/// <summary>
        /// Decrypt the cipher text with the session key. The usage indicated
        /// in section 7 of RFC4210 and section 3 of RFC4757 is used to derive key
        /// from the session key.
        /// </summary>
        /// <param name="type">The decryption type selected.</param>
        /// <param name="sessionKey">An session key used to decrypt and it can be obtained
        /// from the KDC's response. This key size should be equal to the symmetric algorithm
        /// key size. This argument can be null. If it is null, null will be returned.</param>
        /// <param name="cipherData">The text to be decrypted. This argument can be null.
        /// If it is null, null will be returned.</param>
        /// <param name="usage">A 32 bits integer used to derive the key.</param>
        /// <param name="getToBeSignedDateCallback">
        /// A callback to get to-be-signed data.
        /// The method will use decrypted data directly if this parameter is null.
        /// </param>
        /// <returns>The plain text.</returns>
        internal static byte[] Decrypt(EncryptionType type, byte[] sessionKey, byte[] cipherData, int usage, GetToBeSignedDataFunc getToBeSignedDateCallback)
        {
            switch (type)
            {
            case EncryptionType.AES128_CTS_HMAC_SHA1_96:
                return(AesCtsHmacSha1Crypto.Decrypt(sessionKey, cipherData, usage, AesKeyType.Aes128BitsKey, getToBeSignedDateCallback));

            case EncryptionType.AES256_CTS_HMAC_SHA1_96:
                return(AesCtsHmacSha1Crypto.Decrypt(sessionKey, cipherData, usage, AesKeyType.Aes256BitsKey, getToBeSignedDateCallback));

            case EncryptionType.DES_CBC_CRC:
                return(DesCbcCrypto.Decrypt(sessionKey, cipherData, EncryptionType.DES_CBC_CRC, getToBeSignedDateCallback));

            case EncryptionType.DES_CBC_MD5:
                return(DesCbcCrypto.Decrypt(sessionKey, cipherData, EncryptionType.DES_CBC_MD5, getToBeSignedDateCallback));

            case EncryptionType.RC4_HMAC:
                return(Rc4HmacCrypto.Decrypt(sessionKey, cipherData, usage, EncryptionType.RC4_HMAC, getToBeSignedDateCallback));

            case EncryptionType.RC4_HMAC_EXP:
                return(Rc4HmacCrypto.Decrypt(sessionKey, cipherData, usage, EncryptionType.RC4_HMAC_EXP, getToBeSignedDateCallback));

            default:
                throw new ArgumentException("Unsupported encryption type.");
            }
        }
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        /// <summary>
        /// Decrypt specified cypher to plain text, according to specified encryption type.
        /// </summary>
        /// <param name="key">The decrypt key.</param>
        /// <param name="cypher">The specified cypher.</param>
        /// <param name="type">The specified encryption type.</param>
        /// <returns>Yhe decrypted plain text.</returns>
        private static byte[] Decrypt(byte[] key, byte[] cypher, EncryptionType_Values type)
        {
            switch (type)
            {
            case EncryptionType_Values.DES_CBC_CRC:
                return(DesCbcCrypto.Decrypt(key, cypher, EncryptionType.DES_CBC_CRC));

            case EncryptionType_Values.DES_CBC_MD5:
                return(DesCbcCrypto.Decrypt(key, cypher, EncryptionType.DES_CBC_MD5));

            case EncryptionType_Values.AES128_CTS_HMAC_SHA1_96:
                return(AesCtsHmacSha1Crypto.Decrypt(key, cypher, KerbNonKerbSalt, AesKeyType.Aes128BitsKey));

            case EncryptionType_Values.AES256_CTS_HMAC_SHA1_96:
                return(AesCtsHmacSha1Crypto.Decrypt(key, cypher, KerbNonKerbSalt, AesKeyType.Aes256BitsKey));

            case EncryptionType_Values.RC4_HMAC:
                return(Rc4HmacCrypto.Decrypt(key, cypher, KerbNonKerbSalt, EncryptionType.RC4_HMAC));

            default:
                throw new ArgumentOutOfRangeException("type");
            }
        }