c, size);
		return C;
	}

	// PKCS #1 v.2.1, Section 7.2.2
	// RSAES-PKCS1-V1_5-DECRYPT (K, C)
	public static byte[] Decrypt_v15 (RSA rsa, byte[] C) 
	{
		int size = rsa.KeySize / 8;
		if ((size < 11) || (C.Length != size))
			throw new CryptographicException ("decryption error");
		byte[] c = OS2IP (C);
		byte[] m = RSADP (rsa, c);
		byte[] EM = I2OSP (m, size);

		if ((EM [0] != 0x00) || (EM [1] != 0x02))
			return null;

		int mPos = 10;
		// PS is a minimum of 8 bytes + 2 bytes for header
		while ((EM [mPos] != 0x00) && (mPos < EM.Length))
			mPos++;
		if (EM [mPos] != 0x00)
			return null;
		mPos++;
		byte[] M = new byte [EM.Length - mPos];
		Array.Copy (EM, mPos, M, 0, M.Length);
		return M;
	}

	// PKCS #1 v.2.1, Section 8.2.1
	// RSASSA-PKCS1-V1_5-SIGN (K, M)
	public static byte[] Sign_v15 (RSA rsa, string oid, byte[] hash) 
	{
		int size = rsa.KeySize / 8;
		byte[] EM = Encode_v15 (oid, hash, size);
		byte[] m = OS2IP (EM);
		byte[] s = RSASP1 (rsa, m);
		byte[] S = I2OSP (s, size);
		return S;
	}

	// PKCS #1 v.2.1, Section 8.2.2
	// RSASSA-PKCS1-V1_5-VERIFY ((n, e), M, S)
	public static bool Verify_v15 (RSA rsa, string oid, byte[] hash, byte[] signature) 
	{
		int size = rsa.KeySize / 8;
		byte[] s = OS2IP (signature);
		byte[] m = RSAVP1 (rsa, signature);
		byte[] EM2 = I2OSP (m, size);
		byte[] EM = Encode_v15 (oid, hash, size);
		return Compare(EM, EM2);
	}

	// Note: MD2 isn't supported in .NET framework
	private static byte[] md2const = { 0x30, 0x20, 0x30, 0x0c, 0x06, 0x08, 0x2a, 0x86, 0x48, 0x86, 0xf7, 0x0d, 0x02, 0x02, 0x05, 0x00, 0x04, 0x10 };
	private static byte[] md5const = { 0x30, 0x20, 0x30, 0x0c, 0x06, 0x08, 0x2a, 0x86, 0x48, 0x86, 0xf7, 0x0d, 0x02, 0x05, 0x05, 0x00, 0x04, 0x10 };
	private static byte[] sha1const = { 0x30, 0x21, 0x30, 0x09, 0x06, 0x05, 0x2b, 0x0e, 0x03, 0x02, 0x1a, 0x05, 0x00, 0x04, 0x14 };
	private static byte[] sha256const = { 0x30, 0x31, 0x30, 0x0d, 0x06, 0x09, 0x60, 0x86, 0x48, 0x01, 0x65, 0x03, 0x04, 0x02, 0x01, 0x05, 0x00, 0x04, 0x20 };
	private static byte[] sha384const = { 0x30, 0x41, 0x30, 0x0d, 0x06, 0x09, 0x60, 0x86, 0x48, 0x01, 0x65, 0x03, 0x04, 0x02, 0x02, 0x05, 0x00, 0x04, 0x30 };
	private static byte[] sha512const = { 0x30, 0x51, 0x30, 0x0d, 0x06, 0x09, 0x60, 0x86, 0x48, 0x01, 0x65, 0x03, 0x04, 0x02, 0x03, 0x05, 0x00, 0x04, 0x40 };

