/// <summary>
/// Method that implements EME-OAEP decoding
/// </summary>
/// <param name="EM">
/// Message to be decoded. An octet string of length k
/// </param>
/// <param name="label">
/// Optional label to be associated with the message; the
/// default value for L, if L is not provided, is the empty string.
/// </param>
/// <param name="k">
/// Size of public key modulus in octets
/// </param>
/// <param name="hash">
/// Hash function (hLen denotes the length in octets of
/// the hash function output)
/// </param>
/// <returns>
/// Decoded message, octet string of length mLen
/// </returns>
/// <exception cref="DecryptionErrorException">
/// Method can throw exception
/// </exception>
public byte[] EME_OAEP_Decoding(byte[] EM, byte[] label, int k, HashAlgorithm hash)
{
int hLen = hash.HashSize / 8;
byte[] lHash = hash.ComputeHash(label);
if (EM[0] != 0x00)
{
throw new DecryptionErrorException("Decryption error!");
}
byte[] maskedSeed = new byte[hLen];
byte[] maskedDB = new byte[k - hLen - 1];
System.Buffer.BlockCopy(EM, 1, maskedSeed, 0, maskedSeed.Length);
System.Buffer.BlockCopy(EM, 1 + maskedSeed.Length, maskedDB, 0, maskedDB.Length);
byte[] seedMask = mgf.MGF1(maskedDB, hLen, hash);
byte[] seed = ByteArraysUtils.XorBytes(maskedSeed, seedMask);
byte[] dbMask = mgf.MGF1(seed, k - hLen - 1, hash);
byte[] DB = ByteArraysUtils.XorBytes(maskedDB, dbMask);
byte[] lHash_dash = new byte[hLen];
System.Buffer.BlockCopy(DB, 0, lHash_dash, 0, hLen);
if (!lHash.SequenceEqual(lHash_dash))
{
throw new DecryptionErrorException("Decryption error!");
}
int i = Array.FindIndex(DB, hLen, el => el == 0x01);
if (i == -1)
{
throw new DecryptionErrorException("Decryption error!");
}
byte[] M = new byte[DB.Length - 1 - i];
System.Buffer.BlockCopy(DB, i + 1, M, 0, M.Length);
return(M);
}
public void XorBytes()
{
byte[] arg1 = { 97, 29, 31, 55, 17, 0, 129 };
byte[] arg2 = { 12, 33, 14, 40, 199, 244, 87 };
byte[] xor = ByteArraysUtils.XorBytes(arg1, arg2);
byte[] actual = ByteArraysUtils.XorBytes(xor, arg2);
CollectionAssert.AreEqual(arg1, actual);
}
/// <summary>
/// Method that implements EME-OAEP encoding.
/// </summary>
/// <param name="message">
/// Message to be encoded, an octet string of length mLen, where mLen <= k - 2hLen - 2
/// </param>
/// <param name="label">
/// Optional label to be associated with the message; the
/// default value for L, if L is not provided, is the empty string.
/// </param>
/// <param name="k">
/// Size of public key modulus in octets
/// </param>
/// <param name="hash">
/// Hash function (hLen denotes the length in octets of
/// the hash function output)
/// </param>
/// <returns>
/// Encoded message of k length
/// </returns>
public byte[] EME_OAEP_Encoding(byte[] message, byte[] label, int k, HashAlgorithm hash)
{
int hLen = hash.HashSize / 8;
byte[] lHash = hash.ComputeHash(label);
byte[] PS = new byte[k - message.Length - 2 * hLen - 2];
byte[] DB = new byte[k - hLen - 1];
System.Buffer.BlockCopy(lHash, 0, DB, 0, lHash.Length);
System.Buffer.BlockCopy(PS, 0, DB, lHash.Length, PS.Length);
DB[lHash.Length + PS.Length] = 0x01;
System.Buffer.BlockCopy(message, 0, DB, lHash.Length + PS.Length + 1, message.Length);
byte[] seed = ByteArraysUtils.GetRandomOctets(RNGCryptoServiceProvider.Create(), hLen);
byte[] dbMask = mgf.MGF1(seed, k - hLen - 1, hash);
byte[] maskedDB = ByteArraysUtils.XorBytes(DB, dbMask);
byte[] seedMask = mgf.MGF1(maskedDB, hLen, hash);
byte[] maskedSeed = ByteArraysUtils.XorBytes(seed, seedMask);
byte[] EM = new byte[k];
System.Buffer.SetByte(EM, 0, 0x00);
System.Buffer.BlockCopy(maskedSeed, 0, EM, 1, maskedSeed.Length);
System.Buffer.BlockCopy(maskedDB, 0, EM, maskedSeed.Length + 1, maskedDB.Length);
return(EM);
}
public byte[] EMSA_PSS_Encoding(byte[] M, int k, int sLen)
{
int hLen = hash.HashSize;
int emLen = k / 8;
var mHash = hash.ComputeHash(M);
if (emLen < hLen + sLen + 2)
{
throw new EncodingException();
}
byte[] salt = ByteArraysUtils.GetRandomOctets(RNGCryptoServiceProvider.Create(), sLen);
var M_dash = ByteArraysUtils.Concat(new byte[] { 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00 }, ByteArraysUtils.Concat(mHash, salt));
var H = hash.ComputeHash(M_dash);
var PS = new byte[emLen - sLen - hLen - 2];
var DB = ByteArraysUtils.Concat(ByteArraysUtils.Concat(PS, new byte[] { 0x01 }), salt);
var dbMask = mgf.MGF1(H, emLen - hLen - 1, hash);
var maskedDB = ByteArraysUtils.XorBytes(DB, dbMask);
maskedDB[0] &= (byte)(0xFF >> (8 * emLen - k));
var EM = ByteArraysUtils.Concat(ByteArraysUtils.Concat(maskedDB, H), new byte[] { 0xbc });
return(EM);
}
