I need crypting and decrypting functions coded on php and C# .NET

I need crypting and decrypting functions coded on php and C# .NET requirements: 1) reliable algorithm 2)not to use third party libs/components 3) data encrypted in .net must be decrypted in php 4) data encrypted in php must be decrypted in .net //returns base64 encoded encrypted value function php_crypt ($plain_data , $key) ; //returns decrypted value in plain text function php_decrypt ($base64_data , $key) ; //returns base64 encoded encrypted value string net_crypt (string plain_data , string key) ; //returns decrypted value in plain text string net_decrypt (string base64_data , string key) ;