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//
// PKCS1.cs - Implements PKCS#1 primitives.
//
// Author:
// Sebastien Pouliot (spouliot@motus.com)
//
// (C) 2002, 2003 Motus Technologies Inc. (http://www.motus.com)
//
//
// Permission is hereby granted, free of charge, to any person obtaining
// a copy of this software and associated documentation files (the
// "Software"), to deal in the Software without restriction, including
// without limitation the rights to use, copy, modify, merge, publish,
// distribute, sublicense, and/or sell copies of the Software, and to
// permit persons to whom the Software is furnished to do so, subject to
// the following conditions:
//
// The above copyright notice and this permission notice shall be
// included in all copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
// EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
// MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
// NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
// LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
// OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
// WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
//
using System;
using System.Security.Cryptography;
namespace Mono.Security.Cryptography {
// References:
// a. PKCS#1: RSA Cryptography Standard
// http://www.rsasecurity.com/rsalabs/pkcs/pkcs-1/index.html
#if INSIDE_CORLIB
internal
#else
public
#endif
sealed class PKCS1 {
private 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 hash.ComputeHash ((byte[])null);
}
// PKCS #1 v.2.1, Section 4.1
// I2OSP converts a non-negative integer to an octet string of a specified length.
public static byte[] I2OSP (int x, int size)
{
byte[] array = BitConverterLE.GetBytes (x);
Array.Reverse (array, 0, array.Length);
return I2OSP (array, size);
}
public static byte[] I2OSP (byte[] x, int size)
{
byte[] result = new byte [size];
Buffer.BlockCopy (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];
Buffer.BlockCopy (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];
Buffer.BlockCopy (lHash, 0, DB, 0, lHash.Length);
DB [(lHash.Length + PSLength)] = 0x01;
Buffer.BlockCopy (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];
Buffer.BlockCopy (maskedSeed, 0, EM, 1, maskedSeed.Length);
Buffer.BlockCopy (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];
Buffer.BlockCopy (EM, 1, maskedSeed, 0, maskedSeed.Length);
byte[] maskedDB = new byte [size - hLen - 1];
Buffer.BlockCopy (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];
Buffer.BlockCopy (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];
Buffer.BlockCopy (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 = System.Math.Max (8, (size - M.Length - 3));
byte[] PS = new byte [PSLength];
rng.GetNonZeroBytes (PS);
byte[] EM = new byte [size];
EM [1] = 0x02;
Buffer.BlockCopy (PS, 0, EM, 2, PSLength);
Buffer.BlockCopy (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];
Buffer.BlockCopy (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, HashAlgorithm hash, byte[] hashValue)
{
int size = (rsa.KeySize >> 3); // div 8
byte[] EM = Encode_v15 (hash, hashValue, 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, HashAlgorithm hash, byte[] hashValue, byte[] signature)
{
int size = (rsa.KeySize >> 3); // div 8
byte[] s = OS2IP (signature);
byte[] m = RSAVP1 (rsa, s);
byte[] EM2 = I2OSP (m, size);
byte[] EM = Encode_v15 (hash, hashValue, size);
bool result = Compare (EM, EM2);
if (!result) {
// NOTE: some signatures don't include the hash OID (pretty lame but real)
// and compatible with MS implementation
if ((EM2 [0] != 0x00) || (EM2 [1] != 0x01))
return false;
// TODO: add more validation
byte[] decryptedHash = new byte [hashValue.Length];
Buffer.BlockCopy (EM2, EM2.Length - hashValue.Length, decryptedHash, 0, decryptedHash.Length);
result = Compare (decryptedHash, hashValue);
}
return result;
}
// PKCS #1 v.2.1, Section 9.2
// EMSA-PKCS1-v1_5-Encode
public static byte[] Encode_v15 (HashAlgorithm hash, byte[] hashValue, int emLength)
{
if (hashValue.Length != (hash.HashSize >> 3))
throw new CryptographicException ("bad hash length for " + hash.ToString ());
// DigestInfo ::= SEQUENCE {
// digestAlgorithm AlgorithmIdentifier,
// digest OCTET STRING
// }
byte[] t = null;
string oid = CryptoConfig.MapNameToOID (hash.ToString ());
if (oid != null)
{
ASN1 digestAlgorithm = new ASN1 (0x30);
digestAlgorithm.Add (new ASN1 (CryptoConfig.EncodeOID (oid)));
digestAlgorithm.Add (new ASN1 (0x05)); // NULL
ASN1 digest = new ASN1 (0x04, hashValue);
ASN1 digestInfo = new ASN1 (0x30);
digestInfo.Add (digestAlgorithm);
digestInfo.Add (digest);
t = digestInfo.GetBytes ();
}
else
{
// There are no valid OID, in this case t = hashValue
// This is the case of the MD5SHA hash algorithm
t = hashValue;
}
Buffer.BlockCopy (hashValue, 0, t, t.Length - hashValue.Length, hashValue.Length);
int PSLength = System.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;
Buffer.BlockCopy (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 \ceil (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)
Buffer.BlockCopy (mgfSeed, 0, toBeHashed, 0, mgfSeedLength);
Buffer.BlockCopy (C, 0, toBeHashed, mgfSeedLength, 4);
byte[] output = hash.ComputeHash (toBeHashed);
Buffer.BlockCopy (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];
Buffer.BlockCopy (T, 0, mask, 0, maskLen);
return mask;
}
}
}
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