	// PKCS #1 v.2.1, Section 9.2
	// EMSA-PKCS1-v1_5-Encode
	public static byte[] Encode_v15 (string oid, byte[] hash, int emLength) 
	{
		string e = "bad hash length for ";
		byte[] t = null;
		switch (oid) {
			case "1.3.14.3.2.26":
				// SHA1
				if (hash.Length != 20)
					throw new CryptographicException (e + oid);
				t = new byte [35];
				Array.Copy (sha1const, 0, t, 0, sha1const.Length);
				break;
			case "1.2.840.113549.2.2":
				// MD2
				if (hash.Length != 16)
					throw new CryptographicException (e + oid);
				t = new byte [34];
				Array.Copy (md2const, 0, t, 0, md2const.Length);
				break;
			case "1.2.840.113549.2.5":
				// MD5
				if (hash.Length != 16)
					throw new CryptographicException (e + oid);
				t = new byte [34];
				Array.Copy (md5const, 0, t, 0, md5const.Length);
				break;
			case "2.16.840.1.101.3.4.1":
				// SHA256
				if (hash.Length != 32)
					throw new CryptographicException (e + oid);
				t = new byte [51];
				Array.Copy (sha256const, 0, t, 0, sha256const.Length);
				break;
			case "2.16.840.1.101.3.4.2":
				// SHA384
				if (hash.Length != 48)
					throw new CryptographicException (e + oid);
				t = new byte [67];
				Array.Copy (sha384const, 0, t, 0, sha384const.Length);
				break;
			case "2.16.840.1.101.3.4.3":
				// SHA512
				if (hash.Length != 64)
					throw new CryptographicException (e + oid);
				t = new byte [83];
				Array.Copy (sha512const, 0, t, 0, sha512const.Length);
				break;
			default:
				return null;
		}
		Array.Copy (hash, 0, t, t.Length - hash.Length, hash.Length);

		int PSLength = Math.Max (8, emLength - t.Length - 3);
		// PS = PSLength of 0xff

		// EM = 0x00 | 0x01 | PS | 0x00 | T
		byte[] EM = new byte [PSLength + t.Length + 3];
		EM [1] = 0x01;
		for (int i=2; i < PSLength + 2; i++)
			EM[i] = 0xff;
		Array.Copy (t, 0, EM, PSLength + 3, t.Length);

		return EM;
	}

	// PKCS #1 v.2.1, Section B.2.1
	public static byte[] MGF1 (HashAlgorithm hash, byte[] mgfSeed, int maskLen) 
	{
		// 1. If maskLen > 2^32 hLen, output “mask too long” and stop.
		// easy - this is impossible by using a int (31bits) as parameter ;-)
		// BUT with a signed int we do have to check for negative values!
		if (maskLen < 0)
			throw new OverflowException();

		int mgfSeedLength = mgfSeed.Length;
		int hLen = (hash.HashSize >> 3); // from bits to bytes
		int iterations = (maskLen / hLen);
		if (maskLen % hLen != 0)
			iterations++;
		// 2. Let T be the empty octet string.
		byte[] T = new byte [iterations * hLen];

		byte[] toBeHashed = new byte [mgfSeedLength + 4];
		int pos = 0;
		// 3. For counter from 0 to (maskLen / hLen) – 1, do the following:
		for (int counter = 0; counter < iterations; counter++) {
			// a.	Convert counter to an octet string C of length 4 octets
			byte[] C = I2OSP (counter, 4);

			// b.	Concatenate the hash of the seed mgfSeed and C to the octet string T:
			//	T = T || Hash (mgfSeed || C)
			Array.Copy (mgfSeed, 0, toBeHashed, 0, mgfSeedLength);
			Array.Copy (C, 0, toBeHashed, mgfSeedLength, 4);
			byte[] output = hash.ComputeHash (toBeHashed);
			Array.Copy (output, 0, T, pos, hLen);
			pos += mgfSeedLength;
		}
		
		// 4. Output the leading maskLen octets of T as the octet string mask.
		byte[] mask = new byte [maskLen];
		Array.Copy (T, 0, mask, 0, maskLen);
		return mask;
	}
}

}