Question

I need to encrypt and decrypt a string. I can’t use the hash because the decrypted string must be readable. I know about mcrypt but i was looking something that uses a certificate file to encrypt and decrypt.

Thanks.

Answer 1

You can use a public/private key through openssl and is pretty simple once you use it once or twice

function encryptString($clearText)
{
  $keyFile=fopen("public.pem","r");
  $publicKey=fread($keyFile,8192);
  fclose($keyFile);

  openssl_get_publickey($publicKey);
  openssl_public_encrypt($clearText,$cryptText,$publicKey);
  return(base64_encode($cryptText));
}

function decryptString($cryptText)
{
  $keyFile=fopen("private.pem","r");
  $privateKey=fread($keyFile,8192);
  fclose($keyFile);

  openssl_get_privatekey($privateKey);
  $binText = base64_decode($cryptText);
  openssl_private_decrypt($binText,$clearText,$privateKey);
  return($clearText);
}

To generate a keypair, a brief guide is http://en.wikibooks.org/wiki/Transwiki:Generate_a_keypair_using_OpenSSL

In short

openssl rsa -pubout -in private.pem -out public.pem

Update

@keepwalking asked below how to do this from the command line and @vstm responded with a great link http://www.devco.net/archives/2006/02/13/public_-_private_key_encryption_using_openssl.php.

To summarize that page, once you have keys created, you can encrypt a text file file.txt and output it to file.ssl by using the following command.

openssl rsautl -encrypt -inkey public.pem -pubin -in file.txt -out file.ssl

To decrypt file.ssl to another file decrypt.txt, you can use the following command.

openssl rsautl -decrypt -inkey private.pem -in file.ssl -out decrypted.txt