diff --git a/Crypto/src/crypto/encodings/OaepEncoding.cs b/Crypto/src/crypto/encodings/OaepEncoding.cs
new file mode 100644
index 000000000..81561e7f5
--- /dev/null
+++ b/Crypto/src/crypto/encodings/OaepEncoding.cs
@@ -0,0 +1,345 @@
+using System;
+
+using Org.BouncyCastle.Crypto.Digests;
+using Org.BouncyCastle.Crypto.Parameters;
+using Org.BouncyCastle.Security;
+
+namespace Org.BouncyCastle.Crypto.Encodings
+{
+ /**
+ * Optimal Asymmetric Encryption Padding (OAEP) - see PKCS 1 V 2.
+ */
+ public class OaepEncoding
+ : IAsymmetricBlockCipher
+ {
+ private byte[] defHash;
+ private IDigest hash;
+ private IDigest mgf1Hash;
+
+ private IAsymmetricBlockCipher engine;
+ private SecureRandom random;
+ private bool forEncryption;
+
+ public OaepEncoding(
+ IAsymmetricBlockCipher cipher)
+ : this(cipher, new Sha1Digest(), null)
+ {
+ }
+
+ public OaepEncoding(
+ IAsymmetricBlockCipher cipher,
+ IDigest hash)
+ : this(cipher, hash, null)
+ {
+ }
+
+ public OaepEncoding(
+ IAsymmetricBlockCipher cipher,
+ IDigest hash,
+ byte[] encodingParams)
+ : this(cipher, hash, hash, encodingParams)
+ {
+ }
+
+ public OaepEncoding(
+ IAsymmetricBlockCipher cipher,
+ IDigest hash,
+ IDigest mgf1Hash,
+ byte[] encodingParams)
+ {
+ this.engine = cipher;
+ this.hash = hash;
+ this.mgf1Hash = mgf1Hash;
+ this.defHash = new byte[hash.GetDigestSize()];
+
+ if (encodingParams != null)
+ {
+ hash.BlockUpdate(encodingParams, 0, encodingParams.Length);
+ }
+
+ hash.DoFinal(defHash, 0);
+ }
+
+ public IAsymmetricBlockCipher GetUnderlyingCipher()
+ {
+ return engine;
+ }
+
+ public string AlgorithmName
+ {
+ get { return engine.AlgorithmName + "/OAEPPadding"; }
+ }
+
+ public void Init(
+ bool forEncryption,
+ ICipherParameters param)
+ {
+ if (param is ParametersWithRandom)
+ {
+ ParametersWithRandom rParam = (ParametersWithRandom)param;
+ this.random = rParam.Random;
+ }
+ else
+ {
+ this.random = new SecureRandom();
+ }
+
+ engine.Init(forEncryption, param);
+
+ this.forEncryption = forEncryption;
+ }
+
+ public int GetInputBlockSize()
+ {
+ int baseBlockSize = engine.GetInputBlockSize();
+
+ if (forEncryption)
+ {
+ return baseBlockSize - 1 - 2 * defHash.Length;
+ }
+ else
+ {
+ return baseBlockSize;
+ }
+ }
+
+ public int GetOutputBlockSize()
+ {
+ int baseBlockSize = engine.GetOutputBlockSize();
+
+ if (forEncryption)
+ {
+ return baseBlockSize;
+ }
+ else
+ {
+ return baseBlockSize - 1 - 2 * defHash.Length;
+ }
+ }
+
+ public byte[] ProcessBlock(
+ byte[] inBytes,
+ int inOff,
+ int inLen)
+ {
+ if (forEncryption)
+ {
+ return encodeBlock(inBytes, inOff, inLen);
+ }
+ else
+ {
+ return decodeBlock(inBytes, inOff, inLen);
+ }
+ }
+
+ private byte[] encodeBlock(
+ byte[] inBytes,
+ int inOff,
+ int inLen)
+ {
+ byte[] block = new byte[GetInputBlockSize() + 1 + 2 * defHash.Length];
+
+ //
+ // copy in the message
+ //
+ Array.Copy(inBytes, inOff, block, block.Length - inLen, inLen);
+
+ //
+ // add sentinel
+ //
+ block[block.Length - inLen - 1] = 0x01;
+
+ //
+ // as the block is already zeroed - there's no need to add PS (the >= 0 pad of 0)
+ //
+
+ //
+ // add the hash of the encoding params.
+ //
+ Array.Copy(defHash, 0, block, defHash.Length, defHash.Length);
+
+ //
+ // generate the seed.
+ //
+ byte[] seed = random.GenerateSeed(defHash.Length);
+
+ //
+ // mask the message block.
+ //
+ byte[] mask = maskGeneratorFunction1(seed, 0, seed.Length, block.Length - defHash.Length);
+
+ for (int i = defHash.Length; i != block.Length; i++)
+ {
+ block[i] ^= mask[i - defHash.Length];
+ }
+
+ //
+ // add in the seed
+ //
+ Array.Copy(seed, 0, block, 0, defHash.Length);
+
+ //
+ // mask the seed.
+ //
+ mask = maskGeneratorFunction1(
+ block, defHash.Length, block.Length - defHash.Length, defHash.Length);
+
+ for (int i = 0; i != defHash.Length; i++)
+ {
+ block[i] ^= mask[i];
+ }
+
+ return engine.ProcessBlock(block, 0, block.Length);
+ }
+
+ /**
+ * @exception InvalidCipherTextException if the decrypted block turns out to
+ * be badly formatted.
+ */
+ private byte[] decodeBlock(
+ byte[] inBytes,
+ int inOff,
+ int inLen)
+ {
+ byte[] data = engine.ProcessBlock(inBytes, inOff, inLen);
+ byte[] block;
+
+ //
+ // as we may have zeros in our leading bytes for the block we produced
+ // on encryption, we need to make sure our decrypted block comes back
+ // the same size.
+ //
+ if (data.Length < engine.GetOutputBlockSize())
+ {
+ block = new byte[engine.GetOutputBlockSize()];
+
+ Array.Copy(data, 0, block, block.Length - data.Length, data.Length);
+ }
+ else
+ {
+ block = data;
+ }
+
+ if (block.Length < (2 * defHash.Length) + 1)
+ {
+ throw new InvalidCipherTextException("data too short");
+ }
+
+ //
+ // unmask the seed.
+ //
+ byte[] mask = maskGeneratorFunction1(
+ block, defHash.Length, block.Length - defHash.Length, defHash.Length);
+
+ for (int i = 0; i != defHash.Length; i++)
+ {
+ block[i] ^= mask[i];
+ }
+
+ //
+ // unmask the message block.
+ //
+ mask = maskGeneratorFunction1(block, 0, defHash.Length, block.Length - defHash.Length);
+
+ for (int i = defHash.Length; i != block.Length; i++)
+ {
+ block[i] ^= mask[i - defHash.Length];
+ }
+
+ //
+ // check the hash of the encoding params.
+ //
+ for (int i = 0; i != defHash.Length; i++)
+ {
+ if (defHash[i] != block[defHash.Length + i])
+ {
+ throw new InvalidCipherTextException("data hash wrong");
+ }
+ }
+
+ //
+ // find the data block
+ //
+ int start;
+ for (start = 2 * defHash.Length; start != block.Length; start++)
+ {
+ if (block[start] != 0)
+ {
+ break;
+ }
+ }
+
+ if (start >= (block.Length - 1) || block[start] != 1)
+ {
+ throw new InvalidCipherTextException("data start wrong " + start);
+ }
+
+ start++;
+
+ //
+ // extract the data block
+ //
+ byte[] output = new byte[block.Length - start];
+
+ Array.Copy(block, start, output, 0, output.Length);
+
+ return output;
+ }
+
+ /**
+ * int to octet string.
+ */
+ private void ItoOSP(
+ int i,
+ byte[] sp)
+ {
+ sp[0] = (byte)((uint)i >> 24);
+ sp[1] = (byte)((uint)i >> 16);
+ sp[2] = (byte)((uint)i >> 8);
+ sp[3] = (byte)((uint)i >> 0);
+ }
+
+ /**
+ * mask generator function, as described in PKCS1v2.
+ */
+ private byte[] maskGeneratorFunction1(
+ byte[] Z,
+ int zOff,
+ int zLen,
+ int length)
+ {
+ byte[] mask = new byte[length];
+ byte[] hashBuf = new byte[mgf1Hash.GetDigestSize()];
+ byte[] C = new byte[4];
+ int counter = 0;
+
+ hash.Reset();
+
+ do
+ {
+ ItoOSP(counter, C);
+
+ mgf1Hash.BlockUpdate(Z, zOff, zLen);
+ mgf1Hash.BlockUpdate(C, 0, C.Length);
+ mgf1Hash.DoFinal(hashBuf, 0);
+
+ Array.Copy(hashBuf, 0, mask, counter * hashBuf.Length, hashBuf.Length);
+ }
+ while (++counter < (length / hashBuf.Length));
+
+ if ((counter * hashBuf.Length) < length)
+ {
+ ItoOSP(counter, C);
+
+ mgf1Hash.BlockUpdate(Z, zOff, zLen);
+ mgf1Hash.BlockUpdate(C, 0, C.Length);
+ mgf1Hash.DoFinal(hashBuf, 0);
+
+ Array.Copy(hashBuf, 0, mask, counter * hashBuf.Length, mask.Length - (counter * hashBuf.Length));
+ }
+
+ return mask;
+ }
+ }
+}
+
